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 :
18 : #include <asm/pgtable.h>
19 :
20 : /*
21 : * swapper_space is a fiction, retained to simplify the path through
22 : * vmscan's shrink_list, to make sync_page look nicer, and to allow
23 : * future use of radix_tree tags in the swap cache.
24 : */
25 : static struct address_space_operations swap_aops = {
26 : .writepage = swap_writepage,
27 : .sync_page = block_sync_page,
28 : .set_page_dirty = __set_page_dirty_nobuffers,
29 : };
30 :
31 : static struct backing_dev_info swap_backing_dev_info = {
32 : .capabilities = BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
33 : .unplug_io_fn = swap_unplug_io_fn,
34 : };
35 :
36 : struct address_space swapper_space = {
37 : .page_tree = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
38 : .tree_lock = RW_LOCK_UNLOCKED,
39 : .a_ops = &swap_aops,
40 : .i_mmap_nonlinear = LIST_HEAD_INIT(swapper_space.i_mmap_nonlinear),
41 : .backing_dev_info = &swap_backing_dev_info,
42 : };
43 : EXPORT_SYMBOL(swapper_space);
44 :
45 : #define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0)
46 :
47 : static struct {
48 : unsigned long add_total;
49 : unsigned long del_total;
50 : unsigned long find_success;
51 : unsigned long find_total;
52 : unsigned long noent_race;
53 : unsigned long exist_race;
54 : } swap_cache_info;
55 :
56 : void show_swap_cache_info(void)
57 0 : {
58 0 : printk("Swap cache: add %lu, delete %lu, find %lu/%lu, race %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 : swap_cache_info.noent_race, swap_cache_info.exist_race);
62 0 : printk("Free swap = %lukB\n", nr_swap_pages << (PAGE_SHIFT - 10));
63 0 : printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
64 : }
65 :
66 : /*
67 : * __add_to_swap_cache resembles add_to_page_cache on swapper_space,
68 : * but sets SwapCache flag and private instead of mapping and index.
69 : */
70 : static int __add_to_swap_cache(struct page *page, swp_entry_t entry,
71 : gfp_t gfp_mask)
72 0 : {
73 0 : int error;
74 :
75 0 : BUG_ON(PageSwapCache(page));
76 0 : BUG_ON(PagePrivate(page));
77 0 : error = radix_tree_preload(gfp_mask);
78 0 : if (!error) {
79 0 : write_lock_irq(&swapper_space.tree_lock);
80 0 : error = radix_tree_insert(&swapper_space.page_tree,
81 : entry.val, page);
82 0 : if (!error) {
83 0 : page_cache_get(page);
84 0 : SetPageLocked(page);
85 0 : SetPageSwapCache(page);
86 0 : page->private = entry.val;
87 0 : total_swapcache_pages++;
88 0 : pagecache_acct(1);
89 : }
90 0 : write_unlock_irq(&swapper_space.tree_lock);
91 0 : radix_tree_preload_end();
92 : }
93 0 : return error;
94 : }
95 :
96 : static int add_to_swap_cache(struct page *page, swp_entry_t entry)
97 0 : {
98 0 : int error;
99 :
100 0 : if (!swap_duplicate(entry)) {
101 0 : INC_CACHE_INFO(noent_race);
102 0 : return -ENOENT;
103 : }
104 0 : error = __add_to_swap_cache(page, entry, GFP_KERNEL);
105 : /*
106 : * Anon pages are already on the LRU, we don't run lru_cache_add here.
