[PATCH] mm: use __GFP_NOMEMALLOC
[linux-2.6.git] / mm / swap_state.c
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 {
58         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         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  */
70 static int __add_to_swap_cache(struct page *page,
71                 swp_entry_t entry, int gfp_mask)
72 {
73         int error;
74
75         BUG_ON(PageSwapCache(page));
76         BUG_ON(PagePrivate(page));
77         error = radix_tree_preload(gfp_mask);
78         if (!error) {
79                 write_lock_irq(&swapper_space.tree_lock);
80                 error = radix_tree_insert(&swapper_space.page_tree,
81                                                 entry.val, page);
82                 if (!error) {
83                         page_cache_get(page);
84                         SetPageLocked(page);
85                         SetPageSwapCache(page);
86                         page->private = entry.val;
87                         total_swapcache_pages++;
88                         pagecache_acct(1);
89                 }
90                 write_unlock_irq(&swapper_space.tree_lock);
91                 radix_tree_preload_end();
92         }
93         return error;
94 }
95
96 static int add_to_swap_cache(struct page *page, swp_entry_t entry)
97 {
98         int error;
99
100         if (!swap_duplicate(entry)) {
101                 INC_CACHE_INFO(noent_race);
102                 return -ENOENT;
103         }
104         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         if (error) {
109                 swap_free(entry);
110                 if (error == -EEXIST)
111                         INC_CACHE_INFO(exist_race);
112                 return error;
113         }
114         INC_CACHE_INFO(add_total);
115         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 {
124         BUG_ON(!PageLocked(page));
125         BUG_ON(!PageSwapCache(page));
126         BUG_ON(PageWriteback(page));
127
128         radix_tree_delete(&swapper_space.page_tree, page->private);
129         page->private = 0;
130         ClearPageSwapCache(page);
131         total_swapcache_pages--;
132         pagecache_acct(-1);
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         if (!PageLocked(page))
149                 BUG();
150
151         for (;;) {
152                 entry = get_swap_page();
153                 if (!entry.val)
154                         return 0;
155
156                 /*
157                  * Radix-tree node allocations from PF_MEMALLOC contexts could
158                  * completely exhaust the page allocator. __GFP_NOMEMALLOC
159                  * stops emergency reserves from being allocated.
160                  *
161                  * TODO: this could cause a theoretical memory reclaim
162                  * deadlock in the swap out path.
163                  */
164                 /*
165                  * Add it to the swap cache and mark it dirty
166                  */
167                 err = __add_to_swap_cache(page, entry,
168                                 GFP_ATOMIC|__GFP_NOMEMALLOC|__GFP_NOWARN);
169
170                 switch (err) {
171                 case 0:                         /* Success */
172                         SetPageUptodate(page);
173                         SetPageDirty(page);
174                         INC_CACHE_INFO(add_total);
175                         return 1;
176                 case -EEXIST:
177                         /* Raced with "speculative" read_swap_cache_async */
178                         INC_CACHE_INFO(exist_race);
179                         swap_free(entry);
180                         continue;
181                 default:
182                         /* -ENOMEM radix-tree allocation failure */
183                         swap_free(entry);
184                         return 0;
185                 }
186         }
187 }
188
189 /*
190  * This must be called only on pages that have
191  * been verified to be in the swap cache and locked.
192  * It will never put the page into the free list,
193  * the caller has a reference on the page.
194  */
195 void delete_from_swap_cache(struct page *page)
196 {
197         swp_entry_t entry;
198
199         BUG_ON(!PageSwapCache(page));
200         BUG_ON(!PageLocked(page));
201         BUG_ON(PageWriteback(page));
202         BUG_ON(PagePrivate(page));
203   
204         entry.val = page->private;
205
206         write_lock_irq(&swapper_space.tree_lock);
207         __delete_from_swap_cache(page);
208         write_unlock_irq(&swapper_space.tree_lock);
209
210         swap_free(entry);
211         page_cache_release(page);
212 }
213
214 /*
215  * Strange swizzling function only for use by shmem_writepage
216  */
217 int move_to_swap_cache(struct page *page, swp_entry_t entry)
218 {
219         int err = __add_to_swap_cache(page, entry, GFP_ATOMIC);
220         if (!err) {
221                 remove_from_page_cache(page);
222                 page_cache_release(page);       /* pagecache ref */
223                 if (!swap_duplicate(entry))
224                         BUG();
225                 SetPageDirty(page);
226                 INC_CACHE_INFO(add_total);
227         } else if (err == -EEXIST)
228                 INC_CACHE_INFO(exist_race);
229         return err;
230 }
231
232 /*
233  * Strange swizzling function for shmem_getpage (and shmem_unuse)
234  */
235 int move_from_swap_cache(struct page *page, unsigned long index,
236                 struct address_space *mapping)
237 {
238         int err = add_to_page_cache(page, mapping, index, GFP_ATOMIC);
239         if (!err) {
240                 delete_from_swap_cache(page);
241                 /* shift page from clean_pages to dirty_pages list */
242                 ClearPageDirty(page);
243                 set_page_dirty(page);
244         }
245         return err;
246 }
247
248 /* 
249  * If we are the only user, then try to free up the swap cache. 
