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 #include <linux/pagevec.h>
18 #include <linux/migrate.h>
19
20 #include <asm/pgtable.h>
21
22 /*
23 * swapper_space is a fiction, retained to simplify the path through
24 * vmscan's shrink_list, to make sync_page look nicer, and to allow
25 * future use of radix_tree tags in the swap cache.
26 */
27 static struct address_space_operations swap_aops = {
28 .writepage = swap_writepage,
29 .sync_page = block_sync_page,
30 .set_page_dirty = __set_page_dirty_nobuffers,
31 .migratepage = migrate_page,
32 };
33
34 static struct backing_dev_info swap_backing_dev_info = {
35 .capabilities = BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
36 .unplug_io_fn = swap_unplug_io_fn,
37 };
38
39 struct address_space swapper_space = {
40 .page_tree = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
41 .tree_lock = RW_LOCK_UNLOCKED,
42 .a_ops = &swap_aops,
43 .i_mmap_nonlinear = LIST_HEAD_INIT(swapper_space.i_mmap_nonlinear),
44 .backing_dev_info = &swap_backing_dev_info,
45 };
46
47 #define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0)
48
49 static struct {
50 unsigned long add_total;
51 unsigned long del_total;
52 unsigned long find_success;
53 unsigned long find_total;
54 unsigned long noent_race;
55 unsigned long exist_race;
56 } swap_cache_info;
57
58 void show_swap_cache_info(void)
59 {
60 printk("Swap cache: add %lu, delete %lu, find %lu/%lu, race %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 swap_cache_info.noent_race, swap_cache_info.exist_race);
64 printk("Free swap = %lukB\n", nr_swap_pages << (PAGE_SHIFT - 10));
65 printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
66 }
67
68 /*
69 * __add_to_swap_cache resembles add_to_page_cache on swapper_space,
70 * but sets SwapCache flag and private instead of mapping and index.
71 */
72 static int __add_to_swap_cache(struct page *page, swp_entry_t entry,
73 gfp_t gfp_mask)
74 {
75 int error;
76
77 BUG_ON(PageSwapCache(page));
78 BUG_ON(PagePrivate(page));
79 error = radix_tree_preload(gfp_mask);
80 if (!error) {
81 write_lock_irq(&swapper_space.tree_lock);
82 error = radix_tree_insert(&swapper_space.page_tree,
83 entry.val, page);
84 if (!error) {
85 page_cache_get(page);
86 SetPageLocked(page);
87 SetPageSwapCache(page);
88 set_page_private(page, entry.val);
89 total_swapcache_pages++;
90 pagecache_acct(1);
91 }
92 write_unlock_irq(&swapper_space.tree_lock);
93 radix_tree_preload_end();
94 }
95 return error;
96 }
97
98 static int add_to_swap_cache(struct page *page, swp_entry_t entry)
99 {
100 int error;
101
102 if (!swap_duplicate(entry)) {
103 INC_CACHE_INFO(noent_race);
104 return -ENOENT;
105 }
106 error = __add_to_swap_cache(page, entry, GFP_KERNEL);
107 /*
108 * Anon pages are already on the LRU, we don't run lru_cache_add here.
109 */
110 if (error) {
111 swap_free(entry);
112 if (error == -EEXIST)
113 INC_CACHE_INFO(exist_race);
114 return error;
115 }
116 INC_CACHE_INFO(add_total);
117 return 0;
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 BUG_ON(!PageLocked(page));
127 BUG_ON(!PageSwapCache(page));
128 BUG_ON(PageWriteback(page));
129 BUG_ON(PagePrivate(page));
130
131 radix_tree_delete(&swapper_space.page_tree, page_private(page));
132 set_page_private(page, 0);
133 ClearPageSwapCache(page);
134 total_swapcache_pages--;
135 pagecache_acct(-1);
136 INC_CACHE_INFO(del_total);
137 }
138
139 /**
140 * add_to_swap - allocate swap space for a page
141 * @page: page we want to move to swap
142 *
143 * Allocate swap space for the page and add the page to the
144 * swap cache. Caller needs to hold the page lock.
145 */
146 int add_to_swap(struct page * page, gfp_t gfp_mask)
147 {
148 swp_entry_t entry;
149 int err;
150
151 BUG_ON(!PageLocked(page));
152
153 for (;;) {
154 entry = get_swap_page();
155 if (!entry.val)
156 return 0;
157
158 /*
159 * Radix-tree node allocations from PF_MEMALLOC contexts could
160 * completely exhaust the page allocator. __GFP_NOMEMALLOC
161 * stops emergency reserves from being allocated.
162 *
163 * TODO: this could cause a theoretical memory reclaim
164 * deadlock in the swap out path.
165 */
166 /*
167 * Add it to the swap cache and mark it dirty
168 */
169 err = __add_to_swap_cache(page, entry,
170 gfp_mask|__GFP_NOMEMALLOC|__GFP_NOWARN);
171
172 switch (err) {
173 case 0: /* Success */
174 SetPageUptodate(page);
175 SetPageDirty(page);
176 INC_CACHE_INFO(add_total);
177 return 1;
178 case -EEXIST:
179 /* Raced with "speculative" read_swap_cache_async */
180 INC_CACHE_INFO(exist_race);
181 swap_free(entry);
182 continue;
183 default:
184 /* -ENOMEM radix-tree allocation failure */
185 swap_free(entry);
186 return 0;
187 }
188 }
189 }
190
191 /*
192 * This must be called only on pages that have
193 * been verified to be in the swap cache and locked.