107 : */
108 0 : if (error) {
109 0 : swap_free(entry);
110 0 : if (error == -EEXIST)
111 0 : INC_CACHE_INFO(exist_race);
112 0 : return error;
113 : }
114 0 : INC_CACHE_INFO(add_total);
115 0 : return 0;
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 0 : {
124 0 : BUG_ON(!PageLocked(page));
125 0 : BUG_ON(!PageSwapCache(page));
126 0 : BUG_ON(PageWriteback(page));
127 0 : BUG_ON(PagePrivate(page));
128 :
129 0 : radix_tree_delete(&swapper_space.page_tree, page->private);
130 0 : page->private = 0;
131 0 : ClearPageSwapCache(page);
132 0 : total_swapcache_pages--;
133 0 : pagecache_acct(-1);
134 0 : INC_CACHE_INFO(del_total);
135 : }
136 :
137 : /**
138 : * add_to_swap - allocate swap space for a page
139 : * @page: page we want to move to swap
140 : *
141 : * Allocate swap space for the page and add the page to the
142 : * swap cache. Caller needs to hold the page lock.
143 : */
144 : int add_to_swap(struct page * page)
145 0 : {
146 0 : swp_entry_t entry;
147 0 : int err;
148 :
149 0 : if (!PageLocked(page))
150 0 : BUG();
151 :
152 0 : for (;;) {
153 0 : entry = get_swap_page();
154 0 : if (!entry.val)
155 0 : return 0;
156 :
157 : /*
158 : * Radix-tree node allocations from PF_MEMALLOC contexts could
159 : * completely exhaust the page allocator. __GFP_NOMEMALLOC
160 : * stops emergency reserves from being allocated.
161 : *
162 : * TODO: this could cause a theoretical memory reclaim
163 : * deadlock in the swap out path.
164 : */
165 : /*
166 : * Add it to the swap cache and mark it dirty
167 : */
168 0 : err = __add_to_swap_cache(page, entry,
169 : GFP_ATOMIC|__GFP_NOMEMALLOC|__GFP_NOWARN);
170 :
171 0 : switch (err) {
172 : case 0: /* Success */
173 0 : SetPageUptodate(page);
174 0 : SetPageDirty(page);
175 0 : INC_CACHE_INFO(add_total);
176 0 : return 1;
177 : case -EEXIST:
178 : /* Raced with "speculative" read_swap_cache_async */
179 0 : INC_CACHE_INFO(exist_race);
180 0 : swap_free(entry);
181 0 : continue;
182 : default:
183 : /* -ENOMEM radix-tree allocation failure */
184 0 : swap_free(entry);
185 0 : return 0;
186 : }
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 0 : {
198 0 : swp_entry_t entry;
199 :
200 0 : entry.val = page->private;
201 :
202 0 : write_lock_irq(&swapper_space.tree_lock);
203 0 : __delete_from_swap_cache(page);
204 0 : write_unlock_irq(&swapper_space.tree_lock);
205 :
206 0 : swap_free(entry);
207 0 : page_cache_release(page);
208 : }
209 :
210 : /*
211 : * Strange swizzling function only for use by shmem_writepage
212 : */
213 : int move_to_swap_cache(struct page *page, swp_entry_t entry)
214 0 : {
215 0 : int err = __add_to_swap_cache(page, entry, GFP_ATOMIC);
216 0 : if (!err) {
217 0 : remove_from_page_cache(page);
218 0 : page_cache_release(page); /* pagecache ref */
219 0 : if (!swap_duplicate(entry))
220 0 : BUG();
221 0 : SetPageDirty(page);
222 0 : INC_CACHE_INFO(add_total);
223 0 : } else if (err == -EEXIST)
224 0 : INC_CACHE_INFO(exist_race);
225 0 : return err;
226 : }
227 :
228 : /*
229 : * Strange swizzling function for shmem_getpage (and shmem_unuse)
230 : */
231 : int move_from_swap_cache(struct page *page, unsigned long index,
232 : struct address_space *mapping)
233 0 : {
234 0 : int err = add_to_page_cache(page, mapping, index, GFP_ATOMIC);
235 0 : if (!err) {
236 0 : delete_from_swap_cache(page);
237 : /* shift page from clean_pages to dirty_pages list */
238 0 : ClearPageDirty(page);
239 0 : set_page_dirty(page);
240 : }
241 0 : return err;
242 : }
243 :
244 : /*
245 : * If we are the only user, then try to free up the swap cache.
246 : *
247 : * Its ok to check for PageSwapCache without the page lock
248 : * here because we are going to recheck again inside
249 : * exclusive_swap_page() _with_ the lock.
