[linux.git] / lib / lru_cache.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
   lru_cache.c

   This file is part of DRBD by Philipp Reisner and Lars Ellenberg.

   Copyright (C) 2003-2008, LINBIT Information Technologies GmbH.
   Copyright (C) 2003-2008, Philipp Reisner <[email protected]>.
   Copyright (C) 2003-2008, Lars Ellenberg <[email protected]>.


 */

#include <linux/module.h>
#include <linux/bitops.h>
#include <linux/slab.h>
#include <linux/string.h> /* for memset */
#include <linux/seq_file.h> /* for seq_printf */
#include <linux/lru_cache.h>

MODULE_AUTHOR("Philipp Reisner <[email protected]>, "
	      "Lars Ellenberg <[email protected]>");
MODULE_DESCRIPTION("lru_cache - Track sets of hot objects");
MODULE_LICENSE("GPL");

/* this is developers aid only.
 * it catches concurrent access (lack of locking on the users part) */
#define PARANOIA_ENTRY() do {		\
	BUG_ON(!lc);			\
	BUG_ON(!lc->nr_elements);	\
	BUG_ON(test_and_set_bit(__LC_PARANOIA, &lc->flags)); \
} while (0)

#define RETURN(x...)     do { \
	clear_bit_unlock(__LC_PARANOIA, &lc->flags); \
	return x ; } while (0)

/* BUG() if e is not one of the elements tracked by lc */
#define PARANOIA_LC_ELEMENT(lc, e) do {	\
	struct lru_cache *lc_ = (lc);	\
	struct lc_element *e_ = (e);	\
	unsigned i = e_->lc_index;	\
	BUG_ON(i >= lc_->nr_elements);	\
	BUG_ON(lc_->lc_element[i] != e_); } while (0)


/* We need to atomically
 *  - try to grab the lock (set LC_LOCKED)
 *  - only if there is no pending transaction
 *    (neither LC_DIRTY nor LC_STARVING is set)
 * Because of PARANOIA_ENTRY() above abusing lc->flags as well,
 * it is not sufficient to just say
 *	return 0 == cmpxchg(&lc->flags, 0, LC_LOCKED);
 */
int lc_try_lock(struct lru_cache *lc)
{
	unsigned long val;
	do {
		val = cmpxchg(&lc->flags, 0, LC_LOCKED);
	} while (unlikely (val == LC_PARANOIA));
	/* Spin until no-one is inside a PARANOIA_ENTRY()/RETURN() section. */
	return 0 == val;
}

/**
 * lc_create - prepares to track objects in an active set
 * @name: descriptive name only used in lc_seq_printf_stats and lc_seq_dump_details
 * @cache: cache root pointer
 * @max_pending_changes: maximum changes to accumulate until a transaction is required
 * @e_count: number of elements allowed to be active simultaneously
 * @e_size: size of the tracked objects
 * @e_off: offset to the &struct lc_element member in a tracked object
 *
 * Returns a pointer to a newly initialized struct lru_cache on success,
 * or NULL on (allocation) failure.
 */
struct lru_cache *lc_create(const char *name, struct kmem_cache *cache,
		unsigned max_pending_changes,
		unsigned e_count, size_t e_size, size_t e_off)
{
	struct hlist_head *slot = NULL;
	struct lc_element **element = NULL;
	struct lru_cache *lc;
	struct lc_element *e;
	unsigned cache_obj_size = kmem_cache_size(cache);
	unsigned i;

	WARN_ON(cache_obj_size < e_size);
	if (cache_obj_size < e_size)
		return NULL;

	/* e_count too big; would probably fail the allocation below anyways.
	 * for typical use cases, e_count should be few thousand at most. */
	if (e_count > LC_MAX_ACTIVE)
		return NULL;

	slot = kcalloc(e_count, sizeof(struct hlist_head), GFP_KERNEL);
	if (!slot)
		goto out_fail;
	element = kcalloc(e_count, sizeof(struct lc_element *), GFP_KERNEL);
	if (!element)
		goto out_fail;

	lc = kzalloc(sizeof(*lc), GFP_KERNEL);
	if (!lc)
		goto out_fail;

	INIT_LIST_HEAD(&lc->in_use);
	INIT_LIST_HEAD(&lc->lru);
	INIT_LIST_HEAD(&lc->free);
	INIT_LIST_HEAD(&lc->to_be_changed);

	lc->name = name;
	lc->element_size = e_size;
	lc->element_off = e_off;
	lc->nr_elements = e_count;
	lc->max_pending_changes = max_pending_changes;
	lc->lc_cache = cache;
	lc->lc_element = element;
	lc->lc_slot = slot;

	/* preallocate all objects */
	for (i = 0; i < e_count; i++) {
		void *p = kmem_cache_alloc(cache, GFP_KERNEL);
		if (!p)
			break;
		memset(p, 0, lc->element_size);
		e = p + e_off;
		e->lc_index = i;
		e->lc_number = LC_FREE;
		e->lc_new_number = LC_FREE;
		list_add(&e->list, &lc->free);
		element[i] = e;
	}
	if (i == e_count)
		return lc;

	/* else: could not allocate all elements, give up */
	while (i) {
		void *p = element[--i];
		kmem_cache_free(cache, p - e_off);
	}
	kfree(lc);
out_fail:
	kfree(element);
	kfree(slot);
	return NULL;
}

static void lc_free_by_index(struct lru_cache *lc, unsigned i)
{
	void *p = lc->lc_element[i];
	WARN_ON(!p);
	if (p) {
		p -= lc->element_off;
		kmem_cache_free(lc->lc_cache, p);
	}
}

/**
 * lc_destroy - frees memory allocated by lc_create()
 * @lc: the lru cache to destroy
 */
void lc_destroy(struct lru_cache *lc)
{
	unsigned i;
	if (!lc)
		return;
	for (i = 0; i < lc->nr_elements; i++)
		lc_free_by_index(lc, i);
	kfree(lc->lc_element);
	kfree(lc->lc_slot);
	kfree(lc);
}

