mm, counters: fold __sync_task_rss_stat() into sync_mm_rss()
[linux-2.6.git] / mm / swapfile.c
1 /*
2  *  linux/mm/swapfile.c
3  *
4  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
5  *  Swap reorganised 29.12.95, Stephen Tweedie
6  */
7
8 #include <linux/mm.h>
9 #include <linux/hugetlb.h>
10 #include <linux/mman.h>
11 #include <linux/slab.h>
12 #include <linux/kernel_stat.h>
13 #include <linux/swap.h>
14 #include <linux/vmalloc.h>
15 #include <linux/pagemap.h>
16 #include <linux/namei.h>
17 #include <linux/shmem_fs.h>
18 #include <linux/blkdev.h>
19 #include <linux/random.h>
20 #include <linux/writeback.h>
21 #include <linux/proc_fs.h>
22 #include <linux/seq_file.h>
23 #include <linux/init.h>
24 #include <linux/ksm.h>
25 #include <linux/rmap.h>
26 #include <linux/security.h>
27 #include <linux/backing-dev.h>
28 #include <linux/mutex.h>
29 #include <linux/capability.h>
30 #include <linux/syscalls.h>
31 #include <linux/memcontrol.h>
32 #include <linux/poll.h>
33 #include <linux/oom.h>
34
35 #include <asm/pgtable.h>
36 #include <asm/tlbflush.h>
37 #include <linux/swapops.h>
38 #include <linux/page_cgroup.h>
39
40 static bool swap_count_continued(struct swap_info_struct *, pgoff_t,
41                                  unsigned char);
42 static void free_swap_count_continuations(struct swap_info_struct *);
43 static sector_t map_swap_entry(swp_entry_t, struct block_device**);
44
45 static DEFINE_SPINLOCK(swap_lock);
46 static unsigned int nr_swapfiles;
47 long nr_swap_pages;
48 long total_swap_pages;
49 static int least_priority;
50
51 static const char Bad_file[] = "Bad swap file entry ";
52 static const char Unused_file[] = "Unused swap file entry ";
53 static const char Bad_offset[] = "Bad swap offset entry ";
54 static const char Unused_offset[] = "Unused swap offset entry ";
55
56 static struct swap_list_t swap_list = {-1, -1};
57
58 static struct swap_info_struct *swap_info[MAX_SWAPFILES];
59
60 static DEFINE_MUTEX(swapon_mutex);
61
62 static DECLARE_WAIT_QUEUE_HEAD(proc_poll_wait);
63 /* Activity counter to indicate that a swapon or swapoff has occurred */
64 static atomic_t proc_poll_event = ATOMIC_INIT(0);
65
66 static inline unsigned char swap_count(unsigned char ent)
67 {
68         return ent & ~SWAP_HAS_CACHE;   /* may include SWAP_HAS_CONT flag */
69 }
70
71 /* returns 1 if swap entry is freed */
72 static int
73 __try_to_reclaim_swap(struct swap_info_struct *si, unsigned long offset)
74 {
75         swp_entry_t entry = swp_entry(si->type, offset);
76         struct page *page;
77         int ret = 0;
78
79         page = find_get_page(&swapper_space, entry.val);
80         if (!page)
81                 return 0;
82         /*
83          * This function is called from scan_swap_map() and it's called
84          * by vmscan.c at reclaiming pages. So, we hold a lock on a page, here.
85          * We have to use trylock for avoiding deadlock. This is a special
86          * case and you should use try_to_free_swap() with explicit lock_page()
87          * in usual operations.
88          */
89         if (trylock_page(page)) {
90                 ret = try_to_free_swap(page);
91                 unlock_page(page);
92         }
93         page_cache_release(page);
94         return ret;
95 }
96
97 /*
98  * swapon tell device that all the old swap contents can be discarded,
99  * to allow the swap device to optimize its wear-levelling.