250 : * - Marcelo
251 : */
252 : static inline void free_swap_cache(struct page *page)
253 14592 : {
254 14592 : if (PageSwapCache(page) && !TestSetPageLocked(page)) {
255 0 : remove_exclusive_swap_page(page);
256 0 : unlock_page(page);
257 : }
258 : }
259 :
260 : /*
261 : * Perform a free_page(), also freeing any swap cache associated with
262 : * this page if it is the last user of the page. Can not do a lock_page,
263 : * as we are holding the page_table_lock spinlock.
264 : */
265 : void free_page_and_swap_cache(struct page *page)
266 14592 : {
267 14592 : free_swap_cache(page);
268 14592 : 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 0 : {
277 0 : int chunk = 16;
278 0 : struct page **pagep = pages;
279 :
280 0 : lru_add_drain();
281 0 : while (nr) {
282 0 : int todo = min(chunk, nr);
283 0 : int i;
284 :
285 0 : for (i = 0; i < todo; i++)
286 0 : free_swap_cache(pagep[i]);
287 0 : release_pages(pagep, todo, 0);
288 0 : pagep += todo;
289 0 : nr -= todo;
290 : }
291 : }
292 :
293 : /*
294 : * Lookup a swap entry in the swap cache. A found page will be returned
295 : * unlocked and with its refcount incremented - we rely on the kernel
296 : * lock getting page table operations atomic even if we drop the page
297 : * lock before returning.
298 : */
299 : struct page * lookup_swap_cache(swp_entry_t entry)
300 0 : {
301 0 : struct page *page;
302 :
303 0 : page = find_get_page(&swapper_space, entry.val);
304 :
305 0 : if (page)
306 0 : INC_CACHE_INFO(find_success);
307 :
308 0 : INC_CACHE_INFO(find_total);
309 0 : return page;
310 : }
311 :
312 : /*
313 : * Locate a page of swap in physical memory, reserving swap cache space
314 : * and reading the disk if it is not already cached.
315 : * A failure return means that either the page allocation failed or that
316 : * the swap entry is no longer in use.
317 : */
318 : struct page *read_swap_cache_async(swp_entry_t entry,
319 : struct vm_area_struct *vma, unsigned long addr)
320 0 : {
321 0 : struct page *found_page, *new_page = NULL;
322 0 : int err;
323 :
324 0 : do {
325 : /*
326 : * First check the swap cache. Since this is normally
327 : * called after lookup_swap_cache() failed, re-calling
328 : * that would confuse statistics.
329 : */
330 0 : found_page = find_get_page(&swapper_space, entry.val);
331 0 : if (found_page)
332 0 : break;
333 :
334 : /*
335 : * Get a new page to read into from swap.
336 : */
337 0 : if (!new_page) {
338 0 : new_page = alloc_page_vma(GFP_HIGHUSER, vma, addr);
339 0 : if (!new_page)
340 0 : break; /* Out of memory */
341 : }
342 :
343 : /*
344 : * Associate the page with swap entry in the swap cache.
345 : * May fail (-ENOENT) if swap entry has been freed since
346 : * our caller observed it. May fail (-EEXIST) if there
347 : * is already a page associated with this entry in the
348 : * swap cache: added by a racing read_swap_cache_async,
349 : * or by try_to_swap_out (or shmem_writepage) re-using
350 : * the just freed swap entry for an existing page.
351 : * May fail (-ENOMEM) if radix-tree node allocation failed.
352 : */
353 0 : err = add_to_swap_cache(new_page, entry);
354 0 : if (!err) {
355 : /*
356 : * Initiate read into locked page and return.
357 : */
358 0 : lru_cache_add_active(new_page);
359 0 : swap_readpage(NULL, new_page);
360 0 : return new_page;
361 : }
362 0 : } while (err != -ENOENT && err != -ENOMEM);
363 :
364 0 : if (new_page)
365 0 : page_cache_release(new_page);
366 0 : return found_page;
367 : }
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