/**
 * lc_reset - does a full reset for @lc and the hash table slots.
 * @lc: the lru cache to operate on
 *
 * It is roughly the equivalent of re-allocating a fresh lru_cache object,
 * basically a short cut to lc_destroy(lc); lc = lc_create(...);
 */
void lc_reset(struct lru_cache *lc)
{
	unsigned i;

	INIT_LIST_HEAD(&lc->in_use);
	INIT_LIST_HEAD(&lc->lru);
	INIT_LIST_HEAD(&lc->free);
	INIT_LIST_HEAD(&lc->to_be_changed);
	lc->used = 0;
	lc->hits = 0;
	lc->misses = 0;
	lc->starving = 0;
	lc->locked = 0;
	lc->changed = 0;
	lc->pending_changes = 0;
	lc->flags = 0;
	memset(lc->lc_slot, 0, sizeof(struct hlist_head) * lc->nr_elements);

	for (i = 0; i < lc->nr_elements; i++) {
		struct lc_element *e = lc->lc_element[i];
		void *p = e;
		p -= lc->element_off;
		memset(p, 0, lc->element_size);
		/* re-init it */
		e->lc_index = i;
		e->lc_number = LC_FREE;
		e->lc_new_number = LC_FREE;
		list_add(&e->list, &lc->free);
	}
}

/**
 * lc_seq_printf_stats - print stats about @lc into @seq
 * @seq: the seq_file to print into
 * @lc: the lru cache to print statistics of
 */
void lc_seq_printf_stats(struct seq_file *seq, struct lru_cache *lc)
{
	/* NOTE:
	 * total calls to lc_get are
	 * (starving + hits + misses)
	 * misses include "locked" count (update from an other thread in
	 * progress) and "changed", when this in fact lead to an successful
	 * update of the cache.
	 */
	seq_printf(seq, "\t%s: used:%u/%u hits:%lu misses:%lu starving:%lu locked:%lu changed:%lu\n",
		   lc->name, lc->used, lc->nr_elements,
		   lc->hits, lc->misses, lc->starving, lc->locked, lc->changed);
}

static struct hlist_head *lc_hash_slot(struct lru_cache *lc, unsigned int enr)
{
	return  lc->lc_slot + (enr % lc->nr_elements);
}


static struct lc_element *__lc_find(struct lru_cache *lc, unsigned int enr,
		bool include_changing)
{
	struct lc_element *e;

	BUG_ON(!lc);
	BUG_ON(!lc->nr_elements);
	hlist_for_each_entry(e, lc_hash_slot(lc, enr), colision) {
		/* "about to be changed" elements, pending transaction commit,
		 * are hashed by their "new number". "Normal" elements have
		 * lc_number == lc_new_number. */
		if (e->lc_new_number != enr)
			continue;
		if (e->lc_new_number == e->lc_number || include_changing)
			return e;
		break;
	}
	return NULL;
}

/**
 * lc_find - find element by label, if present in the hash table
 * @lc: The lru_cache object
 * @enr: element number
 *
 * Returns the pointer to an element, if the element with the requested
 * "label" or element number is present in the hash table,
 * or NULL if not found. Does not change the refcnt.
 * Ignores elements that are "about to be used", i.e. not yet in the active
 * set, but still pending transaction commit.
 */
struct lc_element *lc_find(struct lru_cache *lc, unsigned int enr)
{
	return __lc_find(lc, enr, 0);
}

/**
 * lc_is_used - find element by label
 * @lc: The lru_cache object
 * @enr: element number
 *
 * Returns true, if the element with the requested "label" or element number is
 * present in the hash table, and is used (refcnt > 0).
 * Also finds elements that are not _currently_ used but only "about to be
 * used", i.e. on the "to_be_changed" list, pending transaction commit.
 */
bool lc_is_used(struct lru_cache *lc, unsigned int enr)
{
	struct lc_element *e = __lc_find(lc, enr, 1);
	return e && e->refcnt;
}

/**
 * lc_del - removes an element from the cache
 * @lc: The lru_cache object
 * @e: The element to remove
 *
 * @e must be unused (refcnt == 0). Moves @e from "lru" to "free" list,
 * sets @e->enr to %LC_FREE.
 */
void lc_del(struct lru_cache *lc, struct lc_element *e)
{
	PARANOIA_ENTRY();
	PARANOIA_LC_ELEMENT(lc, e);
	BUG_ON(e->refcnt);

	e->lc_number = e->lc_new_number = LC_FREE;
	hlist_del_init(&e->colision);
	list_move(&e->list, &lc->free);
	RETURN();
}

static struct lc_element *lc_prepare_for_change(struct lru_cache *lc, unsigned new_number)
{
	struct list_head *n;
	struct lc_element *e;

	if (!list_empty(&lc->free))
		n = lc->free.next;
	else if (!list_empty(&lc->lru))
		n = lc->lru.prev;
	else
		return NULL;

	e = list_entry(n, struct lc_element, list);
	PARANOIA_LC_ELEMENT(lc, e);

	e->lc_new_number = new_number;
	if (!hlist_unhashed(&e->colision))
		__hlist_del(&e->colision);
	hlist_add_head(&e->colision, lc_hash_slot(lc, new_number));
	list_move(&e->list, &lc->to_be_changed);

	return e;
}

static int lc_unused_element_available(struct lru_cache *lc)
{
	if (!list_empty(&lc->free))
		return 1; /* something on the free list */
	if (!list_empty(&lc->lru))
		return 1;  /* something to evict */

	return 0;
}

/* used as internal flags to __lc_get */
enum {
	LC_GET_MAY_CHANGE = 1,
	LC_GET_MAY_USE_UNCOMMITTED = 2,
};

static struct lc_element *__lc_get(struct lru_cache *lc, unsigned int enr, unsigned int flags)
{
	struct lc_element *e;