100  */
101 static int discard_swap(struct swap_info_struct *si)
102 {
103         struct swap_extent *se;
104         sector_t start_block;
105         sector_t nr_blocks;
106         int err = 0;
107
108         /* Do not discard the swap header page! */
109         se = &si->first_swap_extent;
110         start_block = (se->start_block + 1) << (PAGE_SHIFT - 9);
111         nr_blocks = ((sector_t)se->nr_pages - 1) << (PAGE_SHIFT - 9);
112         if (nr_blocks) {
113                 err = blkdev_issue_discard(si->bdev, start_block,
114                                 nr_blocks, GFP_KERNEL, 0);
115                 if (err)
116                         return err;
117                 cond_resched();
118         }
119
120         list_for_each_entry(se, &si->first_swap_extent.list, list) {
121                 start_block = se->start_block << (PAGE_SHIFT - 9);
122                 nr_blocks = (sector_t)se->nr_pages << (PAGE_SHIFT - 9);
123
124                 err = blkdev_issue_discard(si->bdev, start_block,
125                                 nr_blocks, GFP_KERNEL, 0);
126                 if (err)
127                         break;
128
129                 cond_resched();
130         }
131         return err;             /* That will often be -EOPNOTSUPP */
132 }
133
134 /*
135  * swap allocation tell device that a cluster of swap can now be discarded,
136  * to allow the swap device to optimize its wear-levelling.
137  */
138 static void discard_swap_cluster(struct swap_info_struct *si,
139                                  pgoff_t start_page, pgoff_t nr_pages)
140 {
141         struct swap_extent *se = si->curr_swap_extent;
142         int found_extent = 0;
143
144         while (nr_pages) {
145                 struct list_head *lh;
146
147                 if (se->start_page <= start_page &&
148                     start_page < se->start_page + se->nr_pages) {
149                         pgoff_t offset = start_page - se->start_page;
150                         sector_t start_block = se->start_block + offset;
151                         sector_t nr_blocks = se->nr_pages - offset;
152
153                         if (nr_blocks > nr_pages)
154                                 nr_blocks = nr_pages;
155                         start_page += nr_blocks;
156                         nr_pages -= nr_blocks;
157
158                         if (!found_extent++)
159                                 si->curr_swap_extent = se;
160
161                         start_block <<= PAGE_SHIFT - 9;
162                         nr_blocks <<= PAGE_SHIFT - 9;
163                         if (blkdev_issue_discard(si->bdev, start_block,
164                                     nr_blocks, GFP_NOIO, 0))
165                                 break;
166                 }
167
168                 lh = se->list.next;
169                 se = list_entry(lh, struct swap_extent, list);
170         }
171 }
172
173 static int wait_for_discard(void *word)
174 {
175         schedule();
176         return 0;
177 }
178
179 #define SWAPFILE_CLUSTER        256
180 #define LATENCY_LIMIT           256
181
182 static unsigned long scan_swap_map(struct swap_info_struct *si,
183                                    unsigned char usage)
184 {
185         unsigned long offset;
186         unsigned long scan_base;
187         unsigned long last_in_cluster = 0;
188         int latency_ration = LATENCY_LIMIT;
189         int found_free_cluster = 0;
190
191         /*
192          * We try to cluster swap pages by allocating them sequentially
193          * in swap.  Once we've allocated SWAPFILE_CLUSTER pages this
194          * way, however, we resort to first-free allocation, starting
195          * a new cluster.  This prevents us from scattering swap pages
196          * all over the entire swap partition, so that we reduce
197          * overall disk seek times between swap pages.  -- sct
198          * But we do now try to find an empty cluster.  -Andrea
199          * And we let swap pages go all over an SSD partition.  Hugh
200          */
201
202         si->flags += SWP_SCANNING;
203         scan_base = offset = si->cluster_next;
204
205         if (unlikely(!si->cluster_nr--)) {
206                 if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER) {
207                         si->cluster_nr = SWAPFILE_CLUSTER - 1;
208                         goto checks;
209                 }
210                 if (si->flags & SWP_DISCARDABLE) {
211                         /*
212                          * Start range check on racing allocations, in case
213                          * they overlap the cluster we eventually decide on
214                          * (we scan without swap_lock to allow preemption).
215                          * It's hardly conceivable that cluster_nr could be
216                          * wrapped during our scan, but don't depend on it.
217                          */
218                         if (si->lowest_alloc)
219                                 goto checks;
220                         si->lowest_alloc = si->max;
221                         si->highest_alloc = 0;
222                 }
223                 spin_unlock(&swap_lock);
224
225                 /*
226                  * If seek is expensive, start searching for new cluster from
227                  * start of partition, to minimize the span of allocated swap.
