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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/swapops.h> | |
14 | #include <linux/init.h> | |
15 | #include <linux/pagemap.h> | |
16 | #include <linux/buffer_head.h> | |
17 | #include <linux/backing-dev.h> | |
18 | #include <linux/pagevec.h> | |
19 | #include <linux/migrate.h> | |
20 | #include <linux/page_cgroup.h> | |
21 | ||
22 | #include <asm/pgtable.h> | |
23 | ||
24 | /* | |
25 | * swapper_space is a fiction, retained to simplify the path through | |
26 | * vmscan's shrink_page_list, to make sync_page look nicer, and to allow | |
27 | * future use of radix_tree tags in the swap cache. | |
28 | */ | |
29 | static const struct address_space_operations swap_aops = { | |
30 | .writepage = swap_writepage, | |
31 | .sync_page = block_sync_page, | |
32 | .set_page_dirty = __set_page_dirty_nobuffers, | |
33 | .migratepage = migrate_page, | |
34 | }; | |
35 | ||
36 | static struct backing_dev_info swap_backing_dev_info = { | |
37 | .name = "swap", | |
38 | .capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED, | |
39 | .unplug_io_fn = swap_unplug_io_fn, | |
40 | }; | |
41 | ||
42 | struct address_space swapper_space = { | |
43 | .page_tree = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN), | |
44 | .tree_lock = __SPIN_LOCK_UNLOCKED(swapper_space.tree_lock), | |
45 | .a_ops = &swap_aops, | |
46 | .i_mmap_nonlinear = LIST_HEAD_INIT(swapper_space.i_mmap_nonlinear), | |
47 | .backing_dev_info = &swap_backing_dev_info, | |
48 | }; | |
49 | ||
50 | #define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0) | |
51 | ||
52 | static struct { | |
53 | unsigned long add_total; | |
54 | unsigned long del_total; | |
55 | unsigned long find_success; | |
56 | unsigned long find_total; | |
57 | } swap_cache_info; | |
58 | ||
59 | void show_swap_cache_info(void) | |
60 | { | |
61 | printk("%lu pages in swap cache\n", total_swapcache_pages); | |
62 | printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n", | |
63 | swap_cache_info.add_total, swap_cache_info.del_total, | |
64 | swap_cache_info.find_success, swap_cache_info.find_total); | |
65 | printk("Free swap = %ldkB\n", nr_swap_pages << (PAGE_SHIFT - 10)); | |
66 | printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10)); | |
67 | } | |
68 | ||
69 | /* | |
70 | * add_to_swap_cache resembles add_to_page_cache_locked on swapper_space, | |
71 | * but sets SwapCache flag and private instead of mapping and index. | |
72 | */ | |
73 | int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask) | |
74 | { | |
75 | int error; | |
76 | ||
77 | VM_BUG_ON(!PageLocked(page)); | |
78 | VM_BUG_ON(PageSwapCache(page)); | |
79 | VM_BUG_ON(!PageSwapBacked(page)); | |
80 | ||
81 | error = radix_tree_preload(gfp_mask); | |
82 | if (!error) { | |
83 | page_cache_get(page); | |
84 | SetPageSwapCache(page); | |
85 | set_page_private(page, entry.val); | |
86 | ||
87 | spin_lock_irq(&swapper_space.tree_lock); | |
88 | error = radix_tree_insert(&swapper_space.page_tree, | |
89 | entry.val, page); | |
90 | if (likely(!error)) { | |
91 | total_swapcache_pages++; | |
92 | __inc_zone_page_state(page, NR_FILE_PAGES); | |
93 | INC_CACHE_INFO(add_total); | |
94 | } | |
95 | spin_unlock_irq(&swapper_space.tree_lock); | |
96 | radix_tree_preload_end(); | |
97 | ||
98 | if (unlikely(error)) { | |
99 | set_page_private(page, 0UL); | |
100 | ClearPageSwapCache(page); | |
101 | page_cache_release(page); | |
102 | } | |
103 | } | |
104 | return error; | |
105 | } | |
106 | ||
107 | /* | |
108 | * This must be called only on pages that have | |
