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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> | |
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 | */ | |
25 | static 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 | ||
31 | static 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 | ||
36 | struct 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 | }; | |
43 | EXPORT_SYMBOL(swapper_space); | |
44 | ||
45 | #define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0) | |
46 | ||
47 | static struct { | |
48 | unsigned long add_total; | |
49 | unsigned long del_total; | |
50 | unsigned long find_success; | |
51 | unsigned long find_total; | |
52 | unsigned long noent_race; | |
53 | unsigned long exist_race; | |
54 | } swap_cache_info; | |
55 | ||
56 | void show_swap_cache_info(void) | |
57 | { | |
58 | printk("Swap cache: add %lu, delete %lu, find %lu/%lu, race %lu+%lu\n", | |
59 | swap_cache_info.add_total, swap_cache_info.del_total, | |
60 | swap_cache_info.find_success, swap_cache_info.find_total, | |
61 | swap_cache_info.noent_race, swap_cache_info.exist_race); | |
62 | printk("Free swap = %lukB\n", nr_swap_pages << (PAGE_SHIFT - 10)); | |
63 | printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10)); | |
64 | } | |
65 | ||
66 | /* | |
67 | * __add_to_swap_cache resembles add_to_page_cache on swapper_space, | |
68 | * but sets SwapCache flag and private instead of mapping and index. | |
69 | */ | |
70 | static int __add_to_swap_cache(struct page *page, | |
71 | swp_entry_t entry, int gfp_mask) | |
72 | { | |
73 | int error; | |
74 | ||
75 | BUG_ON(PageSwapCache(page)); | |
76 | BUG_ON(PagePrivate(page)); | |
77 | error = radix_tree_preload(gfp_mask); | |
78 | if (!error) { | |
79 | write_lock_irq(&swapper_space.tree_lock); | |
80 | error = radix_tree_insert(&swapper_space.page_tree, | |
81 | entry.val, page); | |
82 | if (!error) { | |
83 | page_cache_get(page); | |
84 | SetPageLocked(page); | |
85 | SetPageSwapCache(page); | |
86 | page->private = entry.val; | |
87 | total_swapcache_pages++; | |
88 | pagecache_acct(1); | |
89 | } | |
90 | write_unlock_irq(&swapper_space.tree_lock); | |
91 | radix_tree_preload_end(); | |
92 | } | |
93 | return error; | |
94 | } | |
95 | ||
96 | static int add_to_swap_cache(struct page *page, swp_entry_t entry) | |
97 | { | |
98 | int error; | |
99 | ||
100 | if (!swap_duplicate(entry)) { | |
101 | INC_CACHE_INFO(noent_race); | |
102 | return -ENOENT; | |
103 | } | |
104 | error = __add_to_swap_cache(page, entry, GFP_KERNEL); | |
105 | /* | |
106 | * Anon pages are already on the LRU, we don't run lru_cache_add here. | |
107 | */ | |
108 | if (error) { | |
109 | swap_free(entry); | |
110 | if (error == -EEXIST) | |
111 | INC_CACHE_INFO(exist_race); | |
112 | return error; | |
113 | } | |
114 | INC_CACHE_INFO(add_total); | |
115 | return 0; | |
116 | } | |
117 | ||
118 | /* | |
119 | * This must be called only on pages that have | |
120 | * been verified to be in the swap cache. | |
121 | */ | |
122 | void __delete_from_swap_cache(struct page *page) | |
123 | { | |
124 | BUG_ON(!PageLocked(page)); | |
125 | BUG_ON(!PageSwapCache(page)); | |
126 | BUG_ON(PageWriteback(page)); | |
127 | ||
128 | radix_tree_delete(&swapper_space.page_tree, page->private); | |
129 | page->private = 0; | |
130 | 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 | */ | |
143 | int add_to_swap(struct page * page) | |
144 | { | |
145 | swp_entry_t entry; | |
1da177e4 LT |
146 | 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 | ||
bd53b714 NP |
156 | /* |
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. | |
1da177e4 | 160 | * |
bd53b714 NP |
161 | * TODO: this could cause a theoretical memory reclaim |
162 | * deadlock in the swap out path. | |
1da177e4 | 163 | */ |
1da177e4 LT |
164 | /* |
165 | * Add it to the swap cache and mark it dirty | |
166 | */ | |
bd53b714 NP |
167 | err = __add_to_swap_cache(page, entry, |
168 | GFP_ATOMIC|__GFP_NOMEMALLOC|__GFP_NOWARN); | |
1da177e4 LT |
169 | |
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 | */ | |
195 | void delete_from_swap_cache(struct page *page) | |
196 | { | |
197 | swp_entry_t entry; | |
