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Linus Torvalds1da177e2005-04-16 15:20:36 -07001/*
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>
Hugh Dickins46017e92008-02-04 22:28:41 -080013#include <linux/swapops.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070014#include <linux/init.h>
15#include <linux/pagemap.h>
16#include <linux/buffer_head.h>
17#include <linux/backing-dev.h>
Hugh Dickinsc484d412006-01-06 00:10:55 -080018#include <linux/pagevec.h>
Christoph Lameterb20a3502006-03-22 00:09:12 -080019#include <linux/migrate.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070020
21#include <asm/pgtable.h>
22
23/*
24 * swapper_space is a fiction, retained to simplify the path through
Anderson Briglia2706a1b2007-07-15 23:38:09 -070025 * vmscan's shrink_page_list, to make sync_page look nicer, and to allow
Linus Torvalds1da177e2005-04-16 15:20:36 -070026 * future use of radix_tree tags in the swap cache.
27 */
Christoph Hellwigf5e54d62006-06-28 04:26:44 -070028static const struct address_space_operations swap_aops = {
Linus Torvalds1da177e2005-04-16 15:20:36 -070029 .writepage = swap_writepage,
30 .sync_page = block_sync_page,
31 .set_page_dirty = __set_page_dirty_nobuffers,
Christoph Lametere965f962006-02-01 03:05:41 -080032 .migratepage = migrate_page,
Linus Torvalds1da177e2005-04-16 15:20:36 -070033};
34
35static struct backing_dev_info swap_backing_dev_info = {
36 .capabilities = BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
37 .unplug_io_fn = swap_unplug_io_fn,
38};
39
40struct address_space swapper_space = {
41 .page_tree = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
Ingo Molnare4d91912006-07-03 00:24:34 -070042 .tree_lock = __RW_LOCK_UNLOCKED(swapper_space.tree_lock),
Linus Torvalds1da177e2005-04-16 15:20:36 -070043 .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};
Linus Torvalds1da177e2005-04-16 15:20:36 -070047
48#define INC_CACHE_INFO(x) do { swap_cache_info.x++; } while (0)
49
50static struct {
51 unsigned long add_total;
52 unsigned long del_total;
53 unsigned long find_success;
54 unsigned long find_total;
Linus Torvalds1da177e2005-04-16 15:20:36 -070055} swap_cache_info;
56
57void show_swap_cache_info(void)
58{
Hugh Dickinsbb63be02008-02-04 22:28:49 -080059 printk("Swap cache: add %lu, delete %lu, find %lu/%lu\n",
Linus Torvalds1da177e2005-04-16 15:20:36 -070060 swap_cache_info.add_total, swap_cache_info.del_total,
Hugh Dickinsbb63be02008-02-04 22:28:49 -080061 swap_cache_info.find_success, swap_cache_info.find_total);
Linus Torvalds1da177e2005-04-16 15:20:36 -070062 printk("Free swap = %lukB\n", nr_swap_pages << (PAGE_SHIFT - 10));
63 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 */
Victor Fusco9de75d12005-09-10 00:26:46 -070070static int __add_to_swap_cache(struct page *page, swp_entry_t entry,
Al Virodd0fc662005-10-07 07:46:04 +010071 gfp_t gfp_mask)
Linus Torvalds1da177e2005-04-16 15:20:36 -070072{
73 int error;
74
Nick Pigginb55ed812007-10-16 01:24:42 -070075 BUG_ON(!PageLocked(page));
Linus Torvalds1da177e2005-04-16 15:20:36 -070076 BUG_ON(PageSwapCache(page));
77 BUG_ON(PagePrivate(page));
78 error = radix_tree_preload(gfp_mask);
79 if (!error) {
80 write_lock_irq(&swapper_space.tree_lock);
81 error = radix_tree_insert(&swapper_space.page_tree,
82 entry.val, page);
83 if (!error) {
84 page_cache_get(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -070085 SetPageSwapCache(page);
Hugh Dickins4c21e2f2005-10-29 18:16:40 -070086 set_page_private(page, entry.val);
Linus Torvalds1da177e2005-04-16 15:20:36 -070087 total_swapcache_pages++;
Christoph Lameter347ce432006-06-30 01:55:35 -070088 __inc_zone_page_state(page, NR_FILE_PAGES);
Hugh Dickinsbb63be02008-02-04 22:28:49 -080089 INC_CACHE_INFO(add_total);
