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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. |
28 | */ |
29 | static const struct address_space_operations swap_aops = { |
30 | .writepage = swap_writepage, |
31 | .set_page_dirty = __set_page_dirty_nobuffers, |
32 | .migratepage = migrate_page, |
33 | }; |
34 | |
35 | static struct backing_dev_info swap_backing_dev_info = { |
36 | .name = "swap", |
37 | .capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED, |
38 | }; |
39 | |
40 | struct address_space swapper_space = { |
41 | .page_tree = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN), |
42 | .tree_lock = __SPIN_LOCK_UNLOCKED(swapper_space.tree_lock), |
43 | .a_ops = &swap_aops, |
44 | .i_mmap_nonlinear = LIST_HEAD_INIT(swapper_space.i_mmap_nonlinear), |
45 | .backing_dev_info = &swap_backing_dev_info, |
46 | }; |
47 | |
48 | #define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0) |
49 | |
50 | static struct { |
51 | unsigned long add_total; |
52 | unsigned long del_total; |
53 | unsigned long find_success; |
54 | unsigned long find_total; |
55 | } swap_cache_info; |
56 | |
57 | void show_swap_cache_info(void) |
58 | { |
59 | printk("%lu pages in swap cache\n", total_swapcache_pages); |
60 | printk("Swap cache stats: add %lu, delete %lu, find %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 | printk("Free swap = %ldkB\n", nr_swap_pages << (PAGE_SHIFT - 10)); |
64 | printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10)); |
65 | } |
66 | |
67 | /* |
68 | * __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space, |
69 | * but sets SwapCache flag and private instead of mapping and index. |
70 | */ |
71 | static int __add_to_swap_cache(struct page *page, swp_entry_t entry) |
72 | { |
73 | int error; |
74 | |
75 | VM_BUG_ON(!PageLocked(page)); |
76 | VM_BUG_ON(PageSwapCache(page)); |
77 | VM_BUG_ON(!PageSwapBacked(page)); |
78 | |
79 | page_cache_get(page); |
80 | SetPageSwapCache(page); |
81 | set_page_private(page, entry.val); |
82 | |
83 | spin_lock_irq(&swapper_space.tree_lock); |
84 | error = radix_tree_insert(&swapper_space.page_tree, entry.val, page); |
85 | if (likely(!error)) { |
86 | total_swapcache_pages++; |
87 | __inc_zone_page_state(page, NR_FILE_PAGES); |
88 | INC_CACHE_INFO(add_total); |
89 | } |
90 | spin_unlock_irq(&swapper_space.tree_lock); |
91 | |
92 | if (unlikely(error)) { |
93 | /* |
94 | * Only the context which have set SWAP_HAS_CACHE flag |
95 | * would call add_to_swap_cache(). |
96 | * So add_to_swap_cache() doesn't returns -EEXIST. |
97 | */ |
98 | VM_BUG_ON(error == -EEXIST); |
99 | set_page_private(page, 0UL); |
100 | ClearPageSwapCache(page); |
101 | page_cache_release(page); |
102 | } |
103 | |
104 | return error; |
105 | } |
106 | |
107 | |
108 | int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask) |
109 | { |
110 | int error; |
111 | |
112 | error = radix_tree_preload(gfp_mask); |
113 | if (!error) { |
114 | error = __add_to_swap_cache(page, entry); |
115 | radix_tree_preload_end(); |
116 | } |
117 | return error; |
118 | } |
119 | |
120 | /* |
121 | * This must be called only on pages that have |
122 | * been verified to be in the swap cache. |
123 | */ |
124 | void __delete_from_swap_cache(struct page *page) |
125 | { |
126 | VM_BUG_ON(!PageLocked(page)); |
127 | VM_BUG_ON(!PageSwapCache(page)); |
128 | VM_BUG_ON(PageWriteback(page)); |
129 | |
130 | radix_tree_delete(&swapper_space.page_tree, page_private(page)); |
131 | set_page_private(page, 0); |
132 | ClearPageSwapCache(page); |
133 | total_swapcache_pages--; |
134 | __dec_zone_page_state(page, NR_FILE_PAGES); |
135 | INC_CACHE_INFO(del_total); |
136 | } |
137 | |
138 | /** |
139 | * add_to_swap - allocate swap space for a page |
140 | * @page: page we want to move to swap |
141 | * |
142 | * Allocate swap space for the page and add the page to the |
143 | * swap cache. Caller needs to hold the page lock. |
144 | */ |
145 | int add_to_swap(struct page *page) |
146 | { |
147 | swp_entry_t entry; |
148 | int err; |
149 | |
150 | VM_BUG_ON(!PageLocked(page)); |
151 | VM_BUG_ON(!PageUptodate(page)); |
152 | |
