[linux.git] / mm / swap_state.c

/*
 *  linux/mm/swap_state.c
 *
 *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 *  Swap reorganised 29.12.95, Stephen Tweedie
 *
 *  Rewritten to use page cache, (C) 1998 Stephen Tweedie
 */
#include <linux/module.h>
#include <linux/mm.h>
#include <linux/kernel_stat.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/init.h>
#include <linux/pagemap.h>
#include <linux/buffer_head.h>
#include <linux/backing-dev.h>
#include <linux/pagevec.h>
#include <linux/migrate.h>

#include <asm/pgtable.h>

/*
 * swapper_space is a fiction, retained to simplify the path through
 * vmscan's shrink_page_list, to make sync_page look nicer, and to allow
 * future use of radix_tree tags in the swap cache.
 */
static const struct address_space_operations swap_aops = {
	.writepage	= swap_writepage,
	.sync_page	= block_sync_page,
	.set_page_dirty	= __set_page_dirty_nobuffers,
	.migratepage	= migrate_page,
};

static struct backing_dev_info swap_backing_dev_info = {
	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK,
	.unplug_io_fn	= swap_unplug_io_fn,
};

struct address_space swapper_space = {
	.page_tree	= RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
	.tree_lock	= __SPIN_LOCK_UNLOCKED(swapper_space.tree_lock),
	.a_ops		= &swap_aops,
	.i_mmap_nonlinear = LIST_HEAD_INIT(swapper_space.i_mmap_nonlinear),
	.backing_dev_info = &swap_backing_dev_info,
};

#define INC_CACHE_INFO(x)	do { swap_cache_info.x++; } while (0)

static struct {
	unsigned long add_total;
	unsigned long del_total;
	unsigned long find_success;
	unsigned long find_total;
} swap_cache_info;

void show_swap_cache_info(void)
{
	printk("%lu pages in swap cache\n", total_swapcache_pages);
	printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
		swap_cache_info.add_total, swap_cache_info.del_total,
		swap_cache_info.find_success, swap_cache_info.find_total);
	printk("Free swap  = %lukB\n", nr_swap_pages << (PAGE_SHIFT - 10));
	printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
}

/*
 * add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
 * but sets SwapCache flag and private instead of mapping and index.
 */
int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
{
	int error;

	BUG_ON(!PageLocked(page));
	BUG_ON(PageSwapCache(page));
	BUG_ON(PagePrivate(page));
	error = radix_tree_preload(gfp_mask);
	if (!error) {
		page_cache_get(page);
		SetPageSwapCache(page);
		set_page_private(page, entry.val);

		spin_lock_irq(&swapper_space.tree_lock);
		error = radix_tree_insert(&swapper_space.page_tree,
						entry.val, page);
		if (likely(!error)) {
			total_swapcache_pages++;
			__inc_zone_page_state(page, NR_FILE_PAGES);
			INC_CACHE_INFO(add_total);
		}
		spin_unlock_irq(&swapper_space.tree_lock);
		radix_tree_preload_end();

		if (unlikely(error)) {
			set_page_private(page, 0UL);
			ClearPageSwapCache(page);
			page_cache_release(page);
		}
	}
	return error;
}

/*
 * This must be called only on pages that have
 * been verified to be in the swap cache.
 */
void __delete_from_swap_cache(struct page *page)
{
	BUG_ON(!PageLocked(page));
	BUG_ON(!PageSwapCache(page));
	BUG_ON(PageWriteback(page));
	BUG_ON(PagePrivate(page));

	radix_tree_delete(&swapper_space.page_tree, page_private(page));
	set_page_private(page, 0);
	ClearPageSwapCache(page);
	total_swapcache_pages--;
	__dec_zone_page_state(page, NR_FILE_PAGES);
	INC_CACHE_INFO(del_total);
}

/**
 * add_to_swap - allocate swap space for a page
 * @page: page we want to move to swap
 * @gfp_mask: memory allocation flags
 *
 * Allocate swap space for the page and add the page to the
 * swap cache.  Caller needs to hold the page lock. 
 */
int add_to_swap(struct page * page, gfp_t gfp_mask)
{
	swp_entry_t entry;
	int err;

	BUG_ON(!PageLocked(page));
	BUG_ON(!PageUptodate(page));

	for (;;) {
		entry = get_swap_page();
		if (!entry.val)
			return 0;