109 | * been verified to be in the swap cache. | |
110 | */ | |
111 | void __delete_from_swap_cache(struct page *page) | |
112 | { | |
113 | VM_BUG_ON(!PageLocked(page)); | |
114 | VM_BUG_ON(!PageSwapCache(page)); | |
115 | VM_BUG_ON(PageWriteback(page)); | |
116 | ||
117 | radix_tree_delete(&swapper_space.page_tree, page_private(page)); | |
118 | set_page_private(page, 0); | |
119 | ClearPageSwapCache(page); | |
120 | total_swapcache_pages--; | |
121 | __dec_zone_page_state(page, NR_FILE_PAGES); | |
122 | INC_CACHE_INFO(del_total); | |
123 | } | |
124 | ||
125 | /** | |
126 | * add_to_swap - allocate swap space for a page | |
127 | * @page: page we want to move to swap | |
128 | * | |
129 | * Allocate swap space for the page and add the page to the | |
130 | * swap cache. Caller needs to hold the page lock. | |
131 | */ | |
132 | int add_to_swap(struct page *page) | |
133 | { | |
134 | swp_entry_t entry; | |
135 | int err; | |
136 | ||
137 | VM_BUG_ON(!PageLocked(page)); | |
138 | VM_BUG_ON(!PageUptodate(page)); | |
139 | ||
140 | for (;;) { | |
141 | entry = get_swap_page(); | |
142 | if (!entry.val) | |
143 | return 0; | |
144 | ||
145 | /* | |
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. | |
149 | * | |
150 | * TODO: this could cause a theoretical memory reclaim | |
151 | * deadlock in the swap out path. | |
152 | */ | |
153 | /* | |
154 | * Add it to the swap cache and mark it dirty | |
155 | */ | |
156 | err = add_to_swap_cache(page, entry, | |
157 | __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN); | |
158 | ||
159 | switch (err) { | |
160 | case 0: /* Success */ | |
161 | SetPageDirty(page); | |
162 | return 1; | |
163 | case -EEXIST: | |
164 | /* Raced with "speculative" read_swap_cache_async */ | |
165 | swapcache_free(entry, NULL); | |
166 | continue; | |
167 | default: | |
168 | /* -ENOMEM radix-tree allocation failure */ | |
169 | swapcache_free(entry, NULL); | |
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 | */ | |
181 | void delete_from_swap_cache(struct page *page) | |
182 | { | |
183 | swp_entry_t entry; | |
184 | ||
185 | entry.val = page_private(page); | |
186 | ||
187 | spin_lock_irq(&swapper_space.tree_lock); | |
188 | __delete_from_swap_cache(page); | |
189 | spin_unlock_irq(&swapper_space.tree_lock); | |
190 | ||
191 | swapcache_free(entry, page); | |
192 | page_cache_release(page); | |
193 | } | |
194 | ||
195 | /* | |
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 | * try_to_free_swap() _with_ the lock. | |
201 | * - Marcelo | |
202 | */ | |
203 | static inline void free_swap_cache(struct page *page) | |
204 | { | |
205 | if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) { | |
206 | try_to_free_swap(page); | |
207 | unlock_page(page); | |
208 | } | |
209 | } | |
210 | ||
211 | /* | |
212 | * Perform a free_page(), also freeing any swap cache associated with | |
213 | * this page if it is the last user of the page. | |
214 | */ | |
215 | void 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 | */ | |
225 | void free_pages_and_swap_cache(struct page **pages, int nr) | |
226 | { | |
227 | struct page **pagep = pages; | |
228 | ||
229 | lru_add_drain(); | |
230 | while (nr) { | |
231 | int todo = min(nr, PAGEVEC_SIZE); | |
232 | 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 | */ | |
248 | struct 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 | */ | |
267 | struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask, | |
268 | 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) { | |
287 | new_page = alloc_page_vma(gfp_mask, vma, addr); | |