153 | entry = get_swap_page(); |
154 | if (!entry.val) |
155 | return 0; |
156 | |
157 | if (unlikely(PageTransHuge(page))) |
158 | if (unlikely(split_huge_page(page))) { |
159 | swapcache_free(entry, NULL); |
160 | return 0; |
161 | } |
162 | |
163 | /* |
164 | * Radix-tree node allocations from PF_MEMALLOC contexts could |
165 | * completely exhaust the page allocator. __GFP_NOMEMALLOC |
166 | * stops emergency reserves from being allocated. |
167 | * |
168 | * TODO: this could cause a theoretical memory reclaim |
169 | * deadlock in the swap out path. |
170 | */ |
171 | /* |
172 | * Add it to the swap cache and mark it dirty |
173 | */ |
174 | err = add_to_swap_cache(page, entry, |
175 | __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN); |
176 | |
177 | if (!err) { /* Success */ |
178 | SetPageDirty(page); |
179 | return 1; |
180 | } else { /* -ENOMEM radix-tree allocation failure */ |
181 | /* |
182 | * add_to_swap_cache() doesn't return -EEXIST, so we can safely |
183 | * clear SWAP_HAS_CACHE flag. |
184 | */ |
185 | swapcache_free(entry, NULL); |
186 | return 0; |
187 | } |
188 | } |
189 | |
190 | /* |
191 | * This must be called only on pages that have |
192 | * been verified to be in the swap cache and locked. |
193 | * It will never put the page into the free list, |
194 | * the caller has a reference on the page. |
195 | */ |
196 | void delete_from_swap_cache(struct page *page) |
197 | { |
198 | swp_entry_t entry; |
199 | |
200 | entry.val = page_private(page); |
201 | |
202 | spin_lock_irq(&swapper_space.tree_lock); |
203 | __delete_from_swap_cache(page); |
204 | spin_unlock_irq(&swapper_space.tree_lock); |
205 | |
206 | swapcache_free(entry, page); |
207 | page_cache_release(page); |
208 | } |
209 | |
210 | /* |
211 | * If we are the only user, then try to free up the swap cache. |
212 | * |
213 | * Its ok to check for PageSwapCache without the page lock |
214 | * here because we are going to recheck again inside |
215 | * try_to_free_swap() _with_ the lock. |
216 | * - Marcelo |
217 | */ |
218 | static inline void free_swap_cache(struct page *page) |
219 | { |
220 | if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) { |
221 | try_to_free_swap(page); |
222 | unlock_page(page); |
223 | } |
224 | } |
225 | |
226 | /* |
227 | * Perform a free_page(), also freeing any swap cache associated with |
228 | * this page if it is the last user of the page. |
229 | */ |
230 | void free_page_and_swap_cache(struct page *page) |
231 | { |
232 | free_swap_cache(page); |
233 | page_cache_release(page); |
234 | } |
235 | |
236 | /* |
237 | * Passed an array of pages, drop them all from swapcache and then release |
238 | * them. They are removed from the LRU and freed if this is their last use. |
239 | */ |
240 | void free_pages_and_swap_cache(struct page **pages, int nr) |
241 | { |
242 | struct page **pagep = pages; |
243 | |
244 | lru_add_drain(); |
245 | while (nr) { |
246 | int todo = min(nr, PAGEVEC_SIZE); |
247 | int i; |
248 | |
249 | for (i = 0; i < todo; i++) |
250 | free_swap_cache(pagep[i]); |
251 | release_pages(pagep, todo, 0); |
252 | pagep += todo; |
253 | nr -= todo; |
254 | } |
255 | } |
256 | |
257 | /* |
258 | * Lookup a swap entry in the swap cache. A found page will be returned |
259 | * unlocked and with its refcount incremented - we rely on the kernel |
260 | * lock getting page table operations atomic even if we drop the page |
261 | * lock before returning. |
262 | */ |
263 | struct page * lookup_swap_cache(swp_entry_t entry) |
264 | { |
265 | struct page *page; |
266 | |
267 | page = find_get_page(&swapper_space, entry.val); |
268 | |
269 | if (page) |
270 | INC_CACHE_INFO(find_success); |
271 | |
272 | INC_CACHE_INFO(find_total); |
273 | return page; |
274 | } |
275 | |
276 | /* |
277 | * Locate a page of swap in physical memory, reserving swap cache space |
278 | * and reading the disk if it is not already cached. |
279 | * A failure return means that either the page allocation failed or that |
280 | * the swap entry is no longer in use. |
281 | */ |
282 | struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask, |
283 | struct vm_area_struct *vma, unsigned long addr) |
