blob: 0df9a57b1de84bca534a9f6cc0c32d1ddefb939a [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>
17
18#include <asm/pgtable.h>
19
20/*
21 * swapper_space is a fiction, retained to simplify the path through
22 * vmscan's shrink_list, to make sync_page look nicer, and to allow
23 * future use of radix_tree tags in the swap cache.
24 */
25static struct address_space_operations swap_aops = {
26 .writepage = swap_writepage,
27 .sync_page = block_sync_page,
28 .set_page_dirty = __set_page_dirty_nobuffers,
29};
30
31static struct backing_dev_info swap_backing_dev_info = {
32 .capabilities = BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
33 .unplug_io_fn = swap_unplug_io_fn,
34};
35
36struct address_space swapper_space = {
37 .page_tree = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
38 .tree_lock = RW_LOCK_UNLOCKED,
39 .a_ops = &swap_aops,
40 .i_mmap_nonlinear = LIST_HEAD_INIT(swapper_space.i_mmap_nonlinear),
41 .backing_dev_info = &swap_backing_dev_info,
42};
Linus Torvalds1da177e2005-04-16 15:20:36 -070043
44#define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0)
45
46static struct {
47 unsigned long add_total;
48 unsigned long del_total;
49 unsigned long find_success;
50 unsigned long find_total;
51 unsigned long noent_race;
52 unsigned long exist_race;
53} swap_cache_info;
54
55void show_swap_cache_info(void)
56{
57 printk("Swap cache: add %lu, delete %lu, find %lu/%lu, race %lu+%lu\n",
58 swap_cache_info.add_total, swap_cache_info.del_total,
59 swap_cache_info.find_success, swap_cache_info.find_total,
60 swap_cache_info.noent_race, swap_cache_info.exist_race);
61 printk("Free swap = %lukB\n", nr_swap_pages << (PAGE_SHIFT - 10));
62 printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
63}
64
65/*
66 * __add_to_swap_cache resembles add_to_page_cache on swapper_space,
67 * but sets SwapCache flag and private instead of mapping and index.
68 */
Victor Fusco9de75d12005-09-10 00:26:46 -070069static int __add_to_swap_cache(struct page *page, swp_entry_t entry,
Al Virodd0fc662005-10-07 07:46:04 +010070 gfp_t gfp_mask)
Linus Torvalds1da177e2005-04-16 15:20:36 -070071{
72 int error;
73
74 BUG_ON(PageSwapCache(page));
75 BUG_ON(PagePrivate(page));
76 error = radix_tree_preload(gfp_mask);
77 if (!error) {
78 write_lock_irq(&swapper_space.tree_lock);
79 error = radix_tree_insert(&swapper_space.page_tree,
80 entry.val, page);
81 if (!error) {
82 page_cache_get(page);
83 SetPageLocked(page);
84 SetPageSwapCache(page);
Hugh Dickins4c21e2f2005-10-29 18:16:40 -070085 set_page_private(page, entry.val);
Linus Torvalds1da177e2005-04-16 15:20:36 -070086 total_swapcache_pages++;
87 pagecache_acct(1);
88 }
89 write_unlock_irq(&swapper_space.tree_lock);
90 radix_tree_preload_end();
91 }
92 return error;
93}
94
95static int add_to_swap_cache(struct page *page, swp_entry_t entry)
96{
97 int error;
98
99 if (!swap_duplicate(entry)) {
100 INC_CACHE_INFO(noent_race);
101 return -ENOENT;
102 }
103 error = __add_to_swap_cache(page, entry, GFP_KERNEL);
104 /*
105 * Anon pages are already on the LRU, we don't run lru_cache_add here.
106 */
107 if (error) {
108 swap_free(entry);
109 if (error == -EEXIST)
110 INC_CACHE_INFO(exist_race);
111 return error;
112 }
113 INC_CACHE_INFO(add_total);
114 return 0;
115}
116
117/*
118 * This must be called only on pages that have
119 * been verified to be in the swap cache.
