[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/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_DIRTY | BDI_CAP_NO_WRITEBACK,
	.unplug_io_fn	= swap_unplug_io_fn,
};

struct address_space swapper_space = {
	.page_tree	= RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
	.tree_lock	= __RW_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;
	unsigned long noent_race;
	unsigned long exist_race;
} swap_cache_info;

void show_swap_cache_info(void)
{
	printk("Swap cache: add %lu, delete %lu, find %lu/%lu, race %lu+%lu\n",
		swap_cache_info.add_total, swap_cache_info.del_total,
		swap_cache_info.find_success, swap_cache_info.find_total,
		swap_cache_info.noent_race, swap_cache_info.exist_race);
	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 on swapper_space,
 * but sets SwapCache flag and private instead of mapping and index.
 */
static 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) {
		write_lock_irq(&swapper_space.tree_lock);
		error = radix_tree_insert(&swapper_space.page_tree,
						entry.val, page);
		if (!error) {
			page_cache_get(page);
			SetPageSwapCache(page);
			set_page_private(page, entry.val);
			total_swapcache_pages++;
			__inc_zone_page_state(page, NR_FILE_PAGES);
		}
		write_unlock_irq(&swapper_space.tree_lock);
		radix_tree_preload_end();
	}
	return error;
}

static int add_to_swap_cache(struct page *page, swp_entry_t entry)
{
	int error;

	BUG_ON(PageLocked(page));
	if (!swap_duplicate(entry)) {
		INC_CACHE_INFO(noent_race);
		return -ENOENT;
	}
	SetPageLocked(page);
	error = __add_to_swap_cache(page, entry, GFP_KERNEL);
	/*
	 * Anon pages are already on the LRU, we don't run lru_cache_add here.
	 */
	if (error) {
		ClearPageLocked(page);
		swap_free(entry);
		if (error == -EEXIST)
			INC_CACHE_INFO(exist_race);
		return error;
	}
	INC_CACHE_INFO(add_total);
	return 0;
}

/*
 * 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
 *
 * 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));

	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 */
			SetPageUptodate(page);
			SetPageDirty(page);
			INC_CACHE_INFO(add_total);
			return 1;
		case -EEXIST:
			/* Raced with "speculative" read_swap_cache_async */
			INC_CACHE_INFO(exist_race);
			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);

	write_lock_irq(&swapper_space.tree_lock);
	__delete_from_swap_cache(page);
	write_unlock_irq(&swapper_space.tree_lock);

	swap_free(entry);
	page_cache_release(page);
}

/*
 * Strange swizzling function only for use by shmem_writepage
 */
int move_to_swap_cache(struct page *page, swp_entry_t entry)
{
	int err = __add_to_swap_cache(page, entry, GFP_ATOMIC);
	if (!err) {
		remove_from_page_cache(page);
		page_cache_release(page);	/* pagecache ref */
		if (!swap_duplicate(entry))
			BUG();
		SetPageDirty(page);
		INC_CACHE_INFO(add_total);
	} else if (err == -EEXIST)
		INC_CACHE_INFO(exist_race);
	return err;
}

/*
 * Strange swizzling function for shmem_getpage (and shmem_unuse)
 */
int move_from_swap_cache(struct page *page, unsigned long index,
		struct address_space *mapping)
{
	int err = add_to_page_cache(page, mapping, index, GFP_ATOMIC);
	if (!err) {
		delete_from_swap_cache(page);
		/* shift page from clean_pages to dirty_pages list */
		ClearPageDirty(page);
		set_page_dirty(page);
	}
	return err;
}

/* 
 * 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,
			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_HIGHUSER_MOVABLE,
								vma, addr);
			if (!new_page)
				break;		/* Out of memory */
		}

		/*
		 * Associate the page with swap entry in the swap cache.
		 * May fail (-ENOENT) if swap entry has been freed since
		 * our caller observed it.  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 by try_to_swap_out (or shmem_writepage) re-using
		 * the just freed swap entry for an existing page.
		 * May fail (-ENOMEM) if radix-tree node allocation failed.
		 */
		err = add_to_swap_cache(new_page, entry);
		if (!err) {
			/*
			 * Initiate read into locked page and return.
			 */
			lru_cache_add_active(new_page);
			swap_readpage(NULL, new_page);
			return new_page;
		}
	} while (err != -ENOENT && err != -ENOMEM);

