modpost: inform compilers that fatal() never returns

[linux.git] / fs / ext4 / mballoc.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (c) 2003-2006, Cluster File Systems, Inc, [email protected]
 * Written by Alex Tomas <[email protected]>
 */


/*
 * mballoc.c contains the multiblocks allocation routines
 */

#include "ext4_jbd2.h"
#include "mballoc.h"
#include <linux/log2.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/nospec.h>
#include <linux/backing-dev.h>
#include <linux/freezer.h>
#include <trace/events/ext4.h>
#include <kunit/static_stub.h>

/*
 * MUSTDO:
 *   - test ext4_ext_search_left() and ext4_ext_search_right()
 *   - search for metadata in few groups
 *
 * TODO v4:
 *   - normalization should take into account whether file is still open
 *   - discard preallocations if no free space left (policy?)
 *   - don't normalize tails
 *   - quota
 *   - reservation for superuser
 *
 * TODO v3:
 *   - bitmap read-ahead (proposed by Oleg Drokin aka green)
 *   - track min/max extents in each group for better group selection
 *   - mb_mark_used() may allocate chunk right after splitting buddy
 *   - tree of groups sorted by number of free blocks
 *   - error handling
 */

/*
 * The allocation request involve request for multiple number of blocks
 * near to the goal(block) value specified.
 *
 * During initialization phase of the allocator we decide to use the
 * group preallocation or inode preallocation depending on the size of
 * the file. The size of the file could be the resulting file size we
 * would have after allocation, or the current file size, which ever
 * is larger. If the size is less than sbi->s_mb_stream_request we
 * select to use the group preallocation. The default value of
 * s_mb_stream_request is 16 blocks. This can also be tuned via
 * /sys/fs/ext4/<partition>/mb_stream_req. The value is represented in
 * terms of number of blocks.
 *
 * The main motivation for having small file use group preallocation is to
 * ensure that we have small files closer together on the disk.
 *
 * First stage the allocator looks at the inode prealloc list,
 * ext4_inode_info->i_prealloc_list, which contains list of prealloc
 * spaces for this particular inode. The inode prealloc space is
 * represented as:
 *
 * pa_lstart -> the logical start block for this prealloc space
 * pa_pstart -> the physical start block for this prealloc space
 * pa_len    -> length for this prealloc space (in clusters)
 * pa_free   ->  free space available in this prealloc space (in clusters)
 *
 * The inode preallocation space is used looking at the _logical_ start
 * block. If only the logical file block falls within the range of prealloc
 * space we will consume the particular prealloc space. This makes sure that
 * we have contiguous physical blocks representing the file blocks
 *
 * The important thing to be noted in case of inode prealloc space is that
 * we don't modify the values associated to inode prealloc space except
 * pa_free.
 *
 * If we are not able to find blocks in the inode prealloc space and if we
 * have the group allocation flag set then we look at the locality group
 * prealloc space. These are per CPU prealloc list represented as
 *
 * ext4_sb_info.s_locality_groups[smp_processor_id()]
 *
 * The reason for having a per cpu locality group is to reduce the contention
 * between CPUs. It is possible to get scheduled at this point.
 *
 * The locality group prealloc space is used looking at whether we have
 * enough free space (pa_free) within the prealloc space.
 *
 * If we can't allocate blocks via inode prealloc or/and locality group
 * prealloc then we look at the buddy cache. The buddy cache is represented
 * by ext4_sb_info.s_buddy_cache (struct inode) whose file offset gets
 * mapped to the buddy and bitmap information regarding different
 * groups. The buddy information is attached to buddy cache inode so that
 * we can access them through the page cache. The information regarding
 * each group is loaded via ext4_mb_load_buddy.  The information involve
 * block bitmap and buddy information. The information are stored in the
 * inode as:
 *
 *  {                        page                        }
 *  [ group 0 bitmap][ group 0 buddy] [group 1][ group 1]...
 *
 *
 * one block each for bitmap and buddy information.  So for each group we
 * take up 2 blocks. A page can contain blocks_per_page (PAGE_SIZE /
 * blocksize) blocks.  So it can have information regarding groups_per_page
 * which is blocks_per_page/2
 *
 * The buddy cache inode is not stored on disk. The inode is thrown
 * away when the filesystem is unmounted.
 *
 * We look for count number of blocks in the buddy cache. If we were able
 * to locate that many free blocks we return with additional information
 * regarding rest of the contiguous physical block available
 *
 * Before allocating blocks via buddy cache we normalize the request
 * blocks. This ensure we ask for more blocks that we needed. The extra
 * blocks that we get after allocation is added to the respective prealloc
 * list. In case of inode preallocation we follow a list of heuristics
 * based on file size. This can be found in ext4_mb_normalize_request. If
 * we are doing a group prealloc we try to normalize the request to
 * sbi->s_mb_group_prealloc.  The default value of s_mb_group_prealloc is
 * dependent on the cluster size; for non-bigalloc file systems, it is
 * 512 blocks. This can be tuned via
 * /sys/fs/ext4/<partition>/mb_group_prealloc. The value is represented in
 * terms of number of blocks. If we have mounted the file system with -O
 * stripe=<value> option the group prealloc request is normalized to the
 * smallest multiple of the stripe value (sbi->s_stripe) which is
 * greater than the default mb_group_prealloc.
 *
 * If "mb_optimize_scan" mount option is set, we maintain in memory group info
 * structures in two data structures:
 *
 * 1) Array of largest free order lists (sbi->s_mb_largest_free_orders)
 *
 *    Locking: sbi->s_mb_largest_free_orders_locks(array of rw locks)
 *
 *    This is an array of lists where the index in the array represents the
 *    largest free order in the buddy bitmap of the participating group infos of
 *    that list. So, there are exactly MB_NUM_ORDERS(sb) (which means total
 *    number of buddy bitmap orders possible) number of lists. Group-infos are
 *    placed in appropriate lists.
 *
 * 2) Average fragment size lists (sbi->s_mb_avg_fragment_size)
 *
 *    Locking: sbi->s_mb_avg_fragment_size_locks(array of rw locks)
 *
 *    This is an array of lists where in the i-th list there are groups with
 *    average fragment size >= 2^i and < 2^(i+1). The average fragment size
 *    is computed as ext4_group_info->bb_free / ext4_group_info->bb_fragments.
 *    Note that we don't bother with a special list for completely empty groups
 *    so we only have MB_NUM_ORDERS(sb) lists.
 *
 * When "mb_optimize_scan" mount option is set, mballoc consults the above data
 * structures to decide the order in which groups are to be traversed for
 * fulfilling an allocation request.
 *
 * At CR_POWER2_ALIGNED , we look for groups which have the largest_free_order
 * >= the order of the request. We directly look at the largest free order list
 * in the data structure (1) above where largest_free_order = order of the
 * request. If that list is empty, we look at remaining list in the increasing
 * order of largest_free_order. This allows us to perform CR_POWER2_ALIGNED
 * lookup in O(1) time.
 *
 * At CR_GOAL_LEN_FAST, we only consider groups where
 * average fragment size > request size. So, we lookup a group which has average
 * fragment size just above or equal to request size using our average fragment
 * size group lists (data structure 2) in O(1) time.
 *
 * At CR_BEST_AVAIL_LEN, we aim to optimize allocations which can't be satisfied
 * in CR_GOAL_LEN_FAST. The fact that we couldn't find a group in
 * CR_GOAL_LEN_FAST suggests that there is no BG that has avg
 * fragment size > goal length. So before falling to the slower
 * CR_GOAL_LEN_SLOW, in CR_BEST_AVAIL_LEN we proactively trim goal length and
 * then use the same fragment lists as CR_GOAL_LEN_FAST to find a BG with a big
 * enough average fragment size. This increases the chances of finding a
 * suitable block group in O(1) time and results in faster allocation at the
 * cost of reduced size of allocation.
 *
 * If "mb_optimize_scan" mount option is not set, mballoc traverses groups in
 * linear order which requires O(N) search time for each CR_POWER2_ALIGNED and
 * CR_GOAL_LEN_FAST phase.
 *
 * The regular allocator (using the buddy cache) supports a few tunables.
 *
 * /sys/fs/ext4/<partition>/mb_min_to_scan
 * /sys/fs/ext4/<partition>/mb_max_to_scan
 * /sys/fs/ext4/<partition>/mb_order2_req
 * /sys/fs/ext4/<partition>/mb_linear_limit
 *
 * The regular allocator uses buddy scan only if the request len is power of
 * 2 blocks and the order of allocation is >= sbi->s_mb_order2_reqs. The
 * value of s_mb_order2_reqs can be tuned via
 * /sys/fs/ext4/<partition>/mb_order2_req.  If the request len is equal to
 * stripe size (sbi->s_stripe), we try to search for contiguous block in
 * stripe size. This should result in better allocation on RAID setups. If
 * not, we search in the specific group using bitmap for best extents. The
 * tunable min_to_scan and max_to_scan control the behaviour here.
 * min_to_scan indicate how long the mballoc __must__ look for a best
 * extent and max_to_scan indicates how long the mballoc __can__ look for a
 * best extent in the found extents. Searching for the blocks starts with
 * the group specified as the goal value in allocation context via
 * ac_g_ex. Each group is first checked based on the criteria whether it
 * can be used for allocation. ext4_mb_good_group explains how the groups are
 * checked.
 *
 * When "mb_optimize_scan" is turned on, as mentioned above, the groups may not
 * get traversed linearly. That may result in subsequent allocations being not
 * close to each other. And so, the underlying device may get filled up in a
 * non-linear fashion. While that may not matter on non-rotational devices, for
 * rotational devices that may result in higher seek times. "mb_linear_limit"
 * tells mballoc how many groups mballoc should search linearly before
 * performing consulting above data structures for more efficient lookups. For
 * non rotational devices, this value defaults to 0 and for rotational devices
 * this is set to MB_DEFAULT_LINEAR_LIMIT.
 *
 * Both the prealloc space are getting populated as above. So for the first
 * request we will hit the buddy cache which will result in this prealloc
 * space getting filled. The prealloc space is then later used for the
 * subsequent request.
 */

/*
 * mballoc operates on the following data:
 *  - on-disk bitmap
 *  - in-core buddy (actually includes buddy and bitmap)
 *  - preallocation descriptors (PAs)
 *
 * there are two types of preallocations:
 *  - inode
 *    assiged to specific inode and can be used for this inode only.
 *    it describes part of inode's space preallocated to specific
 *    physical blocks. any block from that preallocated can be used
 *    independent. the descriptor just tracks number of blocks left
 *    unused. so, before taking some block from descriptor, one must
 *    make sure corresponded logical block isn't allocated yet. this
 *    also means that freeing any block within descriptor's range
 *    must discard all preallocated blocks.
 *  - locality group
 *    assigned to specific locality group which does not translate to
 *    permanent set of inodes: inode can join and leave group. space
 *    from this type of preallocation can be used for any inode. thus
 *    it's consumed from the beginning to the end.
 *
 * relation between them can be expressed as:
 *    in-core buddy = on-disk bitmap + preallocation descriptors
 *
 * this mean blocks mballoc considers used are:
 *  - allocated blocks (persistent)
 *  - preallocated blocks (non-persistent)
 *
 * consistency in mballoc world means that at any time a block is either
 * free or used in ALL structures. notice: "any time" should not be read
 * literally -- time is discrete and delimited by locks.
 *
 *  to keep it simple, we don't use block numbers, instead we count number of
 *  blocks: how many blocks marked used/free in on-disk bitmap, buddy and PA.
 *
 * all operations can be expressed as:
 *  - init buddy:                       buddy = on-disk + PAs
 *  - new PA:                           buddy += N; PA = N
 *  - use inode PA:                     on-disk += N; PA -= N
 *  - discard inode PA                  buddy -= on-disk - PA; PA = 0
 *  - use locality group PA             on-disk += N; PA -= N
 *  - discard locality group PA         buddy -= PA; PA = 0
 *  note: 'buddy -= on-disk - PA' is used to show that on-disk bitmap
 *        is used in real operation because we can't know actual used
 *        bits from PA, only from on-disk bitmap
 *
 * if we follow this strict logic, then all operations above should be atomic.
 * given some of them can block, we'd have to use something like semaphores
 * killing performance on high-end SMP hardware. let's try to relax it using
 * the following knowledge:
 *  1) if buddy is referenced, it's already initialized
 *  2) while block is used in buddy and the buddy is referenced,
 *     nobody can re-allocate that block
 *  3) we work on bitmaps and '+' actually means 'set bits'. if on-disk has
 *     bit set and PA claims same block, it's OK. IOW, one can set bit in
 *     on-disk bitmap if buddy has same bit set or/and PA covers corresponded
 *     block
 *
 * so, now we're building a concurrency table:
 *  - init buddy vs.
 *    - new PA
 *      blocks for PA are allocated in the buddy, buddy must be referenced
 *      until PA is linked to allocation group to avoid concurrent buddy init
 *    - use inode PA
 *      we need to make sure that either on-disk bitmap or PA has uptodate data
 *      given (3) we care that PA-=N operation doesn't interfere with init
 *    - discard inode PA
 *      the simplest way would be to have buddy initialized by the discard
 *    - use locality group PA
 *      again PA-=N must be serialized with init
 *    - discard locality group PA
 *      the simplest way would be to have buddy initialized by the discard
 *  - new PA vs.
 *    - use inode PA
 *      i_data_sem serializes them
 *    - discard inode PA
 *      discard process must wait until PA isn't used by another process
 *    - use locality group PA
 *      some mutex should serialize them
 *    - discard locality group PA
 *      discard process must wait until PA isn't used by another process
 *  - use inode PA
 *    - use inode PA
 *      i_data_sem or another mutex should serializes them
 *    - discard inode PA
 *      discard process must wait until PA isn't used by another process
 *    - use locality group PA
 *      nothing wrong here -- they're different PAs covering different blocks
 *    - discard locality group PA
 *      discard process must wait until PA isn't used by another process
 *
 * now we're ready to make few consequences:
 *  - PA is referenced and while it is no discard is possible
 *  - PA is referenced until block isn't marked in on-disk bitmap
 *  - PA changes only after on-disk bitmap
 *  - discard must not compete with init. either init is done before
 *    any discard or they're serialized somehow
 *  - buddy init as sum of on-disk bitmap and PAs is done atomically
 *
 * a special case when we've used PA to emptiness. no need to modify buddy
 * in this case, but we should care about concurrent init
 *
 */

 /*
 * Logic in few words:
 *
 *  - allocation:
 *    load group
 *    find blocks
 *    mark bits in on-disk bitmap
 *    release group
 *
 *  - use preallocation:
 *    find proper PA (per-inode or group)
 *    load group
 *    mark bits in on-disk bitmap
 *    release group
 *    release PA
 *
 *  - free:
 *    load group
 *    mark bits in on-disk bitmap
 *    release group
 *
 *  - discard preallocations in group:
 *    mark PAs deleted
 *    move them onto local list
 *    load on-disk bitmap
 *    load group
 *    remove PA from object (inode or locality group)
 *    mark free blocks in-core
 *
 *  - discard inode's preallocations:
 */

/*
 * Locking rules
 *
 * Locks:
 *  - bitlock on a group        (group)
 *  - object (inode/locality)   (object)
 *  - per-pa lock               (pa)
 *  - cr_power2_aligned lists lock      (cr_power2_aligned)
 *  - cr_goal_len_fast lists lock       (cr_goal_len_fast)
 *
 * Paths:
 *  - new pa
 *    object
 *    group
 *
 *  - find and use pa:
 *    pa
 *
 *  - release consumed pa:
 *    pa
 *    group
 *    object
 *
 *  - generate in-core bitmap:
 *    group
 *        pa
 *
 *  - discard all for given object (inode, locality group):
 *    object
 *        pa
 *    group
 *
 *  - discard all for given group:
 *    group
 *        pa
 *    group
 *        object
 *
 *  - allocation path (ext4_mb_regular_allocator)
 *    group
 *    cr_power2_aligned/cr_goal_len_fast
 */
static struct kmem_cache *ext4_pspace_cachep;
static struct kmem_cache *ext4_ac_cachep;
static struct kmem_cache *ext4_free_data_cachep;

/* We create slab caches for groupinfo data structures based on the
 * superblock block size.  There will be one per mounted filesystem for
 * each unique s_blocksize_bits */
#define NR_GRPINFO_CACHES 8
static struct kmem_cache *ext4_groupinfo_caches[NR_GRPINFO_CACHES];

static const char * const ext4_groupinfo_slab_names[NR_GRPINFO_CACHES] = {
        "ext4_groupinfo_1k", "ext4_groupinfo_2k", "ext4_groupinfo_4k",
        "ext4_groupinfo_8k", "ext4_groupinfo_16k", "ext4_groupinfo_32k",
        "ext4_groupinfo_64k", "ext4_groupinfo_128k"
};

static void ext4_mb_generate_from_pa(struct super_block *sb, void *bitmap,
                                        ext4_group_t group);
static void ext4_mb_new_preallocation(struct ext4_allocation_context *ac);

static bool ext4_mb_good_group(struct ext4_allocation_context *ac,
                               ext4_group_t group, enum criteria cr);

static int ext4_try_to_trim_range(struct super_block *sb,
                struct ext4_buddy *e4b, ext4_grpblk_t start,
                ext4_grpblk_t max, ext4_grpblk_t minblocks);

/*
 * The algorithm using this percpu seq counter goes below:
 * 1. We sample the percpu discard_pa_seq counter before trying for block
 *    allocation in ext4_mb_new_blocks().
 * 2. We increment this percpu discard_pa_seq counter when we either allocate
 *    or free these blocks i.e. while marking those blocks as used/free in
 *    mb_mark_used()/mb_free_blocks().
 * 3. We also increment this percpu seq counter when we successfully identify
 *    that the bb_prealloc_list is not empty and hence proceed for discarding
 *    of those PAs inside ext4_mb_discard_group_preallocations().
 *
 * Now to make sure that the regular fast path of block allocation is not
 * affected, as a small optimization we only sample the percpu seq counter
 * on that cpu. Only when the block allocation fails and when freed blocks
 * found were 0, that is when we sample percpu seq counter for all cpus using
 * below function ext4_get_discard_pa_seq_sum(). This happens after making
 * sure that all the PAs on grp->bb_prealloc_list got freed or if it's empty.
 */
static DEFINE_PER_CPU(u64, discard_pa_seq);
static inline u64 ext4_get_discard_pa_seq_sum(void)
{
        int __cpu;
        u64 __seq = 0;

        for_each_possible_cpu(__cpu)
                __seq += per_cpu(discard_pa_seq, __cpu);
        return __seq;
}

static inline void *mb_correct_addr_and_bit(int *bit, void *addr)
{
#if BITS_PER_LONG == 64
        *bit += ((unsigned long) addr & 7UL) << 3;
        addr = (void *) ((unsigned long) addr & ~7UL);
#elif BITS_PER_LONG == 32
        *bit += ((unsigned long) addr & 3UL) << 3;
        addr = (void *) ((unsigned long) addr & ~3UL);
#else
#error "how many bits you are?!"
#endif
        return addr;
}

static inline int mb_test_bit(int bit, void *addr)
{
        /*
         * ext4_test_bit on architecture like powerpc
         * needs unsigned long aligned address
         */
        addr = mb_correct_addr_and_bit(&bit, addr);
        return ext4_test_bit(bit, addr);
}

static inline void mb_set_bit(int bit, void *addr)
{
        addr = mb_correct_addr_and_bit(&bit, addr);
        ext4_set_bit(bit, addr);
}

static inline void mb_clear_bit(int bit, void *addr)
{
        addr = mb_correct_addr_and_bit(&bit, addr);
        ext4_clear_bit(bit, addr);
}

static inline int mb_test_and_clear_bit(int bit, void *addr)
{
        addr = mb_correct_addr_and_bit(&bit, addr);
        return ext4_test_and_clear_bit(bit, addr);
}

static inline int mb_find_next_zero_bit(void *addr, int max, int start)
{
        int fix = 0, ret, tmpmax;
        addr = mb_correct_addr_and_bit(&fix, addr);
        tmpmax = max + fix;
        start += fix;

        ret = ext4_find_next_zero_bit(addr, tmpmax, start) - fix;
        if (ret > max)
                return max;
        return ret;
}

static inline int mb_find_next_bit(void *addr, int max, int start)
{
        int fix = 0, ret, tmpmax;
        addr = mb_correct_addr_and_bit(&fix, addr);
        tmpmax = max + fix;
        start += fix;

        ret = ext4_find_next_bit(addr, tmpmax, start) - fix;
        if (ret > max)
                return max;
        return ret;
}

static void *mb_find_buddy(struct ext4_buddy *e4b, int order, int *max)
{
        char *bb;

        BUG_ON(e4b->bd_bitmap == e4b->bd_buddy);
        BUG_ON(max == NULL);

        if (order > e4b->bd_blkbits + 1) {
                *max = 0;
                return NULL;
        }

        /* at order 0 we see each particular block */
        if (order == 0) {
                *max = 1 << (e4b->bd_blkbits + 3);
                return e4b->bd_bitmap;
        }

        bb = e4b->bd_buddy + EXT4_SB(e4b->bd_sb)->s_mb_offsets[order];
        *max = EXT4_SB(e4b->bd_sb)->s_mb_maxs[order];

        return bb;
}

#ifdef DOUBLE_CHECK
static void mb_free_blocks_double(struct inode *inode, struct ext4_buddy *e4b,
                           int first, int count)
{
        int i;
        struct super_block *sb = e4b->bd_sb;

        if (unlikely(e4b->bd_info->bb_bitmap == NULL))
                return;
        assert_spin_locked(ext4_group_lock_ptr(sb, e4b->bd_group));
        for (i = 0; i < count; i++) {
                if (!mb_test_bit(first + i, e4b->bd_info->bb_bitmap)) {
                        ext4_fsblk_t blocknr;

                        blocknr = ext4_group_first_block_no(sb, e4b->bd_group);
                        blocknr += EXT4_C2B(EXT4_SB(sb), first + i);
                        ext4_grp_locked_error(sb, e4b->bd_group,
                                              inode ? inode->i_ino : 0,
                                              blocknr,
                                              "freeing block already freed "
                                              "(bit %u)",
                                              first + i);
                        ext4_mark_group_bitmap_corrupted(sb, e4b->bd_group,
                                        EXT4_GROUP_INFO_BBITMAP_CORRUPT);
                }
                mb_clear_bit(first + i, e4b->bd_info->bb_bitmap);
        }
}

static void mb_mark_used_double(struct ext4_buddy *e4b, int first, int count)
{
        int i;

        if (unlikely(e4b->bd_info->bb_bitmap == NULL))
                return;
        assert_spin_locked(ext4_group_lock_ptr(e4b->bd_sb, e4b->bd_group));
        for (i = 0; i < count; i++) {
                BUG_ON(mb_test_bit(first + i, e4b->bd_info->bb_bitmap));
                mb_set_bit(first + i, e4b->bd_info->bb_bitmap);
        }
}

static void mb_cmp_bitmaps(struct ext4_buddy *e4b, void *bitmap)
{
        if (unlikely(e4b->bd_info->bb_bitmap == NULL))
                return;
        if (memcmp(e4b->bd_info->bb_bitmap, bitmap, e4b->bd_sb->s_blocksize)) {
                unsigned char *b1, *b2;
                int i;
                b1 = (unsigned char *) e4b->bd_info->bb_bitmap;
                b2 = (unsigned char *) bitmap;
                for (i = 0; i < e4b->bd_sb->s_blocksize; i++) {
                        if (b1[i] != b2[i]) {
                                ext4_msg(e4b->bd_sb, KERN_ERR,
                                         "corruption in group %u "
                                         "at byte %u(%u): %x in copy != %x "
                                         "on disk/prealloc",
                                         e4b->bd_group, i, i * 8, b1[i], b2[i]);
                                BUG();
                        }
                }
        }
}

static void mb_group_bb_bitmap_alloc(struct super_block *sb,
                        struct ext4_group_info *grp, ext4_group_t group)
{
        struct buffer_head *bh;

        grp->bb_bitmap = kmalloc(sb->s_blocksize, GFP_NOFS);
        if (!grp->bb_bitmap)
                return;

        bh = ext4_read_block_bitmap(sb, group);
        if (IS_ERR_OR_NULL(bh)) {
                kfree(grp->bb_bitmap);
                grp->bb_bitmap = NULL;
                return;
        }

        memcpy(grp->bb_bitmap, bh->b_data, sb->s_blocksize);
        put_bh(bh);
}

static void mb_group_bb_bitmap_free(struct ext4_group_info *grp)
{
        kfree(grp->bb_bitmap);
}

#else
static inline void mb_free_blocks_double(struct inode *inode,
                                struct ext4_buddy *e4b, int first, int count)
{
        return;
}
static inline void mb_mark_used_double(struct ext4_buddy *e4b,
                                                int first, int count)
{
        return;
}
static inline void mb_cmp_bitmaps(struct ext4_buddy *e4b, void *bitmap)
{
        return;
}

static inline void mb_group_bb_bitmap_alloc(struct super_block *sb,
                        struct ext4_group_info *grp, ext4_group_t group)
{
        return;
}

static inline void mb_group_bb_bitmap_free(struct ext4_group_info *grp)
{
        return;
}
#endif

#ifdef AGGRESSIVE_CHECK

#define MB_CHECK_ASSERT(assert)                                         \
do {                                                                    \
        if (!(assert)) {                                                \
                printk(KERN_EMERG                                       \
                        "Assertion failure in %s() at %s:%d: \"%s\"\n", \
                        function, file, line, # assert);                \
                BUG();                                                  \
        }                                                               \
} while (0)

static int __mb_check_buddy(struct ext4_buddy *e4b, char *file,
                                const char *function, int line)
{
        struct super_block *sb = e4b->bd_sb;
        int order = e4b->bd_blkbits + 1;
        int max;
        int max2;
        int i;
        int j;
        int k;
        int count;
        struct ext4_group_info *grp;
        int fragments = 0;
        int fstart;
        struct list_head *cur;
        void *buddy;
        void *buddy2;

        if (e4b->bd_info->bb_check_counter++ % 10)
                return 0;

        while (order > 1) {
                buddy = mb_find_buddy(e4b, order, &max);
                MB_CHECK_ASSERT(buddy);
                buddy2 = mb_find_buddy(e4b, order - 1, &max2);
                MB_CHECK_ASSERT(buddy2);
                MB_CHECK_ASSERT(buddy != buddy2);
                MB_CHECK_ASSERT(max * 2 == max2);

                count = 0;
                for (i = 0; i < max; i++) {

                        if (mb_test_bit(i, buddy)) {
                                /* only single bit in buddy2 may be 0 */
                                if (!mb_test_bit(i << 1, buddy2)) {
                                        MB_CHECK_ASSERT(
                                                mb_test_bit((i<<1)+1, buddy2));
                                }
                                continue;
                        }

                        /* both bits in buddy2 must be 1 */
                        MB_CHECK_ASSERT(mb_test_bit(i << 1, buddy2));
                        MB_CHECK_ASSERT(mb_test_bit((i << 1) + 1, buddy2));

                        for (j = 0; j < (1 << order); j++) {
                                k = (i * (1 << order)) + j;
                                MB_CHECK_ASSERT(
                                        !mb_test_bit(k, e4b->bd_bitmap));
                        }
                        count++;
                }
                MB_CHECK_ASSERT(e4b->bd_info->bb_counters[order] == count);
                order--;
        }

        fstart = -1;
        buddy = mb_find_buddy(e4b, 0, &max);
        for (i = 0; i < max; i++) {
                if (!mb_test_bit(i, buddy)) {
                        MB_CHECK_ASSERT(i >= e4b->bd_info->bb_first_free);
                        if (fstart == -1) {
                                fragments++;
                                fstart = i;
                        }
                        continue;
                }
                fstart = -1;
                /* check used bits only */
                for (j = 0; j < e4b->bd_blkbits + 1; j++) {
                        buddy2 = mb_find_buddy(e4b, j, &max2);
                        k = i >> j;
                        MB_CHECK_ASSERT(k < max2);
                        MB_CHECK_ASSERT(mb_test_bit(k, buddy2));
                }
        }
        MB_CHECK_ASSERT(!EXT4_MB_GRP_NEED_INIT(e4b->bd_info));
        MB_CHECK_ASSERT(e4b->bd_info->bb_fragments == fragments);

        grp = ext4_get_group_info(sb, e4b->bd_group);
        if (!grp)
                return NULL;
        list_for_each(cur, &grp->bb_prealloc_list) {
                ext4_group_t groupnr;
                struct ext4_prealloc_space *pa;
                pa = list_entry(cur, struct ext4_prealloc_space, pa_group_list);
                ext4_get_group_no_and_offset(sb, pa->pa_pstart, &groupnr, &k);
                MB_CHECK_ASSERT(groupnr == e4b->bd_group);
                for (i = 0; i < pa->pa_len; i++)
                        MB_CHECK_ASSERT(mb_test_bit(k + i, buddy));
        }
        return 0;
}
#undef MB_CHECK_ASSERT
#define mb_check_buddy(e4b) __mb_check_buddy(e4b,       \
                                        __FILE__, __func__, __LINE__)
#else
#define mb_check_buddy(e4b)
#endif

/*
 * Divide blocks started from @first with length @len into
 * smaller chunks with power of 2 blocks.
 * Clear the bits in bitmap which the blocks of the chunk(s) covered,
 * then increase bb_counters[] for corresponded chunk size.
 */
static void ext4_mb_mark_free_simple(struct super_block *sb,
                                void *buddy, ext4_grpblk_t first, ext4_grpblk_t len,
                                        struct ext4_group_info *grp)
{
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        ext4_grpblk_t min;
        ext4_grpblk_t max;
        ext4_grpblk_t chunk;
        unsigned int border;

        BUG_ON(len > EXT4_CLUSTERS_PER_GROUP(sb));

        border = 2 << sb->s_blocksize_bits;

        while (len > 0) {
                /* find how many blocks can be covered since this position */
                max = ffs(first | border) - 1;

                /* find how many blocks of power 2 we need to mark */
                min = fls(len) - 1;

                if (max < min)
                        min = max;
                chunk = 1 << min;

                /* mark multiblock chunks only */
                grp->bb_counters[min]++;
                if (min > 0)
                        mb_clear_bit(first >> min,
                                     buddy + sbi->s_mb_offsets[min]);

                len -= chunk;
                first += chunk;
        }
}

static int mb_avg_fragment_size_order(struct super_block *sb, ext4_grpblk_t len)
{
        int order;

        /*
         * We don't bother with a special lists groups with only 1 block free
         * extents and for completely empty groups.
         */
        order = fls(len) - 2;
        if (order < 0)
                return 0;
        if (order == MB_NUM_ORDERS(sb))
                order--;
        return order;
}

/* Move group to appropriate avg_fragment_size list */
static void
mb_update_avg_fragment_size(struct super_block *sb, struct ext4_group_info *grp)
{
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        int new_order;

        if (!test_opt2(sb, MB_OPTIMIZE_SCAN) || grp->bb_free == 0)
                return;

        new_order = mb_avg_fragment_size_order(sb,
                                        grp->bb_free / grp->bb_fragments);
        if (new_order == grp->bb_avg_fragment_size_order)
                return;

        if (grp->bb_avg_fragment_size_order != -1) {
                write_lock(&sbi->s_mb_avg_fragment_size_locks[
                                        grp->bb_avg_fragment_size_order]);
                list_del(&grp->bb_avg_fragment_size_node);
                write_unlock(&sbi->s_mb_avg_fragment_size_locks[
                                        grp->bb_avg_fragment_size_order]);
        }
        grp->bb_avg_fragment_size_order = new_order;
        write_lock(&sbi->s_mb_avg_fragment_size_locks[
                                        grp->bb_avg_fragment_size_order]);
        list_add_tail(&grp->bb_avg_fragment_size_node,
                &sbi->s_mb_avg_fragment_size[grp->bb_avg_fragment_size_order]);
        write_unlock(&sbi->s_mb_avg_fragment_size_locks[
                                        grp->bb_avg_fragment_size_order]);
}

