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Linux/mm/swap_state.c

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  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/mm.h>
 10 #include <linux/gfp.h>
 11 #include <linux/kernel_stat.h>
 12 #include <linux/swap.h>
 13 #include <linux/swapops.h>
 14 #include <linux/init.h>
 15 #include <linux/pagemap.h>
 16 #include <linux/backing-dev.h>
 17 #include <linux/blkdev.h>
 18 #include <linux/pagevec.h>
 19 #include <linux/migrate.h>
 20 #include <linux/page_cgroup.h>
 21 
 22 #include <asm/pgtable.h>
 23 
 24 /*
 25  * swapper_space is a fiction, retained to simplify the path through
 26  * vmscan's shrink_page_list.
 27  */
 28 static const struct address_space_operations swap_aops = {
 29         .writepage      = swap_writepage,
 30         .set_page_dirty = swap_set_page_dirty,
 31         .migratepage    = migrate_page,
 32 };
 33 
 34 static struct backing_dev_info swap_backing_dev_info = {
 35         .name           = "swap",
 36         .capabilities   = BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED,
 37 };
 38 
 39 struct address_space swapper_space = {
 40         .page_tree      = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
 41         .tree_lock      = __SPIN_LOCK_UNLOCKED(swapper_space.tree_lock),
 42         .a_ops          = &swap_aops,
 43         .i_mmap_nonlinear = LIST_HEAD_INIT(swapper_space.i_mmap_nonlinear),
 44         .backing_dev_info = &swap_backing_dev_info,
 45 };
 46 
 47 #define INC_CACHE_INFO(x)       do { swap_cache_info.x++; } while (0)
 48 
 49 static struct {
 50         unsigned long add_total;
 51         unsigned long del_total;
 52         unsigned long find_success;
 53         unsigned long find_total;
 54 } swap_cache_info;
 55 
 56 void show_swap_cache_info(void)
 57 {
 58         printk("%lu pages in swap cache\n", total_swapcache_pages);
 59         printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
 60                 swap_cache_info.add_total, swap_cache_info.del_total,
 61                 swap_cache_info.find_success, swap_cache_info.find_total);
 62         printk("Free swap  = %ldkB\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_locked 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 {
 72         int error;
 73 
 74         VM_BUG_ON(!PageLocked(page));
 75         VM_BUG_ON(PageSwapCache(page));
 76         VM_BUG_ON(!PageSwapBacked(page));
 77 
 78         page_cache_get(page);
 79         SetPageSwapCache(page);
 80         set_page_private(page, entry.val);
 81 
 82         spin_lock_irq(&swapper_space.tree_lock);
 83         error = radix_tree_insert(&swapper_space.page_tree, entry.val, page);
 84         if (likely(!error)) {
 85                 total_swapcache_pages++;
 86                 __inc_zone_page_state(page, NR_FILE_PAGES);
 87                 INC_CACHE_INFO(add_total);
 88         }
 89         spin_unlock_irq(&swapper_space.tree_lock);
 90 
 91         if (unlikely(error)) {
 92                 /*
 93                  * Only the context which have set SWAP_HAS_CACHE flag
 94                  * would call add_to_swap_cache().
 95                  * So add_to_swap_cache() doesn't returns -EEXIST.
 96                  */
 97                 VM_BUG_ON(error == -EEXIST);
 98                 set_page_private(page, 0UL);
 99                 ClearPageSwapCache(page);
100                 page_cache_release(page);
101         }
102 
103         return error;
104 }
105 
106 
107 int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
108 {
109         int error;
110 
111         error = radix_tree_preload(gfp_mask);
112         if (!error) {
113                 error = __add_to_swap_cache(page, entry);
114                 radix_tree_preload_end();
115         }
116         return error;
117 }
118 
119 /*
120  * This must be called only on pages that have
121  * been verified to be in the swap cache.
