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Linus Torvalds1da177e2005-04-16 15:20:36 -07001/*
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>
Hugh Dickins46017e92008-02-04 22:28:41 -080013#include <linux/swapops.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070014#include <linux/init.h>
15#include <linux/pagemap.h>
16#include <linux/buffer_head.h>
17#include <linux/backing-dev.h>
Hugh Dickinsc484d412006-01-06 00:10:55 -080018#include <linux/pagevec.h>
Christoph Lameterb20a3502006-03-22 00:09:12 -080019#include <linux/migrate.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070020
21#include <asm/pgtable.h>
22
23/*
24 * swapper_space is a fiction, retained to simplify the path through
Anderson Briglia2706a1b2007-07-15 23:38:09 -070025 * vmscan's shrink_page_list, to make sync_page look nicer, and to allow
Linus Torvalds1da177e2005-04-16 15:20:36 -070026 * future use of radix_tree tags in the swap cache.
27 */
Christoph Hellwigf5e54d62006-06-28 04:26:44 -070028static const struct address_space_operations swap_aops = {
Linus Torvalds1da177e2005-04-16 15:20:36 -070029 .writepage = swap_writepage,
30 .sync_page = block_sync_page,
31 .set_page_dirty = __set_page_dirty_nobuffers,
Christoph Lametere965f962006-02-01 03:05:41 -080032 .migratepage = migrate_page,
Linus Torvalds1da177e2005-04-16 15:20:36 -070033};
34
35static struct backing_dev_info swap_backing_dev_info = {
Rik van Riel4f98a2f2008-10-18 20:26:32 -070036 .capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED,
Linus Torvalds1da177e2005-04-16 15:20:36 -070037 .unplug_io_fn = swap_unplug_io_fn,
38};
39
40struct address_space swapper_space = {
41 .page_tree = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
Nick Piggin19fd6232008-07-25 19:45:32 -070042 .tree_lock = __SPIN_LOCK_UNLOCKED(swapper_space.tree_lock),
Linus Torvalds1da177e2005-04-16 15:20:36 -070043 .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};
Linus Torvalds1da177e2005-04-16 15:20:36 -070047
48#define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0)
49
50static struct {
51 unsigned long add_total;
52 unsigned long del_total;
53 unsigned long find_success;
54 unsigned long find_total;
Linus Torvalds1da177e2005-04-16 15:20:36 -070055} swap_cache_info;
56
57void show_swap_cache_info(void)
58{
Johannes Weiner2c97b7f2008-07-25 19:46:01 -070059 printk("%lu pages in swap cache\n", total_swapcache_pages);
60 printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
Linus Torvalds1da177e2005-04-16 15:20:36 -070061 swap_cache_info.add_total, swap_cache_info.del_total,
Hugh Dickinsbb63be02008-02-04 22:28:49 -080062 swap_cache_info.find_success, swap_cache_info.find_total);
Hugh Dickins07279cd2008-08-20 14:09:05 -070063 printk("Free swap = %ldkB\n", nr_swap_pages << (PAGE_SHIFT - 10));
Linus Torvalds1da177e2005-04-16 15:20:36 -070064 printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
65}
66
67/*
Nick Piggine2867812008-07-25 19:45:30 -070068 * add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
Linus Torvalds1da177e2005-04-16 15:20:36 -070069 * but sets SwapCache flag and private instead of mapping and index.