	if (new_page)
		page_cache_release(new_page);
	return found_page;
}
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>
	13	#include <linux/init.h>
	14	#include <linux/pagemap.h>
	15	#include <linux/buffer_head.h>
	16	#include <linux/backing-dev.h>
c484d410	17	#include <linux/pagevec.h>
b20a3503	18	#include <linux/migrate.h>
1da177e4 LT	19
	20	#include <asm/pgtable.h>
	21
	22	/*
	23	* swapper_space is a fiction, retained to simplify the path through
2706a1b8	24	* vmscan's shrink_page_list, to make sync_page look nicer, and to allow
1da177e4 LT	25	* future use of radix_tree tags in the swap cache.
1da177e4 LT	26	*/
f5e54d6e	27	static const struct address_space_operations swap_aops = {
1da177e4 LT	28	.writepage = swap_writepage,
	29	.sync_page = block_sync_page,
	30	.set_page_dirty = __set_page_dirty_nobuffers,
e965f963	31	.migratepage = migrate_page,
1da177e4 LT	32	};
	33
	34	static struct backing_dev_info swap_backing_dev_info = {
	35	.capabilities = BDI_CAP_NO_ACCT_DIRTY \| BDI_CAP_NO_WRITEBACK,
	36	.unplug_io_fn = swap_unplug_io_fn,
	37	};
	38
	39	struct address_space swapper_space = {
	40	.page_tree = RADIX_TREE_INIT(GFP_ATOMIC\|__GFP_NOWARN),
e4d91918	41	.tree_lock = __RW_LOCK_UNLOCKED(swapper_space.tree_lock),
1da177e4 LT	42	.a_ops = &swap_aops,
	43	.i_mmap_nonlinear = LIST_HEAD_INIT(swapper_space.i_mmap_nonlinear),
	44	.backing_dev_info = &swap_backing_dev_info,
	45	};
1da177e4 LT	46
	47	#define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0)
	48
	49	static struct {
	50	unsigned long add_total;
	51	unsigned long del_total;
	52	unsigned long find_success;
	53	unsigned long find_total;
	54	unsigned long noent_race;
	55	unsigned long exist_race;
	56	} swap_cache_info;
	57
	58	void show_swap_cache_info(void)
	59	{
	60	printk("Swap cache: add %lu, delete %lu, find %lu/%lu, race %lu+%lu\n",
	61	swap_cache_info.add_total, swap_cache_info.del_total,
	62	swap_cache_info.find_success, swap_cache_info.find_total,
	63	swap_cache_info.noent_race, swap_cache_info.exist_race);
	64	printk("Free swap = %lukB\n", nr_swap_pages << (PAGE_SHIFT - 10));
	65	printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
	66	}
	67
	68	/*
	69	* __add_to_swap_cache resembles add_to_page_cache on swapper_space,
	70	* but sets SwapCache flag and private instead of mapping and index.
	71	*/
9de75d11	72	static int __add_to_swap_cache(struct page *page, swp_entry_t entry,
dd0fc66f	73	gfp_t gfp_mask)
1da177e4 LT	74	{
	75	int error;
	76
b55ed816	77	BUG_ON(!PageLocked(page));
1da177e4 LT	78	BUG_ON(PageSwapCache(page));
	79	BUG_ON(PagePrivate(page));
	80	error = radix_tree_preload(gfp_mask);
	81	if (!error) {
	82	write_lock_irq(&swapper_space.tree_lock);
	83	error = radix_tree_insert(&swapper_space.page_tree,
	84	entry.val, page);
	85	if (!error) {
	86	page_cache_get(page);
1da177e4	87	SetPageSwapCache(page);
4c21e2f2	88	set_page_private(page, entry.val);
1da177e4	89	total_swapcache_pages++;
347ce434	90	__inc_zone_page_state(page, NR_FILE_PAGES);
1da177e4 LT	91	}
	92	write_unlock_irq(&swapper_space.tree_lock);
	93	radix_tree_preload_end();
	94	}
	95	return error;
	96	}
	97
	98	static int add_to_swap_cache(struct page *page, swp_entry_t entry)
	99	{
	100	int error;
	101
b55ed816	102	BUG_ON(PageLocked(page));
1da177e4 LT	103	if (!swap_duplicate(entry)) {
	104	INC_CACHE_INFO(noent_race);
	105	return -ENOENT;
	106	}
b55ed816	107	SetPageLocked(page);
1da177e4 LT	108	error = __add_to_swap_cache(page, entry, GFP_KERNEL);
	109	/*
	110	* Anon pages are already on the LRU, we don't run lru_cache_add here.
	111	*/
	112	if (error) {
b55ed816	113	ClearPageLocked(page);
1da177e4 LT	114	swap_free(entry);
	115	if (error == -EEXIST)
	116	INC_CACHE_INFO(exist_race);
	117	return error;
	118	}
	119	INC_CACHE_INFO(add_total);