228                  * But if seek is cheap, search from our current position, so
229                  * that swap is allocated from all over the partition: if the
230                  * Flash Translation Layer only remaps within limited zones,
231                  * we don't want to wear out the first zone too quickly.
232                  */
233                 if (!(si->flags & SWP_SOLIDSTATE))
234                         scan_base = offset = si->lowest_bit;
235                 last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
236
237                 /* Locate the first empty (unaligned) cluster */
238                 for (; last_in_cluster <= si->highest_bit; offset++) {
239                         if (si->swap_map[offset])
240                                 last_in_cluster = offset + SWAPFILE_CLUSTER;
241                         else if (offset == last_in_cluster) {
242                                 spin_lock(&swap_lock);
243                                 offset -= SWAPFILE_CLUSTER - 1;
244                                 si->cluster_next = offset;
245                                 si->cluster_nr = SWAPFILE_CLUSTER - 1;
246                                 found_free_cluster = 1;
247                                 goto checks;
248                         }
249                         if (unlikely(--latency_ration < 0)) {
250                                 cond_resched();
251                                 latency_ration = LATENCY_LIMIT;
252                         }
253                 }
254
255                 offset = si->lowest_bit;
256                 last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
257
258                 /* Locate the first empty (unaligned) cluster */
259                 for (; last_in_cluster < scan_base; offset++) {
260                         if (si->swap_map[offset])
261                                 last_in_cluster = offset + SWAPFILE_CLUSTER;
262                         else if (offset == last_in_cluster) {
263                                 spin_lock(&swap_lock);
264                                 offset -= SWAPFILE_CLUSTER - 1;
265                                 si->cluster_next = offset;
266                                 si->cluster_nr = SWAPFILE_CLUSTER - 1;
267                                 found_free_cluster = 1;
268                                 goto checks;
269                         }
270                         if (unlikely(--latency_ration < 0)) {
271                                 cond_resched();
272                                 latency_ration = LATENCY_LIMIT;
273                         }
274                 }
275
276                 offset = scan_base;
277                 spin_lock(&swap_lock);
278                 si->cluster_nr = SWAPFILE_CLUSTER - 1;
279                 si->lowest_alloc = 0;
280         }
281
282 checks:
283         if (!(si->flags & SWP_WRITEOK))
284                 goto no_page;
285         if (!si->highest_bit)
286                 goto no_page;
287         if (offset > si->highest_bit)
288                 scan_base = offset = si->lowest_bit;
289
290         /* reuse swap entry of cache-only swap if not busy. */
291         if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
292                 int swap_was_freed;
293                 spin_unlock(&swap_lock);
294                 swap_was_freed = __try_to_reclaim_swap(si, offset);
295                 spin_lock(&swap_lock);
296                 /* entry was freed successfully, try to use this again */
297                 if (swap_was_freed)
298                         goto checks;
299                 goto scan; /* check next one */
300         }
301
302         if (si->swap_map[offset])
303                 goto scan;
304
305         if (offset == si->lowest_bit)
306                 si->lowest_bit++;
307         if (offset == si->highest_bit)
308                 si->highest_bit--;
309         si->inuse_pages++;
310         if (si->inuse_pages == si->pages) {
311                 si->lowest_bit = si->max;
312                 si->highest_bit = 0;
313         }
314         si->swap_map[offset] = usage;
315         si->cluster_next = offset + 1;
316         si->flags -= SWP_SCANNING;
317
318         if (si->lowest_alloc) {
319                 /*
320                  * Only set when SWP_DISCARDABLE, and there's a scan
321                  * for a free cluster in progress or just completed.
322                  */
323                 if (found_free_cluster) {
324                         /*
325                          * To optimize wear-levelling, discard the
326                          * old data of the cluster, taking care not to
327                          * discard any of its pages that have already
328                          * been allocated by racing tasks (offset has
329                          * already stepped over any at the beginning).
330                          */
331                         if (offset < si->highest_alloc &&
332                             si->lowest_alloc <= last_in_cluster)
333                                 last_in_cluster = si->lowest_alloc - 1;
334                         si->flags |= SWP_DISCARDING;
335                         spin_unlock(&swap_lock);
336
337                         if (offset < last_in_cluster)
338                                 discard_swap_cluster(si, offset,
339                                         last_in_cluster - offset + 1);
340
341                         spin_lock(&swap_lock);
342                         si->lowest_alloc = 0;
343                         si->flags &= ~SWP_DISCARDING;
344
345                         smp_mb();       /* wake_up_bit advises this */
346                         wake_up_bit(&si->flags, ilog2(SWP_DISCARDING));
347
348                 } else if (si->flags & SWP_DISCARDING) {
349                         /*
350                          * Delay using pages allocated by racing tasks
351                          * until the whole discard has been issued. We
352                          * could defer that delay until swap_writepage,
353                          * but it's easier to keep this self-contained.
