[linux-2.6-block.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/mm.h>
#include <linux/gfp.h>
#include <linux/kernel_stat.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/init.h>
#include <linux/pagemap.h>
#include <linux/backing-dev.h>
#include <linux/blkdev.h>
#include <linux/pagevec.h>
#include <linux/migrate.h>
#include <linux/page_cgroup.h>

#include <asm/pgtable.h>

/*
 * swapper_space is a fiction, retained to simplify the path through
 * vmscan's shrink_page_list.
 */
static const struct address_space_operations swap_aops = {
	.writepage	= swap_writepage,
	.set_page_dirty	= swap_set_page_dirty,
	.migratepage	= migrate_page,
};

static struct backing_dev_info swap_backing_dev_info = {
	.name		= "swap",
	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED,
};

struct address_space swapper_spaces[MAX_SWAPFILES] = {
	[0 ... MAX_SWAPFILES - 1] = {
		.page_tree	= RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
		.a_ops		= &swap_aops,
		.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;

unsigned long total_swapcache_pages(void)
{
	int i;
	unsigned long ret = 0;

	for (i = 0; i < MAX_SWAPFILES; i++)
		ret += swapper_spaces[i].nrpages;
	return ret;
}

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  = %ldkB\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.
 */
static int __add_to_swap_cache(struct page *page, swp_entry_t entry)
{
	int error;
	struct address_space *address_space;

	VM_BUG_ON(!PageLocked(page));
	VM_BUG_ON(PageSwapCache(page));
	VM_BUG_ON(!PageSwapBacked(page));

	page_cache_get(page);
	SetPageSwapCache(page);
	set_page_private(page, entry.val);

	address_space = swap_address_space(entry);
	spin_lock_irq(&address_space->tree_lock);
	error = radix_tree_insert(&address_space->page_tree,
					entry.val, page);
	if (likely(!error)) {
		address_space->nrpages++;
		__inc_zone_page_state(page, NR_FILE_PAGES);
		INC_CACHE_INFO(add_total);
	}
	spin_unlock_irq(&address_space->tree_lock);

	if (unlikely(error)) {
		/*
		 * Only the context which have set SWAP_HAS_CACHE flag
		 * would call add_to_swap_cache().
		 * So add_to_swap_cache() doesn't returns -EEXIST.
		 */
		VM_BUG_ON(error == -EEXIST);
		set_page_private(page, 0UL);
		ClearPageSwapCache(page);
		page_cache_release(page);
	}

	return error;
}


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

	error = radix_tree_preload(gfp_mask);
	if (!error) {
		error = __add_to_swap_cache(page, entry);
		radix_tree_preload_end();
	}
	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)
{
	swp_entry_t entry;
	struct address_space *address_space;

	VM_BUG_ON(!PageLocked(page));
	VM_BUG_ON(!PageSwapCache(page));
	VM_BUG_ON(PageWriteback(page));

	entry.val = page_private(page);
	address_space = swap_address_space(entry);
	radix_tree_delete(&address_space->page_tree, page_private(page));
	set_page_private(page, 0);
	ClearPageSwapCache(page);
	address_space->nrpages--;
	__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)
{
	swp_entry_t entry;
	int err;

	VM_BUG_ON(!PageLocked(page));
	VM_BUG_ON(!PageUptodate(page));

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

	if (unlikely(PageTransHuge(page)))
		if (unlikely(split_huge_page(page))) {
			swapcache_free(entry, NULL);
			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_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);

	if (!err) {	/* Success */
		SetPageDirty(page);
		return 1;
	} else {	/* -ENOMEM radix-tree allocation failure */
		/*
		 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
		 * clear SWAP_HAS_CACHE flag.
		 */
		swapcache_free(entry, NULL);
		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;
	struct address_space *address_space;

	entry.val = page_private(page);

	address_space = swap_address_space(entry);
	spin_lock_irq(&address_space->tree_lock);
	__delete_from_swap_cache(page);
	spin_unlock_irq(&address_space->tree_lock);

	swapcache_free(entry, page);
	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
 * try_to_free_swap() _with_ the lock.
 * 					- Marcelo
 */
static inline void free_swap_cache(struct page *page)
{
	if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
		try_to_free_swap(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(swap_address_space(entry), 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(swap_address_space(entry),
					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 */
		}

		/*
		 * call radix_tree_preload() while we can wait.
		 */
		err = radix_tree_preload(gfp_mask & GFP_KERNEL);
		if (err)
			break;