70 */
Hugh Dickins73b12622008-02-04 22:28:50 -080071int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
Linus Torvalds1da177e2005-04-16 15:20:36 -070072{
73 int error;
74
Nick Pigginb55ed812007-10-16 01:24:42 -070075 BUG_ON(!PageLocked(page));
Linus Torvalds1da177e2005-04-16 15:20:36 -070076 BUG_ON(PageSwapCache(page));
77 BUG_ON(PagePrivate(page));
Rik van Rielb2e18532008-10-18 20:26:30 -070078 BUG_ON(!PageSwapBacked(page));
Linus Torvalds1da177e2005-04-16 15:20:36 -070079 error = radix_tree_preload(gfp_mask);
80 if (!error) {
Nick Piggine2867812008-07-25 19:45:30 -070081 page_cache_get(page);
82 SetPageSwapCache(page);
83 set_page_private(page, entry.val);
84
Nick Piggin19fd6232008-07-25 19:45:32 -070085 spin_lock_irq(&swapper_space.tree_lock);
Linus Torvalds1da177e2005-04-16 15:20:36 -070086 error = radix_tree_insert(&swapper_space.page_tree,
87 entry.val, page);
Nick Piggine2867812008-07-25 19:45:30 -070088 if (likely(!error)) {
Linus Torvalds1da177e2005-04-16 15:20:36 -070089 total_swapcache_pages++;
Christoph Lameter347ce432006-06-30 01:55:35 -070090 __inc_zone_page_state(page, NR_FILE_PAGES);
Hugh Dickinsbb63be02008-02-04 22:28:49 -080091 INC_CACHE_INFO(add_total);
Linus Torvalds1da177e2005-04-16 15:20:36 -070092 }
Nick Piggin19fd6232008-07-25 19:45:32 -070093 spin_unlock_irq(&swapper_space.tree_lock);
Linus Torvalds1da177e2005-04-16 15:20:36 -070094 radix_tree_preload_end();
Nick Piggine2867812008-07-25 19:45:30 -070095
96 if (unlikely(error)) {
97 set_page_private(page, 0UL);
98 ClearPageSwapCache(page);
99 page_cache_release(page);
100 }
Hugh Dickinsfa1de902008-02-07 00:14:13 -0800101 }
Linus Torvalds1da177e2005-04-16 15:20:36 -0700102 return error;
103}
104
Linus Torvalds1da177e2005-04-16 15:20:36 -0700105/*
106 * This must be called only on pages that have
107 * been verified to be in the swap cache.
108 */
109void __delete_from_swap_cache(struct page *page)
110{
111 BUG_ON(!PageLocked(page));
112 BUG_ON(!PageSwapCache(page));
113 BUG_ON(PageWriteback(page));
Hugh Dickins3279ffd2005-09-03 15:54:43 -0700114 BUG_ON(PagePrivate(page));
Linus Torvalds1da177e2005-04-16 15:20:36 -0700115
Hugh Dickins4c21e2f2005-10-29 18:16:40 -0700116 radix_tree_delete(&swapper_space.page_tree, page_private(page));
117 set_page_private(page, 0);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700118 ClearPageSwapCache(page);
119 total_swapcache_pages--;
Christoph Lameter347ce432006-06-30 01:55:35 -0700120 __dec_zone_page_state(page, NR_FILE_PAGES);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700121 INC_CACHE_INFO(del_total);
122}
123
124/**
125 * add_to_swap - allocate swap space for a page
126 * @page: page we want to move to swap
Randy Dunlap76824862008-03-19 17:00:40 -0700127 * @gfp_mask: memory allocation flags
Linus Torvalds1da177e2005-04-16 15:20:36 -0700128 *
129 * Allocate swap space for the page and add the page to the
130 * swap cache. Caller needs to hold the page lock.
131 */
Christoph Lameter1480a542006-01-08 01:00:53 -0800132int add_to_swap(struct page * page, gfp_t gfp_mask)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700133{
134 swp_entry_t entry;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700135 int err;
136
Eric Sesterhenne74ca2b2006-04-01 01:25:12 +0200137 BUG_ON(!PageLocked(page));
Nick Piggin0ed361d2008-02-04 22:29:34 -0800138 BUG_ON(!PageUptodate(page));
Linus Torvalds1da177e2005-04-16 15:20:36 -0700139
140 for (;;) {
141 entry = get_swap_page();
142 if (!entry.val)
143 return 0;
144
Nick Pigginbd53b712005-05-01 08:58:37 -0700145 /*
146 * Radix-tree node allocations from PF_MEMALLOC contexts could
147 * completely exhaust the page allocator. __GFP_NOMEMALLOC
148 * stops emergency reserves from being allocated.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700149 *
Nick Pigginbd53b712005-05-01 08:58:37 -0700150 * TODO: this could cause a theoretical memory reclaim
151 * deadlock in the swap out path.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700152 */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700153 /*
154 * Add it to the swap cache and mark it dirty
155 */
Hugh Dickinsf0009442008-02-04 22:28:49 -0800156 err = add_to_swap_cache(page, entry,
Christoph Lameter1480a542006-01-08 01:00:53 -0800157 gfp_mask|__GFP_NOMEMALLOC|__GFP_NOWARN);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700158
159 switch (err) {
160 case 0: /* Success */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700161 SetPageDirty(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700162 return 1;
163 case -EEXIST:
164 /* Raced with "speculative" read_swap_cache_async */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700165 swap_free(entry);
166 continue;
167 default:
168 /* -ENOMEM radix-tree allocation failure */
169 swap_free(entry);
170 return 0;
171 }
172 }
173}
174
175/*
176 * This must be called only on pages that have
177 * been verified to be in the swap cache and locked.