284 | { |
285 | struct page *found_page, *new_page = NULL; |
286 | int err; |
287 | |
288 | do { |
289 | /* |
290 | * First check the swap cache. Since this is normally |
291 | * called after lookup_swap_cache() failed, re-calling |
292 | * that would confuse statistics. |
293 | */ |
294 | found_page = find_get_page(&swapper_space, entry.val); |
295 | if (found_page) |
296 | break; |
297 | |
298 | /* |
299 | * Get a new page to read into from swap. |
300 | */ |
301 | if (!new_page) { |
302 | new_page = alloc_page_vma(gfp_mask, vma, addr); |
303 | if (!new_page) |
304 | break; /* Out of memory */ |
305 | } |
306 | |
307 | /* |
308 | * call radix_tree_preload() while we can wait. |
309 | */ |
310 | err = radix_tree_preload(gfp_mask & GFP_KERNEL); |
311 | if (err) |
312 | break; |
313 | |
314 | /* |
315 | * Swap entry may have been freed since our caller observed it. |
316 | */ |
317 | err = swapcache_prepare(entry); |
318 | if (err == -EEXIST) { /* seems racy */ |
319 | radix_tree_preload_end(); |
320 | continue; |
321 | } |
322 | if (err) { /* swp entry is obsolete ? */ |
323 | radix_tree_preload_end(); |
324 | break; |
325 | } |
326 | |
327 | /* May fail (-ENOMEM) if radix-tree node allocation failed. */ |
328 | __set_page_locked(new_page); |
329 | SetPageSwapBacked(new_page); |
330 | err = __add_to_swap_cache(new_page, entry); |
331 | if (likely(!err)) { |
332 | radix_tree_preload_end(); |
333 | /* |
334 | * Initiate read into locked page and return. |
335 | */ |
336 | lru_cache_add_anon(new_page); |
337 | swap_readpage(new_page); |
338 | return new_page; |
339 | } |
340 | radix_tree_preload_end(); |
341 | ClearPageSwapBacked(new_page); |
342 | __clear_page_locked(new_page); |
343 | /* |
344 | * add_to_swap_cache() doesn't return -EEXIST, so we can safely |
345 | * clear SWAP_HAS_CACHE flag. |
346 | */ |
347 | swapcache_free(entry, NULL); |
348 | } while (err != -ENOMEM); |
349 | |
350 | if (new_page) |
351 | page_cache_release(new_page); |
352 | return found_page; |
353 | } |
354 | |
355 | /** |
356 | * swapin_readahead - swap in pages in hope we need them soon |
357 | * @entry: swap entry of this memory |
358 | * @gfp_mask: memory allocation flags |
359 | * @vma: user vma this address belongs to |
360 | * @addr: target address for mempolicy |
361 | * |
362 | * Returns the struct page for entry and addr, after queueing swapin. |
363 | * |
364 | * Primitive swap readahead code. We simply read an aligned block of |
365 | * (1 << page_cluster) entries in the swap area. This method is chosen |
366 | * because it doesn't cost us any seek time. We also make sure to queue |
367 | * the 'original' request together with the readahead ones... |
368 | * |
369 | * This has been extended to use the NUMA policies from the mm triggering |
370 | * the readahead. |
371 | * |
372 | * Caller must hold down_read on the vma->vm_mm if vma is not NULL. |
373 | */ |
374 | struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask, |
375 | struct vm_area_struct *vma, unsigned long addr) |
376 | { |
377 | int nr_pages; |
378 | struct page *page; |
379 | unsigned long offset; |
380 | unsigned long end_offset; |
381 | |
382 | /* |
383 | * Get starting offset for readaround, and number of pages to read. |
384 | * Adjust starting address by readbehind (for NUMA interleave case)? |
385 | * No, it's very unlikely that swap layout would follow vma layout, |
386 | * more likely that neighbouring swap pages came from the same node: |
387 | * so use the same "addr" to choose the same node for each swap read. |
388 | */ |
389 | nr_pages = valid_swaphandles(entry, &offset); |
390 | for (end_offset = offset + nr_pages; offset < end_offset; offset++) { |
391 | /* Ok, do the async read-ahead now */ |
392 | page = read_swap_cache_async(swp_entry(swp_type(entry), offset), |
393 | gfp_mask, vma, addr); |
394 | if (!page) |
395 | break; |
396 | page_cache_release(page); |
397 | } |
398 | lru_add_drain(); /* Push any new pages onto the LRU now */ |
399 | return read_swap_cache_async(entry, gfp_mask, vma, addr); |
400 | } |
401 |
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