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Linux/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/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 
 21 #include <asm/pgtable.h>
 22 
 23 /*
 24  * swapper_space is a fiction, retained to simplify the path through
 25  * vmscan's shrink_page_list.
 26  */
 27 static const struct address_space_operations swap_aops = {
 28         .writepage      = swap_writepage,
 29         .set_page_dirty = swap_set_page_dirty,
 30 #ifdef CONFIG_MIGRATION
 31         .migratepage    = migrate_page,
 32 #endif
 33 };
 34 
 35 struct address_space swapper_spaces[MAX_SWAPFILES] = {
 36         [0 ... MAX_SWAPFILES - 1] = {
 37                 .page_tree      = RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
 38                 .i_mmap_writable = ATOMIC_INIT(0),
 39                 .a_ops          = &swap_aops,
 40                 /* swap cache doesn't use writeback related tags */
 41                 .flags          = 1 << AS_NO_WRITEBACK_TAGS,
 42         }
 43 };
 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 } swap_cache_info;
 53 
 54 unsigned long total_swapcache_pages(void)
 55 {
 56         int i;
 57         unsigned long ret = 0;
 58 
 59         for (i = 0; i < MAX_SWAPFILES; i++)
 60                 ret += swapper_spaces[i].nrpages;
 61         return ret;
 62 }
 63 
 64 static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);
 65 
 66 void show_swap_cache_info(void)
 67 {
 68         printk("%lu pages in swap cache\n", total_swapcache_pages());
 69         printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
 70                 swap_cache_info.add_total, swap_cache_info.del_total,
 71                 swap_cache_info.find_success, swap_cache_info.find_total);
 72         printk("Free swap  = %ldkB\n",
 73                 get_nr_swap_pages() << (PAGE_SHIFT - 10));
 74         printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
 75 }
 76 
 77 /*
 78  * __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
 79  * but sets SwapCache flag and private instead of mapping and index.
 80  */
 81 int __add_to_swap_cache(struct page *page, swp_entry_t entry)
 82 {
 83         int error;
 84         struct address_space *address_space;
 85 
 86         VM_BUG_ON_PAGE(!PageLocked(page), page);
 87         VM_BUG_ON_PAGE(PageSwapCache(page), page);
 88         VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
 89 
 90         get_page(page);
 91         SetPageSwapCache(page);
 92         set_page_private(page, entry.val);
 93 
 94         address_space = swap_address_space(entry);
 95         spin_lock_irq(&address_space->tree_lock);
 96         error = radix_tree_insert(&address_space->page_tree,
 97                                   swp_offset(entry), page);
 98         if (likely(!error)) {
 99                 address_space->nrpages++;
100                 __inc_node_page_state(page, NR_FILE_PAGES);
101                 INC_CACHE_INFO(add_total);
102         }
103         spin_unlock_irq(&address_space->tree_lock);
104 
105         if (unlikely(error)) {
106                 /*
107                  * Only the context which have set SWAP_HAS_CACHE flag
108                  * would call add_to_swap_cache().
109                  * So add_to_swap_cache() doesn't returns -EEXIST.
110                  */
111                 VM_BUG_ON(error == -EEXIST);
112                 set_page_private(page, 0UL);
113                 ClearPageSwapCache(page);
114                 put_page(page);
115         }
116 
117         return error;
118 }
119 
120 
121 int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
122 {
123         int error;
124 
125         error = radix_tree_maybe_preload(gfp_mask);
126         if (!error) {
127                 error = __add_to_swap_cache(page, entry);
128                 radix_tree_preload_end();
129         }
130         return error;
131 }
132 
133 /*
134  * This must be called only on pages that have
135  * been verified to be in the swap cache.
