[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_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(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);
			SetPageLocked(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;

	if (!swap_duplicate(entry)) {
		INC_CACHE_INFO(noent_race);
		return -ENOENT;
	}
	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) {
		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, 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
	24	* vmscan's shrink_list, to make sync_page look nicer, and to allow
	25	* future use of radix_tree tags in the swap cache.
	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
	77	BUG_ON(PageSwapCache(page));
	78	BUG_ON(PagePrivate(page));
	79	error = radix_tree_preload(gfp_mask);
	80	if (!error) {
	81	write_lock_irq(&swapper_space.tree_lock);
	82	error = radix_tree_insert(&swapper_space.page_tree,
	83	entry.val, page);
	84	if (!error) {
	85	page_cache_get(page);
	86	SetPageLocked(page);
	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
	102	if (!swap_duplicate(entry)) {
	103	INC_CACHE_INFO(noent_race);
	104	return -ENOENT;
	105	}
	106	error = __add_to_swap_cache(page, entry, GFP_KERNEL);
	107	/*
	108	* Anon pages are already on the LRU, we don't run lru_cache_add here.
	109	*/
	110	if (error) {
	111	swap_free(entry);
	112	if (error == -EEXIST)
	113	INC_CACHE_INFO(exist_race);
	114	return error;
	115	}
	116	INC_CACHE_INFO(add_total);
	117	return 0;
	118	}
	119
	120	/*
	121	* This must be called only on pages that have
	122	* been verified to be in the swap cache.
	123	*/
	124	void __delete_from_swap_cache(struct page *page)
	125	{
	126	BUG_ON(!PageLocked(page));
	127	BUG_ON(!PageSwapCache(page));
	128	BUG_ON(PageWriteback(page));
3279ffd9	129	BUG_ON(PagePrivate(page));
1da177e4	130
4c21e2f2 HD	131	radix_tree_delete(&swapper_space.page_tree, page_private(page));
4c21e2f2 HD	132	set_page_private(page, 0);
1da177e4 LT	133	ClearPageSwapCache(page);
1da177e4 LT	134	total_swapcache_pages--;
347ce434	135	__dec_zone_page_state(page, NR_FILE_PAGES);
1da177e4 LT	136	INC_CACHE_INFO(del_total);
	137	}
	138
	139	/**
	140	* add_to_swap - allocate swap space for a page
	141	* @page: page we want to move to swap
	142	*
	143	* Allocate swap space for the page and add the page to the
	144	* swap cache. Caller needs to hold the page lock.
	145	*/
1480a540	146	int add_to_swap(struct page * page, gfp_t gfp_mask)
1da177e4 LT	147	{
1da177e4 LT	148	swp_entry_t entry;
1da177e4 LT	149	int err;
1da177e4 LT	150
e74ca2b4	151	BUG_ON(!PageLocked(page));
1da177e4 LT	152
	153	for (;;) {
	154	entry = get_swap_page();
	155	if (!entry.val)
	156	return 0;
	157
bd53b714 NP	158	/*
	159	* Radix-tree node allocations from PF_MEMALLOC contexts could
	160	* completely exhaust the page allocator. __GFP_NOMEMALLOC
	161	* stops emergency reserves from being allocated.
1da177e4	162	*
bd53b714 NP	163	* TODO: this could cause a theoretical memory reclaim
bd53b714 NP	164	* deadlock in the swap out path.
1da177e4	165	*/
1da177e4 LT	166	/*
	167	* Add it to the swap cache and mark it dirty
	168	*/
bd53b714	169	err = __add_to_swap_cache(page, entry,
1480a540	170	gfp_mask\|__GFP_NOMEMALLOC\|__GFP_NOWARN);
1da177e4 LT	171
	172	switch (err) {
	173	case 0: /* Success */
	174	SetPageUptodate(page);
	175	SetPageDirty(page);
	176	INC_CACHE_INFO(add_total);
	177	return 1;
	178	case -EEXIST:
	179	/* Raced with "speculative" read_swap_cache_async */
	180	INC_CACHE_INFO(exist_race);
	181	swap_free(entry);
	182	continue;
	183	default:
	184	/* -ENOMEM radix-tree allocation failure */
	185	swap_free(entry);
	186	return 0;
	187	}
	188	}
	189	}
	190
	191	/*
	192	* This must be called only on pages that have
	193	* been verified to be in the swap cache and locked.
	194	* It will never put the page into the free list,
	195	* the caller has a reference on the page.