122  */
123 void __delete_from_swap_cache(struct page *page)
124 {
125         VM_BUG_ON(!PageLocked(page));
126         VM_BUG_ON(!PageSwapCache(page));
127         VM_BUG_ON(PageWriteback(page));
128 
129         radix_tree_delete(&swapper_space.page_tree, page_private(page));
130         set_page_private(page, 0);
131         ClearPageSwapCache(page);
132         total_swapcache_pages--;
133         __dec_zone_page_state(page, NR_FILE_PAGES);
134         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 {
146         swp_entry_t entry;
147         int err;
148 
149         VM_BUG_ON(!PageLocked(page));
150         VM_BUG_ON(!PageUptodate(page));
151 
152         entry = get_swap_page();
153         if (!entry.val)
154                 return 0;
155 
156         if (unlikely(PageTransHuge(page)))
157                 if (unlikely(split_huge_page(page))) {
158                         swapcache_free(entry, NULL);
159                         return 0;
160                 }
161 
162         /*
163          * Radix-tree node allocations from PF_MEMALLOC contexts could
164          * completely exhaust the page allocator. __GFP_NOMEMALLOC
165          * stops emergency reserves from being allocated.
166          *
167          * TODO: this could cause a theoretical memory reclaim
168          * deadlock in the swap out path.
169          */
170         /*
171          * Add it to the swap cache and mark it dirty
172          */
173         err = add_to_swap_cache(page, entry,
174                         __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
175 
176         if (!err) {     /* Success */
177                 SetPageDirty(page);
178                 return 1;
179         } else {        /* -ENOMEM radix-tree allocation failure */
180                 /*
181                  * add_to_swap_cache() doesn't return -EEXIST, so we can safely
182                  * clear SWAP_HAS_CACHE flag.
183                  */
184                 swapcache_free(entry, NULL);
185                 return 0;
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         spin_lock_irq(&swapper_space.tree_lock);
202         __delete_from_swap_cache(page);
203         spin_unlock_irq(&swapper_space.tree_lock);
204 
205         swapcache_free(entry, page);
206         page_cache_release(page);
207 }
208 
209 /* 
210  * If we are the only user, then try to free up the swap cache. 
211  * 
212  * Its ok to check for PageSwapCache without the page lock
213  * here because we are going to recheck again inside
214  * try_to_free_swap() _with_ the lock.
215  *                                      - Marcelo
216  */
217 static inline void free_swap_cache(struct page *page)
218 {
219         if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
220                 try_to_free_swap(page);
221                 unlock_page(page);
222         }
223 }
224 
225 /* 
226  * Perform a free_page(), also freeing any swap cache associated with
227  * this page if it is the last user of the page.
228  */
229 void free_page_and_swap_cache(struct page *page)
230 {
231         free_swap_cache(page);
232         page_cache_release(page);
233 }
234 
235 /*
236  * Passed an array of pages, drop them all from swapcache and then release
237  * them.  They are removed from the LRU and freed if this is their last use.
238  */
239 void free_pages_and_swap_cache(struct page **pages, int nr)
240 {
241         struct page **pagep = pages;
242 
243         lru_add_drain();
244         while (nr) {
245                 int todo = min(nr, PAGEVEC_SIZE);
246                 int i;
247 
248                 for (i = 0; i < todo; i++)
249                         free_swap_cache(pagep[i]);
250                 release_pages(pagep, todo, 0);
251                 pagep += todo;
252                 nr -= todo;
253         }
254 }
255 
256 /*
257  * Lookup a swap entry in the swap cache. A found page will be returned
258  * unlocked and with its refcount incremented - we rely on the kernel
259  * lock getting page table operations atomic even if we drop the page
260  * lock before returning.
261  */
262 struct page * lookup_swap_cache(swp_entry_t entry)
263 {
264         struct page *page;
265 
266         page = find_get_page(&swapper_space, entry.val);
267 
268         if (page)
269                 INC_CACHE_INFO(find_success);
270 
271         INC_CACHE_INFO(find_total);
272         return page;
273 }
274 
275 /* 
276  * Locate a page of swap in physical memory, reserving swap cache space
277  * and reading the disk if it is not already cached.
278  * A failure return means that either the page allocation failed or that
279  * the swap entry is no longer in use.