/*
 * Choose next group by traversing largest_free_order lists. Updates *new_cr if
 * cr level needs an update.
 */
static void ext4_mb_choose_next_group_p2_aligned(struct ext4_allocation_context *ac,
                        enum criteria *new_cr, ext4_group_t *group, ext4_group_t ngroups)
{
        struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
        struct ext4_group_info *iter;
        int i;

        if (ac->ac_status == AC_STATUS_FOUND)
                return;

        if (unlikely(sbi->s_mb_stats && ac->ac_flags & EXT4_MB_CR_POWER2_ALIGNED_OPTIMIZED))
                atomic_inc(&sbi->s_bal_p2_aligned_bad_suggestions);

        for (i = ac->ac_2order; i < MB_NUM_ORDERS(ac->ac_sb); i++) {
                if (list_empty(&sbi->s_mb_largest_free_orders[i]))
                        continue;
                read_lock(&sbi->s_mb_largest_free_orders_locks[i]);
                if (list_empty(&sbi->s_mb_largest_free_orders[i])) {
                        read_unlock(&sbi->s_mb_largest_free_orders_locks[i]);
                        continue;
                }
                list_for_each_entry(iter, &sbi->s_mb_largest_free_orders[i],
                                    bb_largest_free_order_node) {
                        if (sbi->s_mb_stats)
                                atomic64_inc(&sbi->s_bal_cX_groups_considered[CR_POWER2_ALIGNED]);
                        if (likely(ext4_mb_good_group(ac, iter->bb_group, CR_POWER2_ALIGNED))) {
                                *group = iter->bb_group;
                                ac->ac_flags |= EXT4_MB_CR_POWER2_ALIGNED_OPTIMIZED;
                                read_unlock(&sbi->s_mb_largest_free_orders_locks[i]);
                                return;
                        }
                }
                read_unlock(&sbi->s_mb_largest_free_orders_locks[i]);
        }

        /* Increment cr and search again if no group is found */
        *new_cr = CR_GOAL_LEN_FAST;
}

/*
 * Find a suitable group of given order from the average fragments list.
 */
static struct ext4_group_info *
ext4_mb_find_good_group_avg_frag_lists(struct ext4_allocation_context *ac, int order)
{
        struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
        struct list_head *frag_list = &sbi->s_mb_avg_fragment_size[order];
        rwlock_t *frag_list_lock = &sbi->s_mb_avg_fragment_size_locks[order];
        struct ext4_group_info *grp = NULL, *iter;
        enum criteria cr = ac->ac_criteria;

        if (list_empty(frag_list))
                return NULL;
        read_lock(frag_list_lock);
        if (list_empty(frag_list)) {
                read_unlock(frag_list_lock);
                return NULL;
        }
        list_for_each_entry(iter, frag_list, bb_avg_fragment_size_node) {
                if (sbi->s_mb_stats)
                        atomic64_inc(&sbi->s_bal_cX_groups_considered[cr]);
                if (likely(ext4_mb_good_group(ac, iter->bb_group, cr))) {
                        grp = iter;
                        break;
                }
        }
        read_unlock(frag_list_lock);
        return grp;
}

/*
 * Choose next group by traversing average fragment size list of suitable
 * order. Updates *new_cr if cr level needs an update.
 */
static void ext4_mb_choose_next_group_goal_fast(struct ext4_allocation_context *ac,
                enum criteria *new_cr, ext4_group_t *group, ext4_group_t ngroups)
{
        struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
        struct ext4_group_info *grp = NULL;
        int i;

        if (unlikely(ac->ac_flags & EXT4_MB_CR_GOAL_LEN_FAST_OPTIMIZED)) {
                if (sbi->s_mb_stats)
                        atomic_inc(&sbi->s_bal_goal_fast_bad_suggestions);
        }

        for (i = mb_avg_fragment_size_order(ac->ac_sb, ac->ac_g_ex.fe_len);
             i < MB_NUM_ORDERS(ac->ac_sb); i++) {
                grp = ext4_mb_find_good_group_avg_frag_lists(ac, i);
                if (grp) {
                        *group = grp->bb_group;
                        ac->ac_flags |= EXT4_MB_CR_GOAL_LEN_FAST_OPTIMIZED;
                        return;
                }
        }

        /*
         * CR_BEST_AVAIL_LEN works based on the concept that we have
         * a larger normalized goal len request which can be trimmed to
         * a smaller goal len such that it can still satisfy original
         * request len. However, allocation request for non-regular
         * files never gets normalized.
         * See function ext4_mb_normalize_request() (EXT4_MB_HINT_DATA).
         */
        if (ac->ac_flags & EXT4_MB_HINT_DATA)
                *new_cr = CR_BEST_AVAIL_LEN;
        else
                *new_cr = CR_GOAL_LEN_SLOW;
}

/*
 * We couldn't find a group in CR_GOAL_LEN_FAST so try to find the highest free fragment
 * order we have and proactively trim the goal request length to that order to
 * find a suitable group faster.
 *
 * This optimizes allocation speed at the cost of slightly reduced
 * preallocations. However, we make sure that we don't trim the request too
 * much and fall to CR_GOAL_LEN_SLOW in that case.
 */
static void ext4_mb_choose_next_group_best_avail(struct ext4_allocation_context *ac,
                enum criteria *new_cr, ext4_group_t *group, ext4_group_t ngroups)
{
        struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
        struct ext4_group_info *grp = NULL;
        int i, order, min_order;
        unsigned long num_stripe_clusters = 0;

        if (unlikely(ac->ac_flags & EXT4_MB_CR_BEST_AVAIL_LEN_OPTIMIZED)) {
                if (sbi->s_mb_stats)
                        atomic_inc(&sbi->s_bal_best_avail_bad_suggestions);
        }

        /*
         * mb_avg_fragment_size_order() returns order in a way that makes
         * retrieving back the length using (1 << order) inaccurate. Hence, use
         * fls() instead since we need to know the actual length while modifying
         * goal length.
         */
        order = fls(ac->ac_g_ex.fe_len) - 1;
        min_order = order - sbi->s_mb_best_avail_max_trim_order;
        if (min_order < 0)
                min_order = 0;

        if (sbi->s_stripe > 0) {
                /*
                 * We are assuming that stripe size is always a multiple of
                 * cluster ratio otherwise __ext4_fill_super exists early.
                 */
                num_stripe_clusters = EXT4_NUM_B2C(sbi, sbi->s_stripe);
                if (1 << min_order < num_stripe_clusters)
                        /*
                         * We consider 1 order less because later we round
                         * up the goal len to num_stripe_clusters
                         */
                        min_order = fls(num_stripe_clusters) - 1;
        }

        if (1 << min_order < ac->ac_o_ex.fe_len)
                min_order = fls(ac->ac_o_ex.fe_len);

        for (i = order; i >= min_order; i--) {
                int frag_order;
                /*
                 * Scale down goal len to make sure we find something
                 * in the free fragments list. Basically, reduce
                 * preallocations.
                 */
                ac->ac_g_ex.fe_len = 1 << i;

                if (num_stripe_clusters > 0) {
                        /*
                         * Try to round up the adjusted goal length to
                         * stripe size (in cluster units) multiple for
                         * efficiency.
                         */
                        ac->ac_g_ex.fe_len = roundup(ac->ac_g_ex.fe_len,
                                                     num_stripe_clusters);
                }

                frag_order = mb_avg_fragment_size_order(ac->ac_sb,
                                                        ac->ac_g_ex.fe_len);

                grp = ext4_mb_find_good_group_avg_frag_lists(ac, frag_order);
                if (grp) {
                        *group = grp->bb_group;
                        ac->ac_flags |= EXT4_MB_CR_BEST_AVAIL_LEN_OPTIMIZED;
                        return;
                }
        }

        /* Reset goal length to original goal length before falling into CR_GOAL_LEN_SLOW */
        ac->ac_g_ex.fe_len = ac->ac_orig_goal_len;
        *new_cr = CR_GOAL_LEN_SLOW;
}

static inline int should_optimize_scan(struct ext4_allocation_context *ac)
{
        if (unlikely(!test_opt2(ac->ac_sb, MB_OPTIMIZE_SCAN)))
                return 0;
        if (ac->ac_criteria >= CR_GOAL_LEN_SLOW)
                return 0;
        if (!ext4_test_inode_flag(ac->ac_inode, EXT4_INODE_EXTENTS))
                return 0;
        return 1;
}

/*
 * Return next linear group for allocation. If linear traversal should not be
 * performed, this function just returns the same group
 */
static ext4_group_t
next_linear_group(struct ext4_allocation_context *ac, ext4_group_t group,
                  ext4_group_t ngroups)
{
        if (!should_optimize_scan(ac))
                goto inc_and_return;

        if (ac->ac_groups_linear_remaining) {
                ac->ac_groups_linear_remaining--;
                goto inc_and_return;
        }

        return group;
inc_and_return:
        /*
         * Artificially restricted ngroups for non-extent
         * files makes group > ngroups possible on first loop.
         */
        return group + 1 >= ngroups ? 0 : group + 1;
}

/*
 * ext4_mb_choose_next_group: choose next group for allocation.
 *
 * @ac        Allocation Context
 * @new_cr    This is an output parameter. If the there is no good group
 *            available at current CR level, this field is updated to indicate
 *            the new cr level that should be used.
 * @group     This is an input / output parameter. As an input it indicates the
 *            next group that the allocator intends to use for allocation. As
 *            output, this field indicates the next group that should be used as
 *            determined by the optimization functions.
 * @ngroups   Total number of groups
 */
static void ext4_mb_choose_next_group(struct ext4_allocation_context *ac,
                enum criteria *new_cr, ext4_group_t *group, ext4_group_t ngroups)
{
        *new_cr = ac->ac_criteria;

        if (!should_optimize_scan(ac) || ac->ac_groups_linear_remaining) {
                *group = next_linear_group(ac, *group, ngroups);
                return;
        }

        if (*new_cr == CR_POWER2_ALIGNED) {
                ext4_mb_choose_next_group_p2_aligned(ac, new_cr, group, ngroups);
        } else if (*new_cr == CR_GOAL_LEN_FAST) {
                ext4_mb_choose_next_group_goal_fast(ac, new_cr, group, ngroups);
        } else if (*new_cr == CR_BEST_AVAIL_LEN) {
                ext4_mb_choose_next_group_best_avail(ac, new_cr, group, ngroups);
        } else {
                /*
                 * TODO: For CR=2, we can arrange groups in an rb tree sorted by
                 * bb_free. But until that happens, we should never come here.
                 */
                WARN_ON(1);
        }
}

/*
 * Cache the order of the largest free extent we have available in this block
 * group.
 */
static void
mb_set_largest_free_order(struct super_block *sb, struct ext4_group_info *grp)
{
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        int i;

        for (i = MB_NUM_ORDERS(sb) - 1; i >= 0; i--)
                if (grp->bb_counters[i] > 0)
                        break;
        /* No need to move between order lists? */
        if (!test_opt2(sb, MB_OPTIMIZE_SCAN) ||
            i == grp->bb_largest_free_order) {
                grp->bb_largest_free_order = i;
                return;
        }

        if (grp->bb_largest_free_order >= 0) {
                write_lock(&sbi->s_mb_largest_free_orders_locks[
                                              grp->bb_largest_free_order]);
                list_del_init(&grp->bb_largest_free_order_node);
                write_unlock(&sbi->s_mb_largest_free_orders_locks[
                                              grp->bb_largest_free_order]);
        }
        grp->bb_largest_free_order = i;
        if (grp->bb_largest_free_order >= 0 && grp->bb_free) {
                write_lock(&sbi->s_mb_largest_free_orders_locks[
                                              grp->bb_largest_free_order]);
                list_add_tail(&grp->bb_largest_free_order_node,
                      &sbi->s_mb_largest_free_orders[grp->bb_largest_free_order]);
                write_unlock(&sbi->s_mb_largest_free_orders_locks[
                                              grp->bb_largest_free_order]);
        }
}

static noinline_for_stack
void ext4_mb_generate_buddy(struct super_block *sb,
                            void *buddy, void *bitmap, ext4_group_t group,
                            struct ext4_group_info *grp)
{
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        ext4_grpblk_t max = EXT4_CLUSTERS_PER_GROUP(sb);
        ext4_grpblk_t i = 0;
        ext4_grpblk_t first;
        ext4_grpblk_t len;
        unsigned free = 0;
        unsigned fragments = 0;
        unsigned long long period = get_cycles();

        /* initialize buddy from bitmap which is aggregation
         * of on-disk bitmap and preallocations */
        i = mb_find_next_zero_bit(bitmap, max, 0);
        grp->bb_first_free = i;
        while (i < max) {
                fragments++;
                first = i;
                i = mb_find_next_bit(bitmap, max, i);
                len = i - first;
                free += len;
                if (len > 1)
                        ext4_mb_mark_free_simple(sb, buddy, first, len, grp);
                else
                        grp->bb_counters[0]++;
                if (i < max)
                        i = mb_find_next_zero_bit(bitmap, max, i);
        }
        grp->bb_fragments = fragments;

        if (free != grp->bb_free) {
                ext4_grp_locked_error(sb, group, 0, 0,
                                      "block bitmap and bg descriptor "
                                      "inconsistent: %u vs %u free clusters",
                                      free, grp->bb_free);
                /*
                 * If we intend to continue, we consider group descriptor
                 * corrupt and update bb_free using bitmap value
                 */
                grp->bb_free = free;
                ext4_mark_group_bitmap_corrupted(sb, group,
                                        EXT4_GROUP_INFO_BBITMAP_CORRUPT);
        }
        mb_set_largest_free_order(sb, grp);
        mb_update_avg_fragment_size(sb, grp);

        clear_bit(EXT4_GROUP_INFO_NEED_INIT_BIT, &(grp->bb_state));

        period = get_cycles() - period;
        atomic_inc(&sbi->s_mb_buddies_generated);
        atomic64_add(period, &sbi->s_mb_generation_time);
}

/* The buddy information is attached the buddy cache inode
 * for convenience. The information regarding each group
 * is loaded via ext4_mb_load_buddy. The information involve
 * block bitmap and buddy information. The information are
 * stored in the inode as
 *
 * {                        page                        }
 * [ group 0 bitmap][ group 0 buddy] [group 1][ group 1]...
 *
 *
 * one block each for bitmap and buddy information.
 * So for each group we take up 2 blocks. A page can
 * contain blocks_per_page (PAGE_SIZE / blocksize)  blocks.
 * So it can have information regarding groups_per_page which
 * is blocks_per_page/2
 *
 * Locking note:  This routine takes the block group lock of all groups
 * for this page; do not hold this lock when calling this routine!
 */

static int ext4_mb_init_cache(struct page *page, char *incore, gfp_t gfp)
{
        ext4_group_t ngroups;
        unsigned int blocksize;
        int blocks_per_page;
        int groups_per_page;
        int err = 0;
        int i;
        ext4_group_t first_group, group;
        int first_block;
        struct super_block *sb;
        struct buffer_head *bhs;
        struct buffer_head **bh = NULL;
        struct inode *inode;
        char *data;
        char *bitmap;
        struct ext4_group_info *grinfo;

        inode = page->mapping->host;
        sb = inode->i_sb;
        ngroups = ext4_get_groups_count(sb);
        blocksize = i_blocksize(inode);
        blocks_per_page = PAGE_SIZE / blocksize;

        mb_debug(sb, "init page %lu\n", page->index);

        groups_per_page = blocks_per_page >> 1;
        if (groups_per_page == 0)
                groups_per_page = 1;

        /* allocate buffer_heads to read bitmaps */
        if (groups_per_page > 1) {
                i = sizeof(struct buffer_head *) * groups_per_page;
                bh = kzalloc(i, gfp);
                if (bh == NULL)
                        return -ENOMEM;
        } else
                bh = &bhs;

        first_group = page->index * blocks_per_page / 2;

        /* read all groups the page covers into the cache */
        for (i = 0, group = first_group; i < groups_per_page; i++, group++) {
                if (group >= ngroups)
                        break;

                grinfo = ext4_get_group_info(sb, group);
                if (!grinfo)
                        continue;
                /*
                 * If page is uptodate then we came here after online resize
                 * which added some new uninitialized group info structs, so
                 * we must skip all initialized uptodate buddies on the page,
                 * which may be currently in use by an allocating task.
                 */
                if (PageUptodate(page) && !EXT4_MB_GRP_NEED_INIT(grinfo)) {
                        bh[i] = NULL;
                        continue;
                }
                bh[i] = ext4_read_block_bitmap_nowait(sb, group, false);
                if (IS_ERR(bh[i])) {
                        err = PTR_ERR(bh[i]);
                        bh[i] = NULL;
                        goto out;
                }
                mb_debug(sb, "read bitmap for group %u\n", group);
        }

        /* wait for I/O completion */
        for (i = 0, group = first_group; i < groups_per_page; i++, group++) {
                int err2;

                if (!bh[i])
                        continue;
                err2 = ext4_wait_block_bitmap(sb, group, bh[i]);
                if (!err)
                        err = err2;
        }

        first_block = page->index * blocks_per_page;
        for (i = 0; i < blocks_per_page; i++) {
                group = (first_block + i) >> 1;
                if (group >= ngroups)
                        break;

                if (!bh[group - first_group])
                        /* skip initialized uptodate buddy */
                        continue;

                if (!buffer_verified(bh[group - first_group]))
                        /* Skip faulty bitmaps */
                        continue;
                err = 0;

                /*
                 * data carry information regarding this
                 * particular group in the format specified
                 * above
                 *
                 */
                data = page_address(page) + (i * blocksize);
                bitmap = bh[group - first_group]->b_data;

                /*
                 * We place the buddy block and bitmap block
                 * close together
                 */
                grinfo = ext4_get_group_info(sb, group);
                if (!grinfo) {
                        err = -EFSCORRUPTED;
                        goto out;
                }
                if ((first_block + i) & 1) {
                        /* this is block of buddy */
                        BUG_ON(incore == NULL);
                        mb_debug(sb, "put buddy for group %u in page %lu/%x\n",
                                group, page->index, i * blocksize);
                        trace_ext4_mb_buddy_bitmap_load(sb, group);
                        grinfo->bb_fragments = 0;
                        memset(grinfo->bb_counters, 0,
                               sizeof(*grinfo->bb_counters) *
                               (MB_NUM_ORDERS(sb)));
                        /*
                         * incore got set to the group block bitmap below
                         */
                        ext4_lock_group(sb, group);
                        /* init the buddy */
                        memset(data, 0xff, blocksize);
                        ext4_mb_generate_buddy(sb, data, incore, group, grinfo);
                        ext4_unlock_group(sb, group);
                        incore = NULL;
                } else {
                        /* this is block of bitmap */
                        BUG_ON(incore != NULL);
                        mb_debug(sb, "put bitmap for group %u in page %lu/%x\n",
                                group, page->index, i * blocksize);
                        trace_ext4_mb_bitmap_load(sb, group);

                        /* see comments in ext4_mb_put_pa() */
                        ext4_lock_group(sb, group);
                        memcpy(data, bitmap, blocksize);

                        /* mark all preallocated blks used in in-core bitmap */
                        ext4_mb_generate_from_pa(sb, data, group);
                        WARN_ON_ONCE(!RB_EMPTY_ROOT(&grinfo->bb_free_root));
                        ext4_unlock_group(sb, group);

                        /* set incore so that the buddy information can be
                         * generated using this
                         */
                        incore = data;
                }
        }
        SetPageUptodate(page);

out:
        if (bh) {
                for (i = 0; i < groups_per_page; i++)
                        brelse(bh[i]);
                if (bh != &bhs)
                        kfree(bh);
        }
        return err;
}

/*
 * Lock the buddy and bitmap pages. This make sure other parallel init_group
 * on the same buddy page doesn't happen whild holding the buddy page lock.
 * Return locked buddy and bitmap pages on e4b struct. If buddy and bitmap
 * are on the same page e4b->bd_buddy_page is NULL and return value is 0.
 */
static int ext4_mb_get_buddy_page_lock(struct super_block *sb,
                ext4_group_t group, struct ext4_buddy *e4b, gfp_t gfp)
{
        struct inode *inode = EXT4_SB(sb)->s_buddy_cache;
        int block, pnum, poff;
        int blocks_per_page;
        struct page *page;

        e4b->bd_buddy_page = NULL;
        e4b->bd_bitmap_page = NULL;

        blocks_per_page = PAGE_SIZE / sb->s_blocksize;
        /*
         * the buddy cache inode stores the block bitmap
         * and buddy information in consecutive blocks.
         * So for each group we need two blocks.
         */
        block = group * 2;
        pnum = block / blocks_per_page;
        poff = block % blocks_per_page;
        page = find_or_create_page(inode->i_mapping, pnum, gfp);
        if (!page)
                return -ENOMEM;
        BUG_ON(page->mapping != inode->i_mapping);
        e4b->bd_bitmap_page = page;
        e4b->bd_bitmap = page_address(page) + (poff * sb->s_blocksize);

        if (blocks_per_page >= 2) {
                /* buddy and bitmap are on the same page */
                return 0;
        }

        block++;
        pnum = block / blocks_per_page;
        page = find_or_create_page(inode->i_mapping, pnum, gfp);
        if (!page)
                return -ENOMEM;
        BUG_ON(page->mapping != inode->i_mapping);
        e4b->bd_buddy_page = page;
        return 0;
}

static void ext4_mb_put_buddy_page_lock(struct ext4_buddy *e4b)
{
        if (e4b->bd_bitmap_page) {
                unlock_page(e4b->bd_bitmap_page);
                put_page(e4b->bd_bitmap_page);
        }
        if (e4b->bd_buddy_page) {
                unlock_page(e4b->bd_buddy_page);
                put_page(e4b->bd_buddy_page);
        }
}

/*
 * Locking note:  This routine calls ext4_mb_init_cache(), which takes the
 * block group lock of all groups for this page; do not hold the BG lock when
 * calling this routine!
 */
static noinline_for_stack
int ext4_mb_init_group(struct super_block *sb, ext4_group_t group, gfp_t gfp)
{

        struct ext4_group_info *this_grp;
        struct ext4_buddy e4b;
        struct page *page;
        int ret = 0;

        might_sleep();
        mb_debug(sb, "init group %u\n", group);
        this_grp = ext4_get_group_info(sb, group);
        if (!this_grp)
                return -EFSCORRUPTED;

        /*
         * This ensures that we don't reinit the buddy cache
         * page which map to the group from which we are already
         * allocating. If we are looking at the buddy cache we would
         * have taken a reference using ext4_mb_load_buddy and that
         * would have pinned buddy page to page cache.
         * The call to ext4_mb_get_buddy_page_lock will mark the
         * page accessed.
         */
        ret = ext4_mb_get_buddy_page_lock(sb, group, &e4b, gfp);
        if (ret || !EXT4_MB_GRP_NEED_INIT(this_grp)) {
                /*
                 * somebody initialized the group
                 * return without doing anything
                 */
                goto err;
        }

        page = e4b.bd_bitmap_page;
        ret = ext4_mb_init_cache(page, NULL, gfp);
        if (ret)
                goto err;
        if (!PageUptodate(page)) {
                ret = -EIO;
                goto err;
        }

        if (e4b.bd_buddy_page == NULL) {
                /*
                 * If both the bitmap and buddy are in
                 * the same page we don't need to force
                 * init the buddy
                 */
                ret = 0;
                goto err;
        }
        /* init buddy cache */
        page = e4b.bd_buddy_page;
        ret = ext4_mb_init_cache(page, e4b.bd_bitmap, gfp);
        if (ret)
                goto err;
        if (!PageUptodate(page)) {
                ret = -EIO;
                goto err;
        }
err:
        ext4_mb_put_buddy_page_lock(&e4b);
        return ret;
}

/*
 * Locking note:  This routine calls ext4_mb_init_cache(), which takes the
 * block group lock of all groups for this page; do not hold the BG lock when
 * calling this routine!
 */
static noinline_for_stack int
ext4_mb_load_buddy_gfp(struct super_block *sb, ext4_group_t group,
                       struct ext4_buddy *e4b, gfp_t gfp)
{
        int blocks_per_page;
        int block;
        int pnum;
        int poff;
        struct page *page;
        int ret;
        struct ext4_group_info *grp;
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        struct inode *inode = sbi->s_buddy_cache;

        might_sleep();
        mb_debug(sb, "load group %u\n", group);

        blocks_per_page = PAGE_SIZE / sb->s_blocksize;
        grp = ext4_get_group_info(sb, group);
        if (!grp)
                return -EFSCORRUPTED;

        e4b->bd_blkbits = sb->s_blocksize_bits;
        e4b->bd_info = grp;
        e4b->bd_sb = sb;
        e4b->bd_group = group;
        e4b->bd_buddy_page = NULL;
        e4b->bd_bitmap_page = NULL;

        if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) {
                /*
                 * we need full data about the group
                 * to make a good selection
                 */
                ret = ext4_mb_init_group(sb, group, gfp);
                if (ret)
                        return ret;
        }

        /*
         * the buddy cache inode stores the block bitmap
         * and buddy information in consecutive blocks.
         * So for each group we need two blocks.
         */
        block = group * 2;
        pnum = block / blocks_per_page;
        poff = block % blocks_per_page;

        /* we could use find_or_create_page(), but it locks page
         * what we'd like to avoid in fast path ... */
        page = find_get_page_flags(inode->i_mapping, pnum, FGP_ACCESSED);
        if (page == NULL || !PageUptodate(page)) {
                if (page)
                        /*
                         * drop the page reference and try
                         * to get the page with lock. If we
                         * are not uptodate that implies
                         * somebody just created the page but
                         * is yet to initialize the same. So
                         * wait for it to initialize.
                         */
                        put_page(page);
                page = find_or_create_page(inode->i_mapping, pnum, gfp);
                if (page) {
                        if (WARN_RATELIMIT(page->mapping != inode->i_mapping,
        "ext4: bitmap's paging->mapping != inode->i_mapping\n")) {
                                /* should never happen */
                                unlock_page(page);
                                ret = -EINVAL;
                                goto err;
                        }
                        if (!PageUptodate(page)) {
                                ret = ext4_mb_init_cache(page, NULL, gfp);
                                if (ret) {
                                        unlock_page(page);
                                        goto err;
                                }
                                mb_cmp_bitmaps(e4b, page_address(page) +
                                               (poff * sb->s_blocksize));
                        }
                        unlock_page(page);
                }
        }
        if (page == NULL) {
                ret = -ENOMEM;
                goto err;
        }
        if (!PageUptodate(page)) {
                ret = -EIO;
                goto err;
        }

        /* Pages marked accessed already */
        e4b->bd_bitmap_page = page;
        e4b->bd_bitmap = page_address(page) + (poff * sb->s_blocksize);

        block++;
        pnum = block / blocks_per_page;
        poff = block % blocks_per_page;

        page = find_get_page_flags(inode->i_mapping, pnum, FGP_ACCESSED);
        if (page == NULL || !PageUptodate(page)) {
                if (page)
                        put_page(page);
                page = find_or_create_page(inode->i_mapping, pnum, gfp);
                if (page) {
                        if (WARN_RATELIMIT(page->mapping != inode->i_mapping,
        "ext4: buddy bitmap's page->mapping != inode->i_mapping\n")) {
                                /* should never happen */
                                unlock_page(page);
                                ret = -EINVAL;
                                goto err;
                        }
                        if (!PageUptodate(page)) {
                                ret = ext4_mb_init_cache(page, e4b->bd_bitmap,
                                                         gfp);
                                if (ret) {
                                        unlock_page(page);
                                        goto err;
                                }
                        }
                        unlock_page(page);
                }
        }
        if (page == NULL) {
                ret = -ENOMEM;
                goto err;
        }
        if (!PageUptodate(page)) {
                ret = -EIO;
                goto err;
        }

        /* Pages marked accessed already */
        e4b->bd_buddy_page = page;
        e4b->bd_buddy = page_address(page) + (poff * sb->s_blocksize);

        return 0;

err:
        if (page)
                put_page(page);
        if (e4b->bd_bitmap_page)
                put_page(e4b->bd_bitmap_page);

        e4b->bd_buddy = NULL;
        e4b->bd_bitmap = NULL;
        return ret;
}

static int ext4_mb_load_buddy(struct super_block *sb, ext4_group_t group,
                              struct ext4_buddy *e4b)
{
        return ext4_mb_load_buddy_gfp(sb, group, e4b, GFP_NOFS);
}

static void ext4_mb_unload_buddy(struct ext4_buddy *e4b)
{
        if (e4b->bd_bitmap_page)
                put_page(e4b->bd_bitmap_page);
        if (e4b->bd_buddy_page)
                put_page(e4b->bd_buddy_page);
}


static int mb_find_order_for_block(struct ext4_buddy *e4b, int block)
{
        int order = 1, max;
        void *bb;

        BUG_ON(e4b->bd_bitmap == e4b->bd_buddy);
        BUG_ON(block >= (1 << (e4b->bd_blkbits + 3)));

        while (order <= e4b->bd_blkbits + 1) {
                bb = mb_find_buddy(e4b, order, &max);
                if (!mb_test_bit(block >> order, bb)) {
                        /* this block is part of buddy of order 'order' */
                        return order;
                }
                order++;
        }
        return 0;
}

static void mb_clear_bits(void *bm, int cur, int len)
{
        __u32 *addr;

        len = cur + len;
        while (cur < len) {
                if ((cur & 31) == 0 && (len - cur) >= 32) {
                        /* fast path: clear whole word at once */
                        addr = bm + (cur >> 3);
                        *addr = 0;
                        cur += 32;
                        continue;
                }
                mb_clear_bit(cur, bm);
                cur++;
        }
}

/* clear bits in given range
 * will return first found zero bit if any, -1 otherwise
 */
static int mb_test_and_clear_bits(void *bm, int cur, int len)
{
        __u32 *addr;
        int zero_bit = -1;

        len = cur + len;
        while (cur < len) {
                if ((cur & 31) == 0 && (len - cur) >= 32) {
                        /* fast path: clear whole word at once */
                        addr = bm + (cur >> 3);
                        if (*addr != (__u32)(-1) && zero_bit == -1)
                                zero_bit = cur + mb_find_next_zero_bit(addr, 32, 0);
                        *addr = 0;
                        cur += 32;
                        continue;
                }
                if (!mb_test_and_clear_bit(cur, bm) && zero_bit == -1)
                        zero_bit = cur;
                cur++;
        }

        return zero_bit;
}

void mb_set_bits(void *bm, int cur, int len)
{
        __u32 *addr;

        len = cur + len;
        while (cur < len) {
                if ((cur & 31) == 0 && (len - cur) >= 32) {
                        /* fast path: set whole word at once */
                        addr = bm + (cur >> 3);
                        *addr = 0xffffffff;
                        cur += 32;
                        continue;
                }
                mb_set_bit(cur, bm);
                cur++;
        }
}

static inline int mb_buddy_adjust_border(int* bit, void* bitmap, int side)
{
        if (mb_test_bit(*bit + side, bitmap)) {
                mb_clear_bit(*bit, bitmap);
                (*bit) -= side;
                return 1;
        }
        else {
                (*bit) += side;
                mb_set_bit(*bit, bitmap);
                return -1;
        }
}

static void mb_buddy_mark_free(struct ext4_buddy *e4b, int first, int last)
{
        int max;
        int order = 1;
        void *buddy = mb_find_buddy(e4b, order, &max);

        while (buddy) {
                void *buddy2;

                /* Bits in range [first; last] are known to be set since
                 * corresponding blocks were allocated. Bits in range
                 * (first; last) will stay set because they form buddies on
                 * upper layer. We just deal with borders if they don't
                 * align with upper layer and then go up.
                 * Releasing entire group is all about clearing
                 * single bit of highest order buddy.
                 */