136  */
137 void __delete_from_swap_cache(struct page *page)
138 {
139         swp_entry_t entry;
140         struct address_space *address_space;
141 
142         VM_BUG_ON_PAGE(!PageLocked(page), page);
143         VM_BUG_ON_PAGE(!PageSwapCache(page), page);
144         VM_BUG_ON_PAGE(PageWriteback(page), page);
145 
146         entry.val = page_private(page);
147         address_space = swap_address_space(entry);
148         radix_tree_delete(&address_space->page_tree, swp_offset(entry));
149         set_page_private(page, 0);
150         ClearPageSwapCache(page);
151         address_space->nrpages--;
152         __dec_node_page_state(page, NR_FILE_PAGES);
153         INC_CACHE_INFO(del_total);
154 }
155 
156 /**
157  * add_to_swap - allocate swap space for a page
158  * @page: page we want to move to swap
159  *
160  * Allocate swap space for the page and add the page to the
161  * swap cache.  Caller needs to hold the page lock. 
162  */
163 int add_to_swap(struct page *page, struct list_head *list)
164 {
165         swp_entry_t entry;
166         int err;
167 
168         VM_BUG_ON_PAGE(!PageLocked(page), page);
169         VM_BUG_ON_PAGE(!PageUptodate(page), page);
170 
171         entry = get_swap_page();
172         if (!entry.val)
173                 return 0;
174 
175         if (mem_cgroup_try_charge_swap(page, entry)) {
176                 swapcache_free(entry);
177                 return 0;
178         }
179 
180         if (unlikely(PageTransHuge(page)))
181                 if (unlikely(split_huge_page_to_list(page, list))) {
182                         swapcache_free(entry);
183                         return 0;
184                 }
185 
186         /*
187          * Radix-tree node allocations from PF_MEMALLOC contexts could
188          * completely exhaust the page allocator. __GFP_NOMEMALLOC
189          * stops emergency reserves from being allocated.
190          *
191          * TODO: this could cause a theoretical memory reclaim
192          * deadlock in the swap out path.
193          */
194         /*
195          * Add it to the swap cache.
196          */
197         err = add_to_swap_cache(page, entry,
198                         __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
199 
200         if (!err) {
201                 return 1;
202         } else {        /* -ENOMEM radix-tree allocation failure */
203                 /*
204                  * add_to_swap_cache() doesn't return -EEXIST, so we can safely
205                  * clear SWAP_HAS_CACHE flag.
206                  */
207                 swapcache_free(entry);
208                 return 0;
209         }
210 }
211 
212 /*
213  * This must be called only on pages that have
214  * been verified to be in the swap cache and locked.
215  * It will never put the page into the free list,
216  * the caller has a reference on the page.
217  */
218 void delete_from_swap_cache(struct page *page)
219 {
220         swp_entry_t entry;
221         struct address_space *address_space;
222 
223         entry.val = page_private(page);
224 
225         address_space = swap_address_space(entry);
226         spin_lock_irq(&address_space->tree_lock);
227         __delete_from_swap_cache(page);
228         spin_unlock_irq(&address_space->tree_lock);
229 
230         swapcache_free(entry);
231         put_page(page);
232 }
233 
234 /* 
235  * If we are the only user, then try to free up the swap cache. 
236  * 
237  * Its ok to check for PageSwapCache without the page lock
238  * here because we are going to recheck again inside
239  * try_to_free_swap() _with_ the lock.
240  *                                      - Marcelo
241  */
242 static inline void free_swap_cache(struct page *page)
243 {
244         if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
245                 try_to_free_swap(page);
246                 unlock_page(page);
247         }
248 }
249 
250 /* 
251  * Perform a free_page(), also freeing any swap cache associated with
252  * this page if it is the last user of the page.
253  */
254 void free_page_and_swap_cache(struct page *page)
255 {
256         free_swap_cache(page);
257         if (!is_huge_zero_page(page))
258                 put_page(page);
259 }
260 
261 /*
262  * Passed an array of pages, drop them all from swapcache and then release
263  * them.  They are removed from the LRU and freed if this is their last use.