		/*
		 * Radix-tree node allocations from PF_MEMALLOC contexts could
		 * completely exhaust the page allocator. __GFP_NOMEMALLOC
		 * stops emergency reserves from being allocated.
		 *
		 * TODO: this could cause a theoretical memory reclaim
		 * deadlock in the swap out path.
		 */
		/*
		 * Add it to the swap cache and mark it dirty
		 */
		err = add_to_swap_cache(page, entry,
				gfp_mask|__GFP_NOMEMALLOC|__GFP_NOWARN);

		switch (err) {
		case 0:				/* Success */
			SetPageDirty(page);
			return 1;
		case -EEXIST:
			/* Raced with "speculative" read_swap_cache_async */
			swap_free(entry);
			continue;
		default:
			/* -ENOMEM radix-tree allocation failure */
			swap_free(entry);
			return 0;
		}
	}
}

/*
 * This must be called only on pages that have
 * been verified to be in the swap cache and locked.
 * It will never put the page into the free list,
 * the caller has a reference on the page.
 */
void delete_from_swap_cache(struct page *page)
{
	swp_entry_t entry;

	entry.val = page_private(page);

	spin_lock_irq(&swapper_space.tree_lock);
	__delete_from_swap_cache(page);
	spin_unlock_irq(&swapper_space.tree_lock);

	swap_free(entry);
	page_cache_release(page);
}

/* 
 * If we are the only user, then try to free up the swap cache. 
 * 
 * Its ok to check for PageSwapCache without the page lock
 * here because we are going to recheck again inside 
 * exclusive_swap_page() _with_ the lock. 
 * 					- Marcelo
 */
static inline void free_swap_cache(struct page *page)
{
	if (PageSwapCache(page) && !TestSetPageLocked(page)) {
		remove_exclusive_swap_page(page);
		unlock_page(page);
	}
}

/* 
 * Perform a free_page(), also freeing any swap cache associated with
 * this page if it is the last user of the page.
 */
void free_page_and_swap_cache(struct page *page)
{
	free_swap_cache(page);
	page_cache_release(page);
}

/*
 * Passed an array of pages, drop them all from swapcache and then release
 * them.  They are removed from the LRU and freed if this is their last use.
 */
void free_pages_and_swap_cache(struct page **pages, int nr)
{
	struct page **pagep = pages;

	lru_add_drain();
	while (nr) {
		int todo = min(nr, PAGEVEC_SIZE);
		int i;

		for (i = 0; i < todo; i++)
			free_swap_cache(pagep[i]);
		release_pages(pagep, todo, 0);
		pagep += todo;
		nr -= todo;
	}
}

/*
 * Lookup a swap entry in the swap cache. A found page will be returned
 * unlocked and with its refcount incremented - we rely on the kernel
 * lock getting page table operations atomic even if we drop the page
 * lock before returning.
 */
struct page * lookup_swap_cache(swp_entry_t entry)
{
	struct page *page;

	page = find_get_page(&swapper_space, entry.val);

	if (page)
		INC_CACHE_INFO(find_success);

	INC_CACHE_INFO(find_total);
	return page;
}

/* 
 * Locate a page of swap in physical memory, reserving swap cache space
 * and reading the disk if it is not already cached.
 * A failure return means that either the page allocation failed or that
 * the swap entry is no longer in use.
 */
struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
			struct vm_area_struct *vma, unsigned long addr)
{
	struct page *found_page, *new_page = NULL;
	int err;

	do {
		/*
		 * First check the swap cache.  Since this is normally
		 * called after lookup_swap_cache() failed, re-calling
		 * that would confuse statistics.
		 */
		found_page = find_get_page(&swapper_space, entry.val);
		if (found_page)
			break;

		/*
		 * Get a new page to read into from swap.
		 */
		if (!new_page) {
			new_page = alloc_page_vma(gfp_mask, vma, addr);
			if (!new_page)
				break;		/* Out of memory */
		}

		/*
		 * Swap entry may have been freed since our caller observed it.
		 */
		if (!swap_duplicate(entry))
			break;