178 * It will never put the page into the free list,
179 * the caller has a reference on the page.
180 */
181void delete_from_swap_cache(struct page *page)
182{
183 swp_entry_t entry;
184
Hugh Dickins4c21e2f2005-10-29 18:16:40 -0700185 entry.val = page_private(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700186
Nick Piggin19fd6232008-07-25 19:45:32 -0700187 spin_lock_irq(&swapper_space.tree_lock);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700188 __delete_from_swap_cache(page);
Nick Piggin19fd6232008-07-25 19:45:32 -0700189 spin_unlock_irq(&swapper_space.tree_lock);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700190
191 swap_free(entry);
192 page_cache_release(page);
193}
194
Linus Torvalds1da177e2005-04-16 15:20:36 -0700195/*
196 * If we are the only user, then try to free up the swap cache.
197 *
198 * Its ok to check for PageSwapCache without the page lock
199 * here because we are going to recheck again inside
200 * exclusive_swap_page() _with_ the lock.
201 * - Marcelo
202 */
203static inline void free_swap_cache(struct page *page)
204{
Nick Piggin529ae9a2008-08-02 12:01:03 +0200205 if (PageSwapCache(page) && trylock_page(page)) {
Linus Torvalds1da177e2005-04-16 15:20:36 -0700206 remove_exclusive_swap_page(page);
207 unlock_page(page);
208 }
209}
210
211/*
212 * Perform a free_page(), also freeing any swap cache associated with
Hugh Dickinsb8072f02005-10-29 18:16:41 -0700213 * this page if it is the last user of the page.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700214 */
215void free_page_and_swap_cache(struct page *page)
216{
217 free_swap_cache(page);
218 page_cache_release(page);
219}
220
221/*
222 * Passed an array of pages, drop them all from swapcache and then release
223 * them. They are removed from the LRU and freed if this is their last use.
224 */
225void free_pages_and_swap_cache(struct page **pages, int nr)
226{
Linus Torvalds1da177e2005-04-16 15:20:36 -0700227 struct page **pagep = pages;
228
229 lru_add_drain();
230 while (nr) {
Hugh Dickinsc484d412006-01-06 00:10:55 -0800231 int todo = min(nr, PAGEVEC_SIZE);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700232 int i;
233
234 for (i = 0; i < todo; i++)
235 free_swap_cache(pagep[i]);
236 release_pages(pagep, todo, 0);
237 pagep += todo;
238 nr -= todo;
239 }
240}
241
242/*
243 * Lookup a swap entry in the swap cache. A found page will be returned
244 * unlocked and with its refcount incremented - we rely on the kernel
245 * lock getting page table operations atomic even if we drop the page
246 * lock before returning.
247 */
248struct page * lookup_swap_cache(swp_entry_t entry)
249{
250 struct page *page;
251
252 page = find_get_page(&swapper_space, entry.val);
253
254 if (page)
255 INC_CACHE_INFO(find_success);
256
257 INC_CACHE_INFO(find_total);
258 return page;
259}
260
261/*
262 * Locate a page of swap in physical memory, reserving swap cache space
263 * and reading the disk if it is not already cached.
264 * A failure return means that either the page allocation failed or that
265 * the swap entry is no longer in use.
266 */
Hugh Dickins02098fe2008-02-04 22:28:42 -0800267struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
Linus Torvalds1da177e2005-04-16 15:20:36 -0700268 struct vm_area_struct *vma, unsigned long addr)
269{
270 struct page *found_page, *new_page = NULL;
271 int err;
272
273 do {
274 /*
275 * First check the swap cache. Since this is normally
276 * called after lookup_swap_cache() failed, re-calling
277 * that would confuse statistics.
278 */
279 found_page = find_get_page(&swapper_space, entry.val);
280 if (found_page)
281 break;
282
283 /*
284 * Get a new page to read into from swap.
285 */
286 if (!new_page) {
Hugh Dickins02098fe2008-02-04 22:28:42 -0800287 new_page = alloc_page_vma(gfp_mask, vma, addr);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700288 if (!new_page)
289 break; /* Out of memory */
290 }
291
292 /*
Hugh Dickinsf0009442008-02-04 22:28:49 -0800293 * Swap entry may have been freed since our caller observed it.