264  */
265 void free_pages_and_swap_cache(struct page **pages, int nr)
266 {
267         struct page **pagep = pages;
268         int i;
269 
270         lru_add_drain();
271         for (i = 0; i < nr; i++)
272                 free_swap_cache(pagep[i]);
273         release_pages(pagep, nr, false);
274 }
275 
276 /*
277  * Lookup a swap entry in the swap cache. A found page will be returned
278  * unlocked and with its refcount incremented - we rely on the kernel
279  * lock getting page table operations atomic even if we drop the page
280  * lock before returning.
281  */
282 struct page * lookup_swap_cache(swp_entry_t entry)
283 {
284         struct page *page;
285 
286         page = find_get_page(swap_address_space(entry), swp_offset(entry));
287 
288         if (page) {
289                 INC_CACHE_INFO(find_success);
290                 if (TestClearPageReadahead(page))
291                         atomic_inc(&swapin_readahead_hits);
292         }
293 
294         INC_CACHE_INFO(find_total);
295         return page;
296 }
297 
298 struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
299                         struct vm_area_struct *vma, unsigned long addr,
300                         bool *new_page_allocated)
301 {
302         struct page *found_page, *new_page = NULL;
303         struct address_space *swapper_space = swap_address_space(entry);
304         int err;
305         *new_page_allocated = false;
306 
307         do {
308                 /*
309                  * First check the swap cache.  Since this is normally
310                  * called after lookup_swap_cache() failed, re-calling
311                  * that would confuse statistics.
312                  */
313                 found_page = find_get_page(swapper_space, swp_offset(entry));
314                 if (found_page)
315                         break;
316 
317                 /*
318                  * Get a new page to read into from swap.
319                  */
320                 if (!new_page) {
321                         new_page = alloc_page_vma(gfp_mask, vma, addr);
322                         if (!new_page)
323                                 break;          /* Out of memory */
324                 }
325 
326                 /*
327                  * call radix_tree_preload() while we can wait.
328                  */
329                 err = radix_tree_maybe_preload(gfp_mask & GFP_KERNEL);
330                 if (err)
331                         break;
332 
333                 /*
334                  * Swap entry may have been freed since our caller observed it.
335                  */
336                 err = swapcache_prepare(entry);
337                 if (err == -EEXIST) {
338                         radix_tree_preload_end();
339                         /*
340                          * We might race against get_swap_page() and stumble
341                          * across a SWAP_HAS_CACHE swap_map entry whose page
342                          * has not been brought into the swapcache yet, while
343                          * the other end is scheduled away waiting on discard
344                          * I/O completion at scan_swap_map().
345                          *
346                          * In order to avoid turning this transitory state
347                          * into a permanent loop around this -EEXIST case
348                          * if !CONFIG_PREEMPT and the I/O completion happens
349                          * to be waiting on the CPU waitqueue where we are now
350                          * busy looping, we just conditionally invoke the
351                          * scheduler here, if there are some more important
352                          * tasks to run.
353                          */
354                         cond_resched();
355                         continue;
356                 }
357                 if (err) {              /* swp entry is obsolete ? */
358                         radix_tree_preload_end();
359                         break;
360                 }
361 
362                 /* May fail (-ENOMEM) if radix-tree node allocation failed. */
363                 __SetPageLocked(new_page);
364                 __SetPageSwapBacked(new_page);
365                 err = __add_to_swap_cache(new_page, entry);
366                 if (likely(!err)) {
367                         radix_tree_preload_end();
368                         /*
369                          * Initiate read into locked page and return.
370                          */
371                         lru_cache_add_anon(new_page);
372                         *new_page_allocated = true;
373                         return new_page;
374                 }
375                 radix_tree_preload_end();
376                 __ClearPageLocked(new_page);
377                 /*
378                  * add_to_swap_cache() doesn't return -EEXIST, so we can safely
379                  * clear SWAP_HAS_CACHE flag.
380                  */
381                 swapcache_free(entry);
382         } while (err != -ENOMEM);
383 
384         if (new_page)
385                 put_page(new_page);
386         return found_page;
387 }
388 
389 /*
390  * Locate a page of swap in physical memory, reserving swap cache space
391  * and reading the disk if it is not already cached.