198 | ||
199 | BUG_ON(!PageSwapCache(page)); | |
200 | BUG_ON(!PageLocked(page)); | |
201 | BUG_ON(PageWriteback(page)); | |
202 | BUG_ON(PagePrivate(page)); | |
203 | ||
204 | entry.val = page->private; | |
205 | ||
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 | */ | |
217 | int 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 | */ | |
235 | int 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 | */ | |
256 | static 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 | |
266 | * this page if it is the last user of the page. Can not do a lock_page, | |
267 | * as we are holding the page_table_lock spinlock. | |
268 | */ | |
269 | void free_page_and_swap_cache(struct page *page) | |
270 | { | |
271 | free_swap_cache(page); | |
272 | page_cache_release(page); | |
273 | } | |
274 | ||
275 | /* | |
276 | * Passed an array of pages, drop them all from swapcache and then release | |
277 | * them. They are removed from the LRU and freed if this is their last use. | |
278 | */ | |
279 | void free_pages_and_swap_cache(struct page **pages, int nr) | |
280 | { | |
281 | int chunk = 16; | |
282 | struct page **pagep = pages; | |
283 | ||
284 | lru_add_drain(); | |
285 | while (nr) { | |
286 | int todo = min(chunk, nr); | |
287 | int i; | |
288 | ||
289 | for (i = 0; i < todo; i++) | |
290 | free_swap_cache(pagep[i]); | |
291 | release_pages(pagep, todo, 0); | |
292 | pagep += todo; | |
293 | nr -= todo; | |
294 | } | |
295 | } | |
296 | ||
297 | /* | |
298 | * Lookup a swap entry in the swap cache. A found page will be returned | |
299 | * unlocked and with its refcount incremented - we rely on the kernel | |
300 | * lock getting page table operations atomic even if we drop the page | |
301 | * lock before returning. | |
302 | */ | |
303 | struct page * lookup_swap_cache(swp_entry_t entry) | |
304 | { | |
305 | struct page *page; | |
306 | ||
307 | page = find_get_page(&swapper_space, entry.val); | |
308 | ||
309 | if (page) | |
310 | INC_CACHE_INFO(find_success); | |
311 | ||
312 | INC_CACHE_INFO(find_total); | |
313 | return page; | |
314 | } | |
315 | ||
316 | /* | |
317 | * Locate a page of swap in physical memory, reserving swap cache space | |
318 | * and reading the disk if it is not already cached. | |
319 | * A failure return means that either the page allocation failed or that | |
320 | * the swap entry is no longer in use. | |
321 | */ | |
322 | struct page *read_swap_cache_async(swp_entry_t entry, | |
323 | struct vm_area_struct *vma, unsigned long addr) | |
324 | { | |
325 | struct page *found_page, *new_page = NULL; | |
326 | int err; | |
327 | ||
328 | do { | |
329 | /* | |
330 | * First check the swap cache. Since this is normally | |
331 | * called after lookup_swap_cache() failed, re-calling | |
332 | * that would confuse statistics. | |
333 | */ | |
334 | found_page = find_get_page(&swapper_space, entry.val); | |
335 | if (found_page) | |
336 | break; | |
337 | ||
338 | /* | |
339 | * Get a new page to read into from swap. | |
340 | */ | |
341 | if (!new_page) { | |
342 | new_page = alloc_page_vma(GFP_HIGHUSER, vma, addr); | |
343 | if (!new_page) | |
344 | break; /* Out of memory */ | |
345 | } | |
346 | ||
347 | /* | |
348 | * Associate the page with swap entry in the swap cache. | |
349 | * May fail (-ENOENT) if swap entry has been freed since | |
350 | * our caller observed it. May fail (-EEXIST) if there | |
351 | * is already a page associated with this entry in the | |
352 | * swap cache: added by a racing read_swap_cache_async, | |
353 | * or by try_to_swap_out (or shmem_writepage) re-using | |
354 | * the just freed swap entry for an existing page. | |
355 | * May fail (-ENOMEM) if radix-tree node allocation failed. | |
356 | */ | |
357 | err = add_to_swap_cache(new_page, entry); | |
358 | if (!err) { | |
359 | /* | |
360 | * Initiate read into locked page and return. | |
361 | */ | |
362 | lru_cache_add_active(new_page); | |
363 | swap_readpage(NULL, new_page); | |
364 | return new_page; | |
365 | } | |
366 | } while (err != -ENOENT && err != -ENOMEM); | |
367 | ||
368 | if (new_page) | |
369 | page_cache_release(new_page); | |
370 | return found_page; | |
371 | } |