194 * It will never put the page into the free list,
195 * the caller has a reference on the page.
196 */
197 void delete_from_swap_cache(struct page *page)
198 {
199 swp_entry_t entry;
200
201 entry.val = page_private(page);
202
203 write_lock_irq(&swapper_space.tree_lock);
204 __delete_from_swap_cache(page);
205 write_unlock_irq(&swapper_space.tree_lock);
206
207 swap_free(entry);
208 page_cache_release(page);
209 }
210
211 /*
212 * Strange swizzling function only for use by shmem_writepage
213 */
214 int move_to_swap_cache(struct page *page, swp_entry_t entry)
215 {
216 int err = __add_to_swap_cache(page, entry, GFP_ATOMIC);
217 if (!err) {
218 remove_from_page_cache(page);
219 page_cache_release(page); /* pagecache ref */
220 if (!swap_duplicate(entry))
221 BUG();
222 SetPageDirty(page);
223 INC_CACHE_INFO(add_total);
224 } else if (err == -EEXIST)
225 INC_CACHE_INFO(exist_race);
226 return err;
227 }
228
229 /*
230 * Strange swizzling function for shmem_getpage (and shmem_unuse)
231 */
232 int move_from_swap_cache(struct page *page, unsigned long index,
233 struct address_space *mapping)
234 {
235 int err = add_to_page_cache(page, mapping, index, GFP_ATOMIC);
236 if (!err) {
237 delete_from_swap_cache(page);
238 /* shift page from clean_pages to dirty_pages list */
239 ClearPageDirty(page);
240 set_page_dirty(page);
241 }
242 return err;
243 }
244
245 /*
246 * If we are the only user, then try to free up the swap cache.
247 *
248 * Its ok to check for PageSwapCache without the page lock
249 * here because we are going to recheck again inside
250 * exclusive_swap_page() _with_ the lock.
251 * - Marcelo
252 */
253 static inline void free_swap_cache(struct page *page)
254 {
255 if (PageSwapCache(page) && !TestSetPageLocked(page)) {
256 remove_exclusive_swap_page(page);
257 unlock_page(page);
258 }
259 }
260
261 /*
262 * Perform a free_page(), also freeing any swap cache associated with
263 * this page if it is the last user of the page.
264 */
265 void free_page_and_swap_cache(struct page *page)
266 {
267 free_swap_cache(page);
268 page_cache_release(page);
269 }
270
271 /*
272 * Passed an array of pages, drop them all from swapcache and then release
273 * them. They are removed from the LRU and freed if this is their last use.
274 */
275 void free_pages_and_swap_cache(struct page **pages, int nr)
276 {
277 struct page **pagep = pages;
278
279 lru_add_drain();
280 while (nr) {
281 int todo = min(nr, PAGEVEC_SIZE);
282 int i;
283
284 for (i = 0; i < todo; i++)
285 free_swap_cache(pagep[i]);
286 release_pages(pagep, todo, 0);
287 pagep += todo;
288 nr -= todo;
289 }
290 }
291
292 /*
293 * Lookup a swap entry in the swap cache. A found page will be returned
294 * unlocked and with its refcount incremented - we rely on the kernel
295 * lock getting page table operations atomic even if we drop the page
296 * lock before returning.
297 */
298 struct page * lookup_swap_cache(swp_entry_t entry)
299 {
300 struct page *page;
301
302 page = find_get_page(&swapper_space, entry.val);
303
304 if (page)
305 INC_CACHE_INFO(find_success);
306
307 INC_CACHE_INFO(find_total);
308 return page;
309 }
310
311 /*
312 * Locate a page of swap in physical memory, reserving swap cache space
313 * and reading the disk if it is not already cached.
314 * A failure return means that either the page allocation failed or that
315 * the swap entry is no longer in use.
316 */
317 struct page *read_swap_cache_async(swp_entry_t entry,
318 struct vm_area_struct *vma, unsigned long addr)
319 {
320 struct page *found_page, *new_page = NULL;
321 int err;
322
323 do {
324 /*
325 * First check the swap cache. Since this is normally
326 * called after lookup_swap_cache() failed, re-calling
327 * that would confuse statistics.
328 */
329 found_page = find_get_page(&swapper_space, entry.val);
330 if (found_page)
331 break;
332
333 /*
334 * Get a new page to read into from swap.
335 */
336 if (!new_page) {
337 new_page = alloc_page_vma(GFP_HIGHUSER, vma, addr);
338 if (!new_page)
339 break; /* Out of memory */
340 }
341
342 /*
343 * Associate the page with swap entry in the swap cache.
344 * May fail (-ENOENT) if swap entry has been freed since
345 * our caller observed it. May fail (-EEXIST) if there
346 * is already a page associated with this entry in the
347 * swap cache: added by a racing read_swap_cache_async,
348 * or by try_to_swap_out (or shmem_writepage) re-using
349 * the just freed swap entry for an existing page.
350 * May fail (-ENOMEM) if radix-tree node allocation failed.
351 */
352 err = add_to_swap_cache(new_page, entry);
353 if (!err) {
354 /*
355 * Initiate read into locked page and return.
356 */
357 lru_cache_add_active(new_page);
358 swap_readpage(NULL, new_page);
359 return new_page;
360 }
361 } while (err != -ENOENT && err != -ENOMEM);
362
363 if (new_page)
364 page_cache_release(new_page);
365 return found_page;
366 }
367
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