288 | if (!new_page) | |
289 | break; /* Out of memory */ | |
290 | } | |
291 | ||
292 | /* | |
293 | * Swap entry may have been freed since our caller observed it. | |
294 | */ | |
295 | err = swapcache_prepare(entry); | |
296 | if (err == -EEXIST) /* seems racy */ | |
297 | continue; | |
298 | if (err) /* swp entry is obsolete ? */ | |
299 | break; | |
300 | ||
301 | /* | |
302 | * Associate the page with swap entry in the swap cache. | |
303 | * May fail (-EEXIST) if there is already a page associated | |
304 | * with this entry in the swap cache: added by a racing | |
305 | * read_swap_cache_async, or add_to_swap or shmem_writepage | |
306 | * re-using the just freed swap entry for an existing page. | |
307 | * May fail (-ENOMEM) if radix-tree node allocation failed. | |
308 | */ | |
309 | __set_page_locked(new_page); | |
310 | SetPageSwapBacked(new_page); | |
311 | err = add_to_swap_cache(new_page, entry, gfp_mask & GFP_KERNEL); | |
312 | if (likely(!err)) { | |
313 | /* | |
314 | * Initiate read into locked page and return. | |
315 | */ | |
316 | lru_cache_add_anon(new_page); | |
317 | swap_readpage(new_page); | |
318 | return new_page; | |
319 | } | |
320 | ClearPageSwapBacked(new_page); | |
321 | __clear_page_locked(new_page); | |
322 | swapcache_free(entry, NULL); | |
323 | } while (err != -ENOMEM); | |
324 | ||
325 | if (new_page) | |
326 | page_cache_release(new_page); | |
327 | return found_page; | |
328 | } | |
329 | ||
330 | /** | |
331 | * swapin_readahead - swap in pages in hope we need them soon | |
332 | * @entry: swap entry of this memory | |
333 | * @gfp_mask: memory allocation flags | |
334 | * @vma: user vma this address belongs to | |
335 | * @addr: target address for mempolicy | |
336 | * | |
337 | * Returns the struct page for entry and addr, after queueing swapin. | |
338 | * | |
339 | * Primitive swap readahead code. We simply read an aligned block of | |
340 | * (1 << page_cluster) entries in the swap area. This method is chosen | |
341 | * because it doesn't cost us any seek time. We also make sure to queue | |
342 | * the 'original' request together with the readahead ones... | |
343 | * | |
344 | * This has been extended to use the NUMA policies from the mm triggering | |
345 | * the readahead. | |
346 | * | |
347 | * Caller must hold down_read on the vma->vm_mm if vma is not NULL. | |
348 | */ | |
349 | struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask, | |
350 | struct vm_area_struct *vma, unsigned long addr) | |
351 | { | |
352 | int nr_pages; | |
353 | struct page *page; | |
354 | unsigned long offset; | |
355 | unsigned long end_offset; | |
356 | ||
357 | /* | |
358 | * Get starting offset for readaround, and number of pages to read. | |
359 | * Adjust starting address by readbehind (for NUMA interleave case)? | |
360 | * No, it's very unlikely that swap layout would follow vma layout, | |
361 | * more likely that neighbouring swap pages came from the same node: | |
362 | * so use the same "addr" to choose the same node for each swap read. | |
363 | */ | |
364 | nr_pages = valid_swaphandles(entry, &offset); | |
365 | for (end_offset = offset + nr_pages; offset < end_offset; offset++) { | |
366 | /* Ok, do the async read-ahead now */ | |
367 | page = read_swap_cache_async(swp_entry(swp_type(entry), offset), | |
368 | gfp_mask, vma, addr); | |
369 | if (!page) | |
370 | break; | |
371 | page_cache_release(page); | |
372 | } | |
373 | lru_add_drain(); /* Push any new pages onto the LRU now */ | |
374 | return read_swap_cache_async(entry, gfp_mask, vma, addr); | |
375 | } |