Linus Torvalds1da177e2005-04-16 15:20:36 -070090 }
91 write_unlock_irq(&swapper_space.tree_lock);
92 radix_tree_preload_end();
93 }
94 return error;
95}
96
Hugh Dickins02098fe2008-02-04 22:28:42 -080097static int add_to_swap_cache(struct page *page, swp_entry_t entry,
98 gfp_t gfp_mask)
Linus Torvalds1da177e2005-04-16 15:20:36 -070099{
100 int error;
101
Nick Pigginb55ed812007-10-16 01:24:42 -0700102 BUG_ON(PageLocked(page));
Hugh Dickinsbb63be02008-02-04 22:28:49 -0800103 if (!swap_duplicate(entry))
Linus Torvalds1da177e2005-04-16 15:20:36 -0700104 return -ENOENT;
Hugh Dickinsbb63be02008-02-04 22:28:49 -0800105
Nick Pigginb55ed812007-10-16 01:24:42 -0700106 SetPageLocked(page);
Hugh Dickins02098fe2008-02-04 22:28:42 -0800107 error = __add_to_swap_cache(page, entry, gfp_mask & GFP_KERNEL);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700108 /*
109 * Anon pages are already on the LRU, we don't run lru_cache_add here.
110 */
111 if (error) {
Nick Pigginb55ed812007-10-16 01:24:42 -0700112 ClearPageLocked(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700113 swap_free(entry);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700114 return error;
115 }
Linus Torvalds1da177e2005-04-16 15:20:36 -0700116 return 0;
117}
118
119/*
120 * This must be called only on pages that have
121 * been verified to be in the swap cache.
122 */
123void __delete_from_swap_cache(struct page *page)
124{
125 BUG_ON(!PageLocked(page));
126 BUG_ON(!PageSwapCache(page));
127 BUG_ON(PageWriteback(page));
Hugh Dickins3279ffd2005-09-03 15:54:43 -0700128 BUG_ON(PagePrivate(page));
Linus Torvalds1da177e2005-04-16 15:20:36 -0700129
Hugh Dickins4c21e2f2005-10-29 18:16:40 -0700130 radix_tree_delete(&swapper_space.page_tree, page_private(page));
131 set_page_private(page, 0);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700132 ClearPageSwapCache(page);
133 total_swapcache_pages--;
Christoph Lameter347ce432006-06-30 01:55:35 -0700134 __dec_zone_page_state(page, NR_FILE_PAGES);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700135 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 */
Christoph Lameter1480a542006-01-08 01:00:53 -0800145int add_to_swap(struct page * page, gfp_t gfp_mask)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700146{
147 swp_entry_t entry;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700148 int err;
149
Eric Sesterhenne74ca2b2006-04-01 01:25:12 +0200150 BUG_ON(!PageLocked(page));
Linus Torvalds1da177e2005-04-16 15:20:36 -0700151
152 for (;;) {
153 entry = get_swap_page();
154 if (!entry.val)
155 return 0;
156
Nick Pigginbd53b712005-05-01 08:58:37 -0700157 /*
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.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700161 *
Nick Pigginbd53b712005-05-01 08:58:37 -0700162 * TODO: this could cause a theoretical memory reclaim
163 * deadlock in the swap out path.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700164 */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700165 /*
166 * Add it to the swap cache and mark it dirty
167 */
Nick Pigginbd53b712005-05-01 08:58:37 -0700168 err = __add_to_swap_cache(page, entry,
Christoph Lameter1480a542006-01-08 01:00:53 -0800169 gfp_mask|__GFP_NOMEMALLOC|__GFP_NOWARN);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700170
171 switch (err) {
172 case 0: /* Success */
173 SetPageUptodate(page);
174 SetPageDirty(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700175 return 1;
176 case -EEXIST:
177 /* Raced with "speculative" read_swap_cache_async */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700178 swap_free(entry);
179 continue;
180 default:
181 /* -ENOMEM radix-tree allocation failure */
