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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/gfp.h> |
12 | #include <linux/kernel_stat.h> |
13 | #include <linux/swap.h> |
14 | #include <linux/swapops.h> |
15 | #include <linux/init.h> |
16 | #include <linux/pagemap.h> |
17 | #include <linux/buffer_head.h> |
18 | #include <linux/backing-dev.h> |
19 | #include <linux/pagevec.h> |
20 | #include <linux/migrate.h> |
21 | #include <linux/page_cgroup.h> |
22 | |
23 | #include <asm/pgtable.h> |
24 | |
25 | /* |
26 | * swapper_space is a fiction, retained to simplify the path through |
27 | * vmscan's shrink_page_list, to make sync_page look nicer, and to allow |
28 | * future use of radix_tree tags in the swap cache. |
29 | */ |
30 | static const struct address_space_operations swap_aops = { |
31 | .writepage = swap_writepage, |
32 | .sync_page = block_sync_page, |
33 | .set_page_dirty = __set_page_dirty_nobuffers, |
34 | .migratepage = migrate_page, |
35 | }; |
36 | |
37 | static struct backing_dev_info swap_backing_dev_info = { |
38 | .name = "swap", |
39 | .capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED, |
40 | .unplug_io_fn = swap_unplug_io_fn, |
41 | }; |
42 | |
43 | struct address_space swapper_space = { |
44 | .page_tree = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN), |
45 | .tree_lock = __SPIN_LOCK_UNLOCKED(swapper_space.tree_lock), |
46 | .a_ops = &swap_aops, |
47 | .i_mmap_nonlinear = LIST_HEAD_INIT(swapper_space.i_mmap_nonlinear), |
48 | .backing_dev_info = &swap_backing_dev_info, |
49 | }; |
50 | |
51 | #define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0) |
52 | |
53 | static struct { |
54 | unsigned long add_total; |
55 | unsigned long del_total; |
56 | unsigned long find_success; |
57 | unsigned long find_total; |
58 | } swap_cache_info; |
59 | |
60 | void show_swap_cache_info(void) |
61 | { |
62 | printk("%lu pages in swap cache\n", total_swapcache_pages); |
63 | printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n", |
64 | swap_cache_info.add_total, swap_cache_info.del_total, |
65 | swap_cache_info.find_success, swap_cache_info.find_total); |
66 | printk("Free swap = %ldkB\n", nr_swap_pages << (PAGE_SHIFT - 10)); |
67 | printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10)); |
68 | } |
69 | |
70 | /* |
71 | * __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space, |
72 | * but sets SwapCache flag and private instead of mapping and index. |
73 | */ |
74 | static int __add_to_swap_cache(struct page *page, swp_entry_t entry) |
75 | { |
76 | int error; |
77 | |
78 | VM_BUG_ON(!PageLocked(page)); |
79 | VM_BUG_ON(PageSwapCache(page)); |
80 | VM_BUG_ON(!PageSwapBacked(page)); |
81 | |
82 | page_cache_get(page); |
83 | SetPageSwapCache(page); |
84 | set_page_private(page, entry.val); |
85 | |
86 | spin_lock_irq(&swapper_space.tree_lock); |
87 | error = radix_tree_insert(&swapper_space.page_tree, entry.val, page); |
88 | if (likely(!error)) { |
89 | total_swapcache_pages++; |
90 | __inc_zone_page_state(page, NR_FILE_PAGES); |
91 | INC_CACHE_INFO(add_total); |
92 | } |
93 | spin_unlock_irq(&swapper_space.tree_lock); |
94 | |
95 | if (unlikely(error)) { |
96 | /* |
97 | * Only the context which have set SWAP_HAS_CACHE flag |
98 | * would call add_to_swap_cache(). |
99 | * So add_to_swap_cache() doesn't returns -EEXIST. |
100 | */ |
101 | VM_BUG_ON(error == -EEXIST); |
102 | set_page_private(page, 0UL); |
103 | ClearPageSwapCache(page); |
104 | page_cache_release(page); |
105 | } |
106 | |
107 | return error; |
108 | } |
109 | |
110 | |
111 | int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask) |
112 | { |
113 | int error; |
114 | |
115 | error = radix_tree_preload(gfp_mask); |
116 | if (!error) { |
117 | error = __add_to_swap_cache(page, entry); |
118 | radix_tree_preload_end(); |
119 | } |
120 | return error; |
121 | } |
122 | |
123 | /* |
124 | * This must be called only on pages that have |
125 | * been verified to be in the swap cache. |
126 | */ |
127 | void __delete_from_swap_cache(struct page *page) |
128 | { |
129 | VM_BUG_ON(!PageLocked(page)); |
130 | VM_BUG_ON(!PageSwapCache(page)); |
131 | VM_BUG_ON(PageWriteback(page)); |
132 | |
133 | radix_tree_delete(&swapper_space.page_tree, page_private(page)); |
134 | set_page_private(page, 0); |
135 | ClearPageSwapCache(page); |
136 | total_swapcache_pages--; |