		/*
		 * Associate the page with swap entry in the swap cache.
		 * May fail (-EEXIST) if there is already a page associated
		 * with this entry in the swap cache: added by a racing
		 * read_swap_cache_async, or add_to_swap or shmem_writepage
		 * re-using the just freed swap entry for an existing page.
		 * May fail (-ENOMEM) if radix-tree node allocation failed.
		 */
		SetPageLocked(new_page);
		err = add_to_swap_cache(new_page, entry, gfp_mask & GFP_KERNEL);
		if (!err) {
			/*
			 * Initiate read into locked page and return.
			 */
			lru_cache_add_active(new_page);
			swap_readpage(NULL, new_page);
			return new_page;
		}
		ClearPageLocked(new_page);
		swap_free(entry);
	} while (err != -ENOMEM);

	if (new_page)
		page_cache_release(new_page);
	return found_page;
}

/**
 * swapin_readahead - swap in pages in hope we need them soon
 * @entry: swap entry of this memory
 * @gfp_mask: memory allocation flags
 * @vma: user vma this address belongs to
 * @addr: target address for mempolicy
 *
 * Returns the struct page for entry and addr, after queueing swapin.
 *
 * Primitive swap readahead code. We simply read an aligned block of
 * (1 << page_cluster) entries in the swap area. This method is chosen
 * because it doesn't cost us any seek time.  We also make sure to queue
 * the 'original' request together with the readahead ones...
 *
 * This has been extended to use the NUMA policies from the mm triggering
 * the readahead.
 *
 * Caller must hold down_read on the vma->vm_mm if vma is not NULL.
 */
struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
			struct vm_area_struct *vma, unsigned long addr)
{
	int nr_pages;
	struct page *page;
	unsigned long offset;
	unsigned long end_offset;

