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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/module.h>
 10 #include <linux/mm.h>
 11 #include <linux/gfp.h>
 12 #include <linux/kernel_stat.h>
 13 #include <linux/swap.h>
 14 #include <linux/swapops.h>
 15 #include <linux/init.h>
 16 #include <linux/pagemap.h>
 17 #include <linux/buffer_head.h>
 18 #include <linux/backing-dev.h>
 19 #include <linux/pagevec.h>
 20 #include <linux/migrate.h>
 21 #include <linux/page_cgroup.h>
 22 
 23 #include <asm/pgtable.h>
 24 
 25 /*
 26  * swapper_space is a fiction, retained to simplify the path through
 27  * vmscan's shrink_page_list.
 28  */
 29 static const struct address_space_operations swap_aops = {
 30         .writepage      = swap_writepage,
 31         .set_page_dirty = __set_page_dirty_nobuffers,
 32         .migratepage    = migrate_page,
 33 };
 34 
 35 static struct backing_dev_info swap_backing_dev_info = {
 36         .name           = "swap",
 37         .capabilities   = BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED,
 38 };
 39 
 40 struct address_space swapper_space = {
 41         .page_tree      = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
 42         .tree_lock      = __SPIN_LOCK_UNLOCKED(swapper_space.tree_lock),
 43         .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 };
 47 
 48 #define INC_CACHE_INFO(x)       do { swap_cache_info.x++; } while (0)
 49 
 50 static struct {
 51         unsigned long add_total;
 52         unsigned long del_total;
 53         unsigned long find_success;
 54         unsigned long find_total;
 55 } swap_cache_info;
 56 
 57 void show_swap_cache_info(void)
 58 {
 59         printk("%lu pages in swap cache\n", total_swapcache_pages);
 60         printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
 61                 swap_cache_info.add_total, swap_cache_info.del_total,
 62                 swap_cache_info.find_success, swap_cache_info.find_total);
 63         printk("Free swap  = %ldkB\n", nr_swap_pages << (PAGE_SHIFT - 10));
 64         printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
 65 }
 66 
 67 /*
 68  * __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
 69  * but sets SwapCache flag and private instead of mapping and index.
 70  */
 71 static int __add_to_swap_cache(struct page *page, swp_entry_t entry)
 72 {
 73         int error;
 74 
 75         VM_BUG_ON(!PageLocked(page));
 76         VM_BUG_ON(PageSwapCache(page));
 77         VM_BUG_ON(!PageSwapBacked(page));
 78 
 79         page_cache_get(page);
 80         SetPageSwapCache(page);
 81         set_page_private(page, entry.val);
 82 
 83         spin_lock_irq(&swapper_space.tree_lock);
 84         error = radix_tree_insert(&swapper_space.page_tree, entry.val, page);
 85         if (likely(!error)) {
 86                 total_swapcache_pages++;
 87                 __inc_zone_page_state(page, NR_FILE_PAGES);
 88                 INC_CACHE_INFO(add_total);
 89         }
 90         spin_unlock_irq(&swapper_space.tree_lock);
 91 
 92         if (unlikely(error)) {
 93                 /*
 94                  * Only the context which have set SWAP_HAS_CACHE flag
 95                  * would call add_to_swap_cache().
 96                  * So add_to_swap_cache() doesn't returns -EEXIST.
 97                  */
 98                 VM_BUG_ON(error == -EEXIST);
 99                 set_page_private(page, 0UL);
100                 ClearPageSwapCache(page);
101                 page_cache_release(page);
102         }
103 
104         return error;
105 }
106 
107 
108 int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
109 {
110         int error;
111 
112         error = radix_tree_preload(gfp_mask);
113         if (!error) {
114                 error = __add_to_swap_cache(page, entry);
115                 radix_tree_preload_end();
116         }
117         return error;
118 }
119 
120 /*
121  * This must be called only on pages that have
122  * been verified to be in the swap cache.
