[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/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 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,
	.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++;
			pagecache_acct(1);
		}
		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--;
	pagecache_acct(-1);
	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;

	if (!PageLocked(page))
		BUG();

	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	*/
	27	static struct address_space_operations swap_aops = {
	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),
	41	.tree_lock = RW_LOCK_UNLOCKED,
	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 LT	89	total_swapcache_pages++;
	90	pagecache_acct(1);
	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);
	134	total_swapcache_pages--;
	135	pagecache_acct(-1);
	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;
	150
	151	if (!PageLocked(page))
	152	BUG();
	153
	154	for (;;) {
	155	entry = get_swap_page();
	156	if (!entry.val)
	157	return 0;
	158
bd53b714 NP	159	/*
	160	* Radix-tree node allocations from PF_MEMALLOC contexts could
	161	* completely exhaust the page allocator. __GFP_NOMEMALLOC
	162	* stops emergency reserves from being allocated.
1da177e4	163	*
bd53b714 NP	164	* TODO: this could cause a theoretical memory reclaim
bd53b714 NP	165	* deadlock in the swap out path.
1da177e4	166	*/
1da177e4 LT	167	/*
	168	* Add it to the swap cache and mark it dirty
	169	*/
bd53b714	170	err = __add_to_swap_cache(page, entry,
1480a540	171	gfp_mask\|__GFP_NOMEMALLOC\|__GFP_NOWARN);
1da177e4 LT	172
	173	switch (err) {
	174	case 0: /* Success */
	175	SetPageUptodate(page);
	176	SetPageDirty(page);
	177	INC_CACHE_INFO(add_total);
	178	return 1;
	179	case -EEXIST:
	180	/* Raced with "speculative" read_swap_cache_async */
	181	INC_CACHE_INFO(exist_race);
	182	swap_free(entry);
	183	continue;
	184	default:
	185	/* -ENOMEM radix-tree allocation failure */
	186	swap_free(entry);
	187	return 0;
	188	}
	189	}
	190	}
	191
	192	/*
	193	* This must be called only on pages that have
	194	* been verified to be in the swap cache and locked.
	195	* It will never put the page into the free list,
	196	* the caller has a reference on the page.
	197	*/
	198	void delete_from_swap_cache(struct page *page)
	199	{
	200	swp_entry_t entry;
	201
4c21e2f2	202	entry.val = page_private(page);
1da177e4 LT	203
	204	write_lock_irq(&swapper_space.tree_lock);
	205	__delete_from_swap_cache(page);
	206	write_unlock_irq(&swapper_space.tree_lock);
	207
	208	swap_free(entry);
	209	page_cache_release(page);
	210	}
	211
	212	/*
	213	* Strange swizzling function only for use by shmem_writepage
	214	*/
	215	int move_to_swap_cache(struct page *page, swp_entry_t entry)
	216	{
	217	int err = __add_to_swap_cache(page, entry, GFP_ATOMIC);
	218	if (!err) {
	219	remove_from_page_cache(page);
	220	page_cache_release(page); /* pagecache ref */
	221	if (!swap_duplicate(entry))
	222	BUG();
	223	SetPageDirty(page);
	224	INC_CACHE_INFO(add_total);
	225	} else if (err == -EEXIST)
	226	INC_CACHE_INFO(exist_race);
	227	return err;
	228	}
	229
	230	/*
	231	* Strange swizzling function for shmem_getpage (and shmem_unuse)
	232	*/
	233	int move_from_swap_cache(struct page *page, unsigned long index,
	234	struct address_space *mapping)
	235	{
	236	int err = add_to_page_cache(page, mapping, index, GFP_ATOMIC);
	237	if (!err) {
	238	delete_from_swap_cache(page);
	239	/* shift page from clean_pages to dirty_pages list */
	240	ClearPageDirty(page);
	241	set_page_dirty(page);
	242	}
	243	return err;
	244	}
	245
	246	/*
	247	* If we are the only user, then try to free up the swap cache.