	/*
	 * Get starting offset for readaround, and number of pages to read.
	 * Adjust starting address by readbehind (for NUMA interleave case)?
	 * No, it's very unlikely that swap layout would follow vma layout,
	 * more likely that neighbouring swap pages came from the same node:
	 * so use the same "addr" to choose the same node for each swap read.
	 */
	nr_pages = valid_swaphandles(entry, &offset);
	for (end_offset = offset + nr_pages; offset < end_offset; offset++) {
		/* Ok, do the async read-ahead now */
		page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
						gfp_mask, vma, addr);
		if (!page)
			break;
		page_cache_release(page);
	}
	lru_add_drain();	/* Push any new pages onto the LRU now */
	return read_swap_cache_async(entry, gfp_mask, vma, addr);
}
Commit	Line	Data
1da177e4 LT	1	/*
	2	* linux/mm/swap_state.c
	3	*
	4	* Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
	5	* Swap reorganised 29.12.95, Stephen Tweedie
	6	*
	7	* Rewritten to use page cache, (C) 1998 Stephen Tweedie
	8	*/
	9	#include <linux/module.h>
	10	#include <linux/mm.h>
	11	#include <linux/kernel_stat.h>
	12	#include <linux/swap.h>
46017e95	13	#include <linux/swapops.h>
1da177e4 LT	14	#include <linux/init.h>
	15	#include <linux/pagemap.h>
	16	#include <linux/buffer_head.h>
	17	#include <linux/backing-dev.h>
c484d410	18	#include <linux/pagevec.h>
b20a3503	19	#include <linux/migrate.h>
1da177e4 LT	20
	21	#include <asm/pgtable.h>
	22
	23	/*
	24	* swapper_space is a fiction, retained to simplify the path through
2706a1b8	25	* vmscan's shrink_page_list, to make sync_page look nicer, and to allow
1da177e4 LT	26	* future use of radix_tree tags in the swap cache.
1da177e4 LT	27	*/
f5e54d6e	28	static const struct address_space_operations swap_aops = {
1da177e4 LT	29	.writepage = swap_writepage,
	30	.sync_page = block_sync_page,
	31	.set_page_dirty = __set_page_dirty_nobuffers,
e965f963	32	.migratepage = migrate_page,
1da177e4 LT	33	};
	34
	35	static struct backing_dev_info swap_backing_dev_info = {
e4ad08fe	36	.capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK,
1da177e4 LT	37	.unplug_io_fn = swap_unplug_io_fn,
	38	};
	39
	40	struct address_space swapper_space = {
	41	.page_tree = RADIX_TREE_INIT(GFP_ATOMIC\|__GFP_NOWARN),
19fd6231	42	.tree_lock = __SPIN_LOCK_UNLOCKED(swapper_space.tree_lock),
1da177e4 LT	43	.a_ops = &swap_aops,
	44	.i_mmap_nonlinear = LIST_HEAD_INIT(swapper_space.i_mmap_nonlinear),
	45	.backing_dev_info = &swap_backing_dev_info,
	46	};
1da177e4 LT	47
	48	#define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0)
	49
	50	static struct {
	51	unsigned long add_total;
	52	unsigned long del_total;
	53	unsigned long find_success;
	54	unsigned long find_total;
1da177e4 LT	55	} swap_cache_info;
	56
	57	void show_swap_cache_info(void)
	58	{
2c97b7fc JW	59	printk("%lu pages in swap cache\n", total_swapcache_pages);
2c97b7fc JW	60	printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
1da177e4	61	swap_cache_info.add_total, swap_cache_info.del_total,
bb63be0a	62	swap_cache_info.find_success, swap_cache_info.find_total);
1da177e4 LT	63	printk("Free swap = %lukB\n", nr_swap_pages << (PAGE_SHIFT - 10));
	64	printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
	65	}
	66
	67	/*
e286781d	68	* add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
1da177e4 LT	69	* but sets SwapCache flag and private instead of mapping and index.
1da177e4 LT	70	*/
73b1262f	71	int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
1da177e4 LT	72	{
	73	int error;
	74
b55ed816	75	BUG_ON(!PageLocked(page));
1da177e4 LT	76	BUG_ON(PageSwapCache(page));
1da177e4 LT	77	BUG_ON(PagePrivate(page));
35c754d7 BS	78	error = radix_tree_preload(gfp_mask);
35c754d7 BS	79	if (!error) {
e286781d NP	80	page_cache_get(page);
	81	SetPageSwapCache(page);
	82	set_page_private(page, entry.val);
	83
19fd6231	84	spin_lock_irq(&swapper_space.tree_lock);
1da177e4 LT	85	error = radix_tree_insert(&swapper_space.page_tree,
1da177e4 LT	86	entry.val, page);
e286781d	87	if (likely(!error)) {
1da177e4	88	total_swapcache_pages++;
347ce434	89	__inc_zone_page_state(page, NR_FILE_PAGES);
bb63be0a	90	INC_CACHE_INFO(add_total);
1da177e4	91	}
19fd6231	92	spin_unlock_irq(&swapper_space.tree_lock);
1da177e4	93	radix_tree_preload_end();
e286781d NP	94
	95	if (unlikely(error)) {
	96	set_page_private(page, 0UL);
	97	ClearPageSwapCache(page);
	98	page_cache_release(page);
	99	}
fa1de900	100	}