		/*
		 * Swap entry may have been freed since our caller observed it.
		 */
		err = swapcache_prepare(entry);
		if (err == -EEXIST) {	/* seems racy */
			radix_tree_preload_end();
			continue;
		}
		if (err) {		/* swp entry is obsolete ? */
			radix_tree_preload_end();
			break;
		}

		/* May fail (-ENOMEM) if radix-tree node allocation failed. */
		__set_page_locked(new_page);
		SetPageSwapBacked(new_page);
		err = __add_to_swap_cache(new_page, entry);
		if (likely(!err)) {
			radix_tree_preload_end();
			/*
			 * Initiate read into locked page and return.
			 */
			lru_cache_add_anon(new_page);
			swap_readpage(new_page);
			return new_page;
		}
		radix_tree_preload_end();
		ClearPageSwapBacked(new_page);
		__clear_page_locked(new_page);
		/*
		 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
		 * clear SWAP_HAS_CACHE flag.
		 */
		swapcache_free(entry, NULL);
	} 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)
{
	struct page *page;
	unsigned long offset = swp_offset(entry);
	unsigned long start_offset, end_offset;
	unsigned long mask = (1UL << page_cluster) - 1;
	struct blk_plug plug;

	/* Read a page_cluster sized and aligned cluster around offset. */
	start_offset = offset & ~mask;
	end_offset = offset | mask;
	if (!start_offset)	/* First page is swap header. */
		start_offset++;

	blk_start_plug(&plug);
	for (offset = start_offset; 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)
			continue;
		page_cache_release(page);
	}
	blk_finish_plug(&plug);