	PARANOIA_ENTRY();
	if (test_bit(__LC_STARVING, &lc->flags)) {
		++lc->starving;
		RETURN(NULL);
	}

	e = __lc_find(lc, enr, 1);
	/* if lc_new_number != lc_number,
	 * this enr is currently being pulled in already,
	 * and will be available once the pending transaction
	 * has been committed. */
	if (e) {
		if (e->lc_new_number != e->lc_number) {
			/* It has been found above, but on the "to_be_changed"
			 * list, not yet committed.  Don't pull it in twice,
			 * wait for the transaction, then try again...
			 */
			if (!(flags & LC_GET_MAY_USE_UNCOMMITTED))
				RETURN(NULL);
			/* ... unless the caller is aware of the implications,
			 * probably preparing a cumulative transaction. */
			++e->refcnt;
			++lc->hits;
			RETURN(e);
		}
		/* else: lc_new_number == lc_number; a real hit. */
		++lc->hits;
		if (e->refcnt++ == 0)
			lc->used++;
		list_move(&e->list, &lc->in_use); /* Not evictable... */
		RETURN(e);
	}
	/* e == NULL */

	++lc->misses;
	if (!(flags & LC_GET_MAY_CHANGE))
		RETURN(NULL);

	/* To avoid races with lc_try_lock(), first, mark us dirty
	 * (using test_and_set_bit, as it implies memory barriers), ... */
	test_and_set_bit(__LC_DIRTY, &lc->flags);

	/* ... only then check if it is locked anyways. If lc_unlock clears
	 * the dirty bit again, that's not a problem, we will come here again.
	 */
	if (test_bit(__LC_LOCKED, &lc->flags)) {
		++lc->locked;
		RETURN(NULL);
	}

	/* In case there is nothing available and we can not kick out
	 * the LRU element, we have to wait ...
	 */
	if (!lc_unused_element_available(lc)) {
		set_bit(__LC_STARVING, &lc->flags);
		RETURN(NULL);
	}

	/* It was not present in the active set.  We are going to recycle an
	 * unused (or even "free") element, but we won't accumulate more than
	 * max_pending_changes changes.  */
	if (lc->pending_changes >= lc->max_pending_changes)
		RETURN(NULL);

	e = lc_prepare_for_change(lc, enr);
	BUG_ON(!e);

	clear_bit(__LC_STARVING, &lc->flags);
	BUG_ON(++e->refcnt != 1);
	lc->used++;
	lc->pending_changes++;

	RETURN(e);
}

/**
 * lc_get - get element by label, maybe change the active set
 * @lc: the lru cache to operate on
 * @enr: the label to look up
 *
 * Finds an element in the cache, increases its usage count,
 * "touches" and returns it.
 *
 * In case the requested number is not present, it needs to be added to the
 * cache. Therefore it is possible that an other element becomes evicted from
 * the cache. In either case, the user is notified so he is able to e.g. keep
 * a persistent log of the cache changes, and therefore the objects in use.
 *
 * Return values:
 *  NULL
 *     The cache was marked %LC_STARVING,
 *     or the requested label was not in the active set
 *     and a changing transaction is still pending (@lc was marked %LC_DIRTY).
 *     Or no unused or free element could be recycled (@lc will be marked as
 *     %LC_STARVING, blocking further lc_get() operations).
 *
 *  pointer to the element with the REQUESTED element number.
 *     In this case, it can be used right away
 *
 *  pointer to an UNUSED element with some different element number,
 *          where that different number may also be %LC_FREE.
 *
 *          In this case, the cache is marked %LC_DIRTY,
 *          so lc_try_lock() will no longer succeed.
 *          The returned element pointer is moved to the "to_be_changed" list,
 *          and registered with the new element number on the hash collision chains,
 *          so it is possible to pick it up from lc_is_used().
 *          Up to "max_pending_changes" (see lc_create()) can be accumulated.
 *          The user now should do whatever housekeeping is necessary,
 *          typically serialize on lc_try_lock_for_transaction(), then call
 *          lc_committed(lc) and lc_unlock(), to finish the change.
 *
 * NOTE: The user needs to check the lc_number on EACH use, so he recognizes
 *       any cache set change.
 */
struct lc_element *lc_get(struct lru_cache *lc, unsigned int enr)
{
	return __lc_get(lc, enr, LC_GET_MAY_CHANGE);
}

/**
 * lc_get_cumulative - like lc_get; also finds to-be-changed elements
 * @lc: the lru cache to operate on
 * @enr: the label to look up
 *
 * Unlike lc_get this also returns the element for @enr, if it is belonging to
 * a pending transaction, so the return values are like for lc_get(),
 * plus:
 *
 * pointer to an element already on the "to_be_changed" list.
 * 	In this case, the cache was already marked %LC_DIRTY.
 *
 * Caller needs to make sure that the pending transaction is completed,
 * before proceeding to actually use this element.
 */
struct lc_element *lc_get_cumulative(struct lru_cache *lc, unsigned int enr)
{
	return __lc_get(lc, enr, LC_GET_MAY_CHANGE|LC_GET_MAY_USE_UNCOMMITTED);
}

/**
 * lc_try_get - get element by label, if present; do not change the active set
 * @lc: the lru cache to operate on
 * @enr: the label to look up
 *
 * Finds an element in the cache, increases its usage count,
 * "touches" and returns it.
 *
 * Return values:
 *  NULL
 *     The cache was marked %LC_STARVING,
 *     or the requested label was not in the active set
 *
 *  pointer to the element with the REQUESTED element number.
 *     In this case, it can be used right away
 */
struct lc_element *lc_try_get(struct lru_cache *lc, unsigned int enr)
{
	return __lc_get(lc, enr, 0);
}

/**
 * lc_committed - tell @lc that pending changes have been recorded
 * @lc: the lru cache to operate on
 *
 * User is expected to serialize on explicit lc_try_lock_for_transaction()
 * before the transaction is started, and later needs to lc_unlock() explicitly
 * as well.
 */
void lc_committed(struct lru_cache *lc)
{
	struct lc_element *e, *tmp;

	PARANOIA_ENTRY();
	list_for_each_entry_safe(e, tmp, &lc->to_be_changed, list) {
		/* count number of changes, not number of transactions */
		++lc->changed;
		e->lc_number = e->lc_new_number;
		list_move(&e->list, &lc->in_use);
	}
	lc->pending_changes = 0;
	RETURN();
}