1da177e4 LT	101	return error;
	102	}
	103
1da177e4 LT	104	/*
	105	* This must be called only on pages that have
	106	* been verified to be in the swap cache.
	107	*/
	108	void __delete_from_swap_cache(struct page *page)
	109	{
	110	BUG_ON(!PageLocked(page));
	111	BUG_ON(!PageSwapCache(page));
	112	BUG_ON(PageWriteback(page));
3279ffd9	113	BUG_ON(PagePrivate(page));
1da177e4	114
4c21e2f2 HD	115	radix_tree_delete(&swapper_space.page_tree, page_private(page));
4c21e2f2 HD	116	set_page_private(page, 0);
1da177e4 LT	117	ClearPageSwapCache(page);
1da177e4 LT	118	total_swapcache_pages--;
347ce434	119	__dec_zone_page_state(page, NR_FILE_PAGES);
1da177e4 LT	120	INC_CACHE_INFO(del_total);
	121	}
	122
	123	/**
	124	* add_to_swap - allocate swap space for a page
	125	* @page: page we want to move to swap
7682486b	126	* @gfp_mask: memory allocation flags
1da177e4 LT	127	*
	128	* Allocate swap space for the page and add the page to the
	129	* swap cache. Caller needs to hold the page lock.
	130	*/
1480a540	131	int add_to_swap(struct page * page, gfp_t gfp_mask)
1da177e4 LT	132	{
1da177e4 LT	133	swp_entry_t entry;
1da177e4 LT	134	int err;
1da177e4 LT	135
e74ca2b4	136	BUG_ON(!PageLocked(page));
0ed361de	137	BUG_ON(!PageUptodate(page));
1da177e4 LT	138
	139	for (;;) {
	140	entry = get_swap_page();
	141	if (!entry.val)
	142	return 0;
	143
bd53b714 NP	144	/*
	145	* Radix-tree node allocations from PF_MEMALLOC contexts could
	146	* completely exhaust the page allocator. __GFP_NOMEMALLOC
	147	* stops emergency reserves from being allocated.
1da177e4	148	*
bd53b714 NP	149	* TODO: this could cause a theoretical memory reclaim
bd53b714 NP	150	* deadlock in the swap out path.
1da177e4	151	*/
1da177e4 LT	152	/*
	153	* Add it to the swap cache and mark it dirty
	154	*/
f000944d	155	err = add_to_swap_cache(page, entry,
1480a540	156	gfp_mask\|__GFP_NOMEMALLOC\|__GFP_NOWARN);
1da177e4 LT	157
	158	switch (err) {
	159	case 0: /* Success */
1da177e4	160	SetPageDirty(page);
1da177e4 LT	161	return 1;
	162	case -EEXIST:
	163	/* Raced with "speculative" read_swap_cache_async */
1da177e4 LT	164	swap_free(entry);
	165	continue;
	166	default:
	167	/* -ENOMEM radix-tree allocation failure */
	168	swap_free(entry);
	169	return 0;
	170	}
	171	}
	172	}
	173
	174	/*
	175	* This must be called only on pages that have
	176	* been verified to be in the swap cache and locked.
	177	* It will never put the page into the free list,
	178	* the caller has a reference on the page.
	179	*/
	180	void delete_from_swap_cache(struct page *page)
	181	{
	182	swp_entry_t entry;
	183
4c21e2f2	184	entry.val = page_private(page);
1da177e4	185
19fd6231	186	spin_lock_irq(&swapper_space.tree_lock);
1da177e4	187	__delete_from_swap_cache(page);
19fd6231	188	spin_unlock_irq(&swapper_space.tree_lock);
1da177e4 LT	189
	190	swap_free(entry);
	191	page_cache_release(page);
	192	}
	193
1da177e4 LT	194	/*
	195	* If we are the only user, then try to free up the swap cache.
	196	*
	197	* Its ok to check for PageSwapCache without the page lock
	198	* here because we are going to recheck again inside
	199	* exclusive_swap_page() _with_ the lock.
	200	* - Marcelo
	201	*/
	202	static inline void free_swap_cache(struct page *page)
	203	{
	204	if (PageSwapCache(page) && !TestSetPageLocked(page)) {
	205	remove_exclusive_swap_page(page);
	206	unlock_page(page);
	207	}
	208	}
	209
	210	/*
	211	* Perform a free_page(), also freeing any swap cache associated with
b8072f09	212	* this page if it is the last user of the page.
1da177e4 LT	213	*/
	214	void free_page_and_swap_cache(struct page *page)
	215	{
	216	free_swap_cache(page);
	217	page_cache_release(page);
	218	}
	219
	220	/*
	221	* Passed an array of pages, drop them all from swapcache and then release
	222	* them. They are removed from the LRU and freed if this is their last use.
	223	*/
	224	void free_pages_and_swap_cache(struct page **pages, int nr)
	225	{
1da177e4 LT	226	struct page **pagep = pages;
	227
	228	lru_add_drain();
	229	while (nr) {
c484d410	230	int todo = min(nr, PAGEVEC_SIZE);
1da177e4 LT	231	int i;
	232
	233	for (i = 0; i < todo; i++)
	234	free_swap_cache(pagep[i]);
	235	release_pages(pagep, todo, 0);
	236	pagep += todo;
	237	nr -= todo;
	238	}
	239	}
	240
	241	/*
	242	* Lookup a swap entry in the swap cache. A found page will be returned
	243	* unlocked and with its refcount incremented - we rely on the kernel