250  * 
251  * Its ok to check for PageSwapCache without the page lock
252  * here because we are going to recheck again inside 
253  * exclusive_swap_page() _with_ the lock. 
254  *                                      - Marcelo
255  */
256 static inline void free_swap_cache(struct page *page)
257 {
258         if (PageSwapCache(page) && !TestSetPageLocked(page)) {
259                 remove_exclusive_swap_page(page);
260                 unlock_page(page);
261         }
262 }
263
264 /* 
265  * Perform a free_page(), also freeing any swap cache associated with
266  * this page if it is the last user of the page. Can not do a lock_page,
267  * as we are holding the page_table_lock spinlock.
268  */
269 void free_page_and_swap_cache(struct page *page)
270 {
271         free_swap_cache(page);
272         page_cache_release(page);
273 }
274
275 /*
276  * Passed an array of pages, drop them all from swapcache and then release
277  * them.  They are removed from the LRU and freed if this is their last use.
278  */
279 void free_pages_and_swap_cache(struct page **pages, int nr)
280 {
281         int chunk = 16;
282         struct page **pagep = pages;
283
284         lru_add_drain();
285         while (nr) {
286                 int todo = min(chunk, nr);
287                 int i;
288
289                 for (i = 0; i < todo; i++)
290                         free_swap_cache(pagep[i]);
291                 release_pages(pagep, todo, 0);
292                 pagep += todo;
293                 nr -= todo;
294         }
295 }
296
297 /*
298  * Lookup a swap entry in the swap cache. A found page will be returned
299  * unlocked and with its refcount incremented - we rely on the kernel
300  * lock getting page table operations atomic even if we drop the page
301  * lock before returning.
302  */
303 struct page * lookup_swap_cache(swp_entry_t entry)
304 {
305         struct page *page;
306
307         page = find_get_page(&swapper_space, entry.val);
308
309         if (page)
310                 INC_CACHE_INFO(find_success);
311
312         INC_CACHE_INFO(find_total);
313         return page;
314 }
315
316 /* 
317  * Locate a page of swap in physical memory, reserving swap cache space
318  * and reading the disk if it is not already cached.
319  * A failure return means that either the page allocation failed or that
320  * the swap entry is no longer in use.
321  */
322 struct page *read_swap_cache_async(swp_entry_t entry,
323                         struct vm_area_struct *vma, unsigned long addr)
324 {
325         struct page *found_page, *new_page = NULL;
326         int err;
327
328         do {
329                 /*
330                  * First check the swap cache.  Since this is normally
331                  * called after lookup_swap_cache() failed, re-calling
332                  * that would confuse statistics.
333                  */
334                 found_page = find_get_page(&swapper_space, entry.val);
335                 if (found_page)
336                         break;
337
338                 /*
339                  * Get a new page to read into from swap.
340                  */
341                 if (!new_page) {
342                         new_page = alloc_page_vma(GFP_HIGHUSER, vma, addr);
343                         if (!new_page)
344                                 break;          /* Out of memory */
345                 }
346
347                 /*
348                  * Associate the page with swap entry in the swap cache.
349                  * May fail (-ENOENT) if swap entry has been freed since
350                  * our caller observed it.  May fail (-EEXIST) if there
351                  * is already a page associated with this entry in the
352                  * swap cache: added by a racing read_swap_cache_async,
353                  * or by try_to_swap_out (or shmem_writepage) re-using
354                  * the just freed swap entry for an existing page.
355                  * May fail (-ENOMEM) if radix-tree node allocation failed.
356                  */
357                 err = add_to_swap_cache(new_page, entry);
358                 if (!err) {
359                         /*
360                          * Initiate read into locked page and return.
361                          */
362                         lru_cache_add_active(new_page);
363                         swap_readpage(NULL, new_page);
364                         return new_page;
365                 }
366         } while (err != -ENOENT && err != -ENOMEM);
367
368         if (new_page)
369                 page_cache_release(new_page);
370         return found_page;
371 }