280  */
281 struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
282                         struct vm_area_struct *vma, unsigned long addr)
283 {
284         struct page *found_page, *new_page = NULL;
285         int err;
286 
287         do {
288                 /*
289                  * First check the swap cache.  Since this is normally
290                  * called after lookup_swap_cache() failed, re-calling
291                  * that would confuse statistics.
292                  */
293                 found_page = find_get_page(&swapper_space, entry.val);
294                 if (found_page)
295                         break;
296 
297                 /*
298                  * Get a new page to read into from swap.
299                  */
300                 if (!new_page) {
301                         new_page = alloc_page_vma(gfp_mask, vma, addr);
302                         if (!new_page)
303                                 break;          /* Out of memory */
304                 }
305 
306                 /*
307                  * call radix_tree_preload() while we can wait.
308                  */
309                 err = radix_tree_preload(gfp_mask & GFP_KERNEL);
310                 if (err)
311                         break;
312 
313                 /*
314                  * Swap entry may have been freed since our caller observed it.
315                  */
316                 err = swapcache_prepare(entry);
317                 if (err == -EEXIST) {   /* seems racy */
318                         radix_tree_preload_end();
319                         continue;
320                 }
321                 if (err) {              /* swp entry is obsolete ? */
322                         radix_tree_preload_end();
323                         break;
324                 }
325 
326                 /* May fail (-ENOMEM) if radix-tree node allocation failed. */
327                 __set_page_locked(new_page);
328                 SetPageSwapBacked(new_page);
329                 err = __add_to_swap_cache(new_page, entry);
330                 if (likely(!err)) {
331                         radix_tree_preload_end();
332                         /*
333                          * Initiate read into locked page and return.
334                          */
335                         lru_cache_add_anon(new_page);
336                         swap_readpage(new_page);
337                         return new_page;
338                 }
339                 radix_tree_preload_end();
340                 ClearPageSwapBacked(new_page);
341                 __clear_page_locked(new_page);
342                 /*
343                  * add_to_swap_cache() doesn't return -EEXIST, so we can safely
344                  * clear SWAP_HAS_CACHE flag.
345                  */
346                 swapcache_free(entry, NULL);
347         } while (err != -ENOMEM);
348 
349         if (new_page)
350                 page_cache_release(new_page);
351         return found_page;
352 }
353 
354 /**
355  * swapin_readahead - swap in pages in hope we need them soon
356  * @entry: swap entry of this memory
357  * @gfp_mask: memory allocation flags
358  * @vma: user vma this address belongs to
359  * @addr: target address for mempolicy
360  *
361  * Returns the struct page for entry and addr, after queueing swapin.
362  *
363  * Primitive swap readahead code. We simply read an aligned block of
364  * (1 << page_cluster) entries in the swap area. This method is chosen
365  * because it doesn't cost us any seek time.  We also make sure to queue
366  * the 'original' request together with the readahead ones...
367  *
368  * This has been extended to use the NUMA policies from the mm triggering
369  * the readahead.
370  *
371  * Caller must hold down_read on the vma->vm_mm if vma is not NULL.
372  */
373 struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
374                         struct vm_area_struct *vma, unsigned long addr)
375 {
376         struct page *page;
377         unsigned long offset = swp_offset(entry);
378         unsigned long start_offset, end_offset;
379         unsigned long mask = (1UL << page_cluster) - 1;
380         struct blk_plug plug;
381 
382         /* Read a page_cluster sized and aligned cluster around offset. */
383         start_offset = offset & ~mask;
384         end_offset = offset | mask;
385         if (!start_offset)      /* First page is swap header. */
386                 start_offset++;
387 
388         blk_start_plug(&plug);
389         for (offset = start_offset; offset <= end_offset ; offset++) {
390                 /* Ok, do the async read-ahead now */
391                 page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
392                                                 gfp_mask, vma, addr);
393                 if (!page)
394                         continue;
395                 page_cache_release(page);
396         }
397         blk_finish_plug(&plug);
398 
399         lru_add_drain();        /* Push any new pages onto the LRU now */
400         return read_swap_cache_async(entry, gfp_mask, vma, addr);
401 }
402 

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