[PATCH] mm/swap_state.c: unexport swapper_space
[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
44 #define INC_CACHE_INFO(x)       do { swap_cache_info.x++; } while (0)
45
46 static struct {
47         unsigned long add_total;
48         unsigned long del_total;
49         unsigned long find_success;
50         unsigned long find_total;
51         unsigned long noent_race;
52         unsigned long exist_race;
53 } swap_cache_info;
54
55 void show_swap_cache_info(void)
56 {
57         printk("Swap cache: add %lu, delete %lu, find %lu/%lu, race %lu+%lu\n",
58                 swap_cache_info.add_total, swap_cache_info.del_total,
59                 swap_cache_info.find_success, swap_cache_info.find_total,
60                 swap_cache_info.noent_race, swap_cache_info.exist_race);
61         printk("Free swap  = %lukB\n", nr_swap_pages << (PAGE_SHIFT - 10));
62         printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
63 }
64
65 /*
66  * __add_to_swap_cache resembles add_to_page_cache on swapper_space,
67  * but sets SwapCache flag and private instead of mapping and index.
68  */
69 static int __add_to_swap_cache(struct page *page, swp_entry_t entry,
70                                gfp_t gfp_mask)
71 {
72         int error;
73
74         BUG_ON(PageSwapCache(page));
75         BUG_ON(PagePrivate(page));
76         error = radix_tree_preload(gfp_mask);
77         if (!error) {
78                 write_lock_irq(&swapper_space.tree_lock);
79                 error = radix_tree_insert(&swapper_space.page_tree,
80                                                 entry.val, page);
81                 if (!error) {
82                         page_cache_get(page);
83                         SetPageLocked(page);
84                         SetPageSwapCache(page);
85                         set_page_private(page, entry.val);
86                         total_swapcache_pages++;
87                         pagecache_acct(1);
88                 }
89                 write_unlock_irq(&swapper_space.tree_lock);
90                 radix_tree_preload_end();
91         }
92         return error;
93 }
94
95 static int add_to_swap_cache(struct page *page, swp_entry_t entry)
96 {
97         int error;
98
99         if (!swap_duplicate(entry)) {
100                 INC_CACHE_INFO(noent_race);
101                 return -ENOENT;
102         }
103         error = __add_to_swap_cache(page, entry, GFP_KERNEL);
104         /*
105          * Anon pages are already on the LRU, we don't run lru_cache_add here.
106          */
107         if (error) {
108                 swap_free(entry);
109                 if (error == -EEXIST)
110                         INC_CACHE_INFO(exist_race);
111                 return error;
112         }
113         INC_CACHE_INFO(add_total);
114         return 0;
115 }
116
117 /*
118  * This must be called only on pages that have
119  * been verified to be in the swap cache.
120  */
121 void __delete_from_swap_cache(struct page *page)
122 {
123         BUG_ON(!PageLocked(page));
124         BUG_ON(!PageSwapCache(page));
125         BUG_ON(PageWriteback(page));
126         BUG_ON(PagePrivate(page));
127
128         radix_tree_delete(&swapper_space.page_tree, page_private(page));
129         set_page_private(page, 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         entry.val = page_private(page);
200
201         write_lock_irq(&swapper_space.tree_lock);
202         __delete_from_swap_cache(page);
203         write_unlock_irq(&swapper_space.tree_lock);
204
205         swap_free(entry);
206         page_cache_release(page);
207 }
208
209 /*
210  * Strange swizzling function only for use by shmem_writepage
211  */
212 int move_to_swap_cache(struct page *page, swp_entry_t entry)
213 {
214         int err = __add_to_swap_cache(page, entry, GFP_ATOMIC);
215         if (!err) {
216                 remove_from_page_cache(page);
217                 page_cache_release(page);       /* pagecache ref */
218                 if (!swap_duplicate(entry))
219                         BUG();
220                 SetPageDirty(page);
221                 INC_CACHE_INFO(add_total);
222         } else if (err == -EEXIST)
223                 INC_CACHE_INFO(exist_race);
224         return err;
225 }
226
227 /*
228  * Strange swizzling function for shmem_getpage (and shmem_unuse)
229  */
230 int move_from_swap_cache(struct page *page, unsigned long index,
231                 struct address_space *mapping)
232 {
233         int err = add_to_page_cache(page, mapping, index, GFP_ATOMIC);
234         if (!err) {
235                 delete_from_swap_cache(page);
236                 /* shift page from clean_pages to dirty_pages list */
237                 ClearPageDirty(page);
238                 set_page_dirty(page);
239         }
240         return err;
241 }
242
243 /* 
244  * If we are the only user, then try to free up the swap cache. 