	244	* lock getting page table operations atomic even if we drop the page
	245	* lock before returning.
	246	*/
	247	struct page * lookup_swap_cache(swp_entry_t entry)
	248	{
	249	struct page *page;
	250
	251	page = find_get_page(&swapper_space, entry.val);
	252
	253	if (page)
	254	INC_CACHE_INFO(find_success);
	255
	256	INC_CACHE_INFO(find_total);
	257	return page;
	258	}
	259
	260	/*
	261	* Locate a page of swap in physical memory, reserving swap cache space
	262	* and reading the disk if it is not already cached.
	263	* A failure return means that either the page allocation failed or that
	264	* the swap entry is no longer in use.
	265	*/
02098fea	266	struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
1da177e4 LT	267	struct vm_area_struct *vma, unsigned long addr)
	268	{
	269	struct page found_page, new_page = NULL;
	270	int err;
	271
	272	do {
	273	/*
	274	* First check the swap cache. Since this is normally
	275	* called after lookup_swap_cache() failed, re-calling
	276	* that would confuse statistics.
	277	*/
	278	found_page = find_get_page(&swapper_space, entry.val);
	279	if (found_page)
	280	break;
	281
	282	/*
	283	* Get a new page to read into from swap.
	284	*/
	285	if (!new_page) {
02098fea	286	new_page = alloc_page_vma(gfp_mask, vma, addr);
1da177e4 LT	287	if (!new_page)
	288	break; /* Out of memory */
	289	}
	290
f000944d HD	291	/*
	292	* Swap entry may have been freed since our caller observed it.
	293	*/
	294	if (!swap_duplicate(entry))
	295	break;
	296
1da177e4 LT	297	/*
1da177e4 LT	298	* Associate the page with swap entry in the swap cache.
f000944d HD	299	* May fail (-EEXIST) if there is already a page associated
	300	* with this entry in the swap cache: added by a racing
	301	* read_swap_cache_async, or add_to_swap or shmem_writepage
	302	* re-using the just freed swap entry for an existing page.
1da177e4 LT	303	* May fail (-ENOMEM) if radix-tree node allocation failed.
1da177e4 LT	304	*/
f000944d HD	305	SetPageLocked(new_page);
f000944d HD	306	err = add_to_swap_cache(new_page, entry, gfp_mask & GFP_KERNEL);
1da177e4 LT	307	if (!err) {
	308	/*
	309	* Initiate read into locked page and return.
	310	*/
	311	lru_cache_add_active(new_page);
	312	swap_readpage(NULL, new_page);
	313	return new_page;
	314	}
f000944d HD	315	ClearPageLocked(new_page);
	316	swap_free(entry);
	317	} while (err != -ENOMEM);
1da177e4 LT	318
	319	if (new_page)
	320	page_cache_release(new_page);
	321	return found_page;
	322	}
46017e95 HD	323
	324	/**
	325	* swapin_readahead - swap in pages in hope we need them soon
	326	* @entry: swap entry of this memory
7682486b	327	* @gfp_mask: memory allocation flags
46017e95 HD	328	* @vma: user vma this address belongs to
	329	* @addr: target address for mempolicy
	330	*
	331	* Returns the struct page for entry and addr, after queueing swapin.
	332	*
	333	* Primitive swap readahead code. We simply read an aligned block of
	334	* (1 << page_cluster) entries in the swap area. This method is chosen
	335	* because it doesn't cost us any seek time. We also make sure to queue
	336	* the 'original' request together with the readahead ones...
	337	*
	338	* This has been extended to use the NUMA policies from the mm triggering
	339	* the readahead.
	340	*
	341	* Caller must hold down_read on the vma->vm_mm if vma is not NULL.
	342	*/
02098fea	343	struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
46017e95 HD	344	struct vm_area_struct *vma, unsigned long addr)
	345	{
	346	int nr_pages;
	347	struct page *page;
	348	unsigned long offset;
	349	unsigned long end_offset;
	350
	351	/*
	352	* Get starting offset for readaround, and number of pages to read.
	353	* Adjust starting address by readbehind (for NUMA interleave case)?
	354	* No, it's very unlikely that swap layout would follow vma layout,
	355	* more likely that neighbouring swap pages came from the same node:
	356	* so use the same "addr" to choose the same node for each swap read.
	357	*/
	358	nr_pages = valid_swaphandles(entry, &offset);
	359	for (end_offset = offset + nr_pages; offset < end_offset; offset++) {
	360	/* Ok, do the async read-ahead now */
	361	page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
02098fea	362	gfp_mask, vma, addr);
46017e95 HD	363	if (!page)
	364	break;
	365	page_cache_release(page);
	366	}
	367	lru_add_drain(); /* Push any new pages onto the LRU now */
02098fea	368	return read_swap_cache_async(entry, gfp_mask, vma, addr);
46017e95	369	}