	120	return 0;
	121	}
	122
	123	/*
	124	* This must be called only on pages that have
	125	* been verified to be in the swap cache.
	126	*/
	127	void __delete_from_swap_cache(struct page *page)
	128	{
	129	BUG_ON(!PageLocked(page));
	130	BUG_ON(!PageSwapCache(page));
	131	BUG_ON(PageWriteback(page));
3279ffd9	132	BUG_ON(PagePrivate(page));
1da177e4	133
4c21e2f2 HD	134	radix_tree_delete(&swapper_space.page_tree, page_private(page));
4c21e2f2 HD	135	set_page_private(page, 0);
1da177e4 LT	136	ClearPageSwapCache(page);
1da177e4 LT	137	total_swapcache_pages--;
347ce434	138	__dec_zone_page_state(page, NR_FILE_PAGES);
1da177e4 LT	139	INC_CACHE_INFO(del_total);
	140	}
	141
	142	/**
	143	* add_to_swap - allocate swap space for a page
	144	* @page: page we want to move to swap
	145	*
	146	* Allocate swap space for the page and add the page to the
	147	* swap cache. Caller needs to hold the page lock.
	148	*/
1480a540	149	int add_to_swap(struct page * page, gfp_t gfp_mask)
1da177e4 LT	150	{
1da177e4 LT	151	swp_entry_t entry;
1da177e4 LT	152	int err;
1da177e4 LT	153
e74ca2b4	154	BUG_ON(!PageLocked(page));
1da177e4 LT	155
	156	for (;;) {
	157	entry = get_swap_page();
	158	if (!entry.val)
	159	return 0;
	160
bd53b714 NP	161	/*
	162	* Radix-tree node allocations from PF_MEMALLOC contexts could
	163	* completely exhaust the page allocator. __GFP_NOMEMALLOC
	164	* stops emergency reserves from being allocated.
1da177e4	165	*
bd53b714 NP	166	* TODO: this could cause a theoretical memory reclaim
bd53b714 NP	167	* deadlock in the swap out path.
1da177e4	168	*/
1da177e4 LT	169	/*
	170	* Add it to the swap cache and mark it dirty
	171	*/
bd53b714	172	err = __add_to_swap_cache(page, entry,
1480a540	173	gfp_mask\|__GFP_NOMEMALLOC\|__GFP_NOWARN);
1da177e4 LT	174
	175	switch (err) {
	176	case 0: /* Success */
	177	SetPageUptodate(page);
	178	SetPageDirty(page);
	179	INC_CACHE_INFO(add_total);
	180	return 1;
	181	case -EEXIST:
	182	/* Raced with "speculative" read_swap_cache_async */
	183	INC_CACHE_INFO(exist_race);
	184	swap_free(entry);
	185	continue;
	186	default:
	187	/* -ENOMEM radix-tree allocation failure */
	188	swap_free(entry);
	189	return 0;
	190	}
	191	}
	192	}
	193
	194	/*
	195	* This must be called only on pages that have
	196	* been verified to be in the swap cache and locked.
	197	* It will never put the page into the free list,
	198	* the caller has a reference on the page.
	199	*/
	200	void delete_from_swap_cache(struct page *page)
	201	{
	202	swp_entry_t entry;
	203
4c21e2f2	204	entry.val = page_private(page);
1da177e4 LT	205
	206	write_lock_irq(&swapper_space.tree_lock);
	207	__delete_from_swap_cache(page);
	208	write_unlock_irq(&swapper_space.tree_lock);
	209
	210	swap_free(entry);
	211	page_cache_release(page);
	212	}
	213
	214	/*
	215	* Strange swizzling function only for use by shmem_writepage
	216	*/
	217	int move_to_swap_cache(struct page *page, swp_entry_t entry)
	218	{
	219	int err = __add_to_swap_cache(page, entry, GFP_ATOMIC);
	220	if (!err) {
	221	remove_from_page_cache(page);
	222	page_cache_release(page); /* pagecache ref */
	223	if (!swap_duplicate(entry))
	224	BUG();
	225	SetPageDirty(page);
	226	INC_CACHE_INFO(add_total);
	227	} else if (err == -EEXIST)
	228	INC_CACHE_INFO(exist_race);
	229	return err;
	230	}
	231
	232	/*
	233	* Strange swizzling function for shmem_getpage (and shmem_unuse)
	234	*/
	235	int move_from_swap_cache(struct page *page, unsigned long index,
	236	struct address_space *mapping)
	237	{
	238	int err = add_to_page_cache(page, mapping, index, GFP_ATOMIC);
	239	if (!err) {
	240	delete_from_swap_cache(page);
	241	/* shift page from clean_pages to dirty_pages list */
	242	ClearPageDirty(page);
	243	set_page_dirty(page);
	244	}
	245	return err;
	246	}