	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	*/
1da177e4	9	#include <linux/mm.h>
5a0e3ad6	10	#include <linux/gfp.h>
1da177e4 LT	11	#include <linux/kernel_stat.h>
1da177e4 LT	12	#include <linux/swap.h>
46017e95	13	#include <linux/swapops.h>
1da177e4 LT	14	#include <linux/init.h>
1da177e4 LT	15	#include <linux/pagemap.h>
1da177e4	16	#include <linux/backing-dev.h>
3fb5c298	17	#include <linux/blkdev.h>
c484d410	18	#include <linux/pagevec.h>
b20a3503	19	#include <linux/migrate.h>
8c7c6e34	20	#include <linux/page_cgroup.h>
1da177e4 LT	21
	22	#include <asm/pgtable.h>
	23
	24	/*
	25	* swapper_space is a fiction, retained to simplify the path through
7eaceacc	26	* vmscan's shrink_page_list.
1da177e4	27	*/
f5e54d6e	28	static const struct address_space_operations swap_aops = {
1da177e4	29	.writepage = swap_writepage,
62c230bc	30	.set_page_dirty = swap_set_page_dirty,
e965f963	31	.migratepage = migrate_page,
1da177e4 LT	32	};
	33
	34	static struct backing_dev_info swap_backing_dev_info = {
d993831f	35	.name = "swap",
4f98a2fe	36	.capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK \| BDI_CAP_SWAP_BACKED,
1da177e4 LT	37	};
1da177e4 LT	38
33806f06 SL	39	struct address_space swapper_spaces[MAX_SWAPFILES] = {
	40	[0 ... MAX_SWAPFILES - 1] = {
	41	.page_tree = RADIX_TREE_INIT(GFP_ATOMIC\|__GFP_NOWARN),
	42	.a_ops = &swap_aops,
	43	.backing_dev_info = &swap_backing_dev_info,
	44	}
1da177e4	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;
1da177e4 LT	54	} swap_cache_info;
1da177e4 LT	55
33806f06 SL	56	unsigned long total_swapcache_pages(void)
	57	{
	58	int i;
	59	unsigned long ret = 0;
	60
	61	for (i = 0; i < MAX_SWAPFILES; i++)
	62	ret += swapper_spaces[i].nrpages;
	63	return ret;
	64	}
	65
1da177e4 LT	66	void show_swap_cache_info(void)
1da177e4 LT	67	{
33806f06	68	printk("%lu pages in swap cache\n", total_swapcache_pages());
2c97b7fc	69	printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
1da177e4	70	swap_cache_info.add_total, swap_cache_info.del_total,
bb63be0a	71	swap_cache_info.find_success, swap_cache_info.find_total);
07279cdf	72	printk("Free swap = %ldkB\n", nr_swap_pages << (PAGE_SHIFT - 10));
1da177e4 LT	73	printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
	74	}
	75
	76	/*
31a56396	77	* __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
1da177e4 LT	78	* but sets SwapCache flag and private instead of mapping and index.
1da177e4 LT	79	*/
31a56396	80	static int __add_to_swap_cache(struct page *page, swp_entry_t entry)
1da177e4 LT	81	{
1da177e4 LT	82	int error;
33806f06	83	struct address_space *address_space;
1da177e4	84
51726b12 HD	85	VM_BUG_ON(!PageLocked(page));
	86	VM_BUG_ON(PageSwapCache(page));
	87	VM_BUG_ON(!PageSwapBacked(page));
	88
31a56396 DN	89	page_cache_get(page);
	90	SetPageSwapCache(page);
	91	set_page_private(page, entry.val);
	92
33806f06 SL	93	address_space = swap_address_space(entry);
	94	spin_lock_irq(&address_space->tree_lock);
	95	error = radix_tree_insert(&address_space->page_tree,
	96	entry.val, page);
31a56396	97	if (likely(!error)) {
33806f06	98	address_space->nrpages++;
31a56396 DN	99	__inc_zone_page_state(page, NR_FILE_PAGES);
	100	INC_CACHE_INFO(add_total);
	101	}
33806f06	102	spin_unlock_irq(&address_space->tree_lock);
31a56396 DN	103
31a56396 DN	104	if (unlikely(error)) {
2ca4532a DN	105	/*
	106	* Only the context which have set SWAP_HAS_CACHE flag
	107	* would call add_to_swap_cache().
	108	* So add_to_swap_cache() doesn't returns -EEXIST.
	109	*/
	110	VM_BUG_ON(error == -EEXIST);
31a56396 DN	111	set_page_private(page, 0UL);
	112	ClearPageSwapCache(page);
	113	page_cache_release(page);
	114	}
	115
	116	return error;
	117	}
	118
	119
	120	int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
	121	{
	122	int error;
	123
35c754d7 BS	124	error = radix_tree_preload(gfp_mask);
35c754d7 BS	125	if (!error) {
31a56396	126	error = __add_to_swap_cache(page, entry);
1da177e4	127	radix_tree_preload_end();
fa1de900	128	}
1da177e4 LT	129	return error;
	130	}
	131
1da177e4 LT	132	/*
	133	* This must be called only on pages that have
	134	* been verified to be in the swap cache.
	135	*/
	136	void __delete_from_swap_cache(struct page *page)
	137	{
33806f06 SL	138	swp_entry_t entry;
	139	struct address_space *address_space;
	140
51726b12 HD	141	VM_BUG_ON(!PageLocked(page));
	142	VM_BUG_ON(!PageSwapCache(page));
	143	VM_BUG_ON(PageWriteback(page));
1da177e4	144
33806f06 SL	145	entry.val = page_private(page);
	146	address_space = swap_address_space(entry);
	147	radix_tree_delete(&address_space->page_tree, page_private(page));