                /* Example:
                 * ---------------------------------
                 * |   1   |   1   |   1   |   1   |
                 * ---------------------------------
                 * | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
                 * ---------------------------------
                 *   0   1   2   3   4   5   6   7
                 *      \_____________________/
                 *
                 * Neither [1] nor [6] is aligned to above layer.
                 * Left neighbour [0] is free, so mark it busy,
                 * decrease bb_counters and extend range to
                 * [0; 6]
                 * Right neighbour [7] is busy. It can't be coaleasced with [6], so
                 * mark [6] free, increase bb_counters and shrink range to
                 * [0; 5].
                 * Then shift range to [0; 2], go up and do the same.
                 */


                if (first & 1)
                        e4b->bd_info->bb_counters[order] += mb_buddy_adjust_border(&first, buddy, -1);
                if (!(last & 1))
                        e4b->bd_info->bb_counters[order] += mb_buddy_adjust_border(&last, buddy, 1);
                if (first > last)
                        break;
                order++;

                buddy2 = mb_find_buddy(e4b, order, &max);
                if (!buddy2) {
                        mb_clear_bits(buddy, first, last - first + 1);
                        e4b->bd_info->bb_counters[order - 1] += last - first + 1;
                        break;
                }
                first >>= 1;
                last >>= 1;
                buddy = buddy2;
        }
}

static void mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b,
                           int first, int count)
{
        int left_is_free = 0;
        int right_is_free = 0;
        int block;
        int last = first + count - 1;
        struct super_block *sb = e4b->bd_sb;

        if (WARN_ON(count == 0))
                return;
        BUG_ON(last >= (sb->s_blocksize << 3));
        assert_spin_locked(ext4_group_lock_ptr(sb, e4b->bd_group));
        /* Don't bother if the block group is corrupt. */
        if (unlikely(EXT4_MB_GRP_BBITMAP_CORRUPT(e4b->bd_info)))
                return;

        mb_check_buddy(e4b);
        mb_free_blocks_double(inode, e4b, first, count);

        this_cpu_inc(discard_pa_seq);
        e4b->bd_info->bb_free += count;
        if (first < e4b->bd_info->bb_first_free)
                e4b->bd_info->bb_first_free = first;

        /* access memory sequentially: check left neighbour,
         * clear range and then check right neighbour
         */
        if (first != 0)
                left_is_free = !mb_test_bit(first - 1, e4b->bd_bitmap);
        block = mb_test_and_clear_bits(e4b->bd_bitmap, first, count);
        if (last + 1 < EXT4_SB(sb)->s_mb_maxs[0])
                right_is_free = !mb_test_bit(last + 1, e4b->bd_bitmap);

        if (unlikely(block != -1)) {
                struct ext4_sb_info *sbi = EXT4_SB(sb);
                ext4_fsblk_t blocknr;

                blocknr = ext4_group_first_block_no(sb, e4b->bd_group);
                blocknr += EXT4_C2B(sbi, block);
                if (!(sbi->s_mount_state & EXT4_FC_REPLAY)) {
                        ext4_grp_locked_error(sb, e4b->bd_group,
                                              inode ? inode->i_ino : 0,
                                              blocknr,
                                              "freeing already freed block (bit %u); block bitmap corrupt.",
                                              block);
                        ext4_mark_group_bitmap_corrupted(
                                sb, e4b->bd_group,
                                EXT4_GROUP_INFO_BBITMAP_CORRUPT);
                }
                goto done;
        }

        /* let's maintain fragments counter */
        if (left_is_free && right_is_free)
                e4b->bd_info->bb_fragments--;
        else if (!left_is_free && !right_is_free)
                e4b->bd_info->bb_fragments++;

        /* buddy[0] == bd_bitmap is a special case, so handle
         * it right away and let mb_buddy_mark_free stay free of
         * zero order checks.
         * Check if neighbours are to be coaleasced,
         * adjust bitmap bb_counters and borders appropriately.
         */
        if (first & 1) {
                first += !left_is_free;
                e4b->bd_info->bb_counters[0] += left_is_free ? -1 : 1;
        }
        if (!(last & 1)) {
                last -= !right_is_free;
                e4b->bd_info->bb_counters[0] += right_is_free ? -1 : 1;
        }

        if (first <= last)
                mb_buddy_mark_free(e4b, first >> 1, last >> 1);

done:
        mb_set_largest_free_order(sb, e4b->bd_info);
        mb_update_avg_fragment_size(sb, e4b->bd_info);
        mb_check_buddy(e4b);
}

static int mb_find_extent(struct ext4_buddy *e4b, int block,
                                int needed, struct ext4_free_extent *ex)
{
        int next = block;
        int max, order;
        void *buddy;

        assert_spin_locked(ext4_group_lock_ptr(e4b->bd_sb, e4b->bd_group));
        BUG_ON(ex == NULL);

        buddy = mb_find_buddy(e4b, 0, &max);
        BUG_ON(buddy == NULL);
        BUG_ON(block >= max);
        if (mb_test_bit(block, buddy)) {
                ex->fe_len = 0;
                ex->fe_start = 0;
                ex->fe_group = 0;
                return 0;
        }

        /* find actual order */
        order = mb_find_order_for_block(e4b, block);
        block = block >> order;

        ex->fe_len = 1 << order;
        ex->fe_start = block << order;
        ex->fe_group = e4b->bd_group;

        /* calc difference from given start */
        next = next - ex->fe_start;
        ex->fe_len -= next;
        ex->fe_start += next;

        while (needed > ex->fe_len &&
               mb_find_buddy(e4b, order, &max)) {

                if (block + 1 >= max)
                        break;

                next = (block + 1) * (1 << order);
                if (mb_test_bit(next, e4b->bd_bitmap))
                        break;

                order = mb_find_order_for_block(e4b, next);

                block = next >> order;
                ex->fe_len += 1 << order;
        }

        if (ex->fe_start + ex->fe_len > EXT4_CLUSTERS_PER_GROUP(e4b->bd_sb)) {
                /* Should never happen! (but apparently sometimes does?!?) */
                WARN_ON(1);
                ext4_grp_locked_error(e4b->bd_sb, e4b->bd_group, 0, 0,
                        "corruption or bug in mb_find_extent "
                        "block=%d, order=%d needed=%d ex=%u/%d/%d@%u",
                        block, order, needed, ex->fe_group, ex->fe_start,
                        ex->fe_len, ex->fe_logical);
                ex->fe_len = 0;
                ex->fe_start = 0;
                ex->fe_group = 0;
        }
        return ex->fe_len;
}

static int mb_mark_used(struct ext4_buddy *e4b, struct ext4_free_extent *ex)
{
        int ord;
        int mlen = 0;
        int max = 0;
        int cur;
        int start = ex->fe_start;
        int len = ex->fe_len;
        unsigned ret = 0;
        int len0 = len;
        void *buddy;
        bool split = false;

        BUG_ON(start + len > (e4b->bd_sb->s_blocksize << 3));
        BUG_ON(e4b->bd_group != ex->fe_group);
        assert_spin_locked(ext4_group_lock_ptr(e4b->bd_sb, e4b->bd_group));
        mb_check_buddy(e4b);
        mb_mark_used_double(e4b, start, len);

        this_cpu_inc(discard_pa_seq);
        e4b->bd_info->bb_free -= len;
        if (e4b->bd_info->bb_first_free == start)
                e4b->bd_info->bb_first_free += len;

        /* let's maintain fragments counter */
        if (start != 0)
                mlen = !mb_test_bit(start - 1, e4b->bd_bitmap);
        if (start + len < EXT4_SB(e4b->bd_sb)->s_mb_maxs[0])
                max = !mb_test_bit(start + len, e4b->bd_bitmap);
        if (mlen && max)
                e4b->bd_info->bb_fragments++;
        else if (!mlen && !max)
                e4b->bd_info->bb_fragments--;

        /* let's maintain buddy itself */
        while (len) {
                if (!split)
                        ord = mb_find_order_for_block(e4b, start);

                if (((start >> ord) << ord) == start && len >= (1 << ord)) {
                        /* the whole chunk may be allocated at once! */
                        mlen = 1 << ord;
                        if (!split)
                                buddy = mb_find_buddy(e4b, ord, &max);
                        else
                                split = false;
                        BUG_ON((start >> ord) >= max);
                        mb_set_bit(start >> ord, buddy);
                        e4b->bd_info->bb_counters[ord]--;
                        start += mlen;
                        len -= mlen;
                        BUG_ON(len < 0);
                        continue;
                }

                /* store for history */
                if (ret == 0)
                        ret = len | (ord << 16);

                /* we have to split large buddy */
                BUG_ON(ord <= 0);
                buddy = mb_find_buddy(e4b, ord, &max);
                mb_set_bit(start >> ord, buddy);
                e4b->bd_info->bb_counters[ord]--;

                ord--;
                cur = (start >> ord) & ~1U;
                buddy = mb_find_buddy(e4b, ord, &max);
                mb_clear_bit(cur, buddy);
                mb_clear_bit(cur + 1, buddy);
                e4b->bd_info->bb_counters[ord]++;
                e4b->bd_info->bb_counters[ord]++;
                split = true;
        }
        mb_set_largest_free_order(e4b->bd_sb, e4b->bd_info);

        mb_update_avg_fragment_size(e4b->bd_sb, e4b->bd_info);
        mb_set_bits(e4b->bd_bitmap, ex->fe_start, len0);
        mb_check_buddy(e4b);

        return ret;
}

/*
 * Must be called under group lock!
 */
static void ext4_mb_use_best_found(struct ext4_allocation_context *ac,
                                        struct ext4_buddy *e4b)
{
        struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
        int ret;

        BUG_ON(ac->ac_b_ex.fe_group != e4b->bd_group);
        BUG_ON(ac->ac_status == AC_STATUS_FOUND);

        ac->ac_b_ex.fe_len = min(ac->ac_b_ex.fe_len, ac->ac_g_ex.fe_len);
        ac->ac_b_ex.fe_logical = ac->ac_g_ex.fe_logical;
        ret = mb_mark_used(e4b, &ac->ac_b_ex);

        /* preallocation can change ac_b_ex, thus we store actually
         * allocated blocks for history */
        ac->ac_f_ex = ac->ac_b_ex;

        ac->ac_status = AC_STATUS_FOUND;
        ac->ac_tail = ret & 0xffff;
        ac->ac_buddy = ret >> 16;

        /*
         * take the page reference. We want the page to be pinned
         * so that we don't get a ext4_mb_init_cache_call for this
         * group until we update the bitmap. That would mean we
         * double allocate blocks. The reference is dropped
         * in ext4_mb_release_context
         */
        ac->ac_bitmap_page = e4b->bd_bitmap_page;
        get_page(ac->ac_bitmap_page);
        ac->ac_buddy_page = e4b->bd_buddy_page;
        get_page(ac->ac_buddy_page);
        /* store last allocated for subsequent stream allocation */
        if (ac->ac_flags & EXT4_MB_STREAM_ALLOC) {
                spin_lock(&sbi->s_md_lock);
                sbi->s_mb_last_group = ac->ac_f_ex.fe_group;
                sbi->s_mb_last_start = ac->ac_f_ex.fe_start;
                spin_unlock(&sbi->s_md_lock);
        }
        /*
         * As we've just preallocated more space than
         * user requested originally, we store allocated
         * space in a special descriptor.
         */
        if (ac->ac_o_ex.fe_len < ac->ac_b_ex.fe_len)
                ext4_mb_new_preallocation(ac);

}

static void ext4_mb_check_limits(struct ext4_allocation_context *ac,
                                        struct ext4_buddy *e4b,
                                        int finish_group)
{
        struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
        struct ext4_free_extent *bex = &ac->ac_b_ex;
        struct ext4_free_extent *gex = &ac->ac_g_ex;

        if (ac->ac_status == AC_STATUS_FOUND)
                return;
        /*
         * We don't want to scan for a whole year
         */
        if (ac->ac_found > sbi->s_mb_max_to_scan &&
                        !(ac->ac_flags & EXT4_MB_HINT_FIRST)) {
                ac->ac_status = AC_STATUS_BREAK;
                return;
        }

        /*
         * Haven't found good chunk so far, let's continue
         */
        if (bex->fe_len < gex->fe_len)
                return;

        if (finish_group || ac->ac_found > sbi->s_mb_min_to_scan)
                ext4_mb_use_best_found(ac, e4b);
}

/*
 * The routine checks whether found extent is good enough. If it is,
 * then the extent gets marked used and flag is set to the context
 * to stop scanning. Otherwise, the extent is compared with the
 * previous found extent and if new one is better, then it's stored
 * in the context. Later, the best found extent will be used, if
 * mballoc can't find good enough extent.
 *
 * The algorithm used is roughly as follows:
 *
 * * If free extent found is exactly as big as goal, then
 *   stop the scan and use it immediately
 *
 * * If free extent found is smaller than goal, then keep retrying
 *   upto a max of sbi->s_mb_max_to_scan times (default 200). After
 *   that stop scanning and use whatever we have.
 *
 * * If free extent found is bigger than goal, then keep retrying
 *   upto a max of sbi->s_mb_min_to_scan times (default 10) before
 *   stopping the scan and using the extent.
 *
 *
 * FIXME: real allocation policy is to be designed yet!
 */
static void ext4_mb_measure_extent(struct ext4_allocation_context *ac,
                                        struct ext4_free_extent *ex,
                                        struct ext4_buddy *e4b)
{
        struct ext4_free_extent *bex = &ac->ac_b_ex;
        struct ext4_free_extent *gex = &ac->ac_g_ex;

        BUG_ON(ex->fe_len <= 0);
        BUG_ON(ex->fe_len > EXT4_CLUSTERS_PER_GROUP(ac->ac_sb));
        BUG_ON(ex->fe_start >= EXT4_CLUSTERS_PER_GROUP(ac->ac_sb));
        BUG_ON(ac->ac_status != AC_STATUS_CONTINUE);

        ac->ac_found++;
        ac->ac_cX_found[ac->ac_criteria]++;

        /*
         * The special case - take what you catch first
         */
        if (unlikely(ac->ac_flags & EXT4_MB_HINT_FIRST)) {
                *bex = *ex;
                ext4_mb_use_best_found(ac, e4b);
                return;
        }

        /*
         * Let's check whether the chuck is good enough
         */
        if (ex->fe_len == gex->fe_len) {
                *bex = *ex;
                ext4_mb_use_best_found(ac, e4b);
                return;
        }

        /*
         * If this is first found extent, just store it in the context
         */
        if (bex->fe_len == 0) {
                *bex = *ex;
                return;
        }

        /*
         * If new found extent is better, store it in the context
         */
        if (bex->fe_len < gex->fe_len) {
                /* if the request isn't satisfied, any found extent
                 * larger than previous best one is better */
                if (ex->fe_len > bex->fe_len)
                        *bex = *ex;
        } else if (ex->fe_len > gex->fe_len) {
                /* if the request is satisfied, then we try to find
                 * an extent that still satisfy the request, but is
                 * smaller than previous one */
                if (ex->fe_len < bex->fe_len)
                        *bex = *ex;
        }

        ext4_mb_check_limits(ac, e4b, 0);
}

static noinline_for_stack
void ext4_mb_try_best_found(struct ext4_allocation_context *ac,
                                        struct ext4_buddy *e4b)
{
        struct ext4_free_extent ex = ac->ac_b_ex;
        ext4_group_t group = ex.fe_group;
        int max;
        int err;

        BUG_ON(ex.fe_len <= 0);
        err = ext4_mb_load_buddy(ac->ac_sb, group, e4b);
        if (err)
                return;

        ext4_lock_group(ac->ac_sb, group);
        max = mb_find_extent(e4b, ex.fe_start, ex.fe_len, &ex);

        if (max > 0) {
                ac->ac_b_ex = ex;
                ext4_mb_use_best_found(ac, e4b);
        }

        ext4_unlock_group(ac->ac_sb, group);
        ext4_mb_unload_buddy(e4b);
}

static noinline_for_stack
int ext4_mb_find_by_goal(struct ext4_allocation_context *ac,
                                struct ext4_buddy *e4b)
{
        ext4_group_t group = ac->ac_g_ex.fe_group;
        int max;
        int err;
        struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
        struct ext4_group_info *grp = ext4_get_group_info(ac->ac_sb, group);
        struct ext4_free_extent ex;

        if (!grp)
                return -EFSCORRUPTED;
        if (!(ac->ac_flags & (EXT4_MB_HINT_TRY_GOAL | EXT4_MB_HINT_GOAL_ONLY)))
                return 0;
        if (grp->bb_free == 0)
                return 0;

        err = ext4_mb_load_buddy(ac->ac_sb, group, e4b);
        if (err)
                return err;

        if (unlikely(EXT4_MB_GRP_BBITMAP_CORRUPT(e4b->bd_info))) {
                ext4_mb_unload_buddy(e4b);
                return 0;
        }

        ext4_lock_group(ac->ac_sb, group);
        max = mb_find_extent(e4b, ac->ac_g_ex.fe_start,
                             ac->ac_g_ex.fe_len, &ex);
        ex.fe_logical = 0xDEADFA11; /* debug value */

        if (max >= ac->ac_g_ex.fe_len &&
            ac->ac_g_ex.fe_len == EXT4_B2C(sbi, sbi->s_stripe)) {
                ext4_fsblk_t start;

                start = ext4_grp_offs_to_block(ac->ac_sb, &ex);
                /* use do_div to get remainder (would be 64-bit modulo) */
                if (do_div(start, sbi->s_stripe) == 0) {
                        ac->ac_found++;
                        ac->ac_b_ex = ex;
                        ext4_mb_use_best_found(ac, e4b);
                }
        } else if (max >= ac->ac_g_ex.fe_len) {
                BUG_ON(ex.fe_len <= 0);
                BUG_ON(ex.fe_group != ac->ac_g_ex.fe_group);
                BUG_ON(ex.fe_start != ac->ac_g_ex.fe_start);
                ac->ac_found++;
                ac->ac_b_ex = ex;
                ext4_mb_use_best_found(ac, e4b);
        } else if (max > 0 && (ac->ac_flags & EXT4_MB_HINT_MERGE)) {
                /* Sometimes, caller may want to merge even small
                 * number of blocks to an existing extent */
                BUG_ON(ex.fe_len <= 0);
                BUG_ON(ex.fe_group != ac->ac_g_ex.fe_group);
                BUG_ON(ex.fe_start != ac->ac_g_ex.fe_start);
                ac->ac_found++;
                ac->ac_b_ex = ex;
                ext4_mb_use_best_found(ac, e4b);
        }
        ext4_unlock_group(ac->ac_sb, group);
        ext4_mb_unload_buddy(e4b);

        return 0;
}

/*
 * The routine scans buddy structures (not bitmap!) from given order
 * to max order and tries to find big enough chunk to satisfy the req
 */
static noinline_for_stack
void ext4_mb_simple_scan_group(struct ext4_allocation_context *ac,
                                        struct ext4_buddy *e4b)
{
        struct super_block *sb = ac->ac_sb;
        struct ext4_group_info *grp = e4b->bd_info;
        void *buddy;
        int i;
        int k;
        int max;

        BUG_ON(ac->ac_2order <= 0);
        for (i = ac->ac_2order; i < MB_NUM_ORDERS(sb); i++) {
                if (grp->bb_counters[i] == 0)
                        continue;

                buddy = mb_find_buddy(e4b, i, &max);
                if (WARN_RATELIMIT(buddy == NULL,
                         "ext4: mb_simple_scan_group: mb_find_buddy failed, (%d)\n", i))
                        continue;

                k = mb_find_next_zero_bit(buddy, max, 0);
                if (k >= max) {
                        ext4_grp_locked_error(ac->ac_sb, e4b->bd_group, 0, 0,
                                "%d free clusters of order %d. But found 0",
                                grp->bb_counters[i], i);
                        ext4_mark_group_bitmap_corrupted(ac->ac_sb,
                                         e4b->bd_group,
                                        EXT4_GROUP_INFO_BBITMAP_CORRUPT);
                        break;
                }
                ac->ac_found++;
                ac->ac_cX_found[ac->ac_criteria]++;

                ac->ac_b_ex.fe_len = 1 << i;
                ac->ac_b_ex.fe_start = k << i;
                ac->ac_b_ex.fe_group = e4b->bd_group;

                ext4_mb_use_best_found(ac, e4b);

                BUG_ON(ac->ac_f_ex.fe_len != ac->ac_g_ex.fe_len);

                if (EXT4_SB(sb)->s_mb_stats)
                        atomic_inc(&EXT4_SB(sb)->s_bal_2orders);

                break;
        }
}

/*
 * The routine scans the group and measures all found extents.
 * In order to optimize scanning, caller must pass number of
 * free blocks in the group, so the routine can know upper limit.
 */
static noinline_for_stack
void ext4_mb_complex_scan_group(struct ext4_allocation_context *ac,
                                        struct ext4_buddy *e4b)
{
        struct super_block *sb = ac->ac_sb;
        void *bitmap = e4b->bd_bitmap;
        struct ext4_free_extent ex;
        int i, j, freelen;
        int free;

        free = e4b->bd_info->bb_free;
        if (WARN_ON(free <= 0))
                return;

        i = e4b->bd_info->bb_first_free;

        while (free && ac->ac_status == AC_STATUS_CONTINUE) {
                i = mb_find_next_zero_bit(bitmap,
                                                EXT4_CLUSTERS_PER_GROUP(sb), i);
                if (i >= EXT4_CLUSTERS_PER_GROUP(sb)) {
                        /*
                         * IF we have corrupt bitmap, we won't find any
                         * free blocks even though group info says we
                         * have free blocks
                         */
                        ext4_grp_locked_error(sb, e4b->bd_group, 0, 0,
                                        "%d free clusters as per "
                                        "group info. But bitmap says 0",
                                        free);
                        ext4_mark_group_bitmap_corrupted(sb, e4b->bd_group,
                                        EXT4_GROUP_INFO_BBITMAP_CORRUPT);
                        break;
                }

                if (!ext4_mb_cr_expensive(ac->ac_criteria)) {
                        /*
                         * In CR_GOAL_LEN_FAST and CR_BEST_AVAIL_LEN, we are
                         * sure that this group will have a large enough
                         * continuous free extent, so skip over the smaller free
                         * extents
                         */
                        j = mb_find_next_bit(bitmap,
                                                EXT4_CLUSTERS_PER_GROUP(sb), i);
                        freelen = j - i;

                        if (freelen < ac->ac_g_ex.fe_len) {
                                i = j;
                                free -= freelen;
                                continue;
                        }
                }

                mb_find_extent(e4b, i, ac->ac_g_ex.fe_len, &ex);
                if (WARN_ON(ex.fe_len <= 0))
                        break;
                if (free < ex.fe_len) {
                        ext4_grp_locked_error(sb, e4b->bd_group, 0, 0,
                                        "%d free clusters as per "
                                        "group info. But got %d blocks",
                                        free, ex.fe_len);
                        ext4_mark_group_bitmap_corrupted(sb, e4b->bd_group,
                                        EXT4_GROUP_INFO_BBITMAP_CORRUPT);
                        /*
                         * The number of free blocks differs. This mostly
                         * indicate that the bitmap is corrupt. So exit
                         * without claiming the space.
                         */
                        break;
                }
                ex.fe_logical = 0xDEADC0DE; /* debug value */
                ext4_mb_measure_extent(ac, &ex, e4b);

                i += ex.fe_len;
                free -= ex.fe_len;
        }

        ext4_mb_check_limits(ac, e4b, 1);
}

/*
 * This is a special case for storages like raid5
 * we try to find stripe-aligned chunks for stripe-size-multiple requests
 */
static noinline_for_stack
void ext4_mb_scan_aligned(struct ext4_allocation_context *ac,
                                 struct ext4_buddy *e4b)
{
        struct super_block *sb = ac->ac_sb;
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        void *bitmap = e4b->bd_bitmap;
        struct ext4_free_extent ex;
        ext4_fsblk_t first_group_block;
        ext4_fsblk_t a;
        ext4_grpblk_t i, stripe;
        int max;

        BUG_ON(sbi->s_stripe == 0);

        /* find first stripe-aligned block in group */
        first_group_block = ext4_group_first_block_no(sb, e4b->bd_group);

        a = first_group_block + sbi->s_stripe - 1;
        do_div(a, sbi->s_stripe);
        i = (a * sbi->s_stripe) - first_group_block;

        stripe = EXT4_B2C(sbi, sbi->s_stripe);
        i = EXT4_B2C(sbi, i);
        while (i < EXT4_CLUSTERS_PER_GROUP(sb)) {
                if (!mb_test_bit(i, bitmap)) {
                        max = mb_find_extent(e4b, i, stripe, &ex);
                        if (max >= stripe) {
                                ac->ac_found++;
                                ac->ac_cX_found[ac->ac_criteria]++;
                                ex.fe_logical = 0xDEADF00D; /* debug value */
                                ac->ac_b_ex = ex;
                                ext4_mb_use_best_found(ac, e4b);
                                break;
                        }
                }
                i += stripe;
        }
}

/*
 * This is also called BEFORE we load the buddy bitmap.
 * Returns either 1 or 0 indicating that the group is either suitable
 * for the allocation or not.
 */
static bool ext4_mb_good_group(struct ext4_allocation_context *ac,
                                ext4_group_t group, enum criteria cr)
{
        ext4_grpblk_t free, fragments;
        int flex_size = ext4_flex_bg_size(EXT4_SB(ac->ac_sb));
        struct ext4_group_info *grp = ext4_get_group_info(ac->ac_sb, group);

        BUG_ON(cr < CR_POWER2_ALIGNED || cr >= EXT4_MB_NUM_CRS);

        if (unlikely(!grp || EXT4_MB_GRP_BBITMAP_CORRUPT(grp)))
                return false;

        free = grp->bb_free;
        if (free == 0)
                return false;

        fragments = grp->bb_fragments;
        if (fragments == 0)
                return false;

        switch (cr) {
        case CR_POWER2_ALIGNED:
                BUG_ON(ac->ac_2order == 0);

                /* Avoid using the first bg of a flexgroup for data files */
                if ((ac->ac_flags & EXT4_MB_HINT_DATA) &&
                    (flex_size >= EXT4_FLEX_SIZE_DIR_ALLOC_SCHEME) &&
                    ((group % flex_size) == 0))
                        return false;

                if (free < ac->ac_g_ex.fe_len)
                        return false;

                if (ac->ac_2order >= MB_NUM_ORDERS(ac->ac_sb))
                        return true;

                if (grp->bb_largest_free_order < ac->ac_2order)
                        return false;

                return true;
        case CR_GOAL_LEN_FAST:
        case CR_BEST_AVAIL_LEN:
                if ((free / fragments) >= ac->ac_g_ex.fe_len)
                        return true;
                break;
        case CR_GOAL_LEN_SLOW:
                if (free >= ac->ac_g_ex.fe_len)
                        return true;
                break;
        case CR_ANY_FREE:
                return true;
        default:
                BUG();
        }

        return false;
}

/*
 * This could return negative error code if something goes wrong
 * during ext4_mb_init_group(). This should not be called with
 * ext4_lock_group() held.
 *
 * Note: because we are conditionally operating with the group lock in
 * the EXT4_MB_STRICT_CHECK case, we need to fake out sparse in this
 * function using __acquire and __release.  This means we need to be
 * super careful before messing with the error path handling via "goto
 * out"!
 */
static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac,
                                     ext4_group_t group, enum criteria cr)
{
        struct ext4_group_info *grp = ext4_get_group_info(ac->ac_sb, group);
        struct super_block *sb = ac->ac_sb;
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        bool should_lock = ac->ac_flags & EXT4_MB_STRICT_CHECK;
        ext4_grpblk_t free;
        int ret = 0;

        if (!grp)
                return -EFSCORRUPTED;
        if (sbi->s_mb_stats)
                atomic64_inc(&sbi->s_bal_cX_groups_considered[ac->ac_criteria]);
        if (should_lock) {
                ext4_lock_group(sb, group);
                __release(ext4_group_lock_ptr(sb, group));
        }
        free = grp->bb_free;
        if (free == 0)
                goto out;
        /*
         * In all criterias except CR_ANY_FREE we try to avoid groups that
         * can't possibly satisfy the full goal request due to insufficient
         * free blocks.
         */
        if (cr < CR_ANY_FREE && free < ac->ac_g_ex.fe_len)
                goto out;
        if (unlikely(EXT4_MB_GRP_BBITMAP_CORRUPT(grp)))
                goto out;
        if (should_lock) {
                __acquire(ext4_group_lock_ptr(sb, group));
                ext4_unlock_group(sb, group);
        }

        /* We only do this if the grp has never been initialized */
        if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) {
                struct ext4_group_desc *gdp =
                        ext4_get_group_desc(sb, group, NULL);
                int ret;

                /*
                 * cr=CR_POWER2_ALIGNED/CR_GOAL_LEN_FAST is a very optimistic
                 * search to find large good chunks almost for free. If buddy
                 * data is not ready, then this optimization makes no sense. But
                 * we never skip the first block group in a flex_bg, since this
                 * gets used for metadata block allocation, and we want to make
                 * sure we locate metadata blocks in the first block group in
                 * the flex_bg if possible.
                 */
                if (!ext4_mb_cr_expensive(cr) &&
                    (!sbi->s_log_groups_per_flex ||
                     ((group & ((1 << sbi->s_log_groups_per_flex) - 1)) != 0)) &&
                    !(ext4_has_group_desc_csum(sb) &&
                      (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT))))
                        return 0;
                ret = ext4_mb_init_group(sb, group, GFP_NOFS);
                if (ret)
                        return ret;
        }

        if (should_lock) {
                ext4_lock_group(sb, group);
                __release(ext4_group_lock_ptr(sb, group));
        }
        ret = ext4_mb_good_group(ac, group, cr);
out:
        if (should_lock) {
                __acquire(ext4_group_lock_ptr(sb, group));
                ext4_unlock_group(sb, group);
        }
        return ret;
}

/*
 * Start prefetching @nr block bitmaps starting at @group.
 * Return the next group which needs to be prefetched.
 */
ext4_group_t ext4_mb_prefetch(struct super_block *sb, ext4_group_t group,
                              unsigned int nr, int *cnt)
{
        ext4_group_t ngroups = ext4_get_groups_count(sb);
        struct buffer_head *bh;
        struct blk_plug plug;

        blk_start_plug(&plug);
        while (nr-- > 0) {
                struct ext4_group_desc *gdp = ext4_get_group_desc(sb, group,
                                                                  NULL);
                struct ext4_group_info *grp = ext4_get_group_info(sb, group);

                /*
                 * Prefetch block groups with free blocks; but don't
                 * bother if it is marked uninitialized on disk, since
                 * it won't require I/O to read.  Also only try to
                 * prefetch once, so we avoid getblk() call, which can
                 * be expensive.
                 */
                if (gdp && grp && !EXT4_MB_GRP_TEST_AND_SET_READ(grp) &&
                    EXT4_MB_GRP_NEED_INIT(grp) &&
                    ext4_free_group_clusters(sb, gdp) > 0 ) {
                        bh = ext4_read_block_bitmap_nowait(sb, group, true);
                        if (bh && !IS_ERR(bh)) {
                                if (!buffer_uptodate(bh) && cnt)
                                        (*cnt)++;
                                brelse(bh);
                        }
                }
                if (++group >= ngroups)
                        group = 0;
        }
        blk_finish_plug(&plug);
        return group;
}