354                          */
355                         spin_unlock(&swap_lock);
356                         wait_on_bit(&si->flags, ilog2(SWP_DISCARDING),
357                                 wait_for_discard, TASK_UNINTERRUPTIBLE);
358                         spin_lock(&swap_lock);
359                 } else {
360                         /*
361                          * Note pages allocated by racing tasks while
362                          * scan for a free cluster is in progress, so
363                          * that its final discard can exclude them.
364                          */
365                         if (offset < si->lowest_alloc)
366                                 si->lowest_alloc = offset;
367                         if (offset > si->highest_alloc)
368                                 si->highest_alloc = offset;
369                 }
370         }
371         return offset;
372
373 scan:
374         spin_unlock(&swap_lock);
375         while (++offset <= si->highest_bit) {
376                 if (!si->swap_map[offset]) {
377                         spin_lock(&swap_lock);
378                         goto checks;
379                 }
380                 if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
381                         spin_lock(&swap_lock);
382                         goto checks;
383                 }
384                 if (unlikely(--latency_ration < 0)) {
385                         cond_resched();
386                         latency_ration = LATENCY_LIMIT;
387                 }
388         }
389         offset = si->lowest_bit;
390         while (++offset < scan_base) {
391                 if (!si->swap_map[offset]) {
392                         spin_lock(&swap_lock);
393                         goto checks;
394                 }
395                 if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
396                         spin_lock(&swap_lock);
397                         goto checks;
398                 }
399                 if (unlikely(--latency_ration < 0)) {
400                         cond_resched();
401                         latency_ration = LATENCY_LIMIT;
402                 }
403         }
404         spin_lock(&swap_lock);
405
406 no_page:
407         si->flags -= SWP_SCANNING;
408         return 0;
409 }
410
411 swp_entry_t get_swap_page(void)
412 {
413         struct swap_info_struct *si;
414         pgoff_t offset;
415         int type, next;
416         int wrapped = 0;
417
418         spin_lock(&swap_lock);
419         if (nr_swap_pages <= 0)
420                 goto noswap;
421         nr_swap_pages--;
422
423         for (type = swap_list.next; type >= 0 && wrapped < 2; type = next) {
424                 si = swap_info[type];
425                 next = si->next;
426                 if (next < 0 ||
427                     (!wrapped && si->prio != swap_info[next]->prio)) {
428                         next = swap_list.head;
429                         wrapped++;
430                 }
431
432                 if (!si->highest_bit)
433                         continue;
434                 if (!(si->flags & SWP_WRITEOK))
435                         continue;
436
437                 swap_list.next = next;
438                 /* This is called for allocating swap entry for cache */
439                 offset = scan_swap_map(si, SWAP_HAS_CACHE);
440                 if (offset) {
441                         spin_unlock(&swap_lock);
442                         return swp_entry(type, offset);
443                 }
444                 next = swap_list.next;
445         }
446
447         nr_swap_pages++;
448 noswap:
449         spin_unlock(&swap_lock);
450         return (swp_entry_t) {0};
451 }
452
453 /* The only caller of this function is now susupend routine */
454 swp_entry_t get_swap_page_of_type(int type)
455 {
456         struct swap_info_struct *si;
457         pgoff_t offset;
458
459         spin_lock(&swap_lock);
460         si = swap_info[type];
461         if (si && (si->flags & SWP_WRITEOK)) {
462                 nr_swap_pages--;
463                 /* This is called for allocating swap entry, not cache */
464                 offset = scan_swap_map(si, 1);
465                 if (offset) {
466                         spin_unlock(&swap_lock);
467                         return swp_entry(type, offset);
468                 }
469                 nr_swap_pages++;
470         }
471         spin_unlock(&swap_lock);