137 | __dec_zone_page_state(page, NR_FILE_PAGES); |
138 | INC_CACHE_INFO(del_total); |
139 | } |
140 | |
141 | /** |
142 | * add_to_swap - allocate swap space for a page |
143 | * @page: page we want to move to swap |
144 | * |
145 | * Allocate swap space for the page and add the page to the |
146 | * swap cache. Caller needs to hold the page lock. |
147 | */ |
148 | int add_to_swap(struct page *page) |
149 | { |
150 | swp_entry_t entry; |
151 | int err; |
152 | |
153 | VM_BUG_ON(!PageLocked(page)); |
154 | VM_BUG_ON(!PageUptodate(page)); |
155 | |
156 | entry = get_swap_page(); |
157 | if (!entry.val) |
158 | return 0; |
159 | |
160 | /* |
161 | * Radix-tree node allocations from PF_MEMALLOC contexts could |
162 | * completely exhaust the page allocator. __GFP_NOMEMALLOC |
163 | * stops emergency reserves from being allocated. |
164 | * |
165 | * TODO: this could cause a theoretical memory reclaim |
166 | * deadlock in the swap out path. |
167 | */ |
168 | /* |
169 | * Add it to the swap cache and mark it dirty |
170 | */ |
171 | err = add_to_swap_cache(page, entry, |
172 | __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN); |
173 | |
174 | if (!err) { /* Success */ |
175 | SetPageDirty(page); |
176 | return 1; |
177 | } else { /* -ENOMEM radix-tree allocation failure */ |
178 | /* |
179 | * add_to_swap_cache() doesn't return -EEXIST, so we can safely |
180 | * clear SWAP_HAS_CACHE flag. |
181 | */ |
182 | swapcache_free(entry, NULL); |
183 | return 0; |
184 | } |
185 | } |
186 | |
187 | /* |
188 | * This must be called only on pages that have |
189 | * been verified to be in the swap cache and locked. |
190 | * It will never put the page into the free list, |
191 | * the caller has a reference on the page. |
192 | */ |
193 | void delete_from_swap_cache(struct page *page) |
194 | { |
195 | swp_entry_t entry; |
196 | |
197 | entry.val = page_private(page); |
198 | |
199 | spin_lock_irq(&swapper_space.tree_lock); |
200 | __delete_from_swap_cache(page); |
201 | spin_unlock_irq(&swapper_space.tree_lock); |
202 | |
203 | swapcache_free(entry, page); |
204 | page_cache_release(page); |
205 | } |
206 | |
207 | /* |
208 | * If we are the only user, then try to free up the swap cache. |
209 | * |
210 | * Its ok to check for PageSwapCache without the page lock |
211 | * here because we are going to recheck again inside |
212 | * try_to_free_swap() _with_ the lock. |
213 | * - Marcelo |
214 | */ |
215 | static inline void free_swap_cache(struct page *page) |
216 | { |
217 | if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) { |
218 | try_to_free_swap(page); |
219 | unlock_page(page); |
220 | } |
221 | } |
222 | |
223 | /* |
224 | * Perform a free_page(), also freeing any swap cache associated with |
225 | * this page if it is the last user of the page. |
226 | */ |
227 | void free_page_and_swap_cache(struct page *page) |
228 | { |
229 | free_swap_cache(page); |
230 | page_cache_release(page); |
231 | } |
232 | |
233 | /* |
234 | * Passed an array of pages, drop them all from swapcache and then release |
235 | * them. They are removed from the LRU and freed if this is their last use. |
236 | */ |
237 | void free_pages_and_swap_cache(struct page **pages, int nr) |
238 | { |
239 | struct page **pagep = pages; |
240 | |
241 | lru_add_drain(); |
242 | while (nr) { |
243 | int todo = min(nr, PAGEVEC_SIZE); |
244 | int i; |
245 | |
246 | for (i = 0; i < todo; i++) |
247 | free_swap_cache(pagep[i]); |
248 | release_pages(pagep, todo, 0); |
249 | pagep += todo; |
250 | nr -= todo; |
251 | } |
252 | } |
253 | |
254 | /* |
255 | * Lookup a swap entry in the swap cache. A found page will be returned |
256 | * unlocked and with its refcount incremented - we rely on the kernel |
257 | * lock getting page table operations atomic even if we drop the page |
258 | * lock before returning. |
259 | */ |
260 | struct page * lookup_swap_cache(swp_entry_t entry) |
261 | { |
262 | struct page *page; |
263 | |
264 | page = find_get_page(&swapper_space, entry.val); |
265 | |
266 | if (page) |
267 | INC_CACHE_INFO(find_success); |
268 | |
269 | INC_CACHE_INFO(find_total); |
270 | return page; |
271 | } |
272 | |
273 | /* |
274 | * Locate a page of swap in physical memory, reserving swap cache space |
275 | * and reading the disk if it is not already cached. |