120 */
121void __delete_from_swap_cache(struct page *page)
122{
123 BUG_ON(!PageLocked(page));
124 BUG_ON(!PageSwapCache(page));
125 BUG_ON(PageWriteback(page));
Hugh Dickins3279ffd2005-09-03 15:54:43 -0700126 BUG_ON(PagePrivate(page));
Linus Torvalds1da177e2005-04-16 15:20:36 -0700127
Hugh Dickins4c21e2f2005-10-29 18:16:40 -0700128 radix_tree_delete(&swapper_space.page_tree, page_private(page));
129 set_page_private(page, 0);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700130 ClearPageSwapCache(page);
131 total_swapcache_pages--;
132 pagecache_acct(-1);
133 INC_CACHE_INFO(del_total);
134}
135
136/**
137 * add_to_swap - allocate swap space for a page
138 * @page: page we want to move to swap
139 *
140 * Allocate swap space for the page and add the page to the
141 * swap cache. Caller needs to hold the page lock.
142 */
143int add_to_swap(struct page * page)
144{
145 swp_entry_t entry;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700146 int err;
147
148 if (!PageLocked(page))
149 BUG();
150
151 for (;;) {
152 entry = get_swap_page();
153 if (!entry.val)
154 return 0;
155
Nick Pigginbd53b712005-05-01 08:58:37 -0700156 /*
157 * Radix-tree node allocations from PF_MEMALLOC contexts could
158 * completely exhaust the page allocator. __GFP_NOMEMALLOC
159 * stops emergency reserves from being allocated.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700160 *
Nick Pigginbd53b712005-05-01 08:58:37 -0700161 * TODO: this could cause a theoretical memory reclaim
162 * deadlock in the swap out path.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700163 */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700164 /*
165 * Add it to the swap cache and mark it dirty
166 */
Nick Pigginbd53b712005-05-01 08:58:37 -0700167 err = __add_to_swap_cache(page, entry,
168 GFP_ATOMIC|__GFP_NOMEMALLOC|__GFP_NOWARN);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700169
170 switch (err) {
171 case 0: /* Success */
172 SetPageUptodate(page);
173 SetPageDirty(page);
174 INC_CACHE_INFO(add_total);
175 return 1;
176 case -EEXIST:
177 /* Raced with "speculative" read_swap_cache_async */
178 INC_CACHE_INFO(exist_race);
179 swap_free(entry);
180 continue;
181 default:
182 /* -ENOMEM radix-tree allocation failure */
183 swap_free(entry);
184 return 0;
185 }
186 }
187}
188
189/*
190 * This must be called only on pages that have
191 * been verified to be in the swap cache and locked.
192 * It will never put the page into the free list,
193 * the caller has a reference on the page.
194 */
195void delete_from_swap_cache(struct page *page)
196{
197 swp_entry_t entry;
198
Hugh Dickins4c21e2f2005-10-29 18:16:40 -0700199 entry.val = page_private(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700200
201 write_lock_irq(&swapper_space.tree_lock);
202 __delete_from_swap_cache(page);
203 write_unlock_irq(&swapper_space.tree_lock);
204
205 swap_free(entry);
206 page_cache_release(page);
207}
208
209/*
210 * Strange swizzling function only for use by shmem_writepage
211 */
212int move_to_swap_cache(struct page *page, swp_entry_t entry)
213{
214 int err = __add_to_swap_cache(page, entry, GFP_ATOMIC);
215 if (!err) {
216 remove_from_page_cache(page);
217 page_cache_release(page); /* pagecache ref */
218 if (!swap_duplicate(entry))
219 BUG();
220 SetPageDirty(page);
221 INC_CACHE_INFO(add_total);
222 } else if (err == -EEXIST)
223 INC_CACHE_INFO(exist_race);
224 return err;
225}
226
227/*
228 * Strange swizzling function for shmem_getpage (and shmem_unuse)
229 */
230int move_from_swap_cache(struct page *page, unsigned long index,
231 struct address_space *mapping)
232{
233 int err = add_to_page_cache(page, mapping, index, GFP_ATOMIC);
234 if (!err) {
235 delete_from_swap_cache(page);
236 /* shift page from clean_pages to dirty_pages list */
237 ClearPageDirty(page);
238 set_page_dirty(page);
239 }
240 return err;
241}
242
243/*
244 * If we are the only user, then try to free up the swap cache.