472         return (swp_entry_t) {0};
473 }
474
475 static struct swap_info_struct *swap_info_get(swp_entry_t entry)
476 {
477         struct swap_info_struct *p;
478         unsigned long offset, type;
479
480         if (!entry.val)
481                 goto out;
482         type = swp_type(entry);
483         if (type >= nr_swapfiles)
484                 goto bad_nofile;
485         p = swap_info[type];
486         if (!(p->flags & SWP_USED))
487                 goto bad_device;
488         offset = swp_offset(entry);
489         if (offset >= p->max)
490                 goto bad_offset;
491         if (!p->swap_map[offset])
492                 goto bad_free;
493         spin_lock(&swap_lock);
494         return p;
495
496 bad_free:
497         printk(KERN_ERR "swap_free: %s%08lx\n", Unused_offset, entry.val);
498         goto out;
499 bad_offset:
500         printk(KERN_ERR "swap_free: %s%08lx\n", Bad_offset, entry.val);
501         goto out;
502 bad_device:
503         printk(KERN_ERR "swap_free: %s%08lx\n", Unused_file, entry.val);
504         goto out;
505 bad_nofile:
506         printk(KERN_ERR "swap_free: %s%08lx\n", Bad_file, entry.val);
507 out:
508         return NULL;
509 }
510
511 static unsigned char swap_entry_free(struct swap_info_struct *p,
512                                      swp_entry_t entry, unsigned char usage)
513 {
514         unsigned long offset = swp_offset(entry);
515         unsigned char count;
516         unsigned char has_cache;
517
518         count = p->swap_map[offset];
519         has_cache = count & SWAP_HAS_CACHE;
520         count &= ~SWAP_HAS_CACHE;
521
522         if (usage == SWAP_HAS_CACHE) {
523                 VM_BUG_ON(!has_cache);
524                 has_cache = 0;
525         } else if (count == SWAP_MAP_SHMEM) {
526                 /*
527                  * Or we could insist on shmem.c using a special
528                  * swap_shmem_free() and free_shmem_swap_and_cache()...
529                  */
530                 count = 0;
531         } else if ((count & ~COUNT_CONTINUED) <= SWAP_MAP_MAX) {
532                 if (count == COUNT_CONTINUED) {
533                         if (swap_count_continued(p, offset, count))
534                                 count = SWAP_MAP_MAX | COUNT_CONTINUED;
535                         else
536                                 count = SWAP_MAP_MAX;
537                 } else
538                         count--;
539         }
540
541         if (!count)
542                 mem_cgroup_uncharge_swap(entry);
543
544         usage = count | has_cache;
545         p->swap_map[offset] = usage;
546
547         /* free if no reference */
548         if (!usage) {
549                 struct gendisk *disk = p->bdev->bd_disk;
550                 if (offset < p->lowest_bit)
551                         p->lowest_bit = offset;
552                 if (offset > p->highest_bit)
553                         p->highest_bit = offset;
554                 if (swap_list.next >= 0 &&
555                     p->prio > swap_info[swap_list.next]->prio)
556                         swap_list.next = p->type;
557                 nr_swap_pages++;
558                 p->inuse_pages--;
559                 if ((p->flags & SWP_BLKDEV) &&
560                                 disk->fops->swap_slot_free_notify)
561                         disk->fops->swap_slot_free_notify(p->bdev, offset);
562         }
563
564         return usage;
565 }
566
567 /*
568  * Caller has made sure that the swapdevice corresponding to entry
569  * is still around or has not been recycled.
570  */
571 void swap_free(swp_entry_t entry)
572 {
573         struct swap_info_struct *p;
574
575         p = swap_info_get(entry);
576         if (p) {
577                 swap_entry_free(p, entry, 1);
578                 spin_unlock(&swap_lock);
579         }
580 }
581
582 /*
583  * Called after dropping swapcache to decrease refcnt to swap entries.
584  */
585 void swapcache_free(swp_entry_t entry, struct page *page)
586 {
587         struct swap_info_struct *p;
588         unsigned char count;
589
590         p = swap_info_get(entry);
591         if (p) {
592                 count = swap_entry_free(p, entry, SWAP_HAS_CACHE);
593                 if (page)
594                         mem_cgroup_uncharge_swapcache(page, entry, count != 0);
595                 spin_unlock(&swap_lock);
596         }
597 }
598
599 /*
600  * How many references to page are currently swapped out?