294 */
295 if (!swap_duplicate(entry))
296 break;
297
298 /*
Linus Torvalds1da177e2005-04-16 15:20:36 -0700299 * Associate the page with swap entry in the swap cache.
Hugh Dickinsf0009442008-02-04 22:28:49 -0800300 * May fail (-EEXIST) if there is already a page associated
301 * with this entry in the swap cache: added by a racing
302 * read_swap_cache_async, or add_to_swap or shmem_writepage
303 * re-using the just freed swap entry for an existing page.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700304 * May fail (-ENOMEM) if radix-tree node allocation failed.
305 */
Nick Piggin529ae9a2008-08-02 12:01:03 +0200306 set_page_locked(new_page);
Rik van Rielb2e18532008-10-18 20:26:30 -0700307 SetPageSwapBacked(new_page);
Hugh Dickinsf0009442008-02-04 22:28:49 -0800308 err = add_to_swap_cache(new_page, entry, gfp_mask & GFP_KERNEL);
Nick Piggin529ae9a2008-08-02 12:01:03 +0200309 if (likely(!err)) {
Linus Torvalds1da177e2005-04-16 15:20:36 -0700310 /*
311 * Initiate read into locked page and return.
312 */
Rik van Riel4f98a2f2008-10-18 20:26:32 -0700313 lru_cache_add_active_anon(new_page);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700314 swap_readpage(NULL, new_page);
315 return new_page;
316 }
Rik van Rielb2e18532008-10-18 20:26:30 -0700317 ClearPageSwapBacked(new_page);
Nick Piggin529ae9a2008-08-02 12:01:03 +0200318 clear_page_locked(new_page);
Hugh Dickinsf0009442008-02-04 22:28:49 -0800319 swap_free(entry);
320 } while (err != -ENOMEM);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700321
322 if (new_page)
323 page_cache_release(new_page);
324 return found_page;
325}
Hugh Dickins46017e92008-02-04 22:28:41 -0800326
327/**
328 * swapin_readahead - swap in pages in hope we need them soon
329 * @entry: swap entry of this memory
Randy Dunlap76824862008-03-19 17:00:40 -0700330 * @gfp_mask: memory allocation flags
Hugh Dickins46017e92008-02-04 22:28:41 -0800331 * @vma: user vma this address belongs to
332 * @addr: target address for mempolicy
333 *
334 * Returns the struct page for entry and addr, after queueing swapin.
335 *
336 * Primitive swap readahead code. We simply read an aligned block of
337 * (1 << page_cluster) entries in the swap area. This method is chosen
338 * because it doesn't cost us any seek time. We also make sure to queue
339 * the 'original' request together with the readahead ones...
340 *
341 * This has been extended to use the NUMA policies from the mm triggering
342 * the readahead.
343 *
344 * Caller must hold down_read on the vma->vm_mm if vma is not NULL.
345 */
Hugh Dickins02098fe2008-02-04 22:28:42 -0800346struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
Hugh Dickins46017e92008-02-04 22:28:41 -0800347 struct vm_area_struct *vma, unsigned long addr)
348{
349 int nr_pages;
350 struct page *page;
351 unsigned long offset;
352 unsigned long end_offset;
353
354 /*
355 * Get starting offset for readaround, and number of pages to read.
356 * Adjust starting address by readbehind (for NUMA interleave case)?
357 * No, it's very unlikely that swap layout would follow vma layout,
358 * more likely that neighbouring swap pages came from the same node:
359 * so use the same "addr" to choose the same node for each swap read.
360 */
361 nr_pages = valid_swaphandles(entry, &offset);
362 for (end_offset = offset + nr_pages; offset < end_offset; offset++) {
363 /* Ok, do the async read-ahead now */
364 page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
Hugh Dickins02098fe2008-02-04 22:28:42 -0800365 gfp_mask, vma, addr);
Hugh Dickins46017e92008-02-04 22:28:41 -0800366 if (!page)
367 break;
368 page_cache_release(page);
369 }
370 lru_add_drain(); /* Push any new pages onto the LRU now */
Hugh Dickins02098fe2008-02-04 22:28:42 -0800371 return read_swap_cache_async(entry, gfp_mask, vma, addr);
Hugh Dickins46017e92008-02-04 22:28:41 -0800372}