/**
 * lc_put - give up refcnt of @e
 * @lc: the lru cache to operate on
 * @e: the element to put
 *
 * If refcnt reaches zero, the element is moved to the lru list,
 * and a %LC_STARVING (if set) is cleared.
 * Returns the new (post-decrement) refcnt.
 */
unsigned int lc_put(struct lru_cache *lc, struct lc_element *e)
{
	PARANOIA_ENTRY();
	PARANOIA_LC_ELEMENT(lc, e);
	BUG_ON(e->refcnt == 0);
	BUG_ON(e->lc_number != e->lc_new_number);
	if (--e->refcnt == 0) {
		/* move it to the front of LRU. */
		list_move(&e->list, &lc->lru);
		lc->used--;
		clear_bit_unlock(__LC_STARVING, &lc->flags);
	}
	RETURN(e->refcnt);
}

/**
 * lc_element_by_index
 * @lc: the lru cache to operate on
 * @i: the index of the element to return
 */
struct lc_element *lc_element_by_index(struct lru_cache *lc, unsigned i)
{
	BUG_ON(i >= lc->nr_elements);
	BUG_ON(lc->lc_element[i] == NULL);
	BUG_ON(lc->lc_element[i]->lc_index != i);
	return lc->lc_element[i];
}

/**
 * lc_seq_dump_details - Dump a complete LRU cache to seq in textual form.
 * @lc: the lru cache to operate on
 * @seq: the &struct seq_file pointer to seq_printf into
 * @utext: user supplied additional "heading" or other info
 * @detail: function pointer the user may provide to dump further details
 * of the object the lc_element is embedded in. May be NULL.
 * Note: a leading space ' ' and trailing newline '\n' is implied.
 */
void lc_seq_dump_details(struct seq_file *seq, struct lru_cache *lc, char *utext,
	     void (*detail) (struct seq_file *, struct lc_element *))
{
	unsigned int nr_elements = lc->nr_elements;
	struct lc_element *e;
	int i;

	seq_printf(seq, "\tnn: lc_number (new nr) refcnt %s\n ", utext);
	for (i = 0; i < nr_elements; i++) {
		e = lc_element_by_index(lc, i);
		if (e->lc_number != e->lc_new_number)
			seq_printf(seq, "\t%5d: %6d %8d %6d ",
				i, e->lc_number, e->lc_new_number, e->refcnt);
		else
			seq_printf(seq, "\t%5d: %6d %-8s %6d ",
				i, e->lc_number, "-\"-", e->refcnt);
		if (detail)
			detail(seq, e);
		seq_putc(seq, '\n');
	}
}