276 | * A failure return means that either the page allocation failed or that |
277 | * the swap entry is no longer in use. |
278 | */ |
279 | struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask, |
280 | struct vm_area_struct *vma, unsigned long addr) |
281 | { |
282 | struct page *found_page, *new_page = NULL; |
283 | int err; |
284 | |
285 | do { |
286 | /* |
287 | * First check the swap cache. Since this is normally |
288 | * called after lookup_swap_cache() failed, re-calling |
289 | * that would confuse statistics. |
290 | */ |
291 | found_page = find_get_page(&swapper_space, entry.val); |
292 | if (found_page) |
293 | break; |
294 | |
295 | /* |
296 | * Get a new page to read into from swap. |
297 | */ |
298 | if (!new_page) { |
299 | new_page = alloc_page_vma(gfp_mask, vma, addr); |
300 | if (!new_page) |
301 | break; /* Out of memory */ |
302 | } |
303 | |
304 | /* |
305 | * call radix_tree_preload() while we can wait. |
306 | */ |
307 | err = radix_tree_preload(gfp_mask & GFP_KERNEL); |
308 | if (err) |
309 | break; |
310 | |
311 | /* |
312 | * Swap entry may have been freed since our caller observed it. |
313 | */ |
314 | err = swapcache_prepare(entry); |
315 | if (err == -EEXIST) { /* seems racy */ |
316 | radix_tree_preload_end(); |
317 | continue; |
318 | } |
319 | if (err) { /* swp entry is obsolete ? */ |
320 | radix_tree_preload_end(); |
321 | break; |
322 | } |
323 | |
324 | /* May fail (-ENOMEM) if radix-tree node allocation failed. */ |
325 | __set_page_locked(new_page); |
326 | SetPageSwapBacked(new_page); |
327 | err = __add_to_swap_cache(new_page, entry); |
328 | if (likely(!err)) { |
329 | radix_tree_preload_end(); |
330 | /* |
331 | * Initiate read into locked page and return. |
332 | */ |
333 | lru_cache_add_anon(new_page); |
334 | swap_readpage(new_page); |
335 | return new_page; |
336 | } |
337 | radix_tree_preload_end(); |
338 | ClearPageSwapBacked(new_page); |
339 | __clear_page_locked(new_page); |
340 | /* |
341 | * add_to_swap_cache() doesn't return -EEXIST, so we can safely |
342 | * clear SWAP_HAS_CACHE flag. |
343 | */ |
344 | swapcache_free(entry, NULL); |
345 | } while (err != -ENOMEM); |
346 | |
347 | if (new_page) |
348 | page_cache_release(new_page); |
349 | return found_page; |
350 | } |
351 | |
352 | /** |
353 | * swapin_readahead - swap in pages in hope we need them soon |
354 | * @entry: swap entry of this memory |
355 | * @gfp_mask: memory allocation flags |
356 | * @vma: user vma this address belongs to |
357 | * @addr: target address for mempolicy |
358 | * |
359 | * Returns the struct page for entry and addr, after queueing swapin. |
360 | * |
361 | * Primitive swap readahead code. We simply read an aligned block of |
362 | * (1 << page_cluster) entries in the swap area. This method is chosen |
363 | * because it doesn't cost us any seek time. We also make sure to queue |
364 | * the 'original' request together with the readahead ones... |
365 | * |
366 | * This has been extended to use the NUMA policies from the mm triggering |
367 | * the readahead. |
368 | * |
369 | * Caller must hold down_read on the vma->vm_mm if vma is not NULL. |
370 | */ |
371 | struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask, |
372 | struct vm_area_struct *vma, unsigned long addr) |
373 | { |
374 | int nr_pages; |
375 | struct page *page; |
376 | unsigned long offset; |
377 | unsigned long end_offset; |
378 | |
379 | /* |
380 | * Get starting offset for readaround, and number of pages to read. |
381 | * Adjust starting address by readbehind (for NUMA interleave case)? |
382 | * No, it's very unlikely that swap layout would follow vma layout, |
383 | * more likely that neighbouring swap pages came from the same node: |
384 | * so use the same "addr" to choose the same node for each swap read. |
385 | */ |
386 | nr_pages = valid_swaphandles(entry, &offset); |
387 | for (end_offset = offset + nr_pages; offset < end_offset; offset++) { |
388 | /* Ok, do the async read-ahead now */ |
389 | page = read_swap_cache_async(swp_entry(swp_type(entry), offset), |
390 | gfp_mask, vma, addr); |
391 | if (!page) |
392 | break; |
393 | page_cache_release(page); |
394 | } |
395 | lru_add_drain(); /* Push any new pages onto the LRU now */ |
396 | return read_swap_cache_async(entry, gfp_mask, vma, addr); |
397 | } |
398 |
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