123  */
124 void __delete_from_swap_cache(struct page *page)
125 {
126         VM_BUG_ON(!PageLocked(page));
127         VM_BUG_ON(!PageSwapCache(page));
128         VM_BUG_ON(PageWriteback(page));
129 
130         radix_tree_delete(&swapper_space.page_tree, page_private(page));
131         set_page_private(page, 0);
132         ClearPageSwapCache(page);
133         total_swapcache_pages--;
134         __dec_zone_page_state(page, NR_FILE_PAGES);
135         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  */
145 int add_to_swap(struct page *page)
146 {
147         swp_entry_t entry;
148         int err;
149 
150         VM_BUG_ON(!PageLocked(page));
151         VM_BUG_ON(!PageUptodate(page));
152 
153         entry = get_swap_page();
154         if (!entry.val)
155                 return 0;
156 
157         if (unlikely(PageTransHuge(page)))
158                 if (unlikely(split_huge_page(page))) {
159                         swapcache_free(entry, NULL);
160                         return 0;
161                 }
162 
163         /*
164          * Radix-tree node allocations from PF_MEMALLOC contexts could
165          * completely exhaust the page allocator. __GFP_NOMEMALLOC
166          * stops emergency reserves from being allocated.
167          *
168          * TODO: this could cause a theoretical memory reclaim
169          * deadlock in the swap out path.
170          */
171         /*
172          * Add it to the swap cache and mark it dirty
173          */
174         err = add_to_swap_cache(page, entry,
175                         __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
176 
177         if (!err) {     /* Success */
178                 SetPageDirty(page);
179                 return 1;
180         } else {        /* -ENOMEM radix-tree allocation failure */
181                 /*
182                  * add_to_swap_cache() doesn't return -EEXIST, so we can safely
183                  * clear SWAP_HAS_CACHE flag.
184                  */
185                 swapcache_free(entry, NULL);
186                 return 0;
187         }
188 }
189 
190 /*
191  * This must be called only on pages that have
192  * been verified to be in the swap cache and locked.
193  * It will never put the page into the free list,
194  * the caller has a reference on the page.
195  */
196 void delete_from_swap_cache(struct page *page)
197 {
198         swp_entry_t entry;
199 
200         entry.val = page_private(page);
201 
202         spin_lock_irq(&swapper_space.tree_lock);
203         __delete_from_swap_cache(page);
204         spin_unlock_irq(&swapper_space.tree_lock);
205 
206         swapcache_free(entry, page);
207         page_cache_release(page);
208 }
209 
210 /* 
211  * If we are the only user, then try to free up the swap cache. 
212  * 
213  * Its ok to check for PageSwapCache without the page lock
214  * here because we are going to recheck again inside
215  * try_to_free_swap() _with_ the lock.
216  *                                      - Marcelo
217  */
218 static inline void free_swap_cache(struct page *page)
219 {
220         if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
221                 try_to_free_swap(page);
222                 unlock_page(page);
223         }
224 }
225 
226 /* 
227  * Perform a free_page(), also freeing any swap cache associated with
228  * this page if it is the last user of the page.
229  */
230 void free_page_and_swap_cache(struct page *page)
231 {
232         free_swap_cache(page);
233         page_cache_release(page);
234 }
235 
236 /*
237  * Passed an array of pages, drop them all from swapcache and then release
238  * them.  They are removed from the LRU and freed if this is their last use.
239  */
240 void free_pages_and_swap_cache(struct page **pages, int nr)
241 {
242         struct page **pagep = pages;
243 
244         lru_add_drain();
245         while (nr) {
246                 int todo = min(nr, PAGEVEC_SIZE);
247                 int i;
248 
249                 for (i = 0; i < todo; i++)
250                         free_swap_cache(pagep[i]);
251                 release_pages(pagep, todo, 0);
252                 pagep += todo;
253                 nr -= todo;
254         }
255 }
256 
257 /*
258  * Lookup a swap entry in the swap cache. A found page will be returned
259  * unlocked and with its refcount incremented - we rely on the kernel
260  * lock getting page table operations atomic even if we drop the page
261  * lock before returning.
262  */
263 struct page * lookup_swap_cache(swp_entry_t entry)
264 {
265         struct page *page;
266 
267         page = find_get_page(&swapper_space, entry.val);
268 
269         if (page)
270                 INC_CACHE_INFO(find_success);
271 
272         INC_CACHE_INFO(find_total);
273         return page;
274 }
275 
276 /* 
277  * Locate a page of swap in physical memory, reserving swap cache space
278  * and reading the disk if it is not already cached.
