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