/*
 * Prefetching reads the block bitmap into the buffer cache; but we
 * need to make sure that the buddy bitmap in the page cache has been
 * initialized.  Note that ext4_mb_init_group() will block if the I/O
 * is not yet completed, or indeed if it was not initiated by
 * ext4_mb_prefetch did not start the I/O.
 *
 * TODO: We should actually kick off the buddy bitmap setup in a work
 * queue when the buffer I/O is completed, so that we don't block
 * waiting for the block allocation bitmap read to finish when
 * ext4_mb_prefetch_fini is called from ext4_mb_regular_allocator().
 */
void ext4_mb_prefetch_fini(struct super_block *sb, ext4_group_t group,
                           unsigned int nr)
{
        struct ext4_group_desc *gdp;
        struct ext4_group_info *grp;

        while (nr-- > 0) {
                if (!group)
                        group = ext4_get_groups_count(sb);
                group--;
                gdp = ext4_get_group_desc(sb, group, NULL);
                grp = ext4_get_group_info(sb, group);

                if (grp && gdp && EXT4_MB_GRP_NEED_INIT(grp) &&
                    ext4_free_group_clusters(sb, gdp) > 0) {
                        if (ext4_mb_init_group(sb, group, GFP_NOFS))
                                break;
                }
        }
}

static noinline_for_stack int
ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
{
        ext4_group_t prefetch_grp = 0, ngroups, group, i;
        enum criteria new_cr, cr = CR_GOAL_LEN_FAST;
        int err = 0, first_err = 0;
        unsigned int nr = 0, prefetch_ios = 0;
        struct ext4_sb_info *sbi;
        struct super_block *sb;
        struct ext4_buddy e4b;
        int lost;

        sb = ac->ac_sb;
        sbi = EXT4_SB(sb);
        ngroups = ext4_get_groups_count(sb);
        /* non-extent files are limited to low blocks/groups */
        if (!(ext4_test_inode_flag(ac->ac_inode, EXT4_INODE_EXTENTS)))
                ngroups = sbi->s_blockfile_groups;

        BUG_ON(ac->ac_status == AC_STATUS_FOUND);

        /* first, try the goal */
        err = ext4_mb_find_by_goal(ac, &e4b);
        if (err || ac->ac_status == AC_STATUS_FOUND)
                goto out;

        if (unlikely(ac->ac_flags & EXT4_MB_HINT_GOAL_ONLY))
                goto out;

        /*
         * ac->ac_2order is set only if the fe_len is a power of 2
         * if ac->ac_2order is set we also set criteria to CR_POWER2_ALIGNED
         * so that we try exact allocation using buddy.
         */
        i = fls(ac->ac_g_ex.fe_len);
        ac->ac_2order = 0;
        /*
         * We search using buddy data only if the order of the request
         * is greater than equal to the sbi_s_mb_order2_reqs
         * You can tune it via /sys/fs/ext4/<partition>/mb_order2_req
         * We also support searching for power-of-two requests only for
         * requests upto maximum buddy size we have constructed.
         */
        if (i >= sbi->s_mb_order2_reqs && i <= MB_NUM_ORDERS(sb)) {
                if (is_power_of_2(ac->ac_g_ex.fe_len))
                        ac->ac_2order = array_index_nospec(i - 1,
                                                           MB_NUM_ORDERS(sb));
        }

        /* if stream allocation is enabled, use global goal */
        if (ac->ac_flags & EXT4_MB_STREAM_ALLOC) {
                /* TBD: may be hot point */
                spin_lock(&sbi->s_md_lock);
                ac->ac_g_ex.fe_group = sbi->s_mb_last_group;
                ac->ac_g_ex.fe_start = sbi->s_mb_last_start;
                spin_unlock(&sbi->s_md_lock);
        }

        /*
         * Let's just scan groups to find more-less suitable blocks We
         * start with CR_GOAL_LEN_FAST, unless it is power of 2
         * aligned, in which case let's do that faster approach first.
         */
        if (ac->ac_2order)
                cr = CR_POWER2_ALIGNED;
repeat:
        for (; cr < EXT4_MB_NUM_CRS && ac->ac_status == AC_STATUS_CONTINUE; cr++) {
                ac->ac_criteria = cr;
                /*
                 * searching for the right group start
                 * from the goal value specified
                 */
                group = ac->ac_g_ex.fe_group;
                ac->ac_groups_linear_remaining = sbi->s_mb_max_linear_groups;
                prefetch_grp = group;

                for (i = 0, new_cr = cr; i < ngroups; i++,
                     ext4_mb_choose_next_group(ac, &new_cr, &group, ngroups)) {
                        int ret = 0;

                        cond_resched();
                        if (new_cr != cr) {
                                cr = new_cr;
                                goto repeat;
                        }

                        /*
                         * Batch reads of the block allocation bitmaps
                         * to get multiple READs in flight; limit
                         * prefetching at inexpensive CR, otherwise mballoc
                         * can spend a lot of time loading imperfect groups
                         */
                        if ((prefetch_grp == group) &&
                            (ext4_mb_cr_expensive(cr) ||
                             prefetch_ios < sbi->s_mb_prefetch_limit)) {
                                nr = sbi->s_mb_prefetch;
                                if (ext4_has_feature_flex_bg(sb)) {
                                        nr = 1 << sbi->s_log_groups_per_flex;
                                        nr -= group & (nr - 1);
                                        nr = min(nr, sbi->s_mb_prefetch);
                                }
                                prefetch_grp = ext4_mb_prefetch(sb, group,
                                                        nr, &prefetch_ios);
                        }

                        /* This now checks without needing the buddy page */
                        ret = ext4_mb_good_group_nolock(ac, group, cr);
                        if (ret <= 0) {
                                if (!first_err)
                                        first_err = ret;
                                continue;
                        }

                        err = ext4_mb_load_buddy(sb, group, &e4b);
                        if (err)
                                goto out;

                        ext4_lock_group(sb, group);

                        /*
                         * We need to check again after locking the
                         * block group
                         */
                        ret = ext4_mb_good_group(ac, group, cr);
                        if (ret == 0) {
                                ext4_unlock_group(sb, group);
                                ext4_mb_unload_buddy(&e4b);
                                continue;
                        }

                        ac->ac_groups_scanned++;
                        if (cr == CR_POWER2_ALIGNED)
                                ext4_mb_simple_scan_group(ac, &e4b);
                        else if ((cr == CR_GOAL_LEN_FAST ||
                                 cr == CR_BEST_AVAIL_LEN) &&
                                 sbi->s_stripe &&
                                 !(ac->ac_g_ex.fe_len %
                                 EXT4_B2C(sbi, sbi->s_stripe)))
                                ext4_mb_scan_aligned(ac, &e4b);
                        else
                                ext4_mb_complex_scan_group(ac, &e4b);

                        ext4_unlock_group(sb, group);
                        ext4_mb_unload_buddy(&e4b);

                        if (ac->ac_status != AC_STATUS_CONTINUE)
                                break;
                }
                /* Processed all groups and haven't found blocks */
                if (sbi->s_mb_stats && i == ngroups)
                        atomic64_inc(&sbi->s_bal_cX_failed[cr]);

                if (i == ngroups && ac->ac_criteria == CR_BEST_AVAIL_LEN)
                        /* Reset goal length to original goal length before
                         * falling into CR_GOAL_LEN_SLOW */
                        ac->ac_g_ex.fe_len = ac->ac_orig_goal_len;
        }

        if (ac->ac_b_ex.fe_len > 0 && ac->ac_status != AC_STATUS_FOUND &&
            !(ac->ac_flags & EXT4_MB_HINT_FIRST)) {
                /*
                 * We've been searching too long. Let's try to allocate
                 * the best chunk we've found so far
                 */
                ext4_mb_try_best_found(ac, &e4b);
                if (ac->ac_status != AC_STATUS_FOUND) {
                        /*
                         * Someone more lucky has already allocated it.
                         * The only thing we can do is just take first
                         * found block(s)
                         */
                        lost = atomic_inc_return(&sbi->s_mb_lost_chunks);
                        mb_debug(sb, "lost chunk, group: %u, start: %d, len: %d, lost: %d\n",
                                 ac->ac_b_ex.fe_group, ac->ac_b_ex.fe_start,
                                 ac->ac_b_ex.fe_len, lost);

                        ac->ac_b_ex.fe_group = 0;
                        ac->ac_b_ex.fe_start = 0;
                        ac->ac_b_ex.fe_len = 0;
                        ac->ac_status = AC_STATUS_CONTINUE;
                        ac->ac_flags |= EXT4_MB_HINT_FIRST;
                        cr = CR_ANY_FREE;
                        goto repeat;
                }
        }

        if (sbi->s_mb_stats && ac->ac_status == AC_STATUS_FOUND)
                atomic64_inc(&sbi->s_bal_cX_hits[ac->ac_criteria]);
out:
        if (!err && ac->ac_status != AC_STATUS_FOUND && first_err)
                err = first_err;

        mb_debug(sb, "Best len %d, origin len %d, ac_status %u, ac_flags 0x%x, cr %d ret %d\n",
                 ac->ac_b_ex.fe_len, ac->ac_o_ex.fe_len, ac->ac_status,
                 ac->ac_flags, cr, err);

        if (nr)
                ext4_mb_prefetch_fini(sb, prefetch_grp, nr);

        return err;
}

static void *ext4_mb_seq_groups_start(struct seq_file *seq, loff_t *pos)
{
        struct super_block *sb = pde_data(file_inode(seq->file));
        ext4_group_t group;

        if (*pos < 0 || *pos >= ext4_get_groups_count(sb))
                return NULL;
        group = *pos + 1;
        return (void *) ((unsigned long) group);
}

static void *ext4_mb_seq_groups_next(struct seq_file *seq, void *v, loff_t *pos)
{
        struct super_block *sb = pde_data(file_inode(seq->file));
        ext4_group_t group;

        ++*pos;
        if (*pos < 0 || *pos >= ext4_get_groups_count(sb))
                return NULL;
        group = *pos + 1;
        return (void *) ((unsigned long) group);
}

static int ext4_mb_seq_groups_show(struct seq_file *seq, void *v)
{
        struct super_block *sb = pde_data(file_inode(seq->file));
        ext4_group_t group = (ext4_group_t) ((unsigned long) v);
        int i;
        int err, buddy_loaded = 0;
        struct ext4_buddy e4b;
        struct ext4_group_info *grinfo;
        unsigned char blocksize_bits = min_t(unsigned char,
                                             sb->s_blocksize_bits,
                                             EXT4_MAX_BLOCK_LOG_SIZE);
        struct sg {
                struct ext4_group_info info;
                ext4_grpblk_t counters[EXT4_MAX_BLOCK_LOG_SIZE + 2];
        } sg;

        group--;
        if (group == 0)
                seq_puts(seq, "#group: free  frags first ["
                              " 2^0   2^1   2^2   2^3   2^4   2^5   2^6  "
                              " 2^7   2^8   2^9   2^10  2^11  2^12  2^13  ]\n");

        i = (blocksize_bits + 2) * sizeof(sg.info.bb_counters[0]) +
                sizeof(struct ext4_group_info);

        grinfo = ext4_get_group_info(sb, group);
        if (!grinfo)
                return 0;
        /* Load the group info in memory only if not already loaded. */
        if (unlikely(EXT4_MB_GRP_NEED_INIT(grinfo))) {
                err = ext4_mb_load_buddy(sb, group, &e4b);
                if (err) {
                        seq_printf(seq, "#%-5u: I/O error\n", group);
                        return 0;
                }
                buddy_loaded = 1;
        }

        memcpy(&sg, grinfo, i);

        if (buddy_loaded)
                ext4_mb_unload_buddy(&e4b);

        seq_printf(seq, "#%-5u: %-5u %-5u %-5u [", group, sg.info.bb_free,
                        sg.info.bb_fragments, sg.info.bb_first_free);
        for (i = 0; i <= 13; i++)
                seq_printf(seq, " %-5u", i <= blocksize_bits + 1 ?
                                sg.info.bb_counters[i] : 0);
        seq_puts(seq, " ]\n");

        return 0;
}

static void ext4_mb_seq_groups_stop(struct seq_file *seq, void *v)
{
}

const struct seq_operations ext4_mb_seq_groups_ops = {
        .start  = ext4_mb_seq_groups_start,
        .next   = ext4_mb_seq_groups_next,
        .stop   = ext4_mb_seq_groups_stop,
        .show   = ext4_mb_seq_groups_show,
};

int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset)
{
        struct super_block *sb = seq->private;
        struct ext4_sb_info *sbi = EXT4_SB(sb);

        seq_puts(seq, "mballoc:\n");
        if (!sbi->s_mb_stats) {
                seq_puts(seq, "\tmb stats collection turned off.\n");
                seq_puts(
                        seq,
                        "\tTo enable, please write \"1\" to sysfs file mb_stats.\n");
                return 0;
        }
        seq_printf(seq, "\treqs: %u\n", atomic_read(&sbi->s_bal_reqs));
        seq_printf(seq, "\tsuccess: %u\n", atomic_read(&sbi->s_bal_success));

        seq_printf(seq, "\tgroups_scanned: %u\n",
                   atomic_read(&sbi->s_bal_groups_scanned));

        /* CR_POWER2_ALIGNED stats */
        seq_puts(seq, "\tcr_p2_aligned_stats:\n");
        seq_printf(seq, "\t\thits: %llu\n",
                   atomic64_read(&sbi->s_bal_cX_hits[CR_POWER2_ALIGNED]));
        seq_printf(
                seq, "\t\tgroups_considered: %llu\n",
                atomic64_read(
                        &sbi->s_bal_cX_groups_considered[CR_POWER2_ALIGNED]));
        seq_printf(seq, "\t\textents_scanned: %u\n",
                   atomic_read(&sbi->s_bal_cX_ex_scanned[CR_POWER2_ALIGNED]));
        seq_printf(seq, "\t\tuseless_loops: %llu\n",
                   atomic64_read(&sbi->s_bal_cX_failed[CR_POWER2_ALIGNED]));
        seq_printf(seq, "\t\tbad_suggestions: %u\n",
                   atomic_read(&sbi->s_bal_p2_aligned_bad_suggestions));

        /* CR_GOAL_LEN_FAST stats */
        seq_puts(seq, "\tcr_goal_fast_stats:\n");
        seq_printf(seq, "\t\thits: %llu\n",
                   atomic64_read(&sbi->s_bal_cX_hits[CR_GOAL_LEN_FAST]));
        seq_printf(seq, "\t\tgroups_considered: %llu\n",
                   atomic64_read(
                           &sbi->s_bal_cX_groups_considered[CR_GOAL_LEN_FAST]));
        seq_printf(seq, "\t\textents_scanned: %u\n",
                   atomic_read(&sbi->s_bal_cX_ex_scanned[CR_GOAL_LEN_FAST]));
        seq_printf(seq, "\t\tuseless_loops: %llu\n",
                   atomic64_read(&sbi->s_bal_cX_failed[CR_GOAL_LEN_FAST]));
        seq_printf(seq, "\t\tbad_suggestions: %u\n",
                   atomic_read(&sbi->s_bal_goal_fast_bad_suggestions));

        /* CR_BEST_AVAIL_LEN stats */
        seq_puts(seq, "\tcr_best_avail_stats:\n");
        seq_printf(seq, "\t\thits: %llu\n",
                   atomic64_read(&sbi->s_bal_cX_hits[CR_BEST_AVAIL_LEN]));
        seq_printf(
                seq, "\t\tgroups_considered: %llu\n",
                atomic64_read(
                        &sbi->s_bal_cX_groups_considered[CR_BEST_AVAIL_LEN]));
        seq_printf(seq, "\t\textents_scanned: %u\n",
                   atomic_read(&sbi->s_bal_cX_ex_scanned[CR_BEST_AVAIL_LEN]));
        seq_printf(seq, "\t\tuseless_loops: %llu\n",
                   atomic64_read(&sbi->s_bal_cX_failed[CR_BEST_AVAIL_LEN]));
        seq_printf(seq, "\t\tbad_suggestions: %u\n",
                   atomic_read(&sbi->s_bal_best_avail_bad_suggestions));

        /* CR_GOAL_LEN_SLOW stats */
        seq_puts(seq, "\tcr_goal_slow_stats:\n");
        seq_printf(seq, "\t\thits: %llu\n",
                   atomic64_read(&sbi->s_bal_cX_hits[CR_GOAL_LEN_SLOW]));
        seq_printf(seq, "\t\tgroups_considered: %llu\n",
                   atomic64_read(
                           &sbi->s_bal_cX_groups_considered[CR_GOAL_LEN_SLOW]));
        seq_printf(seq, "\t\textents_scanned: %u\n",
                   atomic_read(&sbi->s_bal_cX_ex_scanned[CR_GOAL_LEN_SLOW]));
        seq_printf(seq, "\t\tuseless_loops: %llu\n",
                   atomic64_read(&sbi->s_bal_cX_failed[CR_GOAL_LEN_SLOW]));

        /* CR_ANY_FREE stats */
        seq_puts(seq, "\tcr_any_free_stats:\n");
        seq_printf(seq, "\t\thits: %llu\n",
                   atomic64_read(&sbi->s_bal_cX_hits[CR_ANY_FREE]));
        seq_printf(
                seq, "\t\tgroups_considered: %llu\n",
                atomic64_read(&sbi->s_bal_cX_groups_considered[CR_ANY_FREE]));
        seq_printf(seq, "\t\textents_scanned: %u\n",
                   atomic_read(&sbi->s_bal_cX_ex_scanned[CR_ANY_FREE]));
        seq_printf(seq, "\t\tuseless_loops: %llu\n",
                   atomic64_read(&sbi->s_bal_cX_failed[CR_ANY_FREE]));

        /* Aggregates */
        seq_printf(seq, "\textents_scanned: %u\n",
                   atomic_read(&sbi->s_bal_ex_scanned));
        seq_printf(seq, "\t\tgoal_hits: %u\n", atomic_read(&sbi->s_bal_goals));
        seq_printf(seq, "\t\tlen_goal_hits: %u\n",
                   atomic_read(&sbi->s_bal_len_goals));
        seq_printf(seq, "\t\t2^n_hits: %u\n", atomic_read(&sbi->s_bal_2orders));
        seq_printf(seq, "\t\tbreaks: %u\n", atomic_read(&sbi->s_bal_breaks));
        seq_printf(seq, "\t\tlost: %u\n", atomic_read(&sbi->s_mb_lost_chunks));
        seq_printf(seq, "\tbuddies_generated: %u/%u\n",
                   atomic_read(&sbi->s_mb_buddies_generated),
                   ext4_get_groups_count(sb));
        seq_printf(seq, "\tbuddies_time_used: %llu\n",
                   atomic64_read(&sbi->s_mb_generation_time));
        seq_printf(seq, "\tpreallocated: %u\n",
                   atomic_read(&sbi->s_mb_preallocated));
        seq_printf(seq, "\tdiscarded: %u\n", atomic_read(&sbi->s_mb_discarded));
        return 0;
}

static void *ext4_mb_seq_structs_summary_start(struct seq_file *seq, loff_t *pos)
__acquires(&EXT4_SB(sb)->s_mb_rb_lock)
{
        struct super_block *sb = pde_data(file_inode(seq->file));
        unsigned long position;

        if (*pos < 0 || *pos >= 2*MB_NUM_ORDERS(sb))
                return NULL;
        position = *pos + 1;
        return (void *) ((unsigned long) position);
}

static void *ext4_mb_seq_structs_summary_next(struct seq_file *seq, void *v, loff_t *pos)
{
        struct super_block *sb = pde_data(file_inode(seq->file));
        unsigned long position;

        ++*pos;
        if (*pos < 0 || *pos >= 2*MB_NUM_ORDERS(sb))
                return NULL;
        position = *pos + 1;
        return (void *) ((unsigned long) position);
}

static int ext4_mb_seq_structs_summary_show(struct seq_file *seq, void *v)
{
        struct super_block *sb = pde_data(file_inode(seq->file));
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        unsigned long position = ((unsigned long) v);
        struct ext4_group_info *grp;
        unsigned int count;

        position--;
        if (position >= MB_NUM_ORDERS(sb)) {
                position -= MB_NUM_ORDERS(sb);
                if (position == 0)
                        seq_puts(seq, "avg_fragment_size_lists:\n");

                count = 0;
                read_lock(&sbi->s_mb_avg_fragment_size_locks[position]);
                list_for_each_entry(grp, &sbi->s_mb_avg_fragment_size[position],
                                    bb_avg_fragment_size_node)
                        count++;
                read_unlock(&sbi->s_mb_avg_fragment_size_locks[position]);
                seq_printf(seq, "\tlist_order_%u_groups: %u\n",
                                        (unsigned int)position, count);
                return 0;
        }

        if (position == 0) {
                seq_printf(seq, "optimize_scan: %d\n",
                           test_opt2(sb, MB_OPTIMIZE_SCAN) ? 1 : 0);
                seq_puts(seq, "max_free_order_lists:\n");
        }
        count = 0;
        read_lock(&sbi->s_mb_largest_free_orders_locks[position]);
        list_for_each_entry(grp, &sbi->s_mb_largest_free_orders[position],
                            bb_largest_free_order_node)
                count++;
        read_unlock(&sbi->s_mb_largest_free_orders_locks[position]);
        seq_printf(seq, "\tlist_order_%u_groups: %u\n",
                   (unsigned int)position, count);

        return 0;
}

static void ext4_mb_seq_structs_summary_stop(struct seq_file *seq, void *v)
{
}

const struct seq_operations ext4_mb_seq_structs_summary_ops = {
        .start  = ext4_mb_seq_structs_summary_start,
        .next   = ext4_mb_seq_structs_summary_next,
        .stop   = ext4_mb_seq_structs_summary_stop,
        .show   = ext4_mb_seq_structs_summary_show,
};

static struct kmem_cache *get_groupinfo_cache(int blocksize_bits)
{
        int cache_index = blocksize_bits - EXT4_MIN_BLOCK_LOG_SIZE;
        struct kmem_cache *cachep = ext4_groupinfo_caches[cache_index];

        BUG_ON(!cachep);
        return cachep;
}

/*
 * Allocate the top-level s_group_info array for the specified number
 * of groups
 */
int ext4_mb_alloc_groupinfo(struct super_block *sb, ext4_group_t ngroups)
{
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        unsigned size;
        struct ext4_group_info ***old_groupinfo, ***new_groupinfo;

        size = (ngroups + EXT4_DESC_PER_BLOCK(sb) - 1) >>
                EXT4_DESC_PER_BLOCK_BITS(sb);
        if (size <= sbi->s_group_info_size)
                return 0;

        size = roundup_pow_of_two(sizeof(*sbi->s_group_info) * size);
        new_groupinfo = kvzalloc(size, GFP_KERNEL);
        if (!new_groupinfo) {
                ext4_msg(sb, KERN_ERR, "can't allocate buddy meta group");
                return -ENOMEM;
        }
        rcu_read_lock();
        old_groupinfo = rcu_dereference(sbi->s_group_info);
        if (old_groupinfo)
                memcpy(new_groupinfo, old_groupinfo,
                       sbi->s_group_info_size * sizeof(*sbi->s_group_info));
        rcu_read_unlock();
        rcu_assign_pointer(sbi->s_group_info, new_groupinfo);
        sbi->s_group_info_size = size / sizeof(*sbi->s_group_info);
        if (old_groupinfo)
                ext4_kvfree_array_rcu(old_groupinfo);
        ext4_debug("allocated s_groupinfo array for %d meta_bg's\n",
                   sbi->s_group_info_size);
        return 0;
}

/* Create and initialize ext4_group_info data for the given group. */
int ext4_mb_add_groupinfo(struct super_block *sb, ext4_group_t group,
                          struct ext4_group_desc *desc)
{
        int i;
        int metalen = 0;
        int idx = group >> EXT4_DESC_PER_BLOCK_BITS(sb);
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        struct ext4_group_info **meta_group_info;
        struct kmem_cache *cachep = get_groupinfo_cache(sb->s_blocksize_bits);

        /*
         * First check if this group is the first of a reserved block.
         * If it's true, we have to allocate a new table of pointers
         * to ext4_group_info structures
         */
        if (group % EXT4_DESC_PER_BLOCK(sb) == 0) {
                metalen = sizeof(*meta_group_info) <<
                        EXT4_DESC_PER_BLOCK_BITS(sb);
                meta_group_info = kmalloc(metalen, GFP_NOFS);
                if (meta_group_info == NULL) {
                        ext4_msg(sb, KERN_ERR, "can't allocate mem "
                                 "for a buddy group");
                        return -ENOMEM;
                }
                rcu_read_lock();
                rcu_dereference(sbi->s_group_info)[idx] = meta_group_info;
                rcu_read_unlock();
        }

        meta_group_info = sbi_array_rcu_deref(sbi, s_group_info, idx);
        i = group & (EXT4_DESC_PER_BLOCK(sb) - 1);

        meta_group_info[i] = kmem_cache_zalloc(cachep, GFP_NOFS);
        if (meta_group_info[i] == NULL) {
                ext4_msg(sb, KERN_ERR, "can't allocate buddy mem");
                goto exit_group_info;
        }
        set_bit(EXT4_GROUP_INFO_NEED_INIT_BIT,
                &(meta_group_info[i]->bb_state));

        /*
         * initialize bb_free to be able to skip
         * empty groups without initialization
         */
        if (ext4_has_group_desc_csum(sb) &&
            (desc->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT))) {
                meta_group_info[i]->bb_free =
                        ext4_free_clusters_after_init(sb, group, desc);
        } else {
                meta_group_info[i]->bb_free =
                        ext4_free_group_clusters(sb, desc);
        }

        INIT_LIST_HEAD(&meta_group_info[i]->bb_prealloc_list);
        init_rwsem(&meta_group_info[i]->alloc_sem);
        meta_group_info[i]->bb_free_root = RB_ROOT;
        INIT_LIST_HEAD(&meta_group_info[i]->bb_largest_free_order_node);
        INIT_LIST_HEAD(&meta_group_info[i]->bb_avg_fragment_size_node);
        meta_group_info[i]->bb_largest_free_order = -1;  /* uninit */
        meta_group_info[i]->bb_avg_fragment_size_order = -1;  /* uninit */
        meta_group_info[i]->bb_group = group;

        mb_group_bb_bitmap_alloc(sb, meta_group_info[i], group);
        return 0;

exit_group_info:
        /* If a meta_group_info table has been allocated, release it now */
        if (group % EXT4_DESC_PER_BLOCK(sb) == 0) {
                struct ext4_group_info ***group_info;

                rcu_read_lock();
                group_info = rcu_dereference(sbi->s_group_info);
                kfree(group_info[idx]);
                group_info[idx] = NULL;
                rcu_read_unlock();
        }
        return -ENOMEM;
} /* ext4_mb_add_groupinfo */

static int ext4_mb_init_backend(struct super_block *sb)
{
        ext4_group_t ngroups = ext4_get_groups_count(sb);
        ext4_group_t i;
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        int err;
        struct ext4_group_desc *desc;
        struct ext4_group_info ***group_info;
        struct kmem_cache *cachep;

        err = ext4_mb_alloc_groupinfo(sb, ngroups);
        if (err)
                return err;

        sbi->s_buddy_cache = new_inode(sb);
        if (sbi->s_buddy_cache == NULL) {
                ext4_msg(sb, KERN_ERR, "can't get new inode");
                goto err_freesgi;
        }
        /* To avoid potentially colliding with an valid on-disk inode number,
         * use EXT4_BAD_INO for the buddy cache inode number.  This inode is
         * not in the inode hash, so it should never be found by iget(), but
         * this will avoid confusion if it ever shows up during debugging. */
        sbi->s_buddy_cache->i_ino = EXT4_BAD_INO;
        EXT4_I(sbi->s_buddy_cache)->i_disksize = 0;
        for (i = 0; i < ngroups; i++) {
                cond_resched();
                desc = ext4_get_group_desc(sb, i, NULL);
                if (desc == NULL) {
                        ext4_msg(sb, KERN_ERR, "can't read descriptor %u", i);
                        goto err_freebuddy;
                }
                if (ext4_mb_add_groupinfo(sb, i, desc) != 0)
                        goto err_freebuddy;
        }

        if (ext4_has_feature_flex_bg(sb)) {
                /* a single flex group is supposed to be read by a single IO.
                 * 2 ^ s_log_groups_per_flex != UINT_MAX as s_mb_prefetch is
                 * unsigned integer, so the maximum shift is 32.
                 */
                if (sbi->s_es->s_log_groups_per_flex >= 32) {
                        ext4_msg(sb, KERN_ERR, "too many log groups per flexible block group");
                        goto err_freebuddy;
                }
                sbi->s_mb_prefetch = min_t(uint, 1 << sbi->s_es->s_log_groups_per_flex,
                        BLK_MAX_SEGMENT_SIZE >> (sb->s_blocksize_bits - 9));
                sbi->s_mb_prefetch *= 8; /* 8 prefetch IOs in flight at most */
        } else {
                sbi->s_mb_prefetch = 32;
        }
        if (sbi->s_mb_prefetch > ext4_get_groups_count(sb))
                sbi->s_mb_prefetch = ext4_get_groups_count(sb);
        /* now many real IOs to prefetch within a single allocation at cr=0
         * given cr=0 is an CPU-related optimization we shouldn't try to
         * load too many groups, at some point we should start to use what
         * we've got in memory.
         * with an average random access time 5ms, it'd take a second to get
         * 200 groups (* N with flex_bg), so let's make this limit 4
         */
        sbi->s_mb_prefetch_limit = sbi->s_mb_prefetch * 4;
        if (sbi->s_mb_prefetch_limit > ext4_get_groups_count(sb))
                sbi->s_mb_prefetch_limit = ext4_get_groups_count(sb);

        return 0;

err_freebuddy:
        cachep = get_groupinfo_cache(sb->s_blocksize_bits);
        while (i-- > 0) {
                struct ext4_group_info *grp = ext4_get_group_info(sb, i);

                if (grp)
                        kmem_cache_free(cachep, grp);
        }
        i = sbi->s_group_info_size;
        rcu_read_lock();
        group_info = rcu_dereference(sbi->s_group_info);
        while (i-- > 0)
                kfree(group_info[i]);
        rcu_read_unlock();
        iput(sbi->s_buddy_cache);
err_freesgi:
        rcu_read_lock();
        kvfree(rcu_dereference(sbi->s_group_info));
        rcu_read_unlock();
        return -ENOMEM;
}

static void ext4_groupinfo_destroy_slabs(void)
{
        int i;

        for (i = 0; i < NR_GRPINFO_CACHES; i++) {
                kmem_cache_destroy(ext4_groupinfo_caches[i]);
                ext4_groupinfo_caches[i] = NULL;
        }
}

static int ext4_groupinfo_create_slab(size_t size)
{
        static DEFINE_MUTEX(ext4_grpinfo_slab_create_mutex);
        int slab_size;
        int blocksize_bits = order_base_2(size);
        int cache_index = blocksize_bits - EXT4_MIN_BLOCK_LOG_SIZE;
        struct kmem_cache *cachep;

        if (cache_index >= NR_GRPINFO_CACHES)
                return -EINVAL;

        if (unlikely(cache_index < 0))
                cache_index = 0;

        mutex_lock(&ext4_grpinfo_slab_create_mutex);
        if (ext4_groupinfo_caches[cache_index]) {
                mutex_unlock(&ext4_grpinfo_slab_create_mutex);
                return 0;       /* Already created */
        }

        slab_size = offsetof(struct ext4_group_info,
                                bb_counters[blocksize_bits + 2]);

        cachep = kmem_cache_create(ext4_groupinfo_slab_names[cache_index],
                                        slab_size, 0, SLAB_RECLAIM_ACCOUNT,
                                        NULL);

        ext4_groupinfo_caches[cache_index] = cachep;

        mutex_unlock(&ext4_grpinfo_slab_create_mutex);
        if (!cachep) {
                printk(KERN_EMERG
                       "EXT4-fs: no memory for groupinfo slab cache\n");
                return -ENOMEM;
        }

        return 0;
}

static void ext4_discard_work(struct work_struct *work)
{
        struct ext4_sb_info *sbi = container_of(work,
                        struct ext4_sb_info, s_discard_work);
        struct super_block *sb = sbi->s_sb;
        struct ext4_free_data *fd, *nfd;
        struct ext4_buddy e4b;
        LIST_HEAD(discard_list);
        ext4_group_t grp, load_grp;
        int err = 0;

        spin_lock(&sbi->s_md_lock);
        list_splice_init(&sbi->s_discard_list, &discard_list);
        spin_unlock(&sbi->s_md_lock);

        load_grp = UINT_MAX;
        list_for_each_entry_safe(fd, nfd, &discard_list, efd_list) {
                /*
                 * If filesystem is umounting or no memory or suffering
                 * from no space, give up the discard
                 */
                if ((sb->s_flags & SB_ACTIVE) && !err &&
                    !atomic_read(&sbi->s_retry_alloc_pending)) {
                        grp = fd->efd_group;
                        if (grp != load_grp) {
                                if (load_grp != UINT_MAX)
                                        ext4_mb_unload_buddy(&e4b);