	248	*
	249	* Its ok to check for PageSwapCache without the page lock
	250	* here because we are going to recheck again inside
	251	* exclusive_swap_page() _with_ the lock.
	252	* - Marcelo
	253	*/
	254	static inline void free_swap_cache(struct page *page)
	255	{
	256	if (PageSwapCache(page) && !TestSetPageLocked(page)) {
	257	remove_exclusive_swap_page(page);
	258	unlock_page(page);
	259	}
	260	}
	261
	262	/*
	263	* Perform a free_page(), also freeing any swap cache associated with
b8072f09	264	* this page if it is the last user of the page.
1da177e4 LT	265	*/
	266	void free_page_and_swap_cache(struct page *page)
	267	{
	268	free_swap_cache(page);
	269	page_cache_release(page);
	270	}
	271
	272	/*
	273	* Passed an array of pages, drop them all from swapcache and then release
	274	* them. They are removed from the LRU and freed if this is their last use.
	275	*/
	276	void free_pages_and_swap_cache(struct page **pages, int nr)
	277	{
1da177e4 LT	278	struct page **pagep = pages;
	279
	280	lru_add_drain();
	281	while (nr) {
c484d410	282	int todo = min(nr, PAGEVEC_SIZE);
1da177e4 LT	283	int i;
	284
	285	for (i = 0; i < todo; i++)
	286	free_swap_cache(pagep[i]);
	287	release_pages(pagep, todo, 0);
	288	pagep += todo;
	289	nr -= todo;
	290	}
	291	}
	292
	293	/*
	294	* Lookup a swap entry in the swap cache. A found page will be returned
	295	* unlocked and with its refcount incremented - we rely on the kernel
	296	* lock getting page table operations atomic even if we drop the page
	297	* lock before returning.
	298	*/
	299	struct page * lookup_swap_cache(swp_entry_t entry)
	300	{
	301	struct page *page;
	302
	303	page = find_get_page(&swapper_space, entry.val);
	304
	305	if (page)
	306	INC_CACHE_INFO(find_success);
	307
	308	INC_CACHE_INFO(find_total);
	309	return page;
	310	}
	311
	312	/*
	313	* Locate a page of swap in physical memory, reserving swap cache space
	314	* and reading the disk if it is not already cached.
	315	* A failure return means that either the page allocation failed or that
	316	* the swap entry is no longer in use.
	317	*/
	318	struct page *read_swap_cache_async(swp_entry_t entry,
	319	struct vm_area_struct *vma, unsigned long addr)
	320	{
	321	struct page found_page, new_page = NULL;
	322	int err;
	323
	324	do {
	325	/*
	326	* First check the swap cache. Since this is normally
	327	* called after lookup_swap_cache() failed, re-calling
	328	* that would confuse statistics.
	329	*/
	330	found_page = find_get_page(&swapper_space, entry.val);
	331	if (found_page)
	332	break;
	333
	334	/*
	335	* Get a new page to read into from swap.
	336	*/
	337	if (!new_page) {
	338	new_page = alloc_page_vma(GFP_HIGHUSER, vma, addr);
	339	if (!new_page)
	340	break; /* Out of memory */
	341	}
	342
	343	/*
	344	* Associate the page with swap entry in the swap cache.
	345	* May fail (-ENOENT) if swap entry has been freed since
	346	* our caller observed it. May fail (-EEXIST) if there
347	* is already a page associated with this entry in the
348	* swap cache: added by a racing read_swap_cache_async,
349	* or by try_to_swap_out (or shmem_writepage) re-using
350	* the just freed swap entry for an existing page.
351	* May fail (-ENOMEM) if radix-tree node allocation failed.
352	*/
353	err = add_to_swap_cache(new_page, entry);
354	if (!err) {
355	/*
356	* Initiate read into locked page and return.
357	*/
358	lru_cache_add_active(new_page);
359	swap_readpage(NULL, new_page);
360	return new_page;
361	}
362	} while (err != -ENOENT && err != -ENOMEM);
363
364	if (new_page)
365	page_cache_release(new_page);
366	return found_page;
367	}