	247
	248	/*
	249	* If we are the only user, then try to free up the swap cache.
	250	*
	251	* Its ok to check for PageSwapCache without the page lock
	252	* here because we are going to recheck again inside
	253	* exclusive_swap_page() _with_ the lock.
	254	* - Marcelo
	255	*/
	256	static inline void free_swap_cache(struct page *page)
	257	{
	258	if (PageSwapCache(page) && !TestSetPageLocked(page)) {
	259	remove_exclusive_swap_page(page);
	260	unlock_page(page);
	261	}
	262	}
	263
	264	/*
	265	* Perform a free_page(), also freeing any swap cache associated with
b8072f09	266	* this page if it is the last user of the page.
1da177e4 LT	267	*/
	268	void free_page_and_swap_cache(struct page *page)
	269	{
	270	free_swap_cache(page);
	271	page_cache_release(page);
	272	}
	273
	274	/*
	275	* Passed an array of pages, drop them all from swapcache and then release
	276	* them. They are removed from the LRU and freed if this is their last use.
	277	*/
	278	void free_pages_and_swap_cache(struct page **pages, int nr)
	279	{
1da177e4 LT	280	struct page **pagep = pages;
	281
	282	lru_add_drain();
	283	while (nr) {
c484d410	284	int todo = min(nr, PAGEVEC_SIZE);
1da177e4 LT	285	int i;
	286
	287	for (i = 0; i < todo; i++)
	288	free_swap_cache(pagep[i]);
	289	release_pages(pagep, todo, 0);
	290	pagep += todo;
	291	nr -= todo;
	292	}
	293	}
	294
	295	/*
	296	* Lookup a swap entry in the swap cache. A found page will be returned
	297	* unlocked and with its refcount incremented - we rely on the kernel
	298	* lock getting page table operations atomic even if we drop the page
	299	* lock before returning.
	300	*/
	301	struct page * lookup_swap_cache(swp_entry_t entry)
	302	{
	303	struct page *page;
	304
	305	page = find_get_page(&swapper_space, entry.val);
	306
	307	if (page)
	308	INC_CACHE_INFO(find_success);
	309
	310	INC_CACHE_INFO(find_total);
	311	return page;
	312	}
	313
	314	/*
	315	* Locate a page of swap in physical memory, reserving swap cache space
	316	* and reading the disk if it is not already cached.
	317	* A failure return means that either the page allocation failed or that
	318	* the swap entry is no longer in use.
	319	*/
	320	struct page *read_swap_cache_async(swp_entry_t entry,
	321	struct vm_area_struct *vma, unsigned long addr)
	322	{
	323	struct page found_page, new_page = NULL;
	324	int err;
	325
	326	do {
	327	/*
	328	* First check the swap cache. Since this is normally
	329	* called after lookup_swap_cache() failed, re-calling
	330	* that would confuse statistics.
	331	*/
	332	found_page = find_get_page(&swapper_space, entry.val);
	333	if (found_page)
	334	break;
	335
	336	/*
	337	* Get a new page to read into from swap.
	338	*/
	339	if (!new_page) {
769848c0 MG	340	new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE,
769848c0 MG	341	vma, addr);
1da177e4 LT	342	if (!new_page)
	343	break; /* Out of memory */
	344	}
	345
	346	/*
	347	* Associate the page with swap entry in the swap cache.
	348	* May fail (-ENOENT) if swap entry has been freed since
	349	* our caller observed it. May fail (-EEXIST) if there
	350	* is already a page associated with this entry in the
	351	* swap cache: added by a racing read_swap_cache_async,
	352	* or by try_to_swap_out (or shmem_writepage) re-using
	353	* the just freed swap entry for an existing page.
	354	* May fail (-ENOMEM) if radix-tree node allocation failed.
	355	*/
	356	err = add_to_swap_cache(new_page, entry);
	357	if (!err) {
	358	/*
	359	* Initiate read into locked page and return.
	360	*/
	361	lru_cache_add_active(new_page);
	362	swap_readpage(NULL, new_page);
	363	return new_page;
	364	}
	365	} while (err != -ENOENT && err != -ENOMEM);
	366
	367	if (new_page)
	368	page_cache_release(new_page);
	369	return found_page;
	370	}