Linux-2.6.12-rc2
[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 pf_flags;
147         int err;
148
149         if (!PageLocked(page))
150                 BUG();
151
152         for (;;) {
153                 entry = get_swap_page();
154                 if (!entry.val)
155                         return 0;
156
157                 /* Radix-tree node allocations are performing
158                  * GFP_ATOMIC allocations under PF_MEMALLOC.  
159                  * They can completely exhaust the page allocator.  
160                  *
161                  * So PF_MEMALLOC is dropped here.  This causes the slab 
162                  * allocations to fail earlier, so radix-tree nodes will 
163                  * then be allocated from the mempool reserves.
164                  *
165                  * We're still using __GFP_HIGH for radix-tree node
166                  * allocations, so some of the emergency pools are available,
167                  * just not all of them.
168                  */
169
170                 pf_flags = current->flags;
171                 current->flags &= ~PF_MEMALLOC;
172
173                 /*
174                  * Add it to the swap cache and mark it dirty
175                  */
176                 err = __add_to_swap_cache(page, entry, GFP_ATOMIC|__GFP_NOWARN);
177
178                 if (pf_flags & PF_MEMALLOC)
179                         current->flags |= PF_MEMALLOC;
180
181                 switch (err) {
182                 case 0:                         /* Success */
183                         SetPageUptodate(page);
184                         SetPageDirty(page);
185                         INC_CACHE_INFO(add_total);
186                         return 1;
187                 case -EEXIST:
188                         /* Raced with "speculative" read_swap_cache_async */
189                         INC_CACHE_INFO(exist_race);
190                         swap_free(entry);
191                         continue;
192                 default:
193                         /* -ENOMEM radix-tree allocation failure */
194                         swap_free(entry);
195                         return 0;
196                 }
197         }
198 }
199
200 /*
201  * This must be called only on pages that have
202  * been verified to be in the swap cache and locked.
203  * It will never put the page into the free list,
204  * the caller has a reference on the page.
205  */
206 void delete_from_swap_cache(struct page *page)
207 {
208         swp_entry_t entry;
209
210         BUG_ON(!PageSwapCache(page));
211         BUG_ON(!PageLocked(page));
212         BUG_ON(PageWriteback(page));
213         BUG_ON(PagePrivate(page));
214   
215         entry.val = page->private;
216
217         write_lock_irq(&swapper_space.tree_lock);
218         __delete_from_swap_cache(page);
219         write_unlock_irq(&swapper_space.tree_lock);
220
221         swap_free(entry);
222         page_cache_release(page);
223 }
224
225 /*
226  * Strange swizzling function only for use by shmem_writepage
227  */
228 int move_to_swap_cache(struct page *page, swp_entry_t entry)
229 {
230         int err = __add_to_swap_cache(page, entry, GFP_ATOMIC);
231         if (!err) {
232                 remove_from_page_cache(page);
233                 page_cache_release(page);       /* pagecache ref */
234                 if (!swap_duplicate(entry))
235                         BUG();
236                 SetPageDirty(page);
237                 INC_CACHE_INFO(add_total);
238         } else if (err == -EEXIST)
239                 INC_CACHE_INFO(exist_race);
240         return err;
241 }
242
243 /*
244  * Strange swizzling function for shmem_getpage (and shmem_unuse)
245  */
246 int move_from_swap_cache(struct page *page, unsigned long index,
247                 struct address_space *mapping)
248 {
249         int err = add_to_page_cache(page, mapping, index, GFP_ATOMIC);
250         if (!err) {
251                 delete_from_swap_cache(page);
252                 /* shift page from clean_pages to dirty_pages list */
253                 ClearPageDirty(page);
254                 set_page_dirty(page);
255         }
256         return err;
257 }
258
259 /* 
260  * If we are the only user, then try to free up the swap cache. 