EXPORT_SYMBOL(lc_create);
EXPORT_SYMBOL(lc_reset);
EXPORT_SYMBOL(lc_destroy);
EXPORT_SYMBOL(lc_del);
EXPORT_SYMBOL(lc_try_get);
EXPORT_SYMBOL(lc_find);
EXPORT_SYMBOL(lc_get);
EXPORT_SYMBOL(lc_put);
EXPORT_SYMBOL(lc_committed);
EXPORT_SYMBOL(lc_element_by_index);
EXPORT_SYMBOL(lc_seq_printf_stats);
EXPORT_SYMBOL(lc_seq_dump_details);
EXPORT_SYMBOL(lc_try_lock);
EXPORT_SYMBOL(lc_is_used);
EXPORT_SYMBOL(lc_get_cumulative);
Commit	Line	Data
c6ae4c04	1	// SPDX-License-Identifier: GPL-2.0-or-later
b411b363 PR	2	/*
	3	lru_cache.c
	4
	5	This file is part of DRBD by Philipp Reisner and Lars Ellenberg.
	6
	7	Copyright (C) 2003-2008, LINBIT Information Technologies GmbH.
	8	Copyright (C) 2003-2008, Philipp Reisner <[email protected]>.
	9	Copyright (C) 2003-2008, Lars Ellenberg <[email protected]>.
	10
b411b363 PR	11
	12	*/
	13
	14	#include <linux/module.h>
	15	#include <linux/bitops.h>
	16	#include <linux/slab.h>
	17	#include <linux/string.h> /* for memset */
	18	#include <linux/seq_file.h> /* for seq_printf */
	19	#include <linux/lru_cache.h>
	20
	21	MODULE_AUTHOR("Philipp Reisner <[email protected]>, "
	22	"Lars Ellenberg <[email protected]>");
	23	MODULE_DESCRIPTION("lru_cache - Track sets of hot objects");
	24	MODULE_LICENSE("GPL");
	25
	26	/* this is developers aid only.
	27	* it catches concurrent access (lack of locking on the users part) */
	28	#define PARANOIA_ENTRY() do { \
	29	BUG_ON(!lc); \
	30	BUG_ON(!lc->nr_elements); \
	31	BUG_ON(test_and_set_bit(__LC_PARANOIA, &lc->flags)); \
	32	} while (0)
	33
	34	#define RETURN(x...) do { \
4738fa16 LE	35	clear_bit_unlock(__LC_PARANOIA, &lc->flags); \
4738fa16 LE	36	return x ; } while (0)
b411b363 PR	37
	38	/* BUG() if e is not one of the elements tracked by lc */
	39	#define PARANOIA_LC_ELEMENT(lc, e) do { \
	40	struct lru_cache *lc_ = (lc); \
	41	struct lc_element *e_ = (e); \
	42	unsigned i = e_->lc_index; \
	43	BUG_ON(i >= lc_->nr_elements); \
	44	BUG_ON(lc_->lc_element[i] != e_); } while (0)
	45
46a15bc3 LE	46
	47	/* We need to atomically
	48	* - try to grab the lock (set LC_LOCKED)
	49	* - only if there is no pending transaction
	50	* (neither LC_DIRTY nor LC_STARVING is set)
	51	* Because of PARANOIA_ENTRY() above abusing lc->flags as well,
	52	* it is not sufficient to just say
	53	* return 0 == cmpxchg(&lc->flags, 0, LC_LOCKED);
	54	*/
	55	int lc_try_lock(struct lru_cache *lc)
	56	{
	57	unsigned long val;
	58	do {
	59	val = cmpxchg(&lc->flags, 0, LC_LOCKED);
	60	} while (unlikely (val == LC_PARANOIA));
	61	/* Spin until no-one is inside a PARANOIA_ENTRY()/RETURN() section. */
	62	return 0 == val;
46a15bc3 LE	63	}
46a15bc3 LE	64
b411b363 PR	65	/**
	66	* lc_create - prepares to track objects in an active set
	67	* @name: descriptive name only used in lc_seq_printf_stats and lc_seq_dump_details
c95c2d32	68	* @cache: cache root pointer
46a15bc3	69	* @max_pending_changes: maximum changes to accumulate until a transaction is required
b411b363 PR	70	* @e_count: number of elements allowed to be active simultaneously
	71	* @e_size: size of the tracked objects
	72	* @e_off: offset to the &struct lc_element member in a tracked object
	73	*
	74	* Returns a pointer to a newly initialized struct lru_cache on success,
	75	* or NULL on (allocation) failure.
	76	*/
	77	struct lru_cache lc_create(const char name, struct kmem_cache *cache,
46a15bc3	78	unsigned max_pending_changes,
b411b363 PR	79	unsigned e_count, size_t e_size, size_t e_off)
	80	{
	81	struct hlist_head *slot = NULL;
	82	struct lc_element **element = NULL;
	83	struct lru_cache *lc;
	84	struct lc_element *e;
	85	unsigned cache_obj_size = kmem_cache_size(cache);
	86	unsigned i;
	87
	88	WARN_ON(cache_obj_size < e_size);
	89	if (cache_obj_size < e_size)
	90	return NULL;
	91
	92	/* e_count too big; would probably fail the allocation below anyways.
	93	* for typical use cases, e_count should be few thousand at most. */
	94	if (e_count > LC_MAX_ACTIVE)
	95	return NULL;
	96
a08aa355	97	slot = kcalloc(e_count, sizeof(struct hlist_head), GFP_KERNEL);
b411b363 PR	98	if (!slot)
b411b363 PR	99	goto out_fail;
6396bb22	100	element = kcalloc(e_count, sizeof(struct lc_element *), GFP_KERNEL);
b411b363 PR	101	if (!element)
	102	goto out_fail;
	103
	104	lc = kzalloc(sizeof(*lc), GFP_KERNEL);
	105	if (!lc)
	106	goto out_fail;
	107
	108	INIT_LIST_HEAD(&lc->in_use);
	109	INIT_LIST_HEAD(&lc->lru);
	110	INIT_LIST_HEAD(&lc->free);
46a15bc3	111	INIT_LIST_HEAD(&lc->to_be_changed);
b411b363 PR	112
	113	lc->name = name;
	114	lc->element_size = e_size;
	115	lc->element_off = e_off;
	116	lc->nr_elements = e_count;
46a15bc3	117	lc->max_pending_changes = max_pending_changes;
b411b363 PR	118	lc->lc_cache = cache;
	119	lc->lc_element = element;
	120	lc->lc_slot = slot;
	121
	122	/* preallocate all objects */
	123	for (i = 0; i < e_count; i++) {
	124	void *p = kmem_cache_alloc(cache, GFP_KERNEL);
	125	if (!p)
	126	break;
	127	memset(p, 0, lc->element_size);
	128	e = p + e_off;
	129	e->lc_index = i;
	130	e->lc_number = LC_FREE;
46a15bc3	131	e->lc_new_number = LC_FREE;
b411b363 PR	132	list_add(&e->list, &lc->free);
	133	element[i] = e;
	134	}
	135	if (i == e_count)
	136	return lc;
	137
	138	/* else: could not allocate all elements, give up */
5a66fce9	139	while (i) {
5a66fce9	140	void *p = element[--i];
b411b363 PR	141	kmem_cache_free(cache, p - e_off);
	142	}
	143	kfree(lc);
	144	out_fail:
	145	kfree(element);
	146	kfree(slot);
	147	return NULL;
	148	}
	149
8ce953aa	150	static void lc_free_by_index(struct lru_cache *lc, unsigned i)