245  * 
246  * Its ok to check for PageSwapCache without the page lock
247  * here because we are going to recheck again inside 
248  * exclusive_swap_page() _with_ the lock. 
249  *                                      - Marcelo
250  */
251 static inline void free_swap_cache(struct page *page)
252 {
253         if (PageSwapCache(page) && !TestSetPageLocked(page)) {
254                 remove_exclusive_swap_page(page);
255                 unlock_page(page);
256         }
257 }
258
259 /* 
260  * Perform a free_page(), also freeing any swap cache associated with
261  * this page if it is the last user of the page.
262  */
263 void free_page_and_swap_cache(struct page *page)
264 {
265         free_swap_cache(page);
266         page_cache_release(page);
267 }
268
269 /*
270  * Passed an array of pages, drop them all from swapcache and then release
271  * them.  They are removed from the LRU and freed if this is their last use.
272  */
273 void free_pages_and_swap_cache(struct page **pages, int nr)
274 {
275         int chunk = 16;
276         struct page **pagep = pages;
277
278         lru_add_drain();
279         while (nr) {
280                 int todo = min(chunk, nr);
281                 int i;
282
283                 for (i = 0; i < todo; i++)
284                         free_swap_cache(pagep[i]);
285                 release_pages(pagep, todo, 0);
286                 pagep += todo;
287                 nr -= todo;
288         }
289 }
290
291 /*
292  * Lookup a swap entry in the swap cache. A found page will be returned
293  * unlocked and with its refcount incremented - we rely on the kernel
294  * lock getting page table operations atomic even if we drop the page
295  * lock before returning.
296  */
297 struct page * lookup_swap_cache(swp_entry_t entry)
298 {
299         struct page *page;
300
301         page = find_get_page(&swapper_space, entry.val);
302
303         if (page)
304                 INC_CACHE_INFO(find_success);
305
306         INC_CACHE_INFO(find_total);
307         return page;
308 }
309
310 /* 
311  * Locate a page of swap in physical memory, reserving swap cache space
312  * and reading the disk if it is not already cached.
313  * A failure return means that either the page allocation failed or that
314  * the swap entry is no longer in use.
315  */
316 struct page *read_swap_cache_async(swp_entry_t entry,
317                         struct vm_area_struct *vma, unsigned long addr)
318 {
319         struct page *found_page, *new_page = NULL;
320         int err;
321
322         do {
323                 /*
324                  * First check the swap cache.  Since this is normally
325                  * called after lookup_swap_cache() failed, re-calling
326                  * that would confuse statistics.
327                  */
328                 found_page = find_get_page(&swapper_space, entry.val);
329                 if (found_page)
330                         break;
331
332                 /*
333                  * Get a new page to read into from swap.
334                  */
335                 if (!new_page) {
336                         new_page = alloc_page_vma(GFP_HIGHUSER, vma, addr);
337                         if (!new_page)
338                                 break;          /* Out of memory */
339                 }
340
341                 /*
342                  * Associate the page with swap entry in the swap cache.
343                  * May fail (-ENOENT) if swap entry has been freed since
344                  * our caller observed it.  May fail (-EEXIST) if there
345                  * is already a page associated with this entry in the
346                  * swap cache: added by a racing read_swap_cache_async,
347                  * or by try_to_swap_out (or shmem_writepage) re-using
348                  * the just freed swap entry for an existing page.
349                  * May fail (-ENOMEM) if radix-tree node allocation failed.
350                  */
351                 err = add_to_swap_cache(new_page, entry);
352                 if (!err) {
353                         /*
354                          * Initiate read into locked page and return.
355                          */
356                         lru_cache_add_active(new_page);
357                         swap_readpage(NULL, new_page);
358                         return new_page;
359                 }
360         } while (err != -ENOENT && err != -ENOMEM);
361
362         if (new_page)
363                 page_cache_release(new_page);
364         return found_page;
365 }