                                err = ext4_mb_load_buddy(sb, grp, &e4b);
                                if (err) {
                                        kmem_cache_free(ext4_free_data_cachep, fd);
                                        load_grp = UINT_MAX;
                                        continue;
                                } else {
                                        load_grp = grp;
                                }
                        }

                        ext4_lock_group(sb, grp);
                        ext4_try_to_trim_range(sb, &e4b, fd->efd_start_cluster,
                                                fd->efd_start_cluster + fd->efd_count - 1, 1);
                        ext4_unlock_group(sb, grp);
                }
                kmem_cache_free(ext4_free_data_cachep, fd);
        }

        if (load_grp != UINT_MAX)
                ext4_mb_unload_buddy(&e4b);
}

int ext4_mb_init(struct super_block *sb)
{
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        unsigned i, j;
        unsigned offset, offset_incr;
        unsigned max;
        int ret;

        i = MB_NUM_ORDERS(sb) * sizeof(*sbi->s_mb_offsets);

        sbi->s_mb_offsets = kmalloc(i, GFP_KERNEL);
        if (sbi->s_mb_offsets == NULL) {
                ret = -ENOMEM;
                goto out;
        }

        i = MB_NUM_ORDERS(sb) * sizeof(*sbi->s_mb_maxs);
        sbi->s_mb_maxs = kmalloc(i, GFP_KERNEL);
        if (sbi->s_mb_maxs == NULL) {
                ret = -ENOMEM;
                goto out;
        }

        ret = ext4_groupinfo_create_slab(sb->s_blocksize);
        if (ret < 0)
                goto out;

        /* order 0 is regular bitmap */
        sbi->s_mb_maxs[0] = sb->s_blocksize << 3;
        sbi->s_mb_offsets[0] = 0;

        i = 1;
        offset = 0;
        offset_incr = 1 << (sb->s_blocksize_bits - 1);
        max = sb->s_blocksize << 2;
        do {
                sbi->s_mb_offsets[i] = offset;
                sbi->s_mb_maxs[i] = max;
                offset += offset_incr;
                offset_incr = offset_incr >> 1;
                max = max >> 1;
                i++;
        } while (i < MB_NUM_ORDERS(sb));

        sbi->s_mb_avg_fragment_size =
                kmalloc_array(MB_NUM_ORDERS(sb), sizeof(struct list_head),
                        GFP_KERNEL);
        if (!sbi->s_mb_avg_fragment_size) {
                ret = -ENOMEM;
                goto out;
        }
        sbi->s_mb_avg_fragment_size_locks =
                kmalloc_array(MB_NUM_ORDERS(sb), sizeof(rwlock_t),
                        GFP_KERNEL);
        if (!sbi->s_mb_avg_fragment_size_locks) {
                ret = -ENOMEM;
                goto out;
        }
        for (i = 0; i < MB_NUM_ORDERS(sb); i++) {
                INIT_LIST_HEAD(&sbi->s_mb_avg_fragment_size[i]);
                rwlock_init(&sbi->s_mb_avg_fragment_size_locks[i]);
        }
        sbi->s_mb_largest_free_orders =
                kmalloc_array(MB_NUM_ORDERS(sb), sizeof(struct list_head),
                        GFP_KERNEL);
        if (!sbi->s_mb_largest_free_orders) {
                ret = -ENOMEM;
                goto out;
        }
        sbi->s_mb_largest_free_orders_locks =
                kmalloc_array(MB_NUM_ORDERS(sb), sizeof(rwlock_t),
                        GFP_KERNEL);
        if (!sbi->s_mb_largest_free_orders_locks) {
                ret = -ENOMEM;
                goto out;
        }
        for (i = 0; i < MB_NUM_ORDERS(sb); i++) {
                INIT_LIST_HEAD(&sbi->s_mb_largest_free_orders[i]);
                rwlock_init(&sbi->s_mb_largest_free_orders_locks[i]);
        }

        spin_lock_init(&sbi->s_md_lock);
        sbi->s_mb_free_pending = 0;
        INIT_LIST_HEAD(&sbi->s_freed_data_list[0]);
        INIT_LIST_HEAD(&sbi->s_freed_data_list[1]);
        INIT_LIST_HEAD(&sbi->s_discard_list);
        INIT_WORK(&sbi->s_discard_work, ext4_discard_work);
        atomic_set(&sbi->s_retry_alloc_pending, 0);

        sbi->s_mb_max_to_scan = MB_DEFAULT_MAX_TO_SCAN;
        sbi->s_mb_min_to_scan = MB_DEFAULT_MIN_TO_SCAN;
        sbi->s_mb_stats = MB_DEFAULT_STATS;
        sbi->s_mb_stream_request = MB_DEFAULT_STREAM_THRESHOLD;
        sbi->s_mb_order2_reqs = MB_DEFAULT_ORDER2_REQS;
        sbi->s_mb_best_avail_max_trim_order = MB_DEFAULT_BEST_AVAIL_TRIM_ORDER;

        /*
         * The default group preallocation is 512, which for 4k block
         * sizes translates to 2 megabytes.  However for bigalloc file
         * systems, this is probably too big (i.e, if the cluster size
         * is 1 megabyte, then group preallocation size becomes half a
         * gigabyte!).  As a default, we will keep a two megabyte
         * group pralloc size for cluster sizes up to 64k, and after
         * that, we will force a minimum group preallocation size of
         * 32 clusters.  This translates to 8 megs when the cluster
         * size is 256k, and 32 megs when the cluster size is 1 meg,
         * which seems reasonable as a default.
         */
        sbi->s_mb_group_prealloc = max(MB_DEFAULT_GROUP_PREALLOC >>
                                       sbi->s_cluster_bits, 32);
        /*
         * If there is a s_stripe > 1, then we set the s_mb_group_prealloc
         * to the lowest multiple of s_stripe which is bigger than
         * the s_mb_group_prealloc as determined above. We want
         * the preallocation size to be an exact multiple of the
         * RAID stripe size so that preallocations don't fragment
         * the stripes.
         */
        if (sbi->s_stripe > 1) {
                sbi->s_mb_group_prealloc = roundup(
                        sbi->s_mb_group_prealloc, EXT4_B2C(sbi, sbi->s_stripe));
        }

        sbi->s_locality_groups = alloc_percpu(struct ext4_locality_group);
        if (sbi->s_locality_groups == NULL) {
                ret = -ENOMEM;
                goto out;
        }
        for_each_possible_cpu(i) {
                struct ext4_locality_group *lg;
                lg = per_cpu_ptr(sbi->s_locality_groups, i);
                mutex_init(&lg->lg_mutex);
                for (j = 0; j < PREALLOC_TB_SIZE; j++)
                        INIT_LIST_HEAD(&lg->lg_prealloc_list[j]);
                spin_lock_init(&lg->lg_prealloc_lock);
        }

        if (bdev_nonrot(sb->s_bdev))
                sbi->s_mb_max_linear_groups = 0;
        else
                sbi->s_mb_max_linear_groups = MB_DEFAULT_LINEAR_LIMIT;
        /* init file for buddy data */
        ret = ext4_mb_init_backend(sb);
        if (ret != 0)
                goto out_free_locality_groups;

        return 0;

out_free_locality_groups:
        free_percpu(sbi->s_locality_groups);
        sbi->s_locality_groups = NULL;
out:
        kfree(sbi->s_mb_avg_fragment_size);
        kfree(sbi->s_mb_avg_fragment_size_locks);
        kfree(sbi->s_mb_largest_free_orders);
        kfree(sbi->s_mb_largest_free_orders_locks);
        kfree(sbi->s_mb_offsets);
        sbi->s_mb_offsets = NULL;
        kfree(sbi->s_mb_maxs);
        sbi->s_mb_maxs = NULL;
        return ret;
}

/* need to called with the ext4 group lock held */
static int ext4_mb_cleanup_pa(struct ext4_group_info *grp)
{
        struct ext4_prealloc_space *pa;
        struct list_head *cur, *tmp;
        int count = 0;

        list_for_each_safe(cur, tmp, &grp->bb_prealloc_list) {
                pa = list_entry(cur, struct ext4_prealloc_space, pa_group_list);
                list_del(&pa->pa_group_list);
                count++;
                kmem_cache_free(ext4_pspace_cachep, pa);
        }
        return count;
}

int ext4_mb_release(struct super_block *sb)
{
        ext4_group_t ngroups = ext4_get_groups_count(sb);
        ext4_group_t i;
        int num_meta_group_infos;
        struct ext4_group_info *grinfo, ***group_info;
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        struct kmem_cache *cachep = get_groupinfo_cache(sb->s_blocksize_bits);
        int count;

        if (test_opt(sb, DISCARD)) {
                /*
                 * wait the discard work to drain all of ext4_free_data
                 */
                flush_work(&sbi->s_discard_work);
                WARN_ON_ONCE(!list_empty(&sbi->s_discard_list));
        }

        if (sbi->s_group_info) {
                for (i = 0; i < ngroups; i++) {
                        cond_resched();
                        grinfo = ext4_get_group_info(sb, i);
                        if (!grinfo)
                                continue;
                        mb_group_bb_bitmap_free(grinfo);
                        ext4_lock_group(sb, i);
                        count = ext4_mb_cleanup_pa(grinfo);
                        if (count)
                                mb_debug(sb, "mballoc: %d PAs left\n",
                                         count);
                        ext4_unlock_group(sb, i);
                        kmem_cache_free(cachep, grinfo);
                }
                num_meta_group_infos = (ngroups +
                                EXT4_DESC_PER_BLOCK(sb) - 1) >>
                        EXT4_DESC_PER_BLOCK_BITS(sb);
                rcu_read_lock();
                group_info = rcu_dereference(sbi->s_group_info);
                for (i = 0; i < num_meta_group_infos; i++)
                        kfree(group_info[i]);
                kvfree(group_info);
                rcu_read_unlock();
        }
        kfree(sbi->s_mb_avg_fragment_size);
        kfree(sbi->s_mb_avg_fragment_size_locks);
        kfree(sbi->s_mb_largest_free_orders);
        kfree(sbi->s_mb_largest_free_orders_locks);
        kfree(sbi->s_mb_offsets);
        kfree(sbi->s_mb_maxs);
        iput(sbi->s_buddy_cache);
        if (sbi->s_mb_stats) {
                ext4_msg(sb, KERN_INFO,
                       "mballoc: %u blocks %u reqs (%u success)",
                                atomic_read(&sbi->s_bal_allocated),
                                atomic_read(&sbi->s_bal_reqs),
                                atomic_read(&sbi->s_bal_success));
                ext4_msg(sb, KERN_INFO,
                      "mballoc: %u extents scanned, %u groups scanned, %u goal hits, "
                                "%u 2^N hits, %u breaks, %u lost",
                                atomic_read(&sbi->s_bal_ex_scanned),
                                atomic_read(&sbi->s_bal_groups_scanned),
                                atomic_read(&sbi->s_bal_goals),
                                atomic_read(&sbi->s_bal_2orders),
                                atomic_read(&sbi->s_bal_breaks),
                                atomic_read(&sbi->s_mb_lost_chunks));
                ext4_msg(sb, KERN_INFO,
                       "mballoc: %u generated and it took %llu",
                                atomic_read(&sbi->s_mb_buddies_generated),
                                atomic64_read(&sbi->s_mb_generation_time));
                ext4_msg(sb, KERN_INFO,
                       "mballoc: %u preallocated, %u discarded",
                                atomic_read(&sbi->s_mb_preallocated),
                                atomic_read(&sbi->s_mb_discarded));
        }

        free_percpu(sbi->s_locality_groups);

        return 0;
}

static inline int ext4_issue_discard(struct super_block *sb,
                ext4_group_t block_group, ext4_grpblk_t cluster, int count,
                struct bio **biop)
{
        ext4_fsblk_t discard_block;

        discard_block = (EXT4_C2B(EXT4_SB(sb), cluster) +
                         ext4_group_first_block_no(sb, block_group));
        count = EXT4_C2B(EXT4_SB(sb), count);
        trace_ext4_discard_blocks(sb,
                        (unsigned long long) discard_block, count);
        if (biop) {
                return __blkdev_issue_discard(sb->s_bdev,
                        (sector_t)discard_block << (sb->s_blocksize_bits - 9),
                        (sector_t)count << (sb->s_blocksize_bits - 9),
                        GFP_NOFS, biop);
        } else
                return sb_issue_discard(sb, discard_block, count, GFP_NOFS, 0);
}

static void ext4_free_data_in_buddy(struct super_block *sb,
                                    struct ext4_free_data *entry)
{
        struct ext4_buddy e4b;
        struct ext4_group_info *db;
        int err, count = 0;

        mb_debug(sb, "gonna free %u blocks in group %u (0x%p):",
                 entry->efd_count, entry->efd_group, entry);

        err = ext4_mb_load_buddy(sb, entry->efd_group, &e4b);
        /* we expect to find existing buddy because it's pinned */
        BUG_ON(err != 0);

        spin_lock(&EXT4_SB(sb)->s_md_lock);
        EXT4_SB(sb)->s_mb_free_pending -= entry->efd_count;
        spin_unlock(&EXT4_SB(sb)->s_md_lock);

        db = e4b.bd_info;
        /* there are blocks to put in buddy to make them really free */
        count += entry->efd_count;
        ext4_lock_group(sb, entry->efd_group);
        /* Take it out of per group rb tree */
        rb_erase(&entry->efd_node, &(db->bb_free_root));
        mb_free_blocks(NULL, &e4b, entry->efd_start_cluster, entry->efd_count);

        /*
         * Clear the trimmed flag for the group so that the next
         * ext4_trim_fs can trim it.
         * If the volume is mounted with -o discard, online discard
         * is supported and the free blocks will be trimmed online.
         */
        if (!test_opt(sb, DISCARD))
                EXT4_MB_GRP_CLEAR_TRIMMED(db);

        if (!db->bb_free_root.rb_node) {
                /* No more items in the per group rb tree
                 * balance refcounts from ext4_mb_free_metadata()
                 */
                put_page(e4b.bd_buddy_page);
                put_page(e4b.bd_bitmap_page);
        }
        ext4_unlock_group(sb, entry->efd_group);
        ext4_mb_unload_buddy(&e4b);

        mb_debug(sb, "freed %d blocks in 1 structures\n", count);
}

/*
 * This function is called by the jbd2 layer once the commit has finished,
 * so we know we can free the blocks that were released with that commit.
 */
void ext4_process_freed_data(struct super_block *sb, tid_t commit_tid)
{
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        struct ext4_free_data *entry, *tmp;
        LIST_HEAD(freed_data_list);
        struct list_head *s_freed_head = &sbi->s_freed_data_list[commit_tid & 1];
        bool wake;

        list_replace_init(s_freed_head, &freed_data_list);

        list_for_each_entry(entry, &freed_data_list, efd_list)
                ext4_free_data_in_buddy(sb, entry);

        if (test_opt(sb, DISCARD)) {
                spin_lock(&sbi->s_md_lock);
                wake = list_empty(&sbi->s_discard_list);
                list_splice_tail(&freed_data_list, &sbi->s_discard_list);
                spin_unlock(&sbi->s_md_lock);
                if (wake)
                        queue_work(system_unbound_wq, &sbi->s_discard_work);
        } else {
                list_for_each_entry_safe(entry, tmp, &freed_data_list, efd_list)
                        kmem_cache_free(ext4_free_data_cachep, entry);
        }
}

int __init ext4_init_mballoc(void)
{
        ext4_pspace_cachep = KMEM_CACHE(ext4_prealloc_space,
                                        SLAB_RECLAIM_ACCOUNT);
        if (ext4_pspace_cachep == NULL)
                goto out;

        ext4_ac_cachep = KMEM_CACHE(ext4_allocation_context,
                                    SLAB_RECLAIM_ACCOUNT);
        if (ext4_ac_cachep == NULL)
                goto out_pa_free;

        ext4_free_data_cachep = KMEM_CACHE(ext4_free_data,
                                           SLAB_RECLAIM_ACCOUNT);
        if (ext4_free_data_cachep == NULL)
                goto out_ac_free;

        return 0;

out_ac_free:
        kmem_cache_destroy(ext4_ac_cachep);
out_pa_free:
        kmem_cache_destroy(ext4_pspace_cachep);
out:
        return -ENOMEM;
}

void ext4_exit_mballoc(void)
{
        /*
         * Wait for completion of call_rcu()'s on ext4_pspace_cachep
         * before destroying the slab cache.
         */
        rcu_barrier();
        kmem_cache_destroy(ext4_pspace_cachep);
        kmem_cache_destroy(ext4_ac_cachep);
        kmem_cache_destroy(ext4_free_data_cachep);
        ext4_groupinfo_destroy_slabs();
}

#define EXT4_MB_BITMAP_MARKED_CHECK 0x0001
#define EXT4_MB_SYNC_UPDATE 0x0002
static int
ext4_mb_mark_context(handle_t *handle, struct super_block *sb, bool state,
                     ext4_group_t group, ext4_grpblk_t blkoff,
                     ext4_grpblk_t len, int flags, ext4_grpblk_t *ret_changed)
{
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        struct buffer_head *bitmap_bh = NULL;
        struct ext4_group_desc *gdp;
        struct buffer_head *gdp_bh;
        int err;
        unsigned int i, already, changed = len;

        KUNIT_STATIC_STUB_REDIRECT(ext4_mb_mark_context,
                                   handle, sb, state, group, blkoff, len,
                                   flags, ret_changed);

        if (ret_changed)
                *ret_changed = 0;
        bitmap_bh = ext4_read_block_bitmap(sb, group);
        if (IS_ERR(bitmap_bh))
                return PTR_ERR(bitmap_bh);

        if (handle) {
                BUFFER_TRACE(bitmap_bh, "getting write access");
                err = ext4_journal_get_write_access(handle, sb, bitmap_bh,
                                                    EXT4_JTR_NONE);
                if (err)
                        goto out_err;
        }

        err = -EIO;
        gdp = ext4_get_group_desc(sb, group, &gdp_bh);
        if (!gdp)
                goto out_err;

        if (handle) {
                BUFFER_TRACE(gdp_bh, "get_write_access");
                err = ext4_journal_get_write_access(handle, sb, gdp_bh,
                                                    EXT4_JTR_NONE);
                if (err)
                        goto out_err;
        }

        ext4_lock_group(sb, group);
        if (ext4_has_group_desc_csum(sb) &&
            (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT))) {
                gdp->bg_flags &= cpu_to_le16(~EXT4_BG_BLOCK_UNINIT);
                ext4_free_group_clusters_set(sb, gdp,
                        ext4_free_clusters_after_init(sb, group, gdp));
        }

        if (flags & EXT4_MB_BITMAP_MARKED_CHECK) {
                already = 0;
                for (i = 0; i < len; i++)
                        if (mb_test_bit(blkoff + i, bitmap_bh->b_data) ==
                                        state)
                                already++;
                changed = len - already;
        }

        if (state) {
                mb_set_bits(bitmap_bh->b_data, blkoff, len);
                ext4_free_group_clusters_set(sb, gdp,
                        ext4_free_group_clusters(sb, gdp) - changed);
        } else {
                mb_clear_bits(bitmap_bh->b_data, blkoff, len);
                ext4_free_group_clusters_set(sb, gdp,
                        ext4_free_group_clusters(sb, gdp) + changed);
        }

        ext4_block_bitmap_csum_set(sb, gdp, bitmap_bh);
        ext4_group_desc_csum_set(sb, group, gdp);
        ext4_unlock_group(sb, group);
        if (ret_changed)
                *ret_changed = changed;

        if (sbi->s_log_groups_per_flex) {
                ext4_group_t flex_group = ext4_flex_group(sbi, group);
                struct flex_groups *fg = sbi_array_rcu_deref(sbi,
                                           s_flex_groups, flex_group);

                if (state)
                        atomic64_sub(changed, &fg->free_clusters);
                else
                        atomic64_add(changed, &fg->free_clusters);
        }

        err = ext4_handle_dirty_metadata(handle, NULL, bitmap_bh);
        if (err)
                goto out_err;
        err = ext4_handle_dirty_metadata(handle, NULL, gdp_bh);
        if (err)
                goto out_err;

        if (flags & EXT4_MB_SYNC_UPDATE) {
                sync_dirty_buffer(bitmap_bh);
                sync_dirty_buffer(gdp_bh);
        }

out_err:
        brelse(bitmap_bh);
        return err;
}

/*
 * Check quota and mark chosen space (ac->ac_b_ex) non-free in bitmaps
 * Returns 0 if success or error code
 */
static noinline_for_stack int
ext4_mb_mark_diskspace_used(struct ext4_allocation_context *ac,
                                handle_t *handle, unsigned int reserv_clstrs)
{
        struct ext4_group_desc *gdp;
        struct ext4_sb_info *sbi;
        struct super_block *sb;
        ext4_fsblk_t block;
        int err, len;
        int flags = 0;
        ext4_grpblk_t changed;

        BUG_ON(ac->ac_status != AC_STATUS_FOUND);
        BUG_ON(ac->ac_b_ex.fe_len <= 0);

        sb = ac->ac_sb;
        sbi = EXT4_SB(sb);

        gdp = ext4_get_group_desc(sb, ac->ac_b_ex.fe_group, NULL);
        if (!gdp)
                return -EIO;
        ext4_debug("using block group %u(%d)\n", ac->ac_b_ex.fe_group,
                        ext4_free_group_clusters(sb, gdp));

        block = ext4_grp_offs_to_block(sb, &ac->ac_b_ex);
        len = EXT4_C2B(sbi, ac->ac_b_ex.fe_len);
        if (!ext4_inode_block_valid(ac->ac_inode, block, len)) {
                ext4_error(sb, "Allocating blocks %llu-%llu which overlap "
                           "fs metadata", block, block+len);
                /* File system mounted not to panic on error
                 * Fix the bitmap and return EFSCORRUPTED
                 * We leak some of the blocks here.
                 */
                err = ext4_mb_mark_context(handle, sb, true,
                                           ac->ac_b_ex.fe_group,
                                           ac->ac_b_ex.fe_start,
                                           ac->ac_b_ex.fe_len,
                                           0, NULL);
                if (!err)
                        err = -EFSCORRUPTED;
                return err;
        }

#ifdef AGGRESSIVE_CHECK
        flags |= EXT4_MB_BITMAP_MARKED_CHECK;
#endif
        err = ext4_mb_mark_context(handle, sb, true, ac->ac_b_ex.fe_group,
                                   ac->ac_b_ex.fe_start, ac->ac_b_ex.fe_len,
                                   flags, &changed);

        if (err && changed == 0)
                return err;

#ifdef AGGRESSIVE_CHECK
        BUG_ON(changed != ac->ac_b_ex.fe_len);
#endif
        percpu_counter_sub(&sbi->s_freeclusters_counter, ac->ac_b_ex.fe_len);
        /*
         * Now reduce the dirty block count also. Should not go negative
         */
        if (!(ac->ac_flags & EXT4_MB_DELALLOC_RESERVED))
                /* release all the reserved blocks if non delalloc */
                percpu_counter_sub(&sbi->s_dirtyclusters_counter,
                                   reserv_clstrs);

        return err;
}

/*
 * Idempotent helper for Ext4 fast commit replay path to set the state of
 * blocks in bitmaps and update counters.
 */
void ext4_mb_mark_bb(struct super_block *sb, ext4_fsblk_t block,
                     int len, bool state)
{
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        ext4_group_t group;
        ext4_grpblk_t blkoff;
        int err = 0;
        unsigned int clen, thisgrp_len;

        while (len > 0) {
                ext4_get_group_no_and_offset(sb, block, &group, &blkoff);

                /*
                 * Check to see if we are freeing blocks across a group
                 * boundary.
                 * In case of flex_bg, this can happen that (block, len) may
                 * span across more than one group. In that case we need to
                 * get the corresponding group metadata to work with.
                 * For this we have goto again loop.
                 */
                thisgrp_len = min_t(unsigned int, (unsigned int)len,
                        EXT4_BLOCKS_PER_GROUP(sb) - EXT4_C2B(sbi, blkoff));
                clen = EXT4_NUM_B2C(sbi, thisgrp_len);

                if (!ext4_sb_block_valid(sb, NULL, block, thisgrp_len)) {
                        ext4_error(sb, "Marking blocks in system zone - "
                                   "Block = %llu, len = %u",
                                   block, thisgrp_len);
                        break;
                }

                err = ext4_mb_mark_context(NULL, sb, state,
                                           group, blkoff, clen,
                                           EXT4_MB_BITMAP_MARKED_CHECK |
                                           EXT4_MB_SYNC_UPDATE,
                                           NULL);
                if (err)
                        break;

                block += thisgrp_len;
                len -= thisgrp_len;
                BUG_ON(len < 0);
        }
}

/*
 * here we normalize request for locality group
 * Group request are normalized to s_mb_group_prealloc, which goes to
 * s_strip if we set the same via mount option.
 * s_mb_group_prealloc can be configured via
 * /sys/fs/ext4/<partition>/mb_group_prealloc
 *
 * XXX: should we try to preallocate more than the group has now?
 */
static void ext4_mb_normalize_group_request(struct ext4_allocation_context *ac)
{
        struct super_block *sb = ac->ac_sb;
        struct ext4_locality_group *lg = ac->ac_lg;

        BUG_ON(lg == NULL);
        ac->ac_g_ex.fe_len = EXT4_SB(sb)->s_mb_group_prealloc;
        mb_debug(sb, "goal %u blocks for locality group\n", ac->ac_g_ex.fe_len);
}

/*
 * This function returns the next element to look at during inode
 * PA rbtree walk. We assume that we have held the inode PA rbtree lock
 * (ei->i_prealloc_lock)
 *
 * new_start    The start of the range we want to compare
 * cur_start    The existing start that we are comparing against
 * node The node of the rb_tree
 */
static inline struct rb_node*
ext4_mb_pa_rb_next_iter(ext4_lblk_t new_start, ext4_lblk_t cur_start, struct rb_node *node)
{
        if (new_start < cur_start)
                return node->rb_left;
        else
                return node->rb_right;
}

static inline void
ext4_mb_pa_assert_overlap(struct ext4_allocation_context *ac,
                          ext4_lblk_t start, loff_t end)
{
        struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
        struct ext4_inode_info *ei = EXT4_I(ac->ac_inode);
        struct ext4_prealloc_space *tmp_pa;
        ext4_lblk_t tmp_pa_start;
        loff_t tmp_pa_end;
        struct rb_node *iter;

        read_lock(&ei->i_prealloc_lock);
        for (iter = ei->i_prealloc_node.rb_node; iter;
             iter = ext4_mb_pa_rb_next_iter(start, tmp_pa_start, iter)) {
                tmp_pa = rb_entry(iter, struct ext4_prealloc_space,
                                  pa_node.inode_node);
                tmp_pa_start = tmp_pa->pa_lstart;
                tmp_pa_end = pa_logical_end(sbi, tmp_pa);

                spin_lock(&tmp_pa->pa_lock);
                if (tmp_pa->pa_deleted == 0)
                        BUG_ON(!(start >= tmp_pa_end || end <= tmp_pa_start));
                spin_unlock(&tmp_pa->pa_lock);
        }
        read_unlock(&ei->i_prealloc_lock);
}

/*
 * Given an allocation context "ac" and a range "start", "end", check
 * and adjust boundaries if the range overlaps with any of the existing
 * preallocatoins stored in the corresponding inode of the allocation context.
 *
 * Parameters:
 *      ac                      allocation context
 *      start                   start of the new range
 *      end                     end of the new range
 */
static inline void
ext4_mb_pa_adjust_overlap(struct ext4_allocation_context *ac,
                          ext4_lblk_t *start, loff_t *end)
{
        struct ext4_inode_info *ei = EXT4_I(ac->ac_inode);
        struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
        struct ext4_prealloc_space *tmp_pa = NULL, *left_pa = NULL, *right_pa = NULL;
        struct rb_node *iter;
        ext4_lblk_t new_start, tmp_pa_start, right_pa_start = -1;
        loff_t new_end, tmp_pa_end, left_pa_end = -1;

        new_start = *start;
        new_end = *end;

        /*
         * Adjust the normalized range so that it doesn't overlap with any
         * existing preallocated blocks(PAs). Make sure to hold the rbtree lock
         * so it doesn't change underneath us.
         */
        read_lock(&ei->i_prealloc_lock);

        /* Step 1: find any one immediate neighboring PA of the normalized range */
        for (iter = ei->i_prealloc_node.rb_node; iter;
             iter = ext4_mb_pa_rb_next_iter(ac->ac_o_ex.fe_logical,
                                            tmp_pa_start, iter)) {
                tmp_pa = rb_entry(iter, struct ext4_prealloc_space,
                                  pa_node.inode_node);
                tmp_pa_start = tmp_pa->pa_lstart;
                tmp_pa_end = pa_logical_end(sbi, tmp_pa);

                /* PA must not overlap original request */
                spin_lock(&tmp_pa->pa_lock);
                if (tmp_pa->pa_deleted == 0)
                        BUG_ON(!(ac->ac_o_ex.fe_logical >= tmp_pa_end ||
                                 ac->ac_o_ex.fe_logical < tmp_pa_start));
                spin_unlock(&tmp_pa->pa_lock);
        }

        /*
         * Step 2: check if the found PA is left or right neighbor and
         * get the other neighbor
         */
        if (tmp_pa) {
                if (tmp_pa->pa_lstart < ac->ac_o_ex.fe_logical) {
                        struct rb_node *tmp;

                        left_pa = tmp_pa;
                        tmp = rb_next(&left_pa->pa_node.inode_node);
                        if (tmp) {
                                right_pa = rb_entry(tmp,
                                                    struct ext4_prealloc_space,
                                                    pa_node.inode_node);
                        }
                } else {
                        struct rb_node *tmp;

                        right_pa = tmp_pa;
                        tmp = rb_prev(&right_pa->pa_node.inode_node);
                        if (tmp) {
                                left_pa = rb_entry(tmp,
                                                   struct ext4_prealloc_space,
                                                   pa_node.inode_node);
                        }
                }
        }

        /* Step 3: get the non deleted neighbors */
        if (left_pa) {
                for (iter = &left_pa->pa_node.inode_node;;
                     iter = rb_prev(iter)) {
                        if (!iter) {
                                left_pa = NULL;
                                break;
                        }

                        tmp_pa = rb_entry(iter, struct ext4_prealloc_space,
                                          pa_node.inode_node);
                        left_pa = tmp_pa;
                        spin_lock(&tmp_pa->pa_lock);
                        if (tmp_pa->pa_deleted == 0) {
                                spin_unlock(&tmp_pa->pa_lock);
                                break;
                        }
                        spin_unlock(&tmp_pa->pa_lock);
                }
        }

        if (right_pa) {
                for (iter = &right_pa->pa_node.inode_node;;
                     iter = rb_next(iter)) {
                        if (!iter) {
                                right_pa = NULL;
                                break;
                        }

                        tmp_pa = rb_entry(iter, struct ext4_prealloc_space,
                                          pa_node.inode_node);
                        right_pa = tmp_pa;
                        spin_lock(&tmp_pa->pa_lock);
                        if (tmp_pa->pa_deleted == 0) {
                                spin_unlock(&tmp_pa->pa_lock);
                                break;
                        }
                        spin_unlock(&tmp_pa->pa_lock);
                }
        }

        if (left_pa) {
                left_pa_end = pa_logical_end(sbi, left_pa);
                BUG_ON(left_pa_end > ac->ac_o_ex.fe_logical);
        }

        if (right_pa) {
                right_pa_start = right_pa->pa_lstart;
                BUG_ON(right_pa_start <= ac->ac_o_ex.fe_logical);
        }