182 swap_free(entry);
183 return 0;
184 }
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 */
194void delete_from_swap_cache(struct page *page)
195{
196 swp_entry_t entry;
197
Hugh Dickins4c21e2f2005-10-29 18:16:40 -0700198 entry.val = page_private(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700199
200 write_lock_irq(&swapper_space.tree_lock);
201 __delete_from_swap_cache(page);
202 write_unlock_irq(&swapper_space.tree_lock);
203
204 swap_free(entry);
205 page_cache_release(page);
206}
207
208/*
209 * Strange swizzling function only for use by shmem_writepage
210 */
211int move_to_swap_cache(struct page *page, swp_entry_t entry)
212{
213 int err = __add_to_swap_cache(page, entry, GFP_ATOMIC);
214 if (!err) {
215 remove_from_page_cache(page);
216 page_cache_release(page); /* pagecache ref */
217 if (!swap_duplicate(entry))
218 BUG();
219 SetPageDirty(page);
Hugh Dickinsbb63be02008-02-04 22:28:49 -0800220 }
Linus Torvalds1da177e2005-04-16 15:20:36 -0700221 return err;
222}
223
224/*
225 * Strange swizzling function for shmem_getpage (and shmem_unuse)
226 */
227int move_from_swap_cache(struct page *page, unsigned long index,
228 struct address_space *mapping)
229{
230 int err = add_to_page_cache(page, mapping, index, GFP_ATOMIC);
231 if (!err) {
232 delete_from_swap_cache(page);
233 /* shift page from clean_pages to dirty_pages list */
234 ClearPageDirty(page);
235 set_page_dirty(page);
236 }
237 return err;
238}
239
240/*
241 * If we are the only user, then try to free up the swap cache.
242 *
243 * Its ok to check for PageSwapCache without the page lock
244 * here because we are going to recheck again inside
245 * exclusive_swap_page() _with_ the lock.
246 * - Marcelo
247 */
248static inline void free_swap_cache(struct page *page)
249{
250 if (PageSwapCache(page) && !TestSetPageLocked(page)) {
251 remove_exclusive_swap_page(page);
252 unlock_page(page);
253 }
254}
255
256/*
257 * Perform a free_page(), also freeing any swap cache associated with
Hugh Dickinsb8072f02005-10-29 18:16:41 -0700258 * this page if it is the last user of the page.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700259 */
260void free_page_and_swap_cache(struct page *page)
261{
262 free_swap_cache(page);
263 page_cache_release(page);
264}
265
266/*
267 * Passed an array of pages, drop them all from swapcache and then release
268 * them. They are removed from the LRU and freed if this is their last use.
269 */
270void free_pages_and_swap_cache(struct page **pages, int nr)
271{
Linus Torvalds1da177e2005-04-16 15:20:36 -0700272 struct page **pagep = pages;
273
274 lru_add_drain();
275 while (nr) {
Hugh Dickinsc484d412006-01-06 00:10:55 -0800276 int todo = min(nr, PAGEVEC_SIZE);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700277 int i;
278
279 for (i = 0; i < todo; i++)
280 free_swap_cache(pagep[i]);
281 release_pages(pagep, todo, 0);
282 pagep += todo;
283 nr -= todo;
284 }
285}
286
287/*
288 * Lookup a swap entry in the swap cache. A found page will be returned
289 * unlocked and with its refcount incremented - we rely on the kernel
290 * lock getting page table operations atomic even if we drop the page
291 * lock before returning.
292 */
293struct page * lookup_swap_cache(swp_entry_t entry)
294{
295 struct page *page;
296
297 page = find_get_page(&swapper_space, entry.val);
298
299 if (page)
300 INC_CACHE_INFO(find_success);
301
302 INC_CACHE_INFO(find_total);
303 return page;
304}
305
306/*
307 * Locate a page of swap in physical memory, reserving swap cache space
308 * and reading the disk if it is not already cached.
309 * A failure return means that either the page allocation failed or that
310 * the swap entry is no longer in use.