b411b363 PR	151	{
	152	void *p = lc->lc_element[i];
	153	WARN_ON(!p);
	154	if (p) {
	155	p -= lc->element_off;
	156	kmem_cache_free(lc->lc_cache, p);
	157	}
	158	}
	159
	160	/**
	161	* lc_destroy - frees memory allocated by lc_create()
	162	* @lc: the lru cache to destroy
	163	*/
	164	void lc_destroy(struct lru_cache *lc)
	165	{
	166	unsigned i;
	167	if (!lc)
	168	return;
	169	for (i = 0; i < lc->nr_elements; i++)
	170	lc_free_by_index(lc, i);
	171	kfree(lc->lc_element);
	172	kfree(lc->lc_slot);
	173	kfree(lc);
	174	}
	175
	176	/**
	177	* lc_reset - does a full reset for @lc and the hash table slots.
	178	* @lc: the lru cache to operate on
	179	*
	180	* It is roughly the equivalent of re-allocating a fresh lru_cache object,
	181	* basically a short cut to lc_destroy(lc); lc = lc_create(...);
	182	*/
	183	void lc_reset(struct lru_cache *lc)
	184	{
	185	unsigned i;
	186
	187	INIT_LIST_HEAD(&lc->in_use);
	188	INIT_LIST_HEAD(&lc->lru);
	189	INIT_LIST_HEAD(&lc->free);
46a15bc3	190	INIT_LIST_HEAD(&lc->to_be_changed);
b411b363 PR	191	lc->used = 0;
	192	lc->hits = 0;
	193	lc->misses = 0;
	194	lc->starving = 0;
46a15bc3	195	lc->locked = 0;
b411b363	196	lc->changed = 0;
46a15bc3	197	lc->pending_changes = 0;
b411b363	198	lc->flags = 0;
b411b363 PR	199	memset(lc->lc_slot, 0, sizeof(struct hlist_head) * lc->nr_elements);
	200
	201	for (i = 0; i < lc->nr_elements; i++) {
	202	struct lc_element *e = lc->lc_element[i];
	203	void *p = e;
	204	p -= lc->element_off;
	205	memset(p, 0, lc->element_size);
	206	/* re-init it */
	207	e->lc_index = i;
	208	e->lc_number = LC_FREE;
46a15bc3	209	e->lc_new_number = LC_FREE;
b411b363 PR	210	list_add(&e->list, &lc->free);
	211	}
	212	}
	213
	214	/**
	215	* lc_seq_printf_stats - print stats about @lc into @seq
	216	* @seq: the seq_file to print into
	217	* @lc: the lru cache to print statistics of
	218	*/
bb649b34	219	void lc_seq_printf_stats(struct seq_file seq, struct lru_cache lc)
b411b363 PR	220	{
	221	/* NOTE:
	222	* total calls to lc_get are
	223	* (starving + hits + misses)
46a15bc3	224	* misses include "locked" count (update from an other thread in
b411b363 PR	225	* progress) and "changed", when this in fact lead to an successful
	226	* update of the cache.
	227	*/
d50f8f8d JP	228	seq_printf(seq, "\t%s: used:%u/%u hits:%lu misses:%lu starving:%lu locked:%lu changed:%lu\n",
	229	lc->name, lc->used, lc->nr_elements,
	230	lc->hits, lc->misses, lc->starving, lc->locked, lc->changed);
b411b363 PR	231	}
	232
	233	static struct hlist_head lc_hash_slot(struct lru_cache lc, unsigned int enr)
	234	{
	235	return lc->lc_slot + (enr % lc->nr_elements);
	236	}
	237
	238
46a15bc3 LE	239	static struct lc_element __lc_find(struct lru_cache lc, unsigned int enr,
46a15bc3 LE	240	bool include_changing)
b411b363	241	{
b411b363 PR	242	struct lc_element *e;
	243
	244	BUG_ON(!lc);
	245	BUG_ON(!lc->nr_elements);
b67bfe0d	246	hlist_for_each_entry(e, lc_hash_slot(lc, enr), colision) {
46a15bc3 LE	247	/* "about to be changed" elements, pending transaction commit,
	248	* are hashed by their "new number". "Normal" elements have
	249	* lc_number == lc_new_number. */
	250	if (e->lc_new_number != enr)
	251	continue;
	252	if (e->lc_new_number == e->lc_number \|\| include_changing)
b411b363	253	return e;
46a15bc3	254	break;
b411b363 PR	255	}
	256	return NULL;
	257	}
	258
46a15bc3 LE	259	/**
	260	* lc_find - find element by label, if present in the hash table
	261	* @lc: The lru_cache object
	262	* @enr: element number
	263	*
	264	* Returns the pointer to an element, if the element with the requested
	265	* "label" or element number is present in the hash table,
	266	* or NULL if not found. Does not change the refcnt.
	267	* Ignores elements that are "about to be used", i.e. not yet in the active
	268	* set, but still pending transaction commit.
	269	*/
	270	struct lc_element lc_find(struct lru_cache lc, unsigned int enr)
b411b363	271	{
46a15bc3 LE	272	return __lc_find(lc, enr, 0);
46a15bc3 LE	273	}
b411b363	274
46a15bc3 LE	275	/**
	276	* lc_is_used - find element by label
	277	* @lc: The lru_cache object
	278	* @enr: element number
	279	*
	280	* Returns true, if the element with the requested "label" or element number is
	281	* present in the hash table, and is used (refcnt > 0).
	282	* Also finds elements that are not _currently_ used but only "about to be
	283	* used", i.e. on the "to_be_changed" list, pending transaction commit.
	284	*/
	285	bool lc_is_used(struct lru_cache *lc, unsigned int enr)
	286	{
	287	struct lc_element *e = __lc_find(lc, enr, 1);
	288	return e && e->refcnt;
b411b363 PR	289	}
	290
	291	/**
	292	* lc_del - removes an element from the cache
	293	* @lc: The lru_cache object
	294	* @e: The element to remove
	295	*
	296	* @e must be unused (refcnt == 0). Moves @e from "lru" to "free" list,
	297	* sets @e->enr to %LC_FREE.
	298	*/
	299	void lc_del(struct lru_cache lc, struct lc_element e)
	300	{
	301	PARANOIA_ENTRY();
	302	PARANOIA_LC_ELEMENT(lc, e);
	303	BUG_ON(e->refcnt);
	304
46a15bc3	305	e->lc_number = e->lc_new_number = LC_FREE;
b411b363 PR	306	hlist_del_init(&e->colision);
	307	list_move(&e->list, &lc->free);
	308	RETURN();
	309	}
	310
46a15bc3	311	static struct lc_element lc_prepare_for_change(struct lru_cache lc, unsigned new_number)
b411b363 PR	312	{
b411b363 PR	313	struct list_head *n;
46a15bc3 LE	314	struct lc_element *e;
	315
	316	if (!list_empty(&lc->free))
	317	n = lc->free.next;
	318	else if (!list_empty(&lc->lru))