392  * A failure return means that either the page allocation failed or that
393  * the swap entry is no longer in use.
394  */
395 struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
396                         struct vm_area_struct *vma, unsigned long addr)
397 {
398         bool page_was_allocated;
399         struct page *retpage = __read_swap_cache_async(entry, gfp_mask,
400                         vma, addr, &page_was_allocated);
401 
402         if (page_was_allocated)
403                 swap_readpage(retpage);
404 
405         return retpage;
406 }
407 
408 static unsigned long swapin_nr_pages(unsigned long offset)
409 {
410         static unsigned long prev_offset;
411         unsigned int pages, max_pages, last_ra;
412         static atomic_t last_readahead_pages;
413 
414         max_pages = 1 << READ_ONCE(page_cluster);
415         if (max_pages <= 1)
416                 return 1;
417 
418         /*
419          * This heuristic has been found to work well on both sequential and
420          * random loads, swapping to hard disk or to SSD: please don't ask
421          * what the "+ 2" means, it just happens to work well, that's all.
422          */
423         pages = atomic_xchg(&swapin_readahead_hits, 0) + 2;
424         if (pages == 2) {
425                 /*
426                  * We can have no readahead hits to judge by: but must not get
427                  * stuck here forever, so check for an adjacent offset instead
428                  * (and don't even bother to check whether swap type is same).
429                  */
430                 if (offset != prev_offset + 1 && offset != prev_offset - 1)
431                         pages = 1;
432                 prev_offset = offset;
433         } else {
434                 unsigned int roundup = 4;
435                 while (roundup < pages)
436                         roundup <<= 1;
437                 pages = roundup;
438         }
439 
440         if (pages > max_pages)
441                 pages = max_pages;
442 
443         /* Don't shrink readahead too fast */
444         last_ra = atomic_read(&last_readahead_pages) / 2;
445         if (pages < last_ra)
446                 pages = last_ra;
447         atomic_set(&last_readahead_pages, pages);
448 
449         return pages;
450 }
451 
452 /**
453  * swapin_readahead - swap in pages in hope we need them soon
454  * @entry: swap entry of this memory
455  * @gfp_mask: memory allocation flags
456  * @vma: user vma this address belongs to
457  * @addr: target address for mempolicy
458  *
459  * Returns the struct page for entry and addr, after queueing swapin.
460  *
461  * Primitive swap readahead code. We simply read an aligned block of
462  * (1 << page_cluster) entries in the swap area. This method is chosen
463  * because it doesn't cost us any seek time.  We also make sure to queue
464  * the 'original' request together with the readahead ones...
465  *
466  * This has been extended to use the NUMA policies from the mm triggering
467  * the readahead.
468  *
469  * Caller must hold down_read on the vma->vm_mm if vma is not NULL.
470  */
471 struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
472                         struct vm_area_struct *vma, unsigned long addr)
473 {
474         struct page *page;
475         unsigned long entry_offset = swp_offset(entry);
476         unsigned long offset = entry_offset;
477         unsigned long start_offset, end_offset;
478         unsigned long mask;
479         struct blk_plug plug;
480 
481         mask = swapin_nr_pages(offset) - 1;
482         if (!mask)
483                 goto skip;
484 
485         /* Read a page_cluster sized and aligned cluster around offset. */
486         start_offset = offset & ~mask;
487         end_offset = offset | mask;
488         if (!start_offset)      /* First page is swap header. */
489                 start_offset++;
490 
491         blk_start_plug(&plug);
492         for (offset = start_offset; offset <= end_offset ; offset++) {
493                 /* Ok, do the async read-ahead now */
494                 page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
495                                                 gfp_mask, vma, addr);
496                 if (!page)
497                         continue;
498                 if (offset != entry_offset)
499                         SetPageReadahead(page);
500                 put_page(page);
501         }
502         blk_finish_plug(&plug);
503 
504         lru_add_drain();        /* Push any new pages onto the LRU now */
505 skip:
506         return read_swap_cache_async(entry, gfp_mask, vma, addr);
507 }
508 

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