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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
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         }
41 };
42
43 #define INC_CACHE_INFO(x)       do { swap_cache_info.x++; } while (0)
44
45 static struct {
46         unsigned long add_total;
47         unsigned long del_total;
48         unsigned long find_success;
49         unsigned long find_total;
50 } swap_cache_info;
51
52 unsigned long total_swapcache_pages(void)
53 {
54         int i;
55         unsigned long ret = 0;
56
57         for (i = 0; i < MAX_SWAPFILES; i++)
58                 ret += swapper_spaces[i].nrpages;
59         return ret;
60 }
61
62 static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);
63
64 void show_swap_cache_info(void)
65 {
66         printk("%lu pages in swap cache\n", total_swapcache_pages());
67         printk("Swap cache stats: add %lu, delete %lu, find %lu/%lu\n",
68                 swap_cache_info.add_total, swap_cache_info.del_total,
69                 swap_cache_info.find_success, swap_cache_info.find_total);
70         printk("Free swap  = %ldkB\n",
71                 get_nr_swap_pages() << (PAGE_SHIFT - 10));
72         printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
73 }
74
75 /*
76  * __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
77  * but sets SwapCache flag and private instead of mapping and index.
78  */
79 int __add_to_swap_cache(struct page *page, swp_entry_t entry)
80 {
81         int error;
82         struct address_space *address_space;
83
84         VM_BUG_ON_PAGE(!PageLocked(page), page);
85         VM_BUG_ON_PAGE(PageSwapCache(page), page);
86         VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
87
88         get_page(page);
89         SetPageSwapCache(page);
90         set_page_private(page, entry.val);
91
92         address_space = swap_address_space(entry);
93         spin_lock_irq(&address_space->tree_lock);
94         error = radix_tree_insert(&address_space->page_tree,
95                                         entry.val, page);
96         if (likely(!error)) {
97                 address_space->nrpages++;
98                 __inc_node_page_state(page, NR_FILE_PAGES);
99                 INC_CACHE_INFO(add_total);
100         }
101         spin_unlock_irq(&address_space->tree_lock);
102
103         if (unlikely(error)) {
104                 /*
105                  * Only the context which have set SWAP_HAS_CACHE flag
106                  * would call add_to_swap_cache().
107                  * So add_to_swap_cache() doesn't returns -EEXIST.
108                  */
109                 VM_BUG_ON(error == -EEXIST);
110                 set_page_private(page, 0UL);
111                 ClearPageSwapCache(page);
112                 put_page(page);
113         }
114
115         return error;
116 }
117
118
119 int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
120 {
121         int error;
122
123         error = radix_tree_maybe_preload(gfp_mask);
124         if (!error) {
125                 error = __add_to_swap_cache(page, entry);
126                 radix_tree_preload_end();
127         }
128         return error;
129 }
130
131 /*
132  * This must be called only on pages that have
133  * been verified to be in the swap cache.
134  */
135 void __delete_from_swap_cache(struct page *page)
136 {
137         swp_entry_t entry;
138         struct address_space *address_space;
139
140         VM_BUG_ON_PAGE(!PageLocked(page), page);
141         VM_BUG_ON_PAGE(!PageSwapCache(page), page);
142         VM_BUG_ON_PAGE(PageWriteback(page), page);
143
144         entry.val = page_private(page);
145         address_space = swap_address_space(entry);
146         radix_tree_delete(&address_space->page_tree, page_private(page));
147         set_page_private(page, 0);
148         ClearPageSwapCache(page);
149         address_space->nrpages--;
150         __dec_node_page_state(page, NR_FILE_PAGES);
151         INC_CACHE_INFO(del_total);
152 }
153
154 /**
155  * add_to_swap - allocate swap space for a page
156  * @page: page we want to move to swap
157  *
158  * Allocate swap space for the page and add the page to the
159  * swap cache.  Caller needs to hold the page lock. 
160  */
161 int add_to_swap(struct page *page, struct list_head *list)
162 {
163         swp_entry_t entry;
164         int err;
165
166         VM_BUG_ON_PAGE(!PageLocked(page), page);
167         VM_BUG_ON_PAGE(!PageUptodate(page), page);
168
169         entry = get_swap_page();
170         if (!entry.val)
171                 return 0;
172
173         if (mem_cgroup_try_charge_swap(page, entry)) {
174                 swapcache_free(entry);
175                 return 0;
176         }
177
178         if (unlikely(PageTransHuge(page)))
179                 if (unlikely(split_huge_page_to_list(page, list))) {
180                         swapcache_free(entry);
181                         return 0;
182                 }
183
184         /*
185          * Radix-tree node allocations from PF_MEMALLOC contexts could
186          * completely exhaust the page allocator. __GFP_NOMEMALLOC
187          * stops emergency reserves from being allocated.
188          *
189          * TODO: this could cause a theoretical memory reclaim
190          * deadlock in the swap out path.
191          */
192         /*
193          * Add it to the swap cache.
194          */
195         err = add_to_swap_cache(page, entry,
196                         __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
197
198         if (!err) {
199                 return 1;
200         } else {        /* -ENOMEM radix-tree allocation failure */
201                 /*
202                  * add_to_swap_cache() doesn't return -EEXIST, so we can safely
203                  * clear SWAP_HAS_CACHE flag.
204                  */
205                 swapcache_free(entry);
206                 return 0;
207         }
208 }
209
210 /*
211  * This must be called only on pages that have
212  * been verified to be in the swap cache and locked.
213  * It will never put the page into the free list,
214  * the caller has a reference on the page.
215  */
216 void delete_from_swap_cache(struct page *page)
217 {
218         swp_entry_t entry;
219         struct address_space *address_space;
220
221         entry.val = page_private(page);
222
223         address_space = swap_address_space(entry);
224         spin_lock_irq(&address_space->tree_lock);
225         __delete_from_swap_cache(page);
226         spin_unlock_irq(&address_space->tree_lock);
227
228         swapcache_free(entry);
229         put_page(page);
230 }
231
232 /* 
233  * If we are the only user, then try to free up the swap cache. 
234  * 
235  * Its ok to check for PageSwapCache without the page lock
236  * here because we are going to recheck again inside
237  * try_to_free_swap() _with_ the lock.
238  *                                      - Marcelo
239  */
240 static inline void free_swap_cache(struct page *page)
241 {
242         if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
243                 try_to_free_swap(page);
244                 unlock_page(page);
245         }
246 }
247
248 /* 
249  * Perform a free_page(), also freeing any swap cache associated with
250  * this page if it is the last user of the page.
251  */
252 void free_page_and_swap_cache(struct page *page)
253 {
254         free_swap_cache(page);
255         if (is_huge_zero_page(page))
256                 put_huge_zero_page();
257         else
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), entry.val);
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, entry.val);
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 }