        /* Step 4: trim our normalized range to not overlap with the neighbors */
        if (left_pa) {
                if (left_pa_end > new_start)
                        new_start = left_pa_end;
        }

        if (right_pa) {
                if (right_pa_start < new_end)
                        new_end = right_pa_start;
        }
        read_unlock(&ei->i_prealloc_lock);

        /* XXX: extra loop to check we really don't overlap preallocations */
        ext4_mb_pa_assert_overlap(ac, new_start, new_end);

        *start = new_start;
        *end = new_end;
}

/*
 * Normalization means making request better in terms of
 * size and alignment
 */
static noinline_for_stack void
ext4_mb_normalize_request(struct ext4_allocation_context *ac,
                                struct ext4_allocation_request *ar)
{
        struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
        struct ext4_super_block *es = sbi->s_es;
        int bsbits, max;
        loff_t size, start_off, end;
        loff_t orig_size __maybe_unused;
        ext4_lblk_t start;

        /* do normalize only data requests, metadata requests
           do not need preallocation */
        if (!(ac->ac_flags & EXT4_MB_HINT_DATA))
                return;

        /* sometime caller may want exact blocks */
        if (unlikely(ac->ac_flags & EXT4_MB_HINT_GOAL_ONLY))
                return;

        /* caller may indicate that preallocation isn't
         * required (it's a tail, for example) */
        if (ac->ac_flags & EXT4_MB_HINT_NOPREALLOC)
                return;

        if (ac->ac_flags & EXT4_MB_HINT_GROUP_ALLOC) {
                ext4_mb_normalize_group_request(ac);
                return ;
        }

        bsbits = ac->ac_sb->s_blocksize_bits;

        /* first, let's learn actual file size
         * given current request is allocated */
        size = extent_logical_end(sbi, &ac->ac_o_ex);
        size = size << bsbits;
        if (size < i_size_read(ac->ac_inode))
                size = i_size_read(ac->ac_inode);
        orig_size = size;

        /* max size of free chunks */
        max = 2 << bsbits;

#define NRL_CHECK_SIZE(req, size, max, chunk_size)      \
                (req <= (size) || max <= (chunk_size))

        /* first, try to predict filesize */
        /* XXX: should this table be tunable? */
        start_off = 0;
        if (size <= 16 * 1024) {
                size = 16 * 1024;
        } else if (size <= 32 * 1024) {
                size = 32 * 1024;
        } else if (size <= 64 * 1024) {
                size = 64 * 1024;
        } else if (size <= 128 * 1024) {
                size = 128 * 1024;
        } else if (size <= 256 * 1024) {
                size = 256 * 1024;
        } else if (size <= 512 * 1024) {
                size = 512 * 1024;
        } else if (size <= 1024 * 1024) {
                size = 1024 * 1024;
        } else if (NRL_CHECK_SIZE(size, 4 * 1024 * 1024, max, 2 * 1024)) {
                start_off = ((loff_t)ac->ac_o_ex.fe_logical >>
                                                (21 - bsbits)) << 21;
                size = 2 * 1024 * 1024;
        } else if (NRL_CHECK_SIZE(size, 8 * 1024 * 1024, max, 4 * 1024)) {
                start_off = ((loff_t)ac->ac_o_ex.fe_logical >>
                                                        (22 - bsbits)) << 22;
                size = 4 * 1024 * 1024;
        } else if (NRL_CHECK_SIZE(EXT4_C2B(sbi, ac->ac_o_ex.fe_len),
                                        (8<<20)>>bsbits, max, 8 * 1024)) {
                start_off = ((loff_t)ac->ac_o_ex.fe_logical >>
                                                        (23 - bsbits)) << 23;
                size = 8 * 1024 * 1024;
        } else {
                start_off = (loff_t) ac->ac_o_ex.fe_logical << bsbits;
                size      = (loff_t) EXT4_C2B(sbi,
                                              ac->ac_o_ex.fe_len) << bsbits;
        }
        size = size >> bsbits;
        start = start_off >> bsbits;

        /*
         * For tiny groups (smaller than 8MB) the chosen allocation
         * alignment may be larger than group size. Make sure the
         * alignment does not move allocation to a different group which
         * makes mballoc fail assertions later.
         */
        start = max(start, rounddown(ac->ac_o_ex.fe_logical,
                        (ext4_lblk_t)EXT4_BLOCKS_PER_GROUP(ac->ac_sb)));

        /* don't cover already allocated blocks in selected range */
        if (ar->pleft && start <= ar->lleft) {
                size -= ar->lleft + 1 - start;
                start = ar->lleft + 1;
        }
        if (ar->pright && start + size - 1 >= ar->lright)
                size -= start + size - ar->lright;

        /*
         * Trim allocation request for filesystems with artificially small
         * groups.
         */
        if (size > EXT4_BLOCKS_PER_GROUP(ac->ac_sb))
                size = EXT4_BLOCKS_PER_GROUP(ac->ac_sb);

        end = start + size;

        ext4_mb_pa_adjust_overlap(ac, &start, &end);

        size = end - start;

        /*
         * In this function "start" and "size" are normalized for better
         * alignment and length such that we could preallocate more blocks.
         * This normalization is done such that original request of
         * ac->ac_o_ex.fe_logical & fe_len should always lie within "start" and
         * "size" boundaries.
         * (Note fe_len can be relaxed since FS block allocation API does not
         * provide gurantee on number of contiguous blocks allocation since that
         * depends upon free space left, etc).
         * In case of inode pa, later we use the allocated blocks
         * [pa_pstart + fe_logical - pa_lstart, fe_len/size] from the preallocated
         * range of goal/best blocks [start, size] to put it at the
         * ac_o_ex.fe_logical extent of this inode.
         * (See ext4_mb_use_inode_pa() for more details)
         */
        if (start + size <= ac->ac_o_ex.fe_logical ||
                        start > ac->ac_o_ex.fe_logical) {
                ext4_msg(ac->ac_sb, KERN_ERR,
                         "start %lu, size %lu, fe_logical %lu",
                         (unsigned long) start, (unsigned long) size,
                         (unsigned long) ac->ac_o_ex.fe_logical);
                BUG();
        }
        BUG_ON(size <= 0 || size > EXT4_BLOCKS_PER_GROUP(ac->ac_sb));

        /* now prepare goal request */

        /* XXX: is it better to align blocks WRT to logical
         * placement or satisfy big request as is */
        ac->ac_g_ex.fe_logical = start;
        ac->ac_g_ex.fe_len = EXT4_NUM_B2C(sbi, size);
        ac->ac_orig_goal_len = ac->ac_g_ex.fe_len;

        /* define goal start in order to merge */
        if (ar->pright && (ar->lright == (start + size)) &&
            ar->pright >= size &&
            ar->pright - size >= le32_to_cpu(es->s_first_data_block)) {
                /* merge to the right */
                ext4_get_group_no_and_offset(ac->ac_sb, ar->pright - size,
                                                &ac->ac_g_ex.fe_group,
                                                &ac->ac_g_ex.fe_start);
                ac->ac_flags |= EXT4_MB_HINT_TRY_GOAL;
        }
        if (ar->pleft && (ar->lleft + 1 == start) &&
            ar->pleft + 1 < ext4_blocks_count(es)) {
                /* merge to the left */
                ext4_get_group_no_and_offset(ac->ac_sb, ar->pleft + 1,
                                                &ac->ac_g_ex.fe_group,
                                                &ac->ac_g_ex.fe_start);
                ac->ac_flags |= EXT4_MB_HINT_TRY_GOAL;
        }

        mb_debug(ac->ac_sb, "goal: %lld(was %lld) blocks at %u\n", size,
                 orig_size, start);
}

static void ext4_mb_collect_stats(struct ext4_allocation_context *ac)
{
        struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);

        if (sbi->s_mb_stats && ac->ac_g_ex.fe_len >= 1) {
                atomic_inc(&sbi->s_bal_reqs);
                atomic_add(ac->ac_b_ex.fe_len, &sbi->s_bal_allocated);
                if (ac->ac_b_ex.fe_len >= ac->ac_o_ex.fe_len)
                        atomic_inc(&sbi->s_bal_success);

                atomic_add(ac->ac_found, &sbi->s_bal_ex_scanned);
                for (int i=0; i<EXT4_MB_NUM_CRS; i++) {
                        atomic_add(ac->ac_cX_found[i], &sbi->s_bal_cX_ex_scanned[i]);
                }

                atomic_add(ac->ac_groups_scanned, &sbi->s_bal_groups_scanned);
                if (ac->ac_g_ex.fe_start == ac->ac_b_ex.fe_start &&
                                ac->ac_g_ex.fe_group == ac->ac_b_ex.fe_group)
                        atomic_inc(&sbi->s_bal_goals);
                /* did we allocate as much as normalizer originally wanted? */
                if (ac->ac_f_ex.fe_len == ac->ac_orig_goal_len)
                        atomic_inc(&sbi->s_bal_len_goals);

                if (ac->ac_found > sbi->s_mb_max_to_scan)
                        atomic_inc(&sbi->s_bal_breaks);
        }

        if (ac->ac_op == EXT4_MB_HISTORY_ALLOC)
                trace_ext4_mballoc_alloc(ac);
        else
                trace_ext4_mballoc_prealloc(ac);
}

/*
 * Called on failure; free up any blocks from the inode PA for this
 * context.  We don't need this for MB_GROUP_PA because we only change
 * pa_free in ext4_mb_release_context(), but on failure, we've already
 * zeroed out ac->ac_b_ex.fe_len, so group_pa->pa_free is not changed.
 */
static void ext4_discard_allocated_blocks(struct ext4_allocation_context *ac)
{
        struct ext4_prealloc_space *pa = ac->ac_pa;
        struct ext4_buddy e4b;
        int err;

        if (pa == NULL) {
                if (ac->ac_f_ex.fe_len == 0)
                        return;
                err = ext4_mb_load_buddy(ac->ac_sb, ac->ac_f_ex.fe_group, &e4b);
                if (WARN_RATELIMIT(err,
                                   "ext4: mb_load_buddy failed (%d)", err))
                        /*
                         * This should never happen since we pin the
                         * pages in the ext4_allocation_context so
                         * ext4_mb_load_buddy() should never fail.
                         */
                        return;
                ext4_lock_group(ac->ac_sb, ac->ac_f_ex.fe_group);
                mb_free_blocks(ac->ac_inode, &e4b, ac->ac_f_ex.fe_start,
                               ac->ac_f_ex.fe_len);
                ext4_unlock_group(ac->ac_sb, ac->ac_f_ex.fe_group);
                ext4_mb_unload_buddy(&e4b);
                return;
        }
        if (pa->pa_type == MB_INODE_PA) {
                spin_lock(&pa->pa_lock);
                pa->pa_free += ac->ac_b_ex.fe_len;
                spin_unlock(&pa->pa_lock);
        }
}

/*
 * use blocks preallocated to inode
 */
static void ext4_mb_use_inode_pa(struct ext4_allocation_context *ac,
                                struct ext4_prealloc_space *pa)
{
        struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
        ext4_fsblk_t start;
        ext4_fsblk_t end;
        int len;

        /* found preallocated blocks, use them */
        start = pa->pa_pstart + (ac->ac_o_ex.fe_logical - pa->pa_lstart);
        end = min(pa->pa_pstart + EXT4_C2B(sbi, pa->pa_len),
                  start + EXT4_C2B(sbi, ac->ac_o_ex.fe_len));
        len = EXT4_NUM_B2C(sbi, end - start);
        ext4_get_group_no_and_offset(ac->ac_sb, start, &ac->ac_b_ex.fe_group,
                                        &ac->ac_b_ex.fe_start);
        ac->ac_b_ex.fe_len = len;
        ac->ac_status = AC_STATUS_FOUND;
        ac->ac_pa = pa;

        BUG_ON(start < pa->pa_pstart);
        BUG_ON(end > pa->pa_pstart + EXT4_C2B(sbi, pa->pa_len));
        BUG_ON(pa->pa_free < len);
        BUG_ON(ac->ac_b_ex.fe_len <= 0);
        pa->pa_free -= len;

        mb_debug(ac->ac_sb, "use %llu/%d from inode pa %p\n", start, len, pa);
}

/*
 * use blocks preallocated to locality group
 */
static void ext4_mb_use_group_pa(struct ext4_allocation_context *ac,
                                struct ext4_prealloc_space *pa)
{
        unsigned int len = ac->ac_o_ex.fe_len;

        ext4_get_group_no_and_offset(ac->ac_sb, pa->pa_pstart,
                                        &ac->ac_b_ex.fe_group,
                                        &ac->ac_b_ex.fe_start);
        ac->ac_b_ex.fe_len = len;
        ac->ac_status = AC_STATUS_FOUND;
        ac->ac_pa = pa;

        /* we don't correct pa_pstart or pa_len here to avoid
         * possible race when the group is being loaded concurrently
         * instead we correct pa later, after blocks are marked
         * in on-disk bitmap -- see ext4_mb_release_context()
         * Other CPUs are prevented from allocating from this pa by lg_mutex
         */
        mb_debug(ac->ac_sb, "use %u/%u from group pa %p\n",
                 pa->pa_lstart, len, pa);
}

/*
 * Return the prealloc space that have minimal distance
 * from the goal block. @cpa is the prealloc
 * space that is having currently known minimal distance
 * from the goal block.
 */
static struct ext4_prealloc_space *
ext4_mb_check_group_pa(ext4_fsblk_t goal_block,
                        struct ext4_prealloc_space *pa,
                        struct ext4_prealloc_space *cpa)
{
        ext4_fsblk_t cur_distance, new_distance;

        if (cpa == NULL) {
                atomic_inc(&pa->pa_count);
                return pa;
        }
        cur_distance = abs(goal_block - cpa->pa_pstart);
        new_distance = abs(goal_block - pa->pa_pstart);

        if (cur_distance <= new_distance)
                return cpa;

        /* drop the previous reference */
        atomic_dec(&cpa->pa_count);
        atomic_inc(&pa->pa_count);
        return pa;
}

/*
 * check if found pa meets EXT4_MB_HINT_GOAL_ONLY
 */
static bool
ext4_mb_pa_goal_check(struct ext4_allocation_context *ac,
                      struct ext4_prealloc_space *pa)
{
        struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
        ext4_fsblk_t start;

        if (likely(!(ac->ac_flags & EXT4_MB_HINT_GOAL_ONLY)))
                return true;

        /*
         * If EXT4_MB_HINT_GOAL_ONLY is set, ac_g_ex will not be adjusted
         * in ext4_mb_normalize_request and will keep same with ac_o_ex
         * from ext4_mb_initialize_context. Choose ac_g_ex here to keep
         * consistent with ext4_mb_find_by_goal.
         */
        start = pa->pa_pstart +
                (ac->ac_g_ex.fe_logical - pa->pa_lstart);
        if (ext4_grp_offs_to_block(ac->ac_sb, &ac->ac_g_ex) != start)
                return false;

        if (ac->ac_g_ex.fe_len > pa->pa_len -
            EXT4_B2C(sbi, ac->ac_g_ex.fe_logical - pa->pa_lstart))
                return false;

        return true;
}

/*
 * search goal blocks in preallocated space
 */
static noinline_for_stack bool
ext4_mb_use_preallocated(struct ext4_allocation_context *ac)
{
        struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
        int order, i;
        struct ext4_inode_info *ei = EXT4_I(ac->ac_inode);
        struct ext4_locality_group *lg;
        struct ext4_prealloc_space *tmp_pa = NULL, *cpa = NULL;
        struct rb_node *iter;
        ext4_fsblk_t goal_block;

        /* only data can be preallocated */
        if (!(ac->ac_flags & EXT4_MB_HINT_DATA))
                return false;

        /*
         * first, try per-file preallocation by searching the inode pa rbtree.
         *
         * Here, we can't do a direct traversal of the tree because
         * ext4_mb_discard_group_preallocation() can paralelly mark the pa
         * deleted and that can cause direct traversal to skip some entries.
         */
        read_lock(&ei->i_prealloc_lock);

        if (RB_EMPTY_ROOT(&ei->i_prealloc_node)) {
                goto try_group_pa;
        }

        /*
         * Step 1: Find a pa with logical start immediately adjacent to the
         * original logical start. This could be on the left or right.
         *
         * (tmp_pa->pa_lstart never changes so we can skip locking for it).
         */
        for (iter = ei->i_prealloc_node.rb_node; iter;
             iter = ext4_mb_pa_rb_next_iter(ac->ac_o_ex.fe_logical,
                                            tmp_pa->pa_lstart, iter)) {
                tmp_pa = rb_entry(iter, struct ext4_prealloc_space,
                                  pa_node.inode_node);
        }

        /*
         * Step 2: The adjacent pa might be to the right of logical start, find
         * the left adjacent pa. After this step we'd have a valid tmp_pa whose
         * logical start is towards the left of original request's logical start
         */
        if (tmp_pa->pa_lstart > ac->ac_o_ex.fe_logical) {
                struct rb_node *tmp;
                tmp = rb_prev(&tmp_pa->pa_node.inode_node);

                if (tmp) {
                        tmp_pa = rb_entry(tmp, struct ext4_prealloc_space,
                                            pa_node.inode_node);
                } else {
                        /*
                         * If there is no adjacent pa to the left then finding
                         * an overlapping pa is not possible hence stop searching
                         * inode pa tree
                         */
                        goto try_group_pa;
                }
        }

        BUG_ON(!(tmp_pa && tmp_pa->pa_lstart <= ac->ac_o_ex.fe_logical));

        /*
         * Step 3: If the left adjacent pa is deleted, keep moving left to find
         * the first non deleted adjacent pa. After this step we should have a
         * valid tmp_pa which is guaranteed to be non deleted.
         */
        for (iter = &tmp_pa->pa_node.inode_node;; iter = rb_prev(iter)) {
                if (!iter) {
                        /*
                         * no non deleted left adjacent pa, so stop searching
                         * inode pa tree
                         */
                        goto try_group_pa;
                }
                tmp_pa = rb_entry(iter, struct ext4_prealloc_space,
                                  pa_node.inode_node);
                spin_lock(&tmp_pa->pa_lock);
                if (tmp_pa->pa_deleted == 0) {
                        /*
                         * We will keep holding the pa_lock from
                         * this point on because we don't want group discard
                         * to delete this pa underneath us. Since group
                         * discard is anyways an ENOSPC operation it
                         * should be okay for it to wait a few more cycles.
                         */
                        break;
                } else {
                        spin_unlock(&tmp_pa->pa_lock);
                }
        }

        BUG_ON(!(tmp_pa && tmp_pa->pa_lstart <= ac->ac_o_ex.fe_logical));
        BUG_ON(tmp_pa->pa_deleted == 1);

        /*
         * Step 4: We now have the non deleted left adjacent pa. Only this
         * pa can possibly satisfy the request hence check if it overlaps
         * original logical start and stop searching if it doesn't.
         */
        if (ac->ac_o_ex.fe_logical >= pa_logical_end(sbi, tmp_pa)) {
                spin_unlock(&tmp_pa->pa_lock);
                goto try_group_pa;
        }

        /* non-extent files can't have physical blocks past 2^32 */
        if (!(ext4_test_inode_flag(ac->ac_inode, EXT4_INODE_EXTENTS)) &&
            (tmp_pa->pa_pstart + EXT4_C2B(sbi, tmp_pa->pa_len) >
             EXT4_MAX_BLOCK_FILE_PHYS)) {
                /*
                 * Since PAs don't overlap, we won't find any other PA to
                 * satisfy this.
                 */
                spin_unlock(&tmp_pa->pa_lock);
                goto try_group_pa;
        }

        if (tmp_pa->pa_free && likely(ext4_mb_pa_goal_check(ac, tmp_pa))) {
                atomic_inc(&tmp_pa->pa_count);
                ext4_mb_use_inode_pa(ac, tmp_pa);
                spin_unlock(&tmp_pa->pa_lock);
                read_unlock(&ei->i_prealloc_lock);
                return true;
        } else {
                /*
                 * We found a valid overlapping pa but couldn't use it because
                 * it had no free blocks. This should ideally never happen
                 * because:
                 *
                 * 1. When a new inode pa is added to rbtree it must have
                 *    pa_free > 0 since otherwise we won't actually need
                 *    preallocation.
                 *
                 * 2. An inode pa that is in the rbtree can only have it's
                 *    pa_free become zero when another thread calls:
                 *      ext4_mb_new_blocks
                 *       ext4_mb_use_preallocated
                 *        ext4_mb_use_inode_pa
                 *
                 * 3. Further, after the above calls make pa_free == 0, we will
                 *    immediately remove it from the rbtree in:
                 *      ext4_mb_new_blocks
                 *       ext4_mb_release_context
                 *        ext4_mb_put_pa
                 *
                 * 4. Since the pa_free becoming 0 and pa_free getting removed
                 * from tree both happen in ext4_mb_new_blocks, which is always
                 * called with i_data_sem held for data allocations, we can be
                 * sure that another process will never see a pa in rbtree with
                 * pa_free == 0.
                 */
                WARN_ON_ONCE(tmp_pa->pa_free == 0);
        }
        spin_unlock(&tmp_pa->pa_lock);
try_group_pa:
        read_unlock(&ei->i_prealloc_lock);

        /* can we use group allocation? */
        if (!(ac->ac_flags & EXT4_MB_HINT_GROUP_ALLOC))
                return false;

        /* inode may have no locality group for some reason */
        lg = ac->ac_lg;
        if (lg == NULL)
                return false;
        order  = fls(ac->ac_o_ex.fe_len) - 1;
        if (order > PREALLOC_TB_SIZE - 1)
                /* The max size of hash table is PREALLOC_TB_SIZE */
                order = PREALLOC_TB_SIZE - 1;

        goal_block = ext4_grp_offs_to_block(ac->ac_sb, &ac->ac_g_ex);
        /*
         * search for the prealloc space that is having
         * minimal distance from the goal block.
         */
        for (i = order; i < PREALLOC_TB_SIZE; i++) {
                rcu_read_lock();
                list_for_each_entry_rcu(tmp_pa, &lg->lg_prealloc_list[i],
                                        pa_node.lg_list) {
                        spin_lock(&tmp_pa->pa_lock);
                        if (tmp_pa->pa_deleted == 0 &&
                                        tmp_pa->pa_free >= ac->ac_o_ex.fe_len) {

                                cpa = ext4_mb_check_group_pa(goal_block,
                                                                tmp_pa, cpa);
                        }
                        spin_unlock(&tmp_pa->pa_lock);
                }
                rcu_read_unlock();
        }
        if (cpa) {
                ext4_mb_use_group_pa(ac, cpa);
                return true;
        }
        return false;
}

/*
 * the function goes through all preallocation in this group and marks them
 * used in in-core bitmap. buddy must be generated from this bitmap
 * Need to be called with ext4 group lock held
 */
static noinline_for_stack
void ext4_mb_generate_from_pa(struct super_block *sb, void *bitmap,
                                        ext4_group_t group)
{
        struct ext4_group_info *grp = ext4_get_group_info(sb, group);
        struct ext4_prealloc_space *pa;
        struct list_head *cur;
        ext4_group_t groupnr;
        ext4_grpblk_t start;
        int preallocated = 0;
        int len;

        if (!grp)
                return;

        /* all form of preallocation discards first load group,
         * so the only competing code is preallocation use.
         * we don't need any locking here
         * notice we do NOT ignore preallocations with pa_deleted
         * otherwise we could leave used blocks available for
         * allocation in buddy when concurrent ext4_mb_put_pa()
         * is dropping preallocation
         */
        list_for_each(cur, &grp->bb_prealloc_list) {
                pa = list_entry(cur, struct ext4_prealloc_space, pa_group_list);
                spin_lock(&pa->pa_lock);
                ext4_get_group_no_and_offset(sb, pa->pa_pstart,
                                             &groupnr, &start);
                len = pa->pa_len;
                spin_unlock(&pa->pa_lock);
                if (unlikely(len == 0))
                        continue;
                BUG_ON(groupnr != group);
                mb_set_bits(bitmap, start, len);
                preallocated += len;
        }
        mb_debug(sb, "preallocated %d for group %u\n", preallocated, group);
}

static void ext4_mb_mark_pa_deleted(struct super_block *sb,
                                    struct ext4_prealloc_space *pa)
{
        struct ext4_inode_info *ei;

        if (pa->pa_deleted) {
                ext4_warning(sb, "deleted pa, type:%d, pblk:%llu, lblk:%u, len:%d\n",
                             pa->pa_type, pa->pa_pstart, pa->pa_lstart,
                             pa->pa_len);
                return;
        }

        pa->pa_deleted = 1;

        if (pa->pa_type == MB_INODE_PA) {
                ei = EXT4_I(pa->pa_inode);
                atomic_dec(&ei->i_prealloc_active);
        }
}

static inline void ext4_mb_pa_free(struct ext4_prealloc_space *pa)
{
        BUG_ON(!pa);
        BUG_ON(atomic_read(&pa->pa_count));
        BUG_ON(pa->pa_deleted == 0);
        kmem_cache_free(ext4_pspace_cachep, pa);
}

static void ext4_mb_pa_callback(struct rcu_head *head)
{
        struct ext4_prealloc_space *pa;

        pa = container_of(head, struct ext4_prealloc_space, u.pa_rcu);
        ext4_mb_pa_free(pa);
}

/*
 * drops a reference to preallocated space descriptor
 * if this was the last reference and the space is consumed
 */
static void ext4_mb_put_pa(struct ext4_allocation_context *ac,
                        struct super_block *sb, struct ext4_prealloc_space *pa)
{
        ext4_group_t grp;
        ext4_fsblk_t grp_blk;
        struct ext4_inode_info *ei = EXT4_I(ac->ac_inode);

        /* in this short window concurrent discard can set pa_deleted */
        spin_lock(&pa->pa_lock);
        if (!atomic_dec_and_test(&pa->pa_count) || pa->pa_free != 0) {
                spin_unlock(&pa->pa_lock);
                return;
        }

        if (pa->pa_deleted == 1) {
                spin_unlock(&pa->pa_lock);
                return;
        }

        ext4_mb_mark_pa_deleted(sb, pa);
        spin_unlock(&pa->pa_lock);

        grp_blk = pa->pa_pstart;
        /*
         * If doing group-based preallocation, pa_pstart may be in the
         * next group when pa is used up
         */
        if (pa->pa_type == MB_GROUP_PA)
                grp_blk--;

        grp = ext4_get_group_number(sb, grp_blk);

        /*
         * possible race:
         *
         *  P1 (buddy init)                     P2 (regular allocation)
         *                                      find block B in PA
         *  copy on-disk bitmap to buddy
         *                                      mark B in on-disk bitmap
         *                                      drop PA from group
         *  mark all PAs in buddy
         *
         * thus, P1 initializes buddy with B available. to prevent this
         * we make "copy" and "mark all PAs" atomic and serialize "drop PA"
         * against that pair
         */
        ext4_lock_group(sb, grp);
        list_del(&pa->pa_group_list);
        ext4_unlock_group(sb, grp);

        if (pa->pa_type == MB_INODE_PA) {
                write_lock(pa->pa_node_lock.inode_lock);
                rb_erase(&pa->pa_node.inode_node, &ei->i_prealloc_node);
                write_unlock(pa->pa_node_lock.inode_lock);
                ext4_mb_pa_free(pa);
        } else {
                spin_lock(pa->pa_node_lock.lg_lock);
                list_del_rcu(&pa->pa_node.lg_list);
                spin_unlock(pa->pa_node_lock.lg_lock);
                call_rcu(&(pa)->u.pa_rcu, ext4_mb_pa_callback);
        }
}

static void ext4_mb_pa_rb_insert(struct rb_root *root, struct rb_node *new)
{
        struct rb_node **iter = &root->rb_node, *parent = NULL;
        struct ext4_prealloc_space *iter_pa, *new_pa;
        ext4_lblk_t iter_start, new_start;

        while (*iter) {
                iter_pa = rb_entry(*iter, struct ext4_prealloc_space,
                                   pa_node.inode_node);
                new_pa = rb_entry(new, struct ext4_prealloc_space,
                                   pa_node.inode_node);
                iter_start = iter_pa->pa_lstart;
                new_start = new_pa->pa_lstart;

                parent = *iter;
                if (new_start < iter_start)
                        iter = &((*iter)->rb_left);
                else
                        iter = &((*iter)->rb_right);
        }

        rb_link_node(new, parent, iter);
        rb_insert_color(new, root);
}

/*
 * creates new preallocated space for given inode
 */
static noinline_for_stack void
ext4_mb_new_inode_pa(struct ext4_allocation_context *ac)
{
        struct super_block *sb = ac->ac_sb;
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        struct ext4_prealloc_space *pa;
        struct ext4_group_info *grp;
        struct ext4_inode_info *ei;

        /* preallocate only when found space is larger then requested */
        BUG_ON(ac->ac_o_ex.fe_len >= ac->ac_b_ex.fe_len);
        BUG_ON(ac->ac_status != AC_STATUS_FOUND);
        BUG_ON(!S_ISREG(ac->ac_inode->i_mode));
        BUG_ON(ac->ac_pa == NULL);

        pa = ac->ac_pa;

        if (ac->ac_b_ex.fe_len < ac->ac_orig_goal_len) {
                struct ext4_free_extent ex = {
                        .fe_logical = ac->ac_g_ex.fe_logical,
                        .fe_len = ac->ac_orig_goal_len,
                };
                loff_t orig_goal_end = extent_logical_end(sbi, &ex);

                /* we can't allocate as much as normalizer wants.
                 * so, found space must get proper lstart
                 * to cover original request */
                BUG_ON(ac->ac_g_ex.fe_logical > ac->ac_o_ex.fe_logical);
                BUG_ON(ac->ac_g_ex.fe_len < ac->ac_o_ex.fe_len);

                /*
                 * Use the below logic for adjusting best extent as it keeps
                 * fragmentation in check while ensuring logical range of best
                 * extent doesn't overflow out of goal extent:
                 *
                 * 1. Check if best ex can be kept at end of goal (before
                 *    cr_best_avail trimmed it) and still cover original start
                 * 2. Else, check if best ex can be kept at start of goal and
                 *    still cover original start
                 * 3. Else, keep the best ex at start of original request.
                 */
                ex.fe_len = ac->ac_b_ex.fe_len;

                ex.fe_logical = orig_goal_end - EXT4_C2B(sbi, ex.fe_len);
                if (ac->ac_o_ex.fe_logical >= ex.fe_logical)
                        goto adjust_bex;

                ex.fe_logical = ac->ac_g_ex.fe_logical;
                if (ac->ac_o_ex.fe_logical < extent_logical_end(sbi, &ex))
                        goto adjust_bex;

                ex.fe_logical = ac->ac_o_ex.fe_logical;
adjust_bex:
                ac->ac_b_ex.fe_logical = ex.fe_logical;

                BUG_ON(ac->ac_o_ex.fe_logical < ac->ac_b_ex.fe_logical);
                BUG_ON(ac->ac_o_ex.fe_len > ac->ac_b_ex.fe_len);
                BUG_ON(extent_logical_end(sbi, &ex) > orig_goal_end);
        }

        pa->pa_lstart = ac->ac_b_ex.fe_logical;
        pa->pa_pstart = ext4_grp_offs_to_block(sb, &ac->ac_b_ex);
        pa->pa_len = ac->ac_b_ex.fe_len;
        pa->pa_free = pa->pa_len;
        spin_lock_init(&pa->pa_lock);
        INIT_LIST_HEAD(&pa->pa_group_list);
        pa->pa_deleted = 0;
        pa->pa_type = MB_INODE_PA;

        mb_debug(sb, "new inode pa %p: %llu/%d for %u\n", pa, pa->pa_pstart,
                 pa->pa_len, pa->pa_lstart);
        trace_ext4_mb_new_inode_pa(ac, pa);

        atomic_add(pa->pa_free, &sbi->s_mb_preallocated);
        ext4_mb_use_inode_pa(ac, pa);

        ei = EXT4_I(ac->ac_inode);
        grp = ext4_get_group_info(sb, ac->ac_b_ex.fe_group);
        if (!grp)
                return;

        pa->pa_node_lock.inode_lock = &ei->i_prealloc_lock;
        pa->pa_inode = ac->ac_inode;

        list_add(&pa->pa_group_list, &grp->bb_prealloc_list);

        write_lock(pa->pa_node_lock.inode_lock);
        ext4_mb_pa_rb_insert(&ei->i_prealloc_node, &pa->pa_node.inode_node);
        write_unlock(pa->pa_node_lock.inode_lock);
        atomic_inc(&ei->i_prealloc_active);
}