261  * 
262  * Its ok to check for PageSwapCache without the page lock
263  * here because we are going to recheck again inside 
264  * exclusive_swap_page() _with_ the lock. 
265  *                                      - Marcelo
266  */
267 static inline void free_swap_cache(struct page *page)
268 {
269         if (PageSwapCache(page) && !TestSetPageLocked(page)) {
270                 remove_exclusive_swap_page(page);
271                 unlock_page(page);
272         }
273 }
274
275 /* 
276  * Perform a free_page(), also freeing any swap cache associated with
277  * this page if it is the last user of the page. Can not do a lock_page,
278  * as we are holding the page_table_lock spinlock.
279  */
280 void free_page_and_swap_cache(struct page *page)
281 {
282         free_swap_cache(page);
283         page_cache_release(page);
284 }
285
286 /*
287  * Passed an array of pages, drop them all from swapcache and then release
288  * them.  They are removed from the LRU and freed if this is their last use.
289  */
290 void free_pages_and_swap_cache(struct page **pages, int nr)
291 {
292         int chunk = 16;
293         struct page **pagep = pages;
294
295         lru_add_drain();
296         while (nr) {
297                 int todo = min(chunk, nr);
298                 int i;
299
300                 for (i = 0; i < todo; i++)
301                         free_swap_cache(pagep[i]);
302                 release_pages(pagep, todo, 0);
303                 pagep += todo;
304                 nr -= todo;
305         }
306 }
307
308 /*
309  * Lookup a swap entry in the swap cache. A found page will be returned
310  * unlocked and with its refcount incremented - we rely on the kernel
311  * lock getting page table operations atomic even if we drop the page
312  * lock before returning.
313  */
314 struct page * lookup_swap_cache(swp_entry_t entry)
315 {
316         struct page *page;
317
318         page = find_get_page(&swapper_space, entry.val);
319
320         if (page)
321                 INC_CACHE_INFO(find_success);
322
323         INC_CACHE_INFO(find_total);
324         return page;
325 }
326
327 /* 
328  * Locate a page of swap in physical memory, reserving swap cache space
329  * and reading the disk if it is not already cached.
330  * A failure return means that either the page allocation failed or that
331  * the swap entry is no longer in use.
332  */
333 struct page *read_swap_cache_async(swp_entry_t entry,
334                         struct vm_area_struct *vma, unsigned long addr)
335 {
336         struct page *found_page, *new_page = NULL;
337         int err;
338
339         do {
340                 /*
341                  * First check the swap cache.  Since this is normally
342                  * called after lookup_swap_cache() failed, re-calling
343                  * that would confuse statistics.
344                  */
345                 found_page = find_get_page(&swapper_space, entry.val);
346                 if (found_page)
347                         break;
348
349                 /*
350                  * Get a new page to read into from swap.
351                  */
352                 if (!new_page) {
353                         new_page = alloc_page_vma(GFP_HIGHUSER, vma, addr);
354                         if (!new_page)
355                                 break;          /* Out of memory */
356                 }
357
358                 /*
359                  * Associate the page with swap entry in the swap cache.
360                  * May fail (-ENOENT) if swap entry has been freed since
361                  * our caller observed it.  May fail (-EEXIST) if there
362                  * is already a page associated with this entry in the
363                  * swap cache: added by a racing read_swap_cache_async,
364                  * or by try_to_swap_out (or shmem_writepage) re-using
365                  * the just freed swap entry for an existing page.
366                  * May fail (-ENOMEM) if radix-tree node allocation failed.
367                  */
368                 err = add_to_swap_cache(new_page, entry);
369                 if (!err) {
370                         /*
371                          * Initiate read into locked page and return.
372                          */
373                         lru_cache_add_active(new_page);
374                         swap_readpage(NULL, new_page);
375                         return new_page;
376                 }
377         } while (err != -ENOENT && err != -ENOMEM);
378
379         if (new_page)
380                 page_cache_release(new_page);
381         return found_page;
382 }