279  * A failure return means that either the page allocation failed or that
280  * the swap entry is no longer in use.
281  */
282 struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
283                         struct vm_area_struct *vma, unsigned long addr)
284 {
285         struct page *found_page, *new_page = NULL;
286         int err;
287 
288         do {
289                 /*
290                  * First check the swap cache.  Since this is normally
291                  * called after lookup_swap_cache() failed, re-calling
292                  * that would confuse statistics.
293                  */
294                 found_page = find_get_page(&swapper_space, entry.val);
295                 if (found_page)
296                         break;
297 
298                 /*
299                  * Get a new page to read into from swap.
300                  */
301                 if (!new_page) {
302                         new_page = alloc_page_vma(gfp_mask, vma, addr);
303                         if (!new_page)
304                                 break;          /* Out of memory */
305                 }
306 
307                 /*
308                  * call radix_tree_preload() while we can wait.
309                  */
310                 err = radix_tree_preload(gfp_mask & GFP_KERNEL);
311                 if (err)
312                         break;
313 
314                 /*
315                  * Swap entry may have been freed since our caller observed it.
316                  */
317                 err = swapcache_prepare(entry);
318                 if (err == -EEXIST) {   /* seems racy */
319                         radix_tree_preload_end();
320                         continue;
321                 }
322                 if (err) {              /* swp entry is obsolete ? */
323                         radix_tree_preload_end();
324                         break;
325                 }
326 
327                 /* May fail (-ENOMEM) if radix-tree node allocation failed. */
328                 __set_page_locked(new_page);
329                 SetPageSwapBacked(new_page);
330                 err = __add_to_swap_cache(new_page, entry);
331                 if (likely(!err)) {
332                         radix_tree_preload_end();
333                         /*
334                          * Initiate read into locked page and return.
335                          */
336                         lru_cache_add_anon(new_page);
337                         swap_readpage(new_page);
338                         return new_page;
339                 }
340                 radix_tree_preload_end();
341                 ClearPageSwapBacked(new_page);
342                 __clear_page_locked(new_page);
343                 /*
344                  * add_to_swap_cache() doesn't return -EEXIST, so we can safely
345                  * clear SWAP_HAS_CACHE flag.
346                  */
347                 swapcache_free(entry, NULL);
348         } while (err != -ENOMEM);
349 
350         if (new_page)
351                 page_cache_release(new_page);
352         return found_page;
353 }
354 
355 /**
356  * swapin_readahead - swap in pages in hope we need them soon
357  * @entry: swap entry of this memory
358  * @gfp_mask: memory allocation flags
359  * @vma: user vma this address belongs to
360  * @addr: target address for mempolicy
361  *
362  * Returns the struct page for entry and addr, after queueing swapin.
363  *
364  * Primitive swap readahead code. We simply read an aligned block of
365  * (1 << page_cluster) entries in the swap area. This method is chosen
366  * because it doesn't cost us any seek time.  We also make sure to queue
367  * the 'original' request together with the readahead ones...
368  *
369  * This has been extended to use the NUMA policies from the mm triggering
370  * the readahead.
371  *
372  * Caller must hold down_read on the vma->vm_mm if vma is not NULL.
373  */
374 struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
375                         struct vm_area_struct *vma, unsigned long addr)
376 {
377         int nr_pages;
378         struct page *page;
379         unsigned long offset;
380         unsigned long end_offset;
381 
382         /*
383          * Get starting offset for readaround, and number of pages to read.
384          * Adjust starting address by readbehind (for NUMA interleave case)?
385          * No, it's very unlikely that swap layout would follow vma layout,
386          * more likely that neighbouring swap pages came from the same node:
387          * so use the same "addr" to choose the same node for each swap read.
388          */
389         nr_pages = valid_swaphandles(entry, &offset);
390         for (end_offset = offset + nr_pages; offset < end_offset; offset++) {
391                 /* Ok, do the async read-ahead now */
392                 page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
393                                                 gfp_mask, vma, addr);
394                 if (!page)
395                         break;
396                 page_cache_release(page);
397         }
398         lru_add_drain();        /* Push any new pages onto the LRU now */
399         return read_swap_cache_async(entry, gfp_mask, vma, addr);
400 }
401 

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