	319	n = lc->lru.prev;
	320	else
	321	return NULL;
	322
	323	e = list_entry(n, struct lc_element, list);
	324	PARANOIA_LC_ELEMENT(lc, e);
b411b363	325
46a15bc3 LE	326	e->lc_new_number = new_number;
	327	if (!hlist_unhashed(&e->colision))
	328	__hlist_del(&e->colision);
	329	hlist_add_head(&e->colision, lc_hash_slot(lc, new_number));
	330	list_move(&e->list, &lc->to_be_changed);
b411b363	331
46a15bc3	332	return e;
b411b363 PR	333	}
	334
	335	static int lc_unused_element_available(struct lru_cache *lc)
	336	{
	337	if (!list_empty(&lc->free))
	338	return 1; /* something on the free list */
	339	if (!list_empty(&lc->lru))
	340	return 1; /* something to evict */
	341
	342	return 0;
	343	}
	344
cbe5e610 LE	345	/* used as internal flags to __lc_get */
	346	enum {
	347	LC_GET_MAY_CHANGE = 1,
	348	LC_GET_MAY_USE_UNCOMMITTED = 2,
	349	};
	350
	351	static struct lc_element __lc_get(struct lru_cache lc, unsigned int enr, unsigned int flags)
b411b363 PR	352	{
	353	struct lc_element *e;
	354
	355	PARANOIA_ENTRY();
f2d03d89	356	if (test_bit(__LC_STARVING, &lc->flags)) {
b411b363 PR	357	++lc->starving;
	358	RETURN(NULL);
	359	}
	360
46a15bc3 LE	361	e = __lc_find(lc, enr, 1);
	362	/* if lc_new_number != lc_number,
	363	* this enr is currently being pulled in already,
	364	* and will be available once the pending transaction
	365	* has been committed. */
cbe5e610 LE	366	if (e) {
	367	if (e->lc_new_number != e->lc_number) {
	368	/* It has been found above, but on the "to_be_changed"
	369	* list, not yet committed. Don't pull it in twice,
	370	* wait for the transaction, then try again...
	371	*/
	372	if (!(flags & LC_GET_MAY_USE_UNCOMMITTED))
	373	RETURN(NULL);
	374	/* ... unless the caller is aware of the implications,
	375	* probably preparing a cumulative transaction. */
	376	++e->refcnt;
	377	++lc->hits;
	378	RETURN(e);
	379	}
	380	/* else: lc_new_number == lc_number; a real hit. */
b411b363 PR	381	++lc->hits;
	382	if (e->refcnt++ == 0)
	383	lc->used++;
	384	list_move(&e->list, &lc->in_use); /* Not evictable... */
	385	RETURN(e);
	386	}
cbe5e610	387	/* e == NULL */
b411b363 PR	388
b411b363 PR	389	++lc->misses;
cbe5e610	390	if (!(flags & LC_GET_MAY_CHANGE))
46a15bc3 LE	391	RETURN(NULL);
	392
	393	/* To avoid races with lc_try_lock(), first, mark us dirty
	394	* (using test_and_set_bit, as it implies memory barriers), ... */
	395	test_and_set_bit(__LC_DIRTY, &lc->flags);
	396
	397	/* ... only then check if it is locked anyways. If lc_unlock clears
	398	* the dirty bit again, that's not a problem, we will come here again.
	399	*/
	400	if (test_bit(__LC_LOCKED, &lc->flags)) {
	401	++lc->locked;
	402	RETURN(NULL);
	403	}
	404
b411b363 PR	405	/* In case there is nothing available and we can not kick out
	406	* the LRU element, we have to wait ...
	407	*/
	408	if (!lc_unused_element_available(lc)) {
f2d03d89	409	set_bit(__LC_STARVING, &lc->flags);
b411b363 PR	410	RETURN(NULL);
	411	}
	412
46a15bc3 LE	413	/* It was not present in the active set. We are going to recycle an
	414	* unused (or even "free") element, but we won't accumulate more than
	415	* max_pending_changes changes. */
	416	if (lc->pending_changes >= lc->max_pending_changes)
b411b363	417	RETURN(NULL);
b411b363	418
46a15bc3	419	e = lc_prepare_for_change(lc, enr);
b411b363 PR	420	BUG_ON(!e);
	421
	422	clear_bit(__LC_STARVING, &lc->flags);
	423	BUG_ON(++e->refcnt != 1);
	424	lc->used++;
46a15bc3	425	lc->pending_changes++;
b411b363 PR	426
	427	RETURN(e);
	428	}
	429
a9efc748 LE	430	/**
	431	* lc_get - get element by label, maybe change the active set
	432	* @lc: the lru cache to operate on
	433	* @enr: the label to look up
	434	*
	435	* Finds an element in the cache, increases its usage count,
	436	* "touches" and returns it.
	437	*
	438	* In case the requested number is not present, it needs to be added to the
	439	* cache. Therefore it is possible that an other element becomes evicted from
	440	* the cache. In either case, the user is notified so he is able to e.g. keep
	441	* a persistent log of the cache changes, and therefore the objects in use.
	442	*
	443	* Return values:
	444	* NULL
	445	* The cache was marked %LC_STARVING,
	446	* or the requested label was not in the active set
	447	* and a changing transaction is still pending (@lc was marked %LC_DIRTY).
	448	* Or no unused or free element could be recycled (@lc will be marked as
	449	* %LC_STARVING, blocking further lc_get() operations).
	450	*
	451	* pointer to the element with the REQUESTED element number.
	452	* In this case, it can be used right away
	453	*
	454	* pointer to an UNUSED element with some different element number,
	455	* where that different number may also be %LC_FREE.
	456	*
46a15bc3 LE	457	* In this case, the cache is marked %LC_DIRTY,
	458	* so lc_try_lock() will no longer succeed.
	459	* The returned element pointer is moved to the "to_be_changed" list,
	460	* and registered with the new element number on the hash collision chains,
	461	* so it is possible to pick it up from lc_is_used().
	462	* Up to "max_pending_changes" (see lc_create()) can be accumulated.
	463	* The user now should do whatever housekeeping is necessary,
	464	* typically serialize on lc_try_lock_for_transaction(), then call
	465	* lc_committed(lc) and lc_unlock(), to finish the change.
a9efc748 LE	466	*
	467	* NOTE: The user needs to check the lc_number on EACH use, so he recognizes
	468	* any cache set change.
b411b363	469	*/
a9efc748	470	struct lc_element lc_get(struct lru_cache lc, unsigned int enr)