4c21e2f2	148	set_page_private(page, 0);
1da177e4	149	ClearPageSwapCache(page);
33806f06	150	address_space->nrpages--;
347ce434	151	__dec_zone_page_state(page, NR_FILE_PAGES);
1da177e4 LT	152	INC_CACHE_INFO(del_total);
	153	}
	154
	155	/**
	156	* add_to_swap - allocate swap space for a page
	157	* @page: page we want to move to swap
	158	*
	159	* Allocate swap space for the page and add the page to the
	160	* swap cache. Caller needs to hold the page lock.
	161	*/
ac47b003	162	int add_to_swap(struct page *page)
1da177e4 LT	163	{
1da177e4 LT	164	swp_entry_t entry;
1da177e4 LT	165	int err;
1da177e4 LT	166
51726b12 HD	167	VM_BUG_ON(!PageLocked(page));
51726b12 HD	168	VM_BUG_ON(!PageUptodate(page));
1da177e4	169
2ca4532a DN	170	entry = get_swap_page();
	171	if (!entry.val)
	172	return 0;
	173
3f04f62f AA	174	if (unlikely(PageTransHuge(page)))
	175	if (unlikely(split_huge_page(page))) {
	176	swapcache_free(entry, NULL);
	177	return 0;
	178	}
	179
2ca4532a DN	180	/*
	181	* Radix-tree node allocations from PF_MEMALLOC contexts could
	182	* completely exhaust the page allocator. __GFP_NOMEMALLOC
	183	* stops emergency reserves from being allocated.
	184	*
	185	* TODO: this could cause a theoretical memory reclaim
	186	* deadlock in the swap out path.
	187	*/
	188	/*
	189	* Add it to the swap cache and mark it dirty
	190	*/
	191	err = add_to_swap_cache(page, entry,
	192	__GFP_HIGH\|__GFP_NOMEMALLOC\|__GFP_NOWARN);
	193
	194	if (!err) { /* Success */
	195	SetPageDirty(page);
	196	return 1;
	197	} else { /* -ENOMEM radix-tree allocation failure */
bd53b714	198	/*
2ca4532a DN	199	* add_to_swap_cache() doesn't return -EEXIST, so we can safely
2ca4532a DN	200	* clear SWAP_HAS_CACHE flag.
1da177e4	201	*/
2ca4532a DN	202	swapcache_free(entry, NULL);
2ca4532a DN	203	return 0;
1da177e4 LT	204	}
	205	}
	206
	207	/*
	208	* This must be called only on pages that have
	209	* been verified to be in the swap cache and locked.
	210	* It will never put the page into the free list,
	211	* the caller has a reference on the page.
	212	*/
	213	void delete_from_swap_cache(struct page *page)
	214	{
	215	swp_entry_t entry;
33806f06	216	struct address_space *address_space;
1da177e4	217
4c21e2f2	218	entry.val = page_private(page);
1da177e4	219
33806f06 SL	220	address_space = swap_address_space(entry);
33806f06 SL	221	spin_lock_irq(&address_space->tree_lock);
1da177e4	222	__delete_from_swap_cache(page);
33806f06	223	spin_unlock_irq(&address_space->tree_lock);
1da177e4	224
cb4b86ba	225	swapcache_free(entry, page);
1da177e4 LT	226	page_cache_release(page);
	227	}
	228
1da177e4 LT	229	/*
	230	* If we are the only user, then try to free up the swap cache.
	231	*
	232	* Its ok to check for PageSwapCache without the page lock
a2c43eed HD	233	* here because we are going to recheck again inside
a2c43eed HD	234	* try_to_free_swap() _with_ the lock.
1da177e4 LT	235	* - Marcelo
	236	*/
	237	static inline void free_swap_cache(struct page *page)
	238	{
a2c43eed HD	239	if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
a2c43eed HD	240	try_to_free_swap(page);
1da177e4 LT	241	unlock_page(page);
	242	}
	243	}
	244
	245	/*
	246	* Perform a free_page(), also freeing any swap cache associated with
b8072f09	247	* this page if it is the last user of the page.
1da177e4 LT	248	*/
	249	void free_page_and_swap_cache(struct page *page)
	250	{
	251	free_swap_cache(page);
	252	page_cache_release(page);
	253	}
	254
	255	/*
	256	* Passed an array of pages, drop them all from swapcache and then release
	257	* them. They are removed from the LRU and freed if this is their last use.
	258	*/
	259	void free_pages_and_swap_cache(struct page **pages, int nr)
	260	{
1da177e4 LT	261	struct page **pagep = pages;
	262
	263	lru_add_drain();
	264	while (nr) {
c484d410	265	int todo = min(nr, PAGEVEC_SIZE);
1da177e4 LT	266	int i;
	267
	268	for (i = 0; i < todo; i++)
	269	free_swap_cache(pagep[i]);
	270	release_pages(pagep, todo, 0);
	271	pagep += todo;
	272	nr -= todo;
	273	}
	274	}
	275
	276	/*
	277	* Lookup a swap entry in the swap cache. A found page will be returned
	278	* unlocked and with its refcount incremented - we rely on the kernel
	279	* lock getting page table operations atomic even if we drop the page
	280	* lock before returning.
	281	*/
	282	struct page * lookup_swap_cache(swp_entry_t entry)
	283	{
	284	struct page *page;
	285
33806f06	286	page = find_get_page(swap_address_space(entry), entry.val);
1da177e4 LT	287
	288	if (page)
	289	INC_CACHE_INFO(find_success);
	290
	291	INC_CACHE_INFO(find_total);
	292	return page;
	293	}
	294
	295	/*