/*
 * creates new preallocated space for locality group inodes belongs to
 */
static noinline_for_stack void
ext4_mb_new_group_pa(struct ext4_allocation_context *ac)
{
        struct super_block *sb = ac->ac_sb;
        struct ext4_locality_group *lg;
        struct ext4_prealloc_space *pa;
        struct ext4_group_info *grp;

        /* preallocate only when found space is larger then requested */
        BUG_ON(ac->ac_o_ex.fe_len >= ac->ac_b_ex.fe_len);
        BUG_ON(ac->ac_status != AC_STATUS_FOUND);
        BUG_ON(!S_ISREG(ac->ac_inode->i_mode));
        BUG_ON(ac->ac_pa == NULL);

        pa = ac->ac_pa;

        pa->pa_pstart = ext4_grp_offs_to_block(sb, &ac->ac_b_ex);
        pa->pa_lstart = pa->pa_pstart;
        pa->pa_len = ac->ac_b_ex.fe_len;
        pa->pa_free = pa->pa_len;
        spin_lock_init(&pa->pa_lock);
        INIT_LIST_HEAD(&pa->pa_node.lg_list);
        INIT_LIST_HEAD(&pa->pa_group_list);
        pa->pa_deleted = 0;
        pa->pa_type = MB_GROUP_PA;

        mb_debug(sb, "new group pa %p: %llu/%d for %u\n", pa, pa->pa_pstart,
                 pa->pa_len, pa->pa_lstart);
        trace_ext4_mb_new_group_pa(ac, pa);

        ext4_mb_use_group_pa(ac, pa);
        atomic_add(pa->pa_free, &EXT4_SB(sb)->s_mb_preallocated);

        grp = ext4_get_group_info(sb, ac->ac_b_ex.fe_group);
        if (!grp)
                return;
        lg = ac->ac_lg;
        BUG_ON(lg == NULL);

        pa->pa_node_lock.lg_lock = &lg->lg_prealloc_lock;
        pa->pa_inode = NULL;

        list_add(&pa->pa_group_list, &grp->bb_prealloc_list);

        /*
         * We will later add the new pa to the right bucket
         * after updating the pa_free in ext4_mb_release_context
         */
}

static void ext4_mb_new_preallocation(struct ext4_allocation_context *ac)
{
        if (ac->ac_flags & EXT4_MB_HINT_GROUP_ALLOC)
                ext4_mb_new_group_pa(ac);
        else
                ext4_mb_new_inode_pa(ac);
}

/*
 * finds all unused blocks in on-disk bitmap, frees them in
 * in-core bitmap and buddy.
 * @pa must be unlinked from inode and group lists, so that
 * nobody else can find/use it.
 * the caller MUST hold group/inode locks.
 * TODO: optimize the case when there are no in-core structures yet
 */
static noinline_for_stack int
ext4_mb_release_inode_pa(struct ext4_buddy *e4b, struct buffer_head *bitmap_bh,
                        struct ext4_prealloc_space *pa)
{
        struct super_block *sb = e4b->bd_sb;
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        unsigned int end;
        unsigned int next;
        ext4_group_t group;
        ext4_grpblk_t bit;
        unsigned long long grp_blk_start;
        int free = 0;

        BUG_ON(pa->pa_deleted == 0);
        ext4_get_group_no_and_offset(sb, pa->pa_pstart, &group, &bit);
        grp_blk_start = pa->pa_pstart - EXT4_C2B(sbi, bit);
        BUG_ON(group != e4b->bd_group && pa->pa_len != 0);
        end = bit + pa->pa_len;

        while (bit < end) {
                bit = mb_find_next_zero_bit(bitmap_bh->b_data, end, bit);
                if (bit >= end)
                        break;
                next = mb_find_next_bit(bitmap_bh->b_data, end, bit);
                mb_debug(sb, "free preallocated %u/%u in group %u\n",
                         (unsigned) ext4_group_first_block_no(sb, group) + bit,
                         (unsigned) next - bit, (unsigned) group);
                free += next - bit;

                trace_ext4_mballoc_discard(sb, NULL, group, bit, next - bit);
                trace_ext4_mb_release_inode_pa(pa, (grp_blk_start +
                                                    EXT4_C2B(sbi, bit)),
                                               next - bit);
                mb_free_blocks(pa->pa_inode, e4b, bit, next - bit);
                bit = next + 1;
        }
        if (free != pa->pa_free) {
                ext4_msg(e4b->bd_sb, KERN_CRIT,
                         "pa %p: logic %lu, phys. %lu, len %d",
                         pa, (unsigned long) pa->pa_lstart,
                         (unsigned long) pa->pa_pstart,
                         pa->pa_len);
                ext4_grp_locked_error(sb, group, 0, 0, "free %u, pa_free %u",
                                        free, pa->pa_free);
                /*
                 * pa is already deleted so we use the value obtained
                 * from the bitmap and continue.
                 */
        }
        atomic_add(free, &sbi->s_mb_discarded);

        return 0;
}

static noinline_for_stack int
ext4_mb_release_group_pa(struct ext4_buddy *e4b,
                                struct ext4_prealloc_space *pa)
{
        struct super_block *sb = e4b->bd_sb;
        ext4_group_t group;
        ext4_grpblk_t bit;

        trace_ext4_mb_release_group_pa(sb, pa);
        BUG_ON(pa->pa_deleted == 0);
        ext4_get_group_no_and_offset(sb, pa->pa_pstart, &group, &bit);
        if (unlikely(group != e4b->bd_group && pa->pa_len != 0)) {
                ext4_warning(sb, "bad group: expected %u, group %u, pa_start %llu",
                             e4b->bd_group, group, pa->pa_pstart);
                return 0;
        }
        mb_free_blocks(pa->pa_inode, e4b, bit, pa->pa_len);
        atomic_add(pa->pa_len, &EXT4_SB(sb)->s_mb_discarded);
        trace_ext4_mballoc_discard(sb, NULL, group, bit, pa->pa_len);

        return 0;
}

/*
 * releases all preallocations in given group
 *
 * first, we need to decide discard policy:
 * - when do we discard
 *   1) ENOSPC
 * - how many do we discard
 *   1) how many requested
 */
static noinline_for_stack int
ext4_mb_discard_group_preallocations(struct super_block *sb,
                                     ext4_group_t group, int *busy)
{
        struct ext4_group_info *grp = ext4_get_group_info(sb, group);
        struct buffer_head *bitmap_bh = NULL;
        struct ext4_prealloc_space *pa, *tmp;
        LIST_HEAD(list);
        struct ext4_buddy e4b;
        struct ext4_inode_info *ei;
        int err;
        int free = 0;

        if (!grp)
                return 0;
        mb_debug(sb, "discard preallocation for group %u\n", group);
        if (list_empty(&grp->bb_prealloc_list))
                goto out_dbg;

        bitmap_bh = ext4_read_block_bitmap(sb, group);
        if (IS_ERR(bitmap_bh)) {
                err = PTR_ERR(bitmap_bh);
                ext4_error_err(sb, -err,
                               "Error %d reading block bitmap for %u",
                               err, group);
                goto out_dbg;
        }

        err = ext4_mb_load_buddy(sb, group, &e4b);
        if (err) {
                ext4_warning(sb, "Error %d loading buddy information for %u",
                             err, group);
                put_bh(bitmap_bh);
                goto out_dbg;
        }

        ext4_lock_group(sb, group);
        list_for_each_entry_safe(pa, tmp,
                                &grp->bb_prealloc_list, pa_group_list) {
                spin_lock(&pa->pa_lock);
                if (atomic_read(&pa->pa_count)) {
                        spin_unlock(&pa->pa_lock);
                        *busy = 1;
                        continue;
                }
                if (pa->pa_deleted) {
                        spin_unlock(&pa->pa_lock);
                        continue;
                }

                /* seems this one can be freed ... */
                ext4_mb_mark_pa_deleted(sb, pa);

                if (!free)
                        this_cpu_inc(discard_pa_seq);

                /* we can trust pa_free ... */
                free += pa->pa_free;

                spin_unlock(&pa->pa_lock);

                list_del(&pa->pa_group_list);
                list_add(&pa->u.pa_tmp_list, &list);
        }

        /* now free all selected PAs */
        list_for_each_entry_safe(pa, tmp, &list, u.pa_tmp_list) {

                /* remove from object (inode or locality group) */
                if (pa->pa_type == MB_GROUP_PA) {
                        spin_lock(pa->pa_node_lock.lg_lock);
                        list_del_rcu(&pa->pa_node.lg_list);
                        spin_unlock(pa->pa_node_lock.lg_lock);
                } else {
                        write_lock(pa->pa_node_lock.inode_lock);
                        ei = EXT4_I(pa->pa_inode);
                        rb_erase(&pa->pa_node.inode_node, &ei->i_prealloc_node);
                        write_unlock(pa->pa_node_lock.inode_lock);
                }

                list_del(&pa->u.pa_tmp_list);

                if (pa->pa_type == MB_GROUP_PA) {
                        ext4_mb_release_group_pa(&e4b, pa);
                        call_rcu(&(pa)->u.pa_rcu, ext4_mb_pa_callback);
                } else {
                        ext4_mb_release_inode_pa(&e4b, bitmap_bh, pa);
                        ext4_mb_pa_free(pa);
                }
        }

        ext4_unlock_group(sb, group);
        ext4_mb_unload_buddy(&e4b);
        put_bh(bitmap_bh);
out_dbg:
        mb_debug(sb, "discarded (%d) blocks preallocated for group %u bb_free (%d)\n",
                 free, group, grp->bb_free);
        return free;
}

/*
 * releases all non-used preallocated blocks for given inode
 *
 * It's important to discard preallocations under i_data_sem
 * We don't want another block to be served from the prealloc
 * space when we are discarding the inode prealloc space.
 *
 * FIXME!! Make sure it is valid at all the call sites
 */
void ext4_discard_preallocations(struct inode *inode, unsigned int needed)
{
        struct ext4_inode_info *ei = EXT4_I(inode);
        struct super_block *sb = inode->i_sb;
        struct buffer_head *bitmap_bh = NULL;
        struct ext4_prealloc_space *pa, *tmp;
        ext4_group_t group = 0;
        LIST_HEAD(list);
        struct ext4_buddy e4b;
        struct rb_node *iter;
        int err;

        if (!S_ISREG(inode->i_mode)) {
                return;
        }

        if (EXT4_SB(sb)->s_mount_state & EXT4_FC_REPLAY)
                return;

        mb_debug(sb, "discard preallocation for inode %lu\n",
                 inode->i_ino);
        trace_ext4_discard_preallocations(inode,
                        atomic_read(&ei->i_prealloc_active), needed);

        if (needed == 0)
                needed = UINT_MAX;

repeat:
        /* first, collect all pa's in the inode */
        write_lock(&ei->i_prealloc_lock);
        for (iter = rb_first(&ei->i_prealloc_node); iter && needed;
             iter = rb_next(iter)) {
                pa = rb_entry(iter, struct ext4_prealloc_space,
                              pa_node.inode_node);
                BUG_ON(pa->pa_node_lock.inode_lock != &ei->i_prealloc_lock);

                spin_lock(&pa->pa_lock);
                if (atomic_read(&pa->pa_count)) {
                        /* this shouldn't happen often - nobody should
                         * use preallocation while we're discarding it */
                        spin_unlock(&pa->pa_lock);
                        write_unlock(&ei->i_prealloc_lock);
                        ext4_msg(sb, KERN_ERR,
                                 "uh-oh! used pa while discarding");
                        WARN_ON(1);
                        schedule_timeout_uninterruptible(HZ);
                        goto repeat;

                }
                if (pa->pa_deleted == 0) {
                        ext4_mb_mark_pa_deleted(sb, pa);
                        spin_unlock(&pa->pa_lock);
                        rb_erase(&pa->pa_node.inode_node, &ei->i_prealloc_node);
                        list_add(&pa->u.pa_tmp_list, &list);
                        needed--;
                        continue;
                }

                /* someone is deleting pa right now */
                spin_unlock(&pa->pa_lock);
                write_unlock(&ei->i_prealloc_lock);

                /* we have to wait here because pa_deleted
                 * doesn't mean pa is already unlinked from
                 * the list. as we might be called from
                 * ->clear_inode() the inode will get freed
                 * and concurrent thread which is unlinking
                 * pa from inode's list may access already
                 * freed memory, bad-bad-bad */

                /* XXX: if this happens too often, we can
                 * add a flag to force wait only in case
                 * of ->clear_inode(), but not in case of
                 * regular truncate */
                schedule_timeout_uninterruptible(HZ);
                goto repeat;
        }
        write_unlock(&ei->i_prealloc_lock);

        list_for_each_entry_safe(pa, tmp, &list, u.pa_tmp_list) {
                BUG_ON(pa->pa_type != MB_INODE_PA);
                group = ext4_get_group_number(sb, pa->pa_pstart);

                err = ext4_mb_load_buddy_gfp(sb, group, &e4b,
                                             GFP_NOFS|__GFP_NOFAIL);
                if (err) {
                        ext4_error_err(sb, -err, "Error %d loading buddy information for %u",
                                       err, group);
                        continue;
                }

                bitmap_bh = ext4_read_block_bitmap(sb, group);
                if (IS_ERR(bitmap_bh)) {
                        err = PTR_ERR(bitmap_bh);
                        ext4_error_err(sb, -err, "Error %d reading block bitmap for %u",
                                       err, group);
                        ext4_mb_unload_buddy(&e4b);
                        continue;
                }

                ext4_lock_group(sb, group);
                list_del(&pa->pa_group_list);
                ext4_mb_release_inode_pa(&e4b, bitmap_bh, pa);
                ext4_unlock_group(sb, group);

                ext4_mb_unload_buddy(&e4b);
                put_bh(bitmap_bh);

                list_del(&pa->u.pa_tmp_list);
                ext4_mb_pa_free(pa);
        }
}

static int ext4_mb_pa_alloc(struct ext4_allocation_context *ac)
{
        struct ext4_prealloc_space *pa;

        BUG_ON(ext4_pspace_cachep == NULL);
        pa = kmem_cache_zalloc(ext4_pspace_cachep, GFP_NOFS);
        if (!pa)
                return -ENOMEM;
        atomic_set(&pa->pa_count, 1);
        ac->ac_pa = pa;
        return 0;
}

static void ext4_mb_pa_put_free(struct ext4_allocation_context *ac)
{
        struct ext4_prealloc_space *pa = ac->ac_pa;

        BUG_ON(!pa);
        ac->ac_pa = NULL;
        WARN_ON(!atomic_dec_and_test(&pa->pa_count));
        /*
         * current function is only called due to an error or due to
         * len of found blocks < len of requested blocks hence the PA has not
         * been added to grp->bb_prealloc_list. So we don't need to lock it
         */
        pa->pa_deleted = 1;
        ext4_mb_pa_free(pa);
}

#ifdef CONFIG_EXT4_DEBUG
static inline void ext4_mb_show_pa(struct super_block *sb)
{
        ext4_group_t i, ngroups;

        if (ext4_forced_shutdown(sb))
                return;

        ngroups = ext4_get_groups_count(sb);
        mb_debug(sb, "groups: ");
        for (i = 0; i < ngroups; i++) {
                struct ext4_group_info *grp = ext4_get_group_info(sb, i);
                struct ext4_prealloc_space *pa;
                ext4_grpblk_t start;
                struct list_head *cur;

                if (!grp)
                        continue;
                ext4_lock_group(sb, i);
                list_for_each(cur, &grp->bb_prealloc_list) {
                        pa = list_entry(cur, struct ext4_prealloc_space,
                                        pa_group_list);
                        spin_lock(&pa->pa_lock);
                        ext4_get_group_no_and_offset(sb, pa->pa_pstart,
                                                     NULL, &start);
                        spin_unlock(&pa->pa_lock);
                        mb_debug(sb, "PA:%u:%d:%d\n", i, start,
                                 pa->pa_len);
                }
                ext4_unlock_group(sb, i);
                mb_debug(sb, "%u: %d/%d\n", i, grp->bb_free,
                         grp->bb_fragments);
        }
}

static void ext4_mb_show_ac(struct ext4_allocation_context *ac)
{
        struct super_block *sb = ac->ac_sb;

        if (ext4_forced_shutdown(sb))
                return;

        mb_debug(sb, "Can't allocate:"
                        " Allocation context details:");
        mb_debug(sb, "status %u flags 0x%x",
                        ac->ac_status, ac->ac_flags);
        mb_debug(sb, "orig %lu/%lu/%lu@%lu, "
                        "goal %lu/%lu/%lu@%lu, "
                        "best %lu/%lu/%lu@%lu cr %d",
                        (unsigned long)ac->ac_o_ex.fe_group,
                        (unsigned long)ac->ac_o_ex.fe_start,
                        (unsigned long)ac->ac_o_ex.fe_len,
                        (unsigned long)ac->ac_o_ex.fe_logical,
                        (unsigned long)ac->ac_g_ex.fe_group,
                        (unsigned long)ac->ac_g_ex.fe_start,
                        (unsigned long)ac->ac_g_ex.fe_len,
                        (unsigned long)ac->ac_g_ex.fe_logical,
                        (unsigned long)ac->ac_b_ex.fe_group,
                        (unsigned long)ac->ac_b_ex.fe_start,
                        (unsigned long)ac->ac_b_ex.fe_len,
                        (unsigned long)ac->ac_b_ex.fe_logical,
                        (int)ac->ac_criteria);
        mb_debug(sb, "%u found", ac->ac_found);
        mb_debug(sb, "used pa: %s, ", ac->ac_pa ? "yes" : "no");
        if (ac->ac_pa)
                mb_debug(sb, "pa_type %s\n", ac->ac_pa->pa_type == MB_GROUP_PA ?
                         "group pa" : "inode pa");
        ext4_mb_show_pa(sb);
}
#else
static inline void ext4_mb_show_pa(struct super_block *sb)
{
}
static inline void ext4_mb_show_ac(struct ext4_allocation_context *ac)
{
        ext4_mb_show_pa(ac->ac_sb);
}
#endif

/*
 * We use locality group preallocation for small size file. The size of the
 * file is determined by the current size or the resulting size after
 * allocation which ever is larger
 *
 * One can tune this size via /sys/fs/ext4/<partition>/mb_stream_req
 */
static void ext4_mb_group_or_file(struct ext4_allocation_context *ac)
{
        struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
        int bsbits = ac->ac_sb->s_blocksize_bits;
        loff_t size, isize;
        bool inode_pa_eligible, group_pa_eligible;

        if (!(ac->ac_flags & EXT4_MB_HINT_DATA))
                return;

        if (unlikely(ac->ac_flags & EXT4_MB_HINT_GOAL_ONLY))
                return;

        group_pa_eligible = sbi->s_mb_group_prealloc > 0;
        inode_pa_eligible = true;
        size = extent_logical_end(sbi, &ac->ac_o_ex);
        isize = (i_size_read(ac->ac_inode) + ac->ac_sb->s_blocksize - 1)
                >> bsbits;

        /* No point in using inode preallocation for closed files */
        if ((size == isize) && !ext4_fs_is_busy(sbi) &&
            !inode_is_open_for_write(ac->ac_inode))
                inode_pa_eligible = false;

        size = max(size, isize);
        /* Don't use group allocation for large files */
        if (size > sbi->s_mb_stream_request)
                group_pa_eligible = false;

        if (!group_pa_eligible) {
                if (inode_pa_eligible)
                        ac->ac_flags |= EXT4_MB_STREAM_ALLOC;
                else
                        ac->ac_flags |= EXT4_MB_HINT_NOPREALLOC;
                return;
        }

        BUG_ON(ac->ac_lg != NULL);
        /*
         * locality group prealloc space are per cpu. The reason for having
         * per cpu locality group is to reduce the contention between block
         * request from multiple CPUs.
         */
        ac->ac_lg = raw_cpu_ptr(sbi->s_locality_groups);

        /* we're going to use group allocation */
        ac->ac_flags |= EXT4_MB_HINT_GROUP_ALLOC;

        /* serialize all allocations in the group */
        mutex_lock(&ac->ac_lg->lg_mutex);
}

static noinline_for_stack void
ext4_mb_initialize_context(struct ext4_allocation_context *ac,
                                struct ext4_allocation_request *ar)
{
        struct super_block *sb = ar->inode->i_sb;
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        struct ext4_super_block *es = sbi->s_es;
        ext4_group_t group;
        unsigned int len;
        ext4_fsblk_t goal;
        ext4_grpblk_t block;

        /* we can't allocate > group size */
        len = ar->len;

        /* just a dirty hack to filter too big requests  */
        if (len >= EXT4_CLUSTERS_PER_GROUP(sb))
                len = EXT4_CLUSTERS_PER_GROUP(sb);

        /* start searching from the goal */
        goal = ar->goal;
        if (goal < le32_to_cpu(es->s_first_data_block) ||
                        goal >= ext4_blocks_count(es))
                goal = le32_to_cpu(es->s_first_data_block);
        ext4_get_group_no_and_offset(sb, goal, &group, &block);

        /* set up allocation goals */
        ac->ac_b_ex.fe_logical = EXT4_LBLK_CMASK(sbi, ar->logical);
        ac->ac_status = AC_STATUS_CONTINUE;
        ac->ac_sb = sb;
        ac->ac_inode = ar->inode;
        ac->ac_o_ex.fe_logical = ac->ac_b_ex.fe_logical;
        ac->ac_o_ex.fe_group = group;
        ac->ac_o_ex.fe_start = block;
        ac->ac_o_ex.fe_len = len;
        ac->ac_g_ex = ac->ac_o_ex;
        ac->ac_orig_goal_len = ac->ac_g_ex.fe_len;
        ac->ac_flags = ar->flags;

        /* we have to define context: we'll work with a file or
         * locality group. this is a policy, actually */
        ext4_mb_group_or_file(ac);

        mb_debug(sb, "init ac: %u blocks @ %u, goal %u, flags 0x%x, 2^%d, "
                        "left: %u/%u, right %u/%u to %swritable\n",
                        (unsigned) ar->len, (unsigned) ar->logical,
                        (unsigned) ar->goal, ac->ac_flags, ac->ac_2order,
                        (unsigned) ar->lleft, (unsigned) ar->pleft,
                        (unsigned) ar->lright, (unsigned) ar->pright,
                        inode_is_open_for_write(ar->inode) ? "" : "non-");
}

static noinline_for_stack void
ext4_mb_discard_lg_preallocations(struct super_block *sb,
                                        struct ext4_locality_group *lg,
                                        int order, int total_entries)
{
        ext4_group_t group = 0;
        struct ext4_buddy e4b;
        LIST_HEAD(discard_list);
        struct ext4_prealloc_space *pa, *tmp;

        mb_debug(sb, "discard locality group preallocation\n");

        spin_lock(&lg->lg_prealloc_lock);
        list_for_each_entry_rcu(pa, &lg->lg_prealloc_list[order],
                                pa_node.lg_list,
                                lockdep_is_held(&lg->lg_prealloc_lock)) {
                spin_lock(&pa->pa_lock);
                if (atomic_read(&pa->pa_count)) {
                        /*
                         * This is the pa that we just used
                         * for block allocation. So don't
                         * free that
                         */
                        spin_unlock(&pa->pa_lock);
                        continue;
                }
                if (pa->pa_deleted) {
                        spin_unlock(&pa->pa_lock);
                        continue;
                }
                /* only lg prealloc space */
                BUG_ON(pa->pa_type != MB_GROUP_PA);

                /* seems this one can be freed ... */
                ext4_mb_mark_pa_deleted(sb, pa);
                spin_unlock(&pa->pa_lock);

                list_del_rcu(&pa->pa_node.lg_list);
                list_add(&pa->u.pa_tmp_list, &discard_list);

                total_entries--;
                if (total_entries <= 5) {
                        /*
                         * we want to keep only 5 entries
                         * allowing it to grow to 8. This
                         * mak sure we don't call discard
                         * soon for this list.
                         */
                        break;
                }
        }
        spin_unlock(&lg->lg_prealloc_lock);

        list_for_each_entry_safe(pa, tmp, &discard_list, u.pa_tmp_list) {
                int err;

                group = ext4_get_group_number(sb, pa->pa_pstart);
                err = ext4_mb_load_buddy_gfp(sb, group, &e4b,
                                             GFP_NOFS|__GFP_NOFAIL);
                if (err) {
                        ext4_error_err(sb, -err, "Error %d loading buddy information for %u",
                                       err, group);
                        continue;
                }
                ext4_lock_group(sb, group);
                list_del(&pa->pa_group_list);
                ext4_mb_release_group_pa(&e4b, pa);
                ext4_unlock_group(sb, group);

                ext4_mb_unload_buddy(&e4b);
                list_del(&pa->u.pa_tmp_list);
                call_rcu(&(pa)->u.pa_rcu, ext4_mb_pa_callback);
        }
}

/*
 * We have incremented pa_count. So it cannot be freed at this
 * point. Also we hold lg_mutex. So no parallel allocation is
 * possible from this lg. That means pa_free cannot be updated.
 *
 * A parallel ext4_mb_discard_group_preallocations is possible.
 * which can cause the lg_prealloc_list to be updated.
 */

static void ext4_mb_add_n_trim(struct ext4_allocation_context *ac)
{
        int order, added = 0, lg_prealloc_count = 1;
        struct super_block *sb = ac->ac_sb;
        struct ext4_locality_group *lg = ac->ac_lg;
        struct ext4_prealloc_space *tmp_pa, *pa = ac->ac_pa;

        order = fls(pa->pa_free) - 1;
        if (order > PREALLOC_TB_SIZE - 1)
                /* The max size of hash table is PREALLOC_TB_SIZE */
                order = PREALLOC_TB_SIZE - 1;
        /* Add the prealloc space to lg */
        spin_lock(&lg->lg_prealloc_lock);
        list_for_each_entry_rcu(tmp_pa, &lg->lg_prealloc_list[order],
                                pa_node.lg_list,
                                lockdep_is_held(&lg->lg_prealloc_lock)) {
                spin_lock(&tmp_pa->pa_lock);
                if (tmp_pa->pa_deleted) {
                        spin_unlock(&tmp_pa->pa_lock);
                        continue;
                }
                if (!added && pa->pa_free < tmp_pa->pa_free) {
                        /* Add to the tail of the previous entry */
                        list_add_tail_rcu(&pa->pa_node.lg_list,
                                                &tmp_pa->pa_node.lg_list);
                        added = 1;
                        /*
                         * we want to count the total
                         * number of entries in the list
                         */
                }
                spin_unlock(&tmp_pa->pa_lock);
                lg_prealloc_count++;
        }
        if (!added)
                list_add_tail_rcu(&pa->pa_node.lg_list,
                                        &lg->lg_prealloc_list[order]);
        spin_unlock(&lg->lg_prealloc_lock);

        /* Now trim the list to be not more than 8 elements */
        if (lg_prealloc_count > 8)
                ext4_mb_discard_lg_preallocations(sb, lg,
                                                  order, lg_prealloc_count);
}

/*
 * release all resource we used in allocation
 */
static int ext4_mb_release_context(struct ext4_allocation_context *ac)
{
        struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
        struct ext4_prealloc_space *pa = ac->ac_pa;
        if (pa) {
                if (pa->pa_type == MB_GROUP_PA) {
                        /* see comment in ext4_mb_use_group_pa() */
                        spin_lock(&pa->pa_lock);
                        pa->pa_pstart += EXT4_C2B(sbi, ac->ac_b_ex.fe_len);
                        pa->pa_lstart += EXT4_C2B(sbi, ac->ac_b_ex.fe_len);
                        pa->pa_free -= ac->ac_b_ex.fe_len;
                        pa->pa_len -= ac->ac_b_ex.fe_len;
                        spin_unlock(&pa->pa_lock);

                        /*
                         * We want to add the pa to the right bucket.
                         * Remove it from the list and while adding
                         * make sure the list to which we are adding
                         * doesn't grow big.
                         */
                        if (likely(pa->pa_free)) {
                                spin_lock(pa->pa_node_lock.lg_lock);
                                list_del_rcu(&pa->pa_node.lg_list);
                                spin_unlock(pa->pa_node_lock.lg_lock);
                                ext4_mb_add_n_trim(ac);
                        }
                }

                ext4_mb_put_pa(ac, ac->ac_sb, pa);
        }
        if (ac->ac_bitmap_page)
                put_page(ac->ac_bitmap_page);
        if (ac->ac_buddy_page)
                put_page(ac->ac_buddy_page);
        if (ac->ac_flags & EXT4_MB_HINT_GROUP_ALLOC)
                mutex_unlock(&ac->ac_lg->lg_mutex);
        ext4_mb_collect_stats(ac);
        return 0;
}

static int ext4_mb_discard_preallocations(struct super_block *sb, int needed)
{
        ext4_group_t i, ngroups = ext4_get_groups_count(sb);
        int ret;
        int freed = 0, busy = 0;
        int retry = 0;

        trace_ext4_mb_discard_preallocations(sb, needed);

        if (needed == 0)
                needed = EXT4_CLUSTERS_PER_GROUP(sb) + 1;
 repeat:
        for (i = 0; i < ngroups && needed > 0; i++) {
                ret = ext4_mb_discard_group_preallocations(sb, i, &busy);
                freed += ret;
                needed -= ret;
                cond_resched();
        }

        if (needed > 0 && busy && ++retry < 3) {
                busy = 0;
                goto repeat;
        }

        return freed;
}

static bool ext4_mb_discard_preallocations_should_retry(struct super_block *sb,
                        struct ext4_allocation_context *ac, u64 *seq)
{
        int freed;
        u64 seq_retry = 0;
        bool ret = false;

        freed = ext4_mb_discard_preallocations(sb, ac->ac_o_ex.fe_len);
        if (freed) {
                ret = true;
                goto out_dbg;
        }
        seq_retry = ext4_get_discard_pa_seq_sum();
        if (!(ac->ac_flags & EXT4_MB_STRICT_CHECK) || seq_retry != *seq) {
                ac->ac_flags |= EXT4_MB_STRICT_CHECK;
                *seq = seq_retry;
                ret = true;
        }

out_dbg:
        mb_debug(sb, "freed %d, retry ? %s\n", freed, ret ? "yes" : "no");
        return ret;
}