245 *
246 * Its ok to check for PageSwapCache without the page lock
247 * here because we are going to recheck again inside
248 * exclusive_swap_page() _with_ the lock.
249 * - Marcelo
250 */
251static inline void free_swap_cache(struct page *page)
252{
253 if (PageSwapCache(page) && !TestSetPageLocked(page)) {
254 remove_exclusive_swap_page(page);
255 unlock_page(page);
256 }
257}
258
259/*
260 * Perform a free_page(), also freeing any swap cache associated with
Hugh Dickinsb8072f02005-10-29 18:16:41 -0700261 * this page if it is the last user of the page.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700262 */
263void free_page_and_swap_cache(struct page *page)
264{
265 free_swap_cache(page);
266 page_cache_release(page);
267}
268
269/*
270 * Passed an array of pages, drop them all from swapcache and then release
271 * them. They are removed from the LRU and freed if this is their last use.
272 */
273void free_pages_and_swap_cache(struct page **pages, int nr)
274{
275 int chunk = 16;
276 struct page **pagep = pages;
277
278 lru_add_drain();
279 while (nr) {
280 int todo = min(chunk, nr);
281 int i;
282
283 for (i = 0; i < todo; i++)
284 free_swap_cache(pagep[i]);
285 release_pages(pagep, todo, 0);
286 pagep += todo;
287 nr -= todo;
288 }
289}
290
291/*
292 * Lookup a swap entry in the swap cache. A found page will be returned
293 * unlocked and with its refcount incremented - we rely on the kernel
294 * lock getting page table operations atomic even if we drop the page
295 * lock before returning.
296 */
297struct page * lookup_swap_cache(swp_entry_t entry)
298{
299 struct page *page;
300
301 page = find_get_page(&swapper_space, entry.val);
302
303 if (page)
304 INC_CACHE_INFO(find_success);
305
306 INC_CACHE_INFO(find_total);
307 return page;
308}
309
310/*
311 * Locate a page of swap in physical memory, reserving swap cache space
312 * and reading the disk if it is not already cached.
313 * A failure return means that either the page allocation failed or that
314 * the swap entry is no longer in use.
315 */
316struct page *read_swap_cache_async(swp_entry_t entry,
317 struct vm_area_struct *vma, unsigned long addr)
318{
319 struct page *found_page, *new_page = NULL;
320 int err;
321
322 do {
323 /*
324 * First check the swap cache. Since this is normally
325 * called after lookup_swap_cache() failed, re-calling
326 * that would confuse statistics.
327 */
328 found_page = find_get_page(&swapper_space, entry.val);
329 if (found_page)
330 break;
331
332 /*
333 * Get a new page to read into from swap.
334 */
335 if (!new_page) {
336 new_page = alloc_page_vma(GFP_HIGHUSER, vma, addr);
337 if (!new_page)
338 break; /* Out of memory */
339 }
340
341 /*
342 * Associate the page with swap entry in the swap cache.
343 * May fail (-ENOENT) if swap entry has been freed since
344 * our caller observed it. May fail (-EEXIST) if there
345 * is already a page associated with this entry in the
346 * swap cache: added by a racing read_swap_cache_async,
347 * or by try_to_swap_out (or shmem_writepage) re-using
348 * the just freed swap entry for an existing page.
349 * May fail (-ENOMEM) if radix-tree node allocation failed.
350 */
351 err = add_to_swap_cache(new_page, entry);
352 if (!err) {
353 /*
354 * Initiate read into locked page and return.
355 */
356 lru_cache_add_active(new_page);
357 swap_readpage(NULL, new_page);
358 return new_page;
359 }
360 } while (err != -ENOENT && err != -ENOMEM);
361
362 if (new_page)
363 page_cache_release(new_page);
364 return found_page;
365}