	296	* Locate a page of swap in physical memory, reserving swap cache space
	297	* and reading the disk if it is not already cached.
	298	* A failure return means that either the page allocation failed or that
	299	* the swap entry is no longer in use.
	300	*/
02098fea	301	struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
1da177e4 LT	302	struct vm_area_struct *vma, unsigned long addr)
	303	{
	304	struct page found_page, new_page = NULL;
	305	int err;
	306
	307	do {
	308	/*
	309	* First check the swap cache. Since this is normally
	310	* called after lookup_swap_cache() failed, re-calling
	311	* that would confuse statistics.
	312	*/
33806f06 SL	313	found_page = find_get_page(swap_address_space(entry),
33806f06 SL	314	entry.val);
1da177e4 LT	315	if (found_page)
	316	break;
	317
	318	/*
	319	* Get a new page to read into from swap.
	320	*/
	321	if (!new_page) {
02098fea	322	new_page = alloc_page_vma(gfp_mask, vma, addr);
1da177e4 LT	323	if (!new_page)
	324	break; /* Out of memory */
	325	}
	326
31a56396 DN	327	/*
	328	* call radix_tree_preload() while we can wait.
	329	*/
	330	err = radix_tree_preload(gfp_mask & GFP_KERNEL);
	331	if (err)
	332	break;
	333
f000944d HD	334	/*
	335	* Swap entry may have been freed since our caller observed it.
	336	*/
355cfa73	337	err = swapcache_prepare(entry);
31a56396 DN	338	if (err == -EEXIST) { /* seems racy */
31a56396 DN	339	radix_tree_preload_end();
355cfa73	340	continue;
31a56396 DN	341	}
	342	if (err) { /* swp entry is obsolete ? */
	343	radix_tree_preload_end();
f000944d	344	break;
31a56396	345	}
f000944d	346
2ca4532a	347	/* May fail (-ENOMEM) if radix-tree node allocation failed. */
f45840b5	348	__set_page_locked(new_page);
b2e18538	349	SetPageSwapBacked(new_page);
31a56396	350	err = __add_to_swap_cache(new_page, entry);
529ae9aa	351	if (likely(!err)) {
31a56396	352	radix_tree_preload_end();
1da177e4 LT	353	/*
	354	* Initiate read into locked page and return.
	355	*/
c5fdae46	356	lru_cache_add_anon(new_page);
aca8bf32	357	swap_readpage(new_page);
1da177e4 LT	358	return new_page;
1da177e4 LT	359	}
31a56396	360	radix_tree_preload_end();
b2e18538	361	ClearPageSwapBacked(new_page);
f45840b5	362	__clear_page_locked(new_page);
2ca4532a DN	363	/*
	364	* add_to_swap_cache() doesn't return -EEXIST, so we can safely
	365	* clear SWAP_HAS_CACHE flag.
	366	*/
cb4b86ba	367	swapcache_free(entry, NULL);
f000944d	368	} while (err != -ENOMEM);
1da177e4 LT	369
	370	if (new_page)
	371	page_cache_release(new_page);
	372	return found_page;
	373	}
46017e95 HD	374
	375	/**
	376	* swapin_readahead - swap in pages in hope we need them soon
	377	* @entry: swap entry of this memory
7682486b	378	* @gfp_mask: memory allocation flags
46017e95 HD	379	* @vma: user vma this address belongs to
	380	* @addr: target address for mempolicy
	381	*
	382	* Returns the struct page for entry and addr, after queueing swapin.
	383	*
	384	* Primitive swap readahead code. We simply read an aligned block of
	385	* (1 << page_cluster) entries in the swap area. This method is chosen
	386	* because it doesn't cost us any seek time. We also make sure to queue
	387	* the 'original' request together with the readahead ones...
	388	*
	389	* This has been extended to use the NUMA policies from the mm triggering
	390	* the readahead.
	391	*
	392	* Caller must hold down_read on the vma->vm_mm if vma is not NULL.
	393	*/
02098fea	394	struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
46017e95 HD	395	struct vm_area_struct *vma, unsigned long addr)
46017e95 HD	396	{
46017e95	397	struct page *page;
67f96aa2 RR	398	unsigned long offset = swp_offset(entry);
	399	unsigned long start_offset, end_offset;
	400	unsigned long mask = (1UL << page_cluster) - 1;
3fb5c298	401	struct blk_plug plug;
46017e95	402
67f96aa2 RR	403	/* Read a page_cluster sized and aligned cluster around offset. */
	404	start_offset = offset & ~mask;
	405	end_offset = offset \| mask;
	406	if (!start_offset) /* First page is swap header. */
	407	start_offset++;
	408
3fb5c298	409	blk_start_plug(&plug);
67f96aa2	410	for (offset = start_offset; offset <= end_offset ; offset++) {
46017e95 HD	411	/* Ok, do the async read-ahead now */
46017e95 HD	412	page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
02098fea	413	gfp_mask, vma, addr);
46017e95	414	if (!page)
67f96aa2	415	continue;
46017e95 HD	416	page_cache_release(page);
46017e95 HD	417	}
3fb5c298 CE	418	blk_finish_plug(&plug);
3fb5c298 CE	419
46017e95	420	lru_add_drain(); /* Push any new pages onto the LRU now */
02098fea	421	return read_swap_cache_async(entry, gfp_mask, vma, addr);
46017e95	422	}