311 */
Hugh Dickins02098fe2008-02-04 22:28:42 -0800312struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
Linus Torvalds1da177e2005-04-16 15:20:36 -0700313 struct vm_area_struct *vma, unsigned long addr)
314{
315 struct page *found_page, *new_page = NULL;
316 int err;
317
318 do {
319 /*
320 * First check the swap cache. Since this is normally
321 * called after lookup_swap_cache() failed, re-calling
322 * that would confuse statistics.
323 */
324 found_page = find_get_page(&swapper_space, entry.val);
325 if (found_page)
326 break;
327
328 /*
329 * Get a new page to read into from swap.
330 */
331 if (!new_page) {
Hugh Dickins02098fe2008-02-04 22:28:42 -0800332 new_page = alloc_page_vma(gfp_mask, vma, addr);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700333 if (!new_page)
334 break; /* Out of memory */
335 }
336
337 /*
338 * Associate the page with swap entry in the swap cache.
339 * May fail (-ENOENT) if swap entry has been freed since
340 * our caller observed it. May fail (-EEXIST) if there
341 * is already a page associated with this entry in the
342 * swap cache: added by a racing read_swap_cache_async,
343 * or by try_to_swap_out (or shmem_writepage) re-using
344 * the just freed swap entry for an existing page.
345 * May fail (-ENOMEM) if radix-tree node allocation failed.
346 */
Hugh Dickins02098fe2008-02-04 22:28:42 -0800347 err = add_to_swap_cache(new_page, entry, gfp_mask);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700348 if (!err) {
349 /*
350 * Initiate read into locked page and return.
351 */
352 lru_cache_add_active(new_page);
353 swap_readpage(NULL, new_page);
354 return new_page;
355 }
356 } while (err != -ENOENT && err != -ENOMEM);
357
358 if (new_page)
359 page_cache_release(new_page);
360 return found_page;
361}
Hugh Dickins46017e92008-02-04 22:28:41 -0800362
363/**
364 * swapin_readahead - swap in pages in hope we need them soon
365 * @entry: swap entry of this memory
366 * @vma: user vma this address belongs to
367 * @addr: target address for mempolicy
368 *
369 * Returns the struct page for entry and addr, after queueing swapin.
370 *
371 * Primitive swap readahead code. We simply read an aligned block of
372 * (1 << page_cluster) entries in the swap area. This method is chosen
373 * because it doesn't cost us any seek time. We also make sure to queue
374 * the 'original' request together with the readahead ones...
375 *
376 * This has been extended to use the NUMA policies from the mm triggering
377 * the readahead.
378 *
379 * Caller must hold down_read on the vma->vm_mm if vma is not NULL.
380 */
Hugh Dickins02098fe2008-02-04 22:28:42 -0800381struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
Hugh Dickins46017e92008-02-04 22:28:41 -0800382 struct vm_area_struct *vma, unsigned long addr)
383{
384 int nr_pages;
385 struct page *page;
386 unsigned long offset;
387 unsigned long end_offset;
388
389 /*
390 * Get starting offset for readaround, and number of pages to read.
391 * Adjust starting address by readbehind (for NUMA interleave case)?
392 * No, it's very unlikely that swap layout would follow vma layout,
393 * more likely that neighbouring swap pages came from the same node:
394 * so use the same "addr" to choose the same node for each swap read.
395 */
396 nr_pages = valid_swaphandles(entry, &offset);
397 for (end_offset = offset + nr_pages; offset < end_offset; offset++) {
398 /* Ok, do the async read-ahead now */
399 page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
Hugh Dickins02098fe2008-02-04 22:28:42 -0800400 gfp_mask, vma, addr);
Hugh Dickins46017e92008-02-04 22:28:41 -0800401 if (!page)
402 break;
403 page_cache_release(page);
404 }
405 lru_add_drain(); /* Push any new pages onto the LRU now */
Hugh Dickins02098fe2008-02-04 22:28:42 -0800406 return read_swap_cache_async(entry, gfp_mask, vma, addr);
Hugh Dickins46017e92008-02-04 22:28:41 -0800407}