	196	*/
	197	void delete_from_swap_cache(struct page *page)
	198	{
	199	swp_entry_t entry;
	200
4c21e2f2	201	entry.val = page_private(page);
1da177e4 LT	202
	203	write_lock_irq(&swapper_space.tree_lock);
	204	__delete_from_swap_cache(page);
	205	write_unlock_irq(&swapper_space.tree_lock);
	206
	207	swap_free(entry);
	208	page_cache_release(page);
	209	}
	210
	211	/*
	212	* Strange swizzling function only for use by shmem_writepage
	213	*/
	214	int move_to_swap_cache(struct page *page, swp_entry_t entry)
	215	{
	216	int err = __add_to_swap_cache(page, entry, GFP_ATOMIC);
	217	if (!err) {
	218	remove_from_page_cache(page);
	219	page_cache_release(page); /* pagecache ref */
	220	if (!swap_duplicate(entry))
	221	BUG();
	222	SetPageDirty(page);
	223	INC_CACHE_INFO(add_total);
	224	} else if (err == -EEXIST)
	225	INC_CACHE_INFO(exist_race);
	226	return err;
	227	}
	228
	229	/*
	230	* Strange swizzling function for shmem_getpage (and shmem_unuse)
	231	*/
	232	int move_from_swap_cache(struct page *page, unsigned long index,
	233	struct address_space *mapping)
	234	{
	235	int err = add_to_page_cache(page, mapping, index, GFP_ATOMIC);
	236	if (!err) {
	237	delete_from_swap_cache(page);
	238	/* shift page from clean_pages to dirty_pages list */
	239	ClearPageDirty(page);
	240	set_page_dirty(page);
	241	}
	242	return err;
	243	}
	244
	245	/*
	246	* If we are the only user, then try to free up the swap cache.
	247	*
	248	* Its ok to check for PageSwapCache without the page lock
	249	* here because we are going to recheck again inside
	250	* exclusive_swap_page() _with_ the lock.
	251	* - Marcelo
	252	*/
	253	static inline void free_swap_cache(struct page *page)
	254	{
	255	if (PageSwapCache(page) && !TestSetPageLocked(page)) {
	256	remove_exclusive_swap_page(page);
	257	unlock_page(page);
	258	}
	259	}
	260
	261	/*
	262	* Perform a free_page(), also freeing any swap cache associated with
b8072f09	263	* this page if it is the last user of the page.
1da177e4 LT	264	*/
	265	void free_page_and_swap_cache(struct page *page)
	266	{
	267	free_swap_cache(page);
	268	page_cache_release(page);
	269	}
	270
	271	/*
	272	* Passed an array of pages, drop them all from swapcache and then release
	273	* them. They are removed from the LRU and freed if this is their last use.
	274	*/
	275	void free_pages_and_swap_cache(struct page **pages, int nr)
	276	{
1da177e4 LT	277	struct page **pagep = pages;
	278
	279	lru_add_drain();
	280	while (nr) {
c484d410	281	int todo = min(nr, PAGEVEC_SIZE);
1da177e4 LT	282	int i;
	283
	284	for (i = 0; i < todo; i++)
	285	free_swap_cache(pagep[i]);
	286	release_pages(pagep, todo, 0);
	287	pagep += todo;
	288	nr -= todo;
	289	}
	290	}
	291
	292	/*
	293	* Lookup a swap entry in the swap cache. A found page will be returned
	294	* unlocked and with its refcount incremented - we rely on the kernel
	295	* lock getting page table operations atomic even if we drop the page
	296	* lock before returning.
	297	*/
	298	struct page * lookup_swap_cache(swp_entry_t entry)
	299	{
	300	struct page *page;
	301
	302	page = find_get_page(&swapper_space, entry.val);
	303
	304	if (page)
	305	INC_CACHE_INFO(find_success);
	306
	307	INC_CACHE_INFO(find_total);
	308	return page;
	309	}
	310
	311	/*
	312	* Locate a page of swap in physical memory, reserving swap cache space
	313	* and reading the disk if it is not already cached.
	314	* A failure return means that either the page allocation failed or that
	315	* the swap entry is no longer in use.
	316	*/
	317	struct page *read_swap_cache_async(swp_entry_t entry,
	318	struct vm_area_struct *vma, unsigned long addr)
	319	{
	320	struct page found_page, new_page = NULL;
	321	int err;
	322
	323	do {
	324	/*
	325	* First check the swap cache. Since this is normally
	326	* called after lookup_swap_cache() failed, re-calling
	327	* that would confuse statistics.
	328	*/
	329	found_page = find_get_page(&swapper_space, entry.val);
	330	if (found_page)
	331	break;
	332
	333	/*
	334	* Get a new page to read into from swap.
	335	*/
	336	if (!new_page) {
	337	new_page = alloc_page_vma(GFP_HIGHUSER, vma, addr);
	338	if (!new_page)
	339	break; /* Out of memory */
	340	}
	341
	342	/*
	343	* Associate the page with swap entry in the swap cache.
	344	* May fail (-ENOENT) if swap entry has been freed since
	345	* our caller observed it. May fail (-EEXIST) if there
346	* is already a page associated with this entry in the
347	* swap cache: added by a racing read_swap_cache_async,
348	* or by try_to_swap_out (or shmem_writepage) re-using
349	* the just freed swap entry for an existing page.
350	* May fail (-ENOMEM) if radix-tree node allocation failed.
351	*/
352	err = add_to_swap_cache(new_page, entry);
353	if (!err) {
354	/*
355	* Initiate read into locked page and return.
356	*/
357	lru_cache_add_active(new_page);
358	swap_readpage(NULL, new_page);
359	return new_page;
360	}
361	} while (err != -ENOENT && err != -ENOMEM);
362
363	if (new_page)
364	page_cache_release(new_page);
365	return found_page;
366	}