/*
 * Simple allocator for Ext4 fast commit replay path. It searches for blocks
 * linearly starting at the goal block and also excludes the blocks which
 * are going to be in use after fast commit replay.
 */
static ext4_fsblk_t
ext4_mb_new_blocks_simple(struct ext4_allocation_request *ar, int *errp)
{
        struct buffer_head *bitmap_bh;
        struct super_block *sb = ar->inode->i_sb;
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        ext4_group_t group, nr;
        ext4_grpblk_t blkoff;
        ext4_grpblk_t max = EXT4_CLUSTERS_PER_GROUP(sb);
        ext4_grpblk_t i = 0;
        ext4_fsblk_t goal, block;
        struct ext4_super_block *es = sbi->s_es;

        goal = ar->goal;
        if (goal < le32_to_cpu(es->s_first_data_block) ||
                        goal >= ext4_blocks_count(es))
                goal = le32_to_cpu(es->s_first_data_block);

        ar->len = 0;
        ext4_get_group_no_and_offset(sb, goal, &group, &blkoff);
        for (nr = ext4_get_groups_count(sb); nr > 0; nr--) {
                bitmap_bh = ext4_read_block_bitmap(sb, group);
                if (IS_ERR(bitmap_bh)) {
                        *errp = PTR_ERR(bitmap_bh);
                        pr_warn("Failed to read block bitmap\n");
                        return 0;
                }

                while (1) {
                        i = mb_find_next_zero_bit(bitmap_bh->b_data, max,
                                                blkoff);
                        if (i >= max)
                                break;
                        if (ext4_fc_replay_check_excluded(sb,
                                ext4_group_first_block_no(sb, group) +
                                EXT4_C2B(sbi, i))) {
                                blkoff = i + 1;
                        } else
                                break;
                }
                brelse(bitmap_bh);
                if (i < max)
                        break;

                if (++group >= ext4_get_groups_count(sb))
                        group = 0;

                blkoff = 0;
        }

        if (i >= max) {
                *errp = -ENOSPC;
                return 0;
        }

        block = ext4_group_first_block_no(sb, group) + EXT4_C2B(sbi, i);
        ext4_mb_mark_bb(sb, block, 1, true);
        ar->len = 1;

        return block;
}

/*
 * Main entry point into mballoc to allocate blocks
 * it tries to use preallocation first, then falls back
 * to usual allocation
 */
ext4_fsblk_t ext4_mb_new_blocks(handle_t *handle,
                                struct ext4_allocation_request *ar, int *errp)
{
        struct ext4_allocation_context *ac = NULL;
        struct ext4_sb_info *sbi;
        struct super_block *sb;
        ext4_fsblk_t block = 0;
        unsigned int inquota = 0;
        unsigned int reserv_clstrs = 0;
        int retries = 0;
        u64 seq;

        might_sleep();
        sb = ar->inode->i_sb;
        sbi = EXT4_SB(sb);

        trace_ext4_request_blocks(ar);
        if (sbi->s_mount_state & EXT4_FC_REPLAY)
                return ext4_mb_new_blocks_simple(ar, errp);

        /* Allow to use superuser reservation for quota file */
        if (ext4_is_quota_file(ar->inode))
                ar->flags |= EXT4_MB_USE_ROOT_BLOCKS;

        if ((ar->flags & EXT4_MB_DELALLOC_RESERVED) == 0) {
                /* Without delayed allocation we need to verify
                 * there is enough free blocks to do block allocation
                 * and verify allocation doesn't exceed the quota limits.
                 */
                while (ar->len &&
                        ext4_claim_free_clusters(sbi, ar->len, ar->flags)) {

                        /* let others to free the space */
                        cond_resched();
                        ar->len = ar->len >> 1;
                }
                if (!ar->len) {
                        ext4_mb_show_pa(sb);
                        *errp = -ENOSPC;
                        return 0;
                }
                reserv_clstrs = ar->len;
                if (ar->flags & EXT4_MB_USE_ROOT_BLOCKS) {
                        dquot_alloc_block_nofail(ar->inode,
                                                 EXT4_C2B(sbi, ar->len));
                } else {
                        while (ar->len &&
                                dquot_alloc_block(ar->inode,
                                                  EXT4_C2B(sbi, ar->len))) {

                                ar->flags |= EXT4_MB_HINT_NOPREALLOC;
                                ar->len--;
                        }
                }
                inquota = ar->len;
                if (ar->len == 0) {
                        *errp = -EDQUOT;
                        goto out;
                }
        }

        ac = kmem_cache_zalloc(ext4_ac_cachep, GFP_NOFS);
        if (!ac) {
                ar->len = 0;
                *errp = -ENOMEM;
                goto out;
        }

        ext4_mb_initialize_context(ac, ar);

        ac->ac_op = EXT4_MB_HISTORY_PREALLOC;
        seq = this_cpu_read(discard_pa_seq);
        if (!ext4_mb_use_preallocated(ac)) {
                ac->ac_op = EXT4_MB_HISTORY_ALLOC;
                ext4_mb_normalize_request(ac, ar);

                *errp = ext4_mb_pa_alloc(ac);
                if (*errp)
                        goto errout;
repeat:
                /* allocate space in core */
                *errp = ext4_mb_regular_allocator(ac);
                /*
                 * pa allocated above is added to grp->bb_prealloc_list only
                 * when we were able to allocate some block i.e. when
                 * ac->ac_status == AC_STATUS_FOUND.
                 * And error from above mean ac->ac_status != AC_STATUS_FOUND
                 * So we have to free this pa here itself.
                 */
                if (*errp) {
                        ext4_mb_pa_put_free(ac);
                        ext4_discard_allocated_blocks(ac);
                        goto errout;
                }
                if (ac->ac_status == AC_STATUS_FOUND &&
                        ac->ac_o_ex.fe_len >= ac->ac_f_ex.fe_len)
                        ext4_mb_pa_put_free(ac);
        }
        if (likely(ac->ac_status == AC_STATUS_FOUND)) {
                *errp = ext4_mb_mark_diskspace_used(ac, handle, reserv_clstrs);
                if (*errp) {
                        ext4_discard_allocated_blocks(ac);
                        goto errout;
                } else {
                        block = ext4_grp_offs_to_block(sb, &ac->ac_b_ex);
                        ar->len = ac->ac_b_ex.fe_len;
                }
        } else {
                if (++retries < 3 &&
                    ext4_mb_discard_preallocations_should_retry(sb, ac, &seq))
                        goto repeat;
                /*
                 * If block allocation fails then the pa allocated above
                 * needs to be freed here itself.
                 */
                ext4_mb_pa_put_free(ac);
                *errp = -ENOSPC;
        }

        if (*errp) {
errout:
                ac->ac_b_ex.fe_len = 0;
                ar->len = 0;
                ext4_mb_show_ac(ac);
        }
        ext4_mb_release_context(ac);
        kmem_cache_free(ext4_ac_cachep, ac);
out:
        if (inquota && ar->len < inquota)
                dquot_free_block(ar->inode, EXT4_C2B(sbi, inquota - ar->len));
        if (!ar->len) {
                if ((ar->flags & EXT4_MB_DELALLOC_RESERVED) == 0)
                        /* release all the reserved blocks if non delalloc */
                        percpu_counter_sub(&sbi->s_dirtyclusters_counter,
                                                reserv_clstrs);
        }

        trace_ext4_allocate_blocks(ar, (unsigned long long)block);

        return block;
}

/*
 * We can merge two free data extents only if the physical blocks
 * are contiguous, AND the extents were freed by the same transaction,
 * AND the blocks are associated with the same group.
 */
static void ext4_try_merge_freed_extent(struct ext4_sb_info *sbi,
                                        struct ext4_free_data *entry,
                                        struct ext4_free_data *new_entry,
                                        struct rb_root *entry_rb_root)
{
        if ((entry->efd_tid != new_entry->efd_tid) ||
            (entry->efd_group != new_entry->efd_group))
                return;
        if (entry->efd_start_cluster + entry->efd_count ==
            new_entry->efd_start_cluster) {
                new_entry->efd_start_cluster = entry->efd_start_cluster;
                new_entry->efd_count += entry->efd_count;
        } else if (new_entry->efd_start_cluster + new_entry->efd_count ==
                   entry->efd_start_cluster) {
                new_entry->efd_count += entry->efd_count;
        } else
                return;
        spin_lock(&sbi->s_md_lock);
        list_del(&entry->efd_list);
        spin_unlock(&sbi->s_md_lock);
        rb_erase(&entry->efd_node, entry_rb_root);
        kmem_cache_free(ext4_free_data_cachep, entry);
}

static noinline_for_stack void
ext4_mb_free_metadata(handle_t *handle, struct ext4_buddy *e4b,
                      struct ext4_free_data *new_entry)
{
        ext4_group_t group = e4b->bd_group;
        ext4_grpblk_t cluster;
        ext4_grpblk_t clusters = new_entry->efd_count;
        struct ext4_free_data *entry;
        struct ext4_group_info *db = e4b->bd_info;
        struct super_block *sb = e4b->bd_sb;
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        struct rb_node **n = &db->bb_free_root.rb_node, *node;
        struct rb_node *parent = NULL, *new_node;

        BUG_ON(!ext4_handle_valid(handle));
        BUG_ON(e4b->bd_bitmap_page == NULL);
        BUG_ON(e4b->bd_buddy_page == NULL);

        new_node = &new_entry->efd_node;
        cluster = new_entry->efd_start_cluster;

        if (!*n) {
                /* first free block exent. We need to
                   protect buddy cache from being freed,
                 * otherwise we'll refresh it from
                 * on-disk bitmap and lose not-yet-available
                 * blocks */
                get_page(e4b->bd_buddy_page);
                get_page(e4b->bd_bitmap_page);
        }
        while (*n) {
                parent = *n;
                entry = rb_entry(parent, struct ext4_free_data, efd_node);
                if (cluster < entry->efd_start_cluster)
                        n = &(*n)->rb_left;
                else if (cluster >= (entry->efd_start_cluster + entry->efd_count))
                        n = &(*n)->rb_right;
                else {
                        ext4_grp_locked_error(sb, group, 0,
                                ext4_group_first_block_no(sb, group) +
                                EXT4_C2B(sbi, cluster),
                                "Block already on to-be-freed list");
                        kmem_cache_free(ext4_free_data_cachep, new_entry);
                        return;
                }
        }

        rb_link_node(new_node, parent, n);
        rb_insert_color(new_node, &db->bb_free_root);

        /* Now try to see the extent can be merged to left and right */
        node = rb_prev(new_node);
        if (node) {
                entry = rb_entry(node, struct ext4_free_data, efd_node);
                ext4_try_merge_freed_extent(sbi, entry, new_entry,
                                            &(db->bb_free_root));
        }

        node = rb_next(new_node);
        if (node) {
                entry = rb_entry(node, struct ext4_free_data, efd_node);
                ext4_try_merge_freed_extent(sbi, entry, new_entry,
                                            &(db->bb_free_root));
        }

        spin_lock(&sbi->s_md_lock);
        list_add_tail(&new_entry->efd_list, &sbi->s_freed_data_list[new_entry->efd_tid & 1]);
        sbi->s_mb_free_pending += clusters;
        spin_unlock(&sbi->s_md_lock);
}

static void ext4_free_blocks_simple(struct inode *inode, ext4_fsblk_t block,
                                        unsigned long count)
{
        struct super_block *sb = inode->i_sb;
        ext4_group_t group;
        ext4_grpblk_t blkoff;

        ext4_get_group_no_and_offset(sb, block, &group, &blkoff);
        ext4_mb_mark_context(NULL, sb, false, group, blkoff, count,
                             EXT4_MB_BITMAP_MARKED_CHECK |
                             EXT4_MB_SYNC_UPDATE,
                             NULL);
}

/**
 * ext4_mb_clear_bb() -- helper function for freeing blocks.
 *                      Used by ext4_free_blocks()
 * @handle:             handle for this transaction
 * @inode:              inode
 * @block:              starting physical block to be freed
 * @count:              number of blocks to be freed
 * @flags:              flags used by ext4_free_blocks
 */
static void ext4_mb_clear_bb(handle_t *handle, struct inode *inode,
                               ext4_fsblk_t block, unsigned long count,
                               int flags)
{
        struct super_block *sb = inode->i_sb;
        struct ext4_group_info *grp;
        unsigned int overflow;
        ext4_grpblk_t bit;
        ext4_group_t block_group;
        struct ext4_sb_info *sbi;
        struct ext4_buddy e4b;
        unsigned int count_clusters;
        int err = 0;
        int mark_flags = 0;
        ext4_grpblk_t changed;

        sbi = EXT4_SB(sb);

        if (!(flags & EXT4_FREE_BLOCKS_VALIDATED) &&
            !ext4_inode_block_valid(inode, block, count)) {
                ext4_error(sb, "Freeing blocks in system zone - "
                           "Block = %llu, count = %lu", block, count);
                /* err = 0. ext4_std_error should be a no op */
                goto error_out;
        }
        flags |= EXT4_FREE_BLOCKS_VALIDATED;

do_more:
        overflow = 0;
        ext4_get_group_no_and_offset(sb, block, &block_group, &bit);

        grp = ext4_get_group_info(sb, block_group);
        if (unlikely(!grp || EXT4_MB_GRP_BBITMAP_CORRUPT(grp)))
                return;

        /*
         * Check to see if we are freeing blocks across a group
         * boundary.
         */
        if (EXT4_C2B(sbi, bit) + count > EXT4_BLOCKS_PER_GROUP(sb)) {
                overflow = EXT4_C2B(sbi, bit) + count -
                        EXT4_BLOCKS_PER_GROUP(sb);
                count -= overflow;
                /* The range changed so it's no longer validated */
                flags &= ~EXT4_FREE_BLOCKS_VALIDATED;
        }
        count_clusters = EXT4_NUM_B2C(sbi, count);
        trace_ext4_mballoc_free(sb, inode, block_group, bit, count_clusters);

        /* __GFP_NOFAIL: retry infinitely, ignore TIF_MEMDIE and memcg limit. */
        err = ext4_mb_load_buddy_gfp(sb, block_group, &e4b,
                                     GFP_NOFS|__GFP_NOFAIL);
        if (err)
                goto error_out;

        if (!(flags & EXT4_FREE_BLOCKS_VALIDATED) &&
            !ext4_inode_block_valid(inode, block, count)) {
                ext4_error(sb, "Freeing blocks in system zone - "
                           "Block = %llu, count = %lu", block, count);
                /* err = 0. ext4_std_error should be a no op */
                goto error_clean;
        }

#ifdef AGGRESSIVE_CHECK
        mark_flags |= EXT4_MB_BITMAP_MARKED_CHECK;
#endif
        err = ext4_mb_mark_context(handle, sb, false, block_group, bit,
                                   count_clusters, mark_flags, &changed);


        if (err && changed == 0)
                goto error_clean;

#ifdef AGGRESSIVE_CHECK
        BUG_ON(changed != count_clusters);
#endif

        /*
         * We need to make sure we don't reuse the freed block until after the
         * transaction is committed. We make an exception if the inode is to be
         * written in writeback mode since writeback mode has weak data
         * consistency guarantees.
         */
        if (ext4_handle_valid(handle) &&
            ((flags & EXT4_FREE_BLOCKS_METADATA) ||
             !ext4_should_writeback_data(inode))) {
                struct ext4_free_data *new_entry;
                /*
                 * We use __GFP_NOFAIL because ext4_free_blocks() is not allowed
                 * to fail.
                 */
                new_entry = kmem_cache_alloc(ext4_free_data_cachep,
                                GFP_NOFS|__GFP_NOFAIL);
                new_entry->efd_start_cluster = bit;
                new_entry->efd_group = block_group;
                new_entry->efd_count = count_clusters;
                new_entry->efd_tid = handle->h_transaction->t_tid;

                ext4_lock_group(sb, block_group);
                ext4_mb_free_metadata(handle, &e4b, new_entry);
        } else {
                if (test_opt(sb, DISCARD)) {
                        err = ext4_issue_discard(sb, block_group, bit,
                                                 count_clusters, NULL);
                        if (err && err != -EOPNOTSUPP)
                                ext4_msg(sb, KERN_WARNING, "discard request in"
                                         " group:%u block:%d count:%lu failed"
                                         " with %d", block_group, bit, count,
                                         err);
                } else
                        EXT4_MB_GRP_CLEAR_TRIMMED(e4b.bd_info);

                ext4_lock_group(sb, block_group);
                mb_free_blocks(inode, &e4b, bit, count_clusters);
        }

        ext4_unlock_group(sb, block_group);

        /*
         * on a bigalloc file system, defer the s_freeclusters_counter
         * update to the caller (ext4_remove_space and friends) so they
         * can determine if a cluster freed here should be rereserved
         */
        if (!(flags & EXT4_FREE_BLOCKS_RERESERVE_CLUSTER)) {
                if (!(flags & EXT4_FREE_BLOCKS_NO_QUOT_UPDATE))
                        dquot_free_block(inode, EXT4_C2B(sbi, count_clusters));
                percpu_counter_add(&sbi->s_freeclusters_counter,
                                   count_clusters);
        }

        if (overflow && !err) {
                block += count;
                count = overflow;
                ext4_mb_unload_buddy(&e4b);
                /* The range changed so it's no longer validated */
                flags &= ~EXT4_FREE_BLOCKS_VALIDATED;
                goto do_more;
        }

error_clean:
        ext4_mb_unload_buddy(&e4b);
error_out:
        ext4_std_error(sb, err);
}

/**
 * ext4_free_blocks() -- Free given blocks and update quota
 * @handle:             handle for this transaction
 * @inode:              inode
 * @bh:                 optional buffer of the block to be freed
 * @block:              starting physical block to be freed
 * @count:              number of blocks to be freed
 * @flags:              flags used by ext4_free_blocks
 */
void ext4_free_blocks(handle_t *handle, struct inode *inode,
                      struct buffer_head *bh, ext4_fsblk_t block,
                      unsigned long count, int flags)
{
        struct super_block *sb = inode->i_sb;
        unsigned int overflow;
        struct ext4_sb_info *sbi;

        sbi = EXT4_SB(sb);

        if (bh) {
                if (block)
                        BUG_ON(block != bh->b_blocknr);
                else
                        block = bh->b_blocknr;
        }

        if (sbi->s_mount_state & EXT4_FC_REPLAY) {
                ext4_free_blocks_simple(inode, block, EXT4_NUM_B2C(sbi, count));
                return;
        }

        might_sleep();

        if (!(flags & EXT4_FREE_BLOCKS_VALIDATED) &&
            !ext4_inode_block_valid(inode, block, count)) {
                ext4_error(sb, "Freeing blocks not in datazone - "
                           "block = %llu, count = %lu", block, count);
                return;
        }
        flags |= EXT4_FREE_BLOCKS_VALIDATED;

        ext4_debug("freeing block %llu\n", block);
        trace_ext4_free_blocks(inode, block, count, flags);

        if (bh && (flags & EXT4_FREE_BLOCKS_FORGET)) {
                BUG_ON(count > 1);

                ext4_forget(handle, flags & EXT4_FREE_BLOCKS_METADATA,
                            inode, bh, block);
        }

        /*
         * If the extent to be freed does not begin on a cluster
         * boundary, we need to deal with partial clusters at the
         * beginning and end of the extent.  Normally we will free
         * blocks at the beginning or the end unless we are explicitly
         * requested to avoid doing so.
         */
        overflow = EXT4_PBLK_COFF(sbi, block);
        if (overflow) {
                if (flags & EXT4_FREE_BLOCKS_NOFREE_FIRST_CLUSTER) {
                        overflow = sbi->s_cluster_ratio - overflow;
                        block += overflow;
                        if (count > overflow)
                                count -= overflow;
                        else
                                return;
                } else {
                        block -= overflow;
                        count += overflow;
                }
                /* The range changed so it's no longer validated */
                flags &= ~EXT4_FREE_BLOCKS_VALIDATED;
        }
        overflow = EXT4_LBLK_COFF(sbi, count);
        if (overflow) {
                if (flags & EXT4_FREE_BLOCKS_NOFREE_LAST_CLUSTER) {
                        if (count > overflow)
                                count -= overflow;
                        else
                                return;
                } else
                        count += sbi->s_cluster_ratio - overflow;
                /* The range changed so it's no longer validated */
                flags &= ~EXT4_FREE_BLOCKS_VALIDATED;
        }

        if (!bh && (flags & EXT4_FREE_BLOCKS_FORGET)) {
                int i;
                int is_metadata = flags & EXT4_FREE_BLOCKS_METADATA;

                for (i = 0; i < count; i++) {
                        cond_resched();
                        if (is_metadata)
                                bh = sb_find_get_block(inode->i_sb, block + i);
                        ext4_forget(handle, is_metadata, inode, bh, block + i);
                }
        }

        ext4_mb_clear_bb(handle, inode, block, count, flags);
}

/**
 * ext4_group_add_blocks() -- Add given blocks to an existing group
 * @handle:                     handle to this transaction
 * @sb:                         super block
 * @block:                      start physical block to add to the block group
 * @count:                      number of blocks to free
 *
 * This marks the blocks as free in the bitmap and buddy.
 */
int ext4_group_add_blocks(handle_t *handle, struct super_block *sb,
                         ext4_fsblk_t block, unsigned long count)
{
        ext4_group_t block_group;
        ext4_grpblk_t bit;
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        struct ext4_buddy e4b;
        int err = 0;
        ext4_fsblk_t first_cluster = EXT4_B2C(sbi, block);
        ext4_fsblk_t last_cluster = EXT4_B2C(sbi, block + count - 1);
        unsigned long cluster_count = last_cluster - first_cluster + 1;
        ext4_grpblk_t changed;

        ext4_debug("Adding block(s) %llu-%llu\n", block, block + count - 1);

        if (cluster_count == 0)
                return 0;

        ext4_get_group_no_and_offset(sb, block, &block_group, &bit);
        /*
         * Check to see if we are freeing blocks across a group
         * boundary.
         */
        if (bit + cluster_count > EXT4_CLUSTERS_PER_GROUP(sb)) {
                ext4_warning(sb, "too many blocks added to group %u",
                             block_group);
                err = -EINVAL;
                goto error_out;
        }

        err = ext4_mb_load_buddy(sb, block_group, &e4b);
        if (err)
                goto error_out;

        if (!ext4_sb_block_valid(sb, NULL, block, count)) {
                ext4_error(sb, "Adding blocks in system zones - "
                           "Block = %llu, count = %lu",
                           block, count);
                err = -EINVAL;
                goto error_clean;
        }

        err = ext4_mb_mark_context(handle, sb, false, block_group, bit,
                                   cluster_count, EXT4_MB_BITMAP_MARKED_CHECK,
                                   &changed);
        if (err && changed == 0)
                goto error_clean;

        if (changed != cluster_count)
                ext4_error(sb, "bit already cleared in group %u", block_group);

        ext4_lock_group(sb, block_group);
        mb_free_blocks(NULL, &e4b, bit, cluster_count);
        ext4_unlock_group(sb, block_group);
        percpu_counter_add(&sbi->s_freeclusters_counter,
                           changed);

error_clean:
        ext4_mb_unload_buddy(&e4b);
error_out:
        ext4_std_error(sb, err);
        return err;
}

/**
 * ext4_trim_extent -- function to TRIM one single free extent in the group
 * @sb:         super block for the file system
 * @start:      starting block of the free extent in the alloc. group
 * @count:      number of blocks to TRIM
 * @e4b:        ext4 buddy for the group
 *
 * Trim "count" blocks starting at "start" in the "group". To assure that no
 * one will allocate those blocks, mark it as used in buddy bitmap. This must
 * be called with under the group lock.
 */
static int ext4_trim_extent(struct super_block *sb,
                int start, int count, struct ext4_buddy *e4b)
__releases(bitlock)
__acquires(bitlock)
{
        struct ext4_free_extent ex;
        ext4_group_t group = e4b->bd_group;
        int ret = 0;

        trace_ext4_trim_extent(sb, group, start, count);

        assert_spin_locked(ext4_group_lock_ptr(sb, group));

        ex.fe_start = start;
        ex.fe_group = group;
        ex.fe_len = count;

        /*
         * Mark blocks used, so no one can reuse them while
         * being trimmed.
         */
        mb_mark_used(e4b, &ex);
        ext4_unlock_group(sb, group);
        ret = ext4_issue_discard(sb, group, start, count, NULL);
        ext4_lock_group(sb, group);
        mb_free_blocks(NULL, e4b, start, ex.fe_len);
        return ret;
}

static ext4_grpblk_t ext4_last_grp_cluster(struct super_block *sb,
                                           ext4_group_t grp)
{
        if (grp < ext4_get_groups_count(sb))
                return EXT4_CLUSTERS_PER_GROUP(sb) - 1;
        return (ext4_blocks_count(EXT4_SB(sb)->s_es) -
                ext4_group_first_block_no(sb, grp) - 1) >>
                                        EXT4_CLUSTER_BITS(sb);
}

static bool ext4_trim_interrupted(void)
{
        return fatal_signal_pending(current) || freezing(current);
}

static int ext4_try_to_trim_range(struct super_block *sb,
                struct ext4_buddy *e4b, ext4_grpblk_t start,
                ext4_grpblk_t max, ext4_grpblk_t minblocks)
__acquires(ext4_group_lock_ptr(sb, e4b->bd_group))
__releases(ext4_group_lock_ptr(sb, e4b->bd_group))
{
        ext4_grpblk_t next, count, free_count;
        bool set_trimmed = false;
        void *bitmap;

        bitmap = e4b->bd_bitmap;
        if (start == 0 && max >= ext4_last_grp_cluster(sb, e4b->bd_group))
                set_trimmed = true;
        start = max(e4b->bd_info->bb_first_free, start);
        count = 0;
        free_count = 0;

        while (start <= max) {
                start = mb_find_next_zero_bit(bitmap, max + 1, start);
                if (start > max)
                        break;
                next = mb_find_next_bit(bitmap, max + 1, start);

                if ((next - start) >= minblocks) {
                        int ret = ext4_trim_extent(sb, start, next - start, e4b);

                        if (ret && ret != -EOPNOTSUPP)
                                return count;
                        count += next - start;
                }
                free_count += next - start;
                start = next + 1;

                if (ext4_trim_interrupted())
                        return count;

                if (need_resched()) {
                        ext4_unlock_group(sb, e4b->bd_group);
                        cond_resched();
                        ext4_lock_group(sb, e4b->bd_group);
                }

                if ((e4b->bd_info->bb_free - free_count) < minblocks)
                        break;
        }

        if (set_trimmed)
                EXT4_MB_GRP_SET_TRIMMED(e4b->bd_info);

        return count;
}

/**
 * ext4_trim_all_free -- function to trim all free space in alloc. group
 * @sb:                 super block for file system
 * @group:              group to be trimmed
 * @start:              first group block to examine
 * @max:                last group block to examine
 * @minblocks:          minimum extent block count
 *
 * ext4_trim_all_free walks through group's block bitmap searching for free
 * extents. When the free extent is found, mark it as used in group buddy
 * bitmap. Then issue a TRIM command on this extent and free the extent in
 * the group buddy bitmap.
 */
static ext4_grpblk_t
ext4_trim_all_free(struct super_block *sb, ext4_group_t group,
                   ext4_grpblk_t start, ext4_grpblk_t max,
                   ext4_grpblk_t minblocks)
{
        struct ext4_buddy e4b;
        int ret;

        trace_ext4_trim_all_free(sb, group, start, max);

        ret = ext4_mb_load_buddy(sb, group, &e4b);
        if (ret) {
                ext4_warning(sb, "Error %d loading buddy information for %u",
                             ret, group);
                return ret;
        }

        ext4_lock_group(sb, group);

        if (!EXT4_MB_GRP_WAS_TRIMMED(e4b.bd_info) ||
            minblocks < EXT4_SB(sb)->s_last_trim_minblks)
                ret = ext4_try_to_trim_range(sb, &e4b, start, max, minblocks);
        else
                ret = 0;

        ext4_unlock_group(sb, group);
        ext4_mb_unload_buddy(&e4b);

        ext4_debug("trimmed %d blocks in the group %d\n",
                ret, group);

        return ret;
}

/**
 * ext4_trim_fs() -- trim ioctl handle function
 * @sb:                 superblock for filesystem
 * @range:              fstrim_range structure
 *
 * start:       First Byte to trim
 * len:         number of Bytes to trim from start
 * minlen:      minimum extent length in Bytes
 * ext4_trim_fs goes through all allocation groups containing Bytes from
 * start to start+len. For each such a group ext4_trim_all_free function
 * is invoked to trim all free space.
 */
int ext4_trim_fs(struct super_block *sb, struct fstrim_range *range)
{
        unsigned int discard_granularity = bdev_discard_granularity(sb->s_bdev);
        struct ext4_group_info *grp;
        ext4_group_t group, first_group, last_group;
        ext4_grpblk_t cnt = 0, first_cluster, last_cluster;
        uint64_t start, end, minlen, trimmed = 0;
        ext4_fsblk_t first_data_blk =
                        le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block);
        ext4_fsblk_t max_blks = ext4_blocks_count(EXT4_SB(sb)->s_es);
        int ret = 0;

        start = range->start >> sb->s_blocksize_bits;
        end = start + (range->len >> sb->s_blocksize_bits) - 1;
        minlen = EXT4_NUM_B2C(EXT4_SB(sb),
                              range->minlen >> sb->s_blocksize_bits);

        if (minlen > EXT4_CLUSTERS_PER_GROUP(sb) ||
            start >= max_blks ||
            range->len < sb->s_blocksize)
                return -EINVAL;
        /* No point to try to trim less than discard granularity */
        if (range->minlen < discard_granularity) {
                minlen = EXT4_NUM_B2C(EXT4_SB(sb),
                                discard_granularity >> sb->s_blocksize_bits);
                if (minlen > EXT4_CLUSTERS_PER_GROUP(sb))
                        goto out;
        }
        if (end >= max_blks - 1)
                end = max_blks - 1;
        if (end <= first_data_blk)
                goto out;
        if (start < first_data_blk)
                start = first_data_blk;

        /* Determine first and last group to examine based on start and end */
        ext4_get_group_no_and_offset(sb, (ext4_fsblk_t) start,
                                     &first_group, &first_cluster);
        ext4_get_group_no_and_offset(sb, (ext4_fsblk_t) end,
                                     &last_group, &last_cluster);

        /* end now represents the last cluster to discard in this group */
        end = EXT4_CLUSTERS_PER_GROUP(sb) - 1;

        for (group = first_group; group <= last_group; group++) {
                if (ext4_trim_interrupted())
                        break;
                grp = ext4_get_group_info(sb, group);
                if (!grp)
                        continue;
                /* We only do this if the grp has never been initialized */
                if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) {
                        ret = ext4_mb_init_group(sb, group, GFP_NOFS);
                        if (ret)
                                break;
                }

                /*
                 * For all the groups except the last one, last cluster will
                 * always be EXT4_CLUSTERS_PER_GROUP(sb)-1, so we only need to
                 * change it for the last group, note that last_cluster is
                 * already computed earlier by ext4_get_group_no_and_offset()
                 */
                if (group == last_group)
                        end = last_cluster;
                if (grp->bb_free >= minlen) {
                        cnt = ext4_trim_all_free(sb, group, first_cluster,
                                                 end, minlen);
                        if (cnt < 0) {
                                ret = cnt;
                                break;
                        }
                        trimmed += cnt;
                }

                /*
                 * For every group except the first one, we are sure
                 * that the first cluster to discard will be cluster #0.
                 */
                first_cluster = 0;
        }

        if (!ret)
                EXT4_SB(sb)->s_last_trim_minblks = minlen;

out:
        range->len = EXT4_C2B(EXT4_SB(sb), trimmed) << sb->s_blocksize_bits;
        return ret;
}

/* Iterate all the free extents in the group. */
int
ext4_mballoc_query_range(
        struct super_block              *sb,
        ext4_group_t                    group,
        ext4_grpblk_t                   start,
        ext4_grpblk_t                   end,
        ext4_mballoc_query_range_fn     formatter,
        void                            *priv)
{
        void                            *bitmap;
        ext4_grpblk_t                   next;
        struct ext4_buddy               e4b;
        int                             error;

        error = ext4_mb_load_buddy(sb, group, &e4b);
        if (error)
                return error;
        bitmap = e4b.bd_bitmap;

        ext4_lock_group(sb, group);

        start = max(e4b.bd_info->bb_first_free, start);
        if (end >= EXT4_CLUSTERS_PER_GROUP(sb))
                end = EXT4_CLUSTERS_PER_GROUP(sb) - 1;

        while (start <= end) {
                start = mb_find_next_zero_bit(bitmap, end + 1, start);
                if (start > end)
                        break;
                next = mb_find_next_bit(bitmap, end + 1, start);

                ext4_unlock_group(sb, group);
                error = formatter(sb, group, start, next - start, priv);
                if (error)
                        goto out_unload;
                ext4_lock_group(sb, group);

                start = next + 1;
        }

        ext4_unlock_group(sb, group);
out_unload:
        ext4_mb_unload_buddy(&e4b);

        return error;
}

#ifdef CONFIG_EXT4_KUNIT_TESTS
#include "mballoc-test.c"
#endif