b411b363	471	{
cbe5e610 LE	472	return __lc_get(lc, enr, LC_GET_MAY_CHANGE);
	473	}
	474
	475	/**
	476	* lc_get_cumulative - like lc_get; also finds to-be-changed elements
	477	* @lc: the lru cache to operate on
	478	* @enr: the label to look up
	479	*
	480	* Unlike lc_get this also returns the element for @enr, if it is belonging to
	481	* a pending transaction, so the return values are like for lc_get(),
	482	* plus:
	483	*
	484	* pointer to an element already on the "to_be_changed" list.
	485	* In this case, the cache was already marked %LC_DIRTY.
	486	*
	487	* Caller needs to make sure that the pending transaction is completed,
	488	* before proceeding to actually use this element.
	489	*/
	490	struct lc_element lc_get_cumulative(struct lru_cache lc, unsigned int enr)
	491	{
	492	return __lc_get(lc, enr, LC_GET_MAY_CHANGE\|LC_GET_MAY_USE_UNCOMMITTED);
a9efc748	493	}
b411b363	494
a9efc748 LE	495	/**
	496	* lc_try_get - get element by label, if present; do not change the active set
	497	* @lc: the lru cache to operate on
	498	* @enr: the label to look up
	499	*
	500	* Finds an element in the cache, increases its usage count,
	501	* "touches" and returns it.
	502	*
	503	* Return values:
	504	* NULL
	505	* The cache was marked %LC_STARVING,
	506	* or the requested label was not in the active set
	507	*
	508	* pointer to the element with the REQUESTED element number.
	509	* In this case, it can be used right away
	510	*/
	511	struct lc_element lc_try_get(struct lru_cache lc, unsigned int enr)
	512	{
	513	return __lc_get(lc, enr, 0);
b411b363 PR	514	}
	515
	516	/**
46a15bc3	517	* lc_committed - tell @lc that pending changes have been recorded
b411b363	518	* @lc: the lru cache to operate on
46a15bc3 LE	519	*
	520	* User is expected to serialize on explicit lc_try_lock_for_transaction()
	521	* before the transaction is started, and later needs to lc_unlock() explicitly
	522	* as well.
b411b363	523	*/
46a15bc3	524	void lc_committed(struct lru_cache *lc)
b411b363	525	{
46a15bc3 LE	526	struct lc_element e, tmp;
46a15bc3 LE	527
b411b363	528	PARANOIA_ENTRY();
46a15bc3 LE	529	list_for_each_entry_safe(e, tmp, &lc->to_be_changed, list) {
	530	/* count number of changes, not number of transactions */
	531	++lc->changed;
	532	e->lc_number = e->lc_new_number;
	533	list_move(&e->list, &lc->in_use);
	534	}
	535	lc->pending_changes = 0;
b411b363 PR	536	RETURN();
	537	}
	538
	539
	540	/**
	541	* lc_put - give up refcnt of @e
	542	* @lc: the lru cache to operate on
	543	* @e: the element to put
	544	*
	545	* If refcnt reaches zero, the element is moved to the lru list,
	546	* and a %LC_STARVING (if set) is cleared.
	547	* Returns the new (post-decrement) refcnt.
	548	*/
	549	unsigned int lc_put(struct lru_cache lc, struct lc_element e)
	550	{
	551	PARANOIA_ENTRY();
	552	PARANOIA_LC_ELEMENT(lc, e);
	553	BUG_ON(e->refcnt == 0);
46a15bc3	554	BUG_ON(e->lc_number != e->lc_new_number);
b411b363 PR	555	if (--e->refcnt == 0) {
	556	/* move it to the front of LRU. */
	557	list_move(&e->list, &lc->lru);
	558	lc->used--;
4738fa16	559	clear_bit_unlock(__LC_STARVING, &lc->flags);
b411b363 PR	560	}
	561	RETURN(e->refcnt);
	562	}
	563
	564	/**
	565	* lc_element_by_index
	566	* @lc: the lru cache to operate on
	567	* @i: the index of the element to return
	568	*/
	569	struct lc_element lc_element_by_index(struct lru_cache lc, unsigned i)
	570	{
	571	BUG_ON(i >= lc->nr_elements);
	572	BUG_ON(lc->lc_element[i] == NULL);
	573	BUG_ON(lc->lc_element[i]->lc_index != i);
	574	return lc->lc_element[i];
	575	}
	576
b411b363	577	/**
c95c2d32	578	* lc_seq_dump_details - Dump a complete LRU cache to seq in textual form.
b411b363 PR	579	* @lc: the lru cache to operate on
b411b363 PR	580	* @seq: the &struct seq_file pointer to seq_printf into
54e6fc38	581	* @utext: user supplied additional "heading" or other info
b411b363	582	* @detail: function pointer the user may provide to dump further details
54e6fc38 LE	583	* of the object the lc_element is embedded in. May be NULL.
54e6fc38 LE	584	* Note: a leading space ' ' and trailing newline '\n' is implied.
b411b363 PR	585	*/
	586	void lc_seq_dump_details(struct seq_file seq, struct lru_cache lc, char *utext,
	587	void (detail) (struct seq_file , struct lc_element *))
	588	{
	589	unsigned int nr_elements = lc->nr_elements;
	590	struct lc_element *e;
	591	int i;
	592
54e6fc38	593	seq_printf(seq, "\tnn: lc_number (new nr) refcnt %s\n ", utext);
b411b363 PR	594	for (i = 0; i < nr_elements; i++) {
b411b363 PR	595	e = lc_element_by_index(lc, i);
54e6fc38 LE	596	if (e->lc_number != e->lc_new_number)
	597	seq_printf(seq, "\t%5d: %6d %8d %6d ",
	598	i, e->lc_number, e->lc_new_number, e->refcnt);
	599	else
	600	seq_printf(seq, "\t%5d: %6d %-8s %6d ",
	601	i, e->lc_number, "-\"-", e->refcnt);
	602	if (detail)
b411b363	603	detail(seq, e);
54e6fc38	604	seq_putc(seq, '\n');
b411b363 PR	605	}
	606	}
	607
	608	EXPORT_SYMBOL(lc_create);
	609	EXPORT_SYMBOL(lc_reset);
	610	EXPORT_SYMBOL(lc_destroy);
b411b363 PR	611	EXPORT_SYMBOL(lc_del);
	612	EXPORT_SYMBOL(lc_try_get);
	613	EXPORT_SYMBOL(lc_find);
	614	EXPORT_SYMBOL(lc_get);
	615	EXPORT_SYMBOL(lc_put);
46a15bc3	616	EXPORT_SYMBOL(lc_committed);
b411b363	617	EXPORT_SYMBOL(lc_element_by_index);
b411b363 PR	618	EXPORT_SYMBOL(lc_seq_printf_stats);
b411b363 PR	619	EXPORT_SYMBOL(lc_seq_dump_details);
46a15bc3 LE	620	EXPORT_SYMBOL(lc_try_lock);
46a15bc3 LE	621	EXPORT_SYMBOL(lc_is_used);
cbe5e610	622	EXPORT_SYMBOL(lc_get_cumulative);