blob: b52635601dfe0054ea4a4eddbba6317b71e93272 [file] [log] [blame]
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>
13#include <linux/init.h>
14#include <linux/pagemap.h>
15#include <linux/buffer_head.h>
16#include <linux/backing-dev.h>
Hugh Dickinsc484d412006-01-06 00:10:55 -080017#include <linux/pagevec.h>
Christoph Lameterb20a3502006-03-22 00:09:12 -080018#include <linux/migrate.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070019
20#include <asm/pgtable.h>
21
22/*
23 * swapper_space is a fiction, retained to simplify the path through
Anderson Briglia2706a1b2007-07-15 23:38:09 -070024 * vmscan's shrink_page_list, to make sync_page look nicer, and to allow
Linus Torvalds1da177e2005-04-16 15:20:36 -070025 * future use of radix_tree tags in the swap cache.
26 */
Christoph Hellwigf5e54d62006-06-28 04:26:44 -070027static const struct address_space_operations swap_aops = {
Linus Torvalds1da177e2005-04-16 15:20:36 -070028 .writepage = swap_writepage,
29 .sync_page = block_sync_page,
30 .set_page_dirty = __set_page_dirty_nobuffers,
Christoph Lametere965f962006-02-01 03:05:41 -080031 .migratepage = migrate_page,
Linus Torvalds1da177e2005-04-16 15:20:36 -070032};
33
34static 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
39struct address_space swapper_space = {
40 .page_tree = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
Ingo Molnare4d91912006-07-03 00:24:34 -070041 .tree_lock = __RW_LOCK_UNLOCKED(swapper_space.tree_lock),
Linus Torvalds1da177e2005-04-16 15:20:36 -070042 .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};
Linus Torvalds1da177e2005-04-16 15:20:36 -070046
47#define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0)
48
49static 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
58void 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 */
Victor Fusco9de75d12005-09-10 00:26:46 -070072static int __add_to_swap_cache(struct page *page, swp_entry_t entry,
Al Virodd0fc662005-10-07 07:46:04 +010073 gfp_t gfp_mask)
Linus Torvalds1da177e2005-04-16 15:20:36 -070074{
75 int error;
76
Nick Pigginb55ed812007-10-16 01:24:42 -070077 BUG_ON(!PageLocked(page));
Linus Torvalds1da177e2005-04-16 15:20:36 -070078 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);
Linus Torvalds1da177e2005-04-16 15:20:36 -070087 SetPageSwapCache(page);
Hugh Dickins4c21e2f2005-10-29 18:16:40 -070088 set_page_private(page, entry.val);
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);
Linus Torvalds1da177e2005-04-16 15:20:36 -070091 }
92 write_unlock_irq(&swapper_space.tree_lock);
93 radix_tree_preload_end();
94 }
95 return error;
96}
97
98static int add_to_swap_cache(struct page *page, swp_entry_t entry)
99{
100 int error;
101
Nick Pigginb55ed812007-10-16 01:24:42 -0700102 BUG_ON(PageLocked(page));
Linus Torvalds1da177e2005-04-16 15:20:36 -0700103 if (!swap_duplicate(entry)) {
104 INC_CACHE_INFO(noent_race);
105 return -ENOENT;
106 }
Nick Pigginb55ed812007-10-16 01:24:42 -0700107 SetPageLocked(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700108 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) {
Nick Pigginb55ed812007-10-16 01:24:42 -0700113 ClearPageLocked(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700114 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 */
127void __delete_from_swap_cache(struct page *page)
128{
129 BUG_ON(!PageLocked(page));
130 BUG_ON(!PageSwapCache(page));
131 BUG_ON(PageWriteback(page));
Hugh Dickins3279ffd2005-09-03 15:54:43 -0700132 BUG_ON(PagePrivate(page));
Linus Torvalds1da177e2005-04-16 15:20:36 -0700133
Hugh Dickins4c21e2f2005-10-29 18:16:40 -0700134 radix_tree_delete(&swapper_space.page_tree, page_private(page));
135 set_page_private(page, 0);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700136 ClearPageSwapCache(page);
137 total_swapcache_pages--;
Christoph Lameter347ce432006-06-30 01:55:35 -0700138 __dec_zone_page_state(page, NR_FILE_PAGES);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700139 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 */
Christoph Lameter1480a542006-01-08 01:00:53 -0800149int add_to_swap(struct page * page, gfp_t gfp_mask)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700150{
151 swp_entry_t entry;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700152 int err;
153
Eric Sesterhenne74ca2b2006-04-01 01:25:12 +0200154 BUG_ON(!PageLocked(page));
Linus Torvalds1da177e2005-04-16 15:20:36 -0700155
156 for (;;) {
157 entry = get_swap_page();
158 if (!entry.val)
159 return 0;
160
Nick Pigginbd53b712005-05-01 08:58:37 -0700161 /*
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.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700165 *
Nick Pigginbd53b712005-05-01 08:58:37 -0700166 * TODO: this could cause a theoretical memory reclaim
167 * deadlock in the swap out path.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700168 */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700169 /*
170 * Add it to the swap cache and mark it dirty
171 */
Nick Pigginbd53b712005-05-01 08:58:37 -0700172 err = __add_to_swap_cache(page, entry,
Christoph Lameter1480a542006-01-08 01:00:53 -0800173 gfp_mask|__GFP_NOMEMALLOC|__GFP_NOWARN);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700174
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 */
200void delete_from_swap_cache(struct page *page)
201{
202 swp_entry_t entry;
203
Hugh Dickins4c21e2f2005-10-29 18:16:40 -0700204 entry.val = page_private(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700205
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 */
217int 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 */
235int 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 */
256static 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
Hugh Dickinsb8072f02005-10-29 18:16:41 -0700266 * this page if it is the last user of the page.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700267 */
268void 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 */
278void free_pages_and_swap_cache(struct page **pages, int nr)
279{
Linus Torvalds1da177e2005-04-16 15:20:36 -0700280 struct page **pagep = pages;
281
282 lru_add_drain();
283 while (nr) {
Hugh Dickinsc484d412006-01-06 00:10:55 -0800284 int todo = min(nr, PAGEVEC_SIZE);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700285 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 */
301struct 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 */
320struct 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) {
Mel Gorman769848c2007-07-17 04:03:05 -0700340 new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE,
341 vma, addr);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700342 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}