601  * This does not give an exact answer when swap count is continued,
602  * but does include the high COUNT_CONTINUED flag to allow for that.
603  */
604 static inline int page_swapcount(struct page *page)
605 {
606         int count = 0;
607         struct swap_info_struct *p;
608         swp_entry_t entry;
609
610         entry.val = page_private(page);
611         p = swap_info_get(entry);
612         if (p) {
613                 count = swap_count(p->swap_map[swp_offset(entry)]);
614                 spin_unlock(&swap_lock);
615         }
616         return count;
617 }
618
619 /*
620  * We can write to an anon page without COW if there are no other references
621  * to it.  And as a side-effect, free up its swap: because the old content
622  * on disk will never be read, and seeking back there to write new content
623  * later would only waste time away from clustering.
624  */
625 int reuse_swap_page(struct page *page)
626 {
627         int count;
628
629         VM_BUG_ON(!PageLocked(page));
630         if (unlikely(PageKsm(page)))
631                 return 0;
632         count = page_mapcount(page);
633         if (count <= 1 && PageSwapCache(page)) {
634                 count += page_swapcount(page);
635                 if (count == 1 && !PageWriteback(page)) {
636                         delete_from_swap_cache(page);
637                         SetPageDirty(page);
638                 }
639         }
640         return count <= 1;
641 }
642
643 /*
644  * If swap is getting full, or if there are no more mappings of this page,
645  * then try_to_free_swap is called to free its swap space.
646  */
647 int try_to_free_swap(struct page *page)
648 {
649         VM_BUG_ON(!PageLocked(page));
650
651         if (!PageSwapCache(page))
652                 return 0;
653         if (PageWriteback(page))
654                 return 0;
655         if (page_swapcount(page))
656                 return 0;
657
658         /*
659          * Once hibernation has begun to create its image of memory,
660          * there's a danger that one of the calls to try_to_free_swap()
661          * - most probably a call from __try_to_reclaim_swap() while
662          * hibernation is allocating its own swap pages for the image,
663          * but conceivably even a call from memory reclaim - will free
664          * the swap from a page which has already been recorded in the
665          * image as a clean swapcache page, and then reuse its swap for
666          * another page of the image.  On waking from hibernation, the
667          * original page might be freed under memory pressure, then
668          * later read back in from swap, now with the wrong data.
669          *
670          * Hibration suspends storage while it is writing the image
671          * to disk so check that here.
672          */
673         if (pm_suspended_storage())
674                 return 0;
675
676         delete_from_swap_cache(page);
677         SetPageDirty(page);
678         return 1;
679 }
680
681 /*
682  * Free the swap entry like above, but also try to
683  * free the page cache entry if it is the last user.
684  */
685 int free_swap_and_cache(swp_entry_t entry)
686 {
687         struct swap_info_struct *p;
688         struct page *page = NULL;
689
690         if (non_swap_entry(entry))
691                 return 1;
692
693         p = swap_info_get(entry);
694         if (p) {
695                 if (swap_entry_free(p, entry, 1) == SWAP_HAS_CACHE) {
696                         page = find_get_page(&swapper_space, entry.val);
697                         if (page && !trylock_page(page)) {
698                                 page_cache_release(page);
699                                 page = NULL;
700                         }
701                 }
702                 spin_unlock(&swap_lock);
703         }
704         if (page) {
705                 /*
706                  * Not mapped elsewhere, or swap space full? Free it!
707                  * Also recheck PageSwapCache now page is locked (above).
708                  */
709                 if (PageSwapCache(page) && !PageWriteback(page) &&
710                                 (!page_mapped(page) || vm_swap_full())) {
711                         delete_from_swap_cache(page);
712                         SetPageDirty(page);
713                 }
714                 unlock_page(page);
715                 page_cache_release(page);
716         }
717         return p != NULL;
718 }
719
720 #ifdef CONFIG_CGROUP_MEM_RES_CTLR
721 /**
722  * mem_cgroup_count_swap_user - count the user of a swap entry
723  * @ent: the swap entry to be checked
724  * @pagep: the pointer for the swap cache page of the entry to be stored
725  *
726  * Returns the number of the user of the swap entry. The number is valid only
727  * for swaps of anonymous pages.
728  * If the entry is found on swap cache, the page is stored to pagep with
729  * refcount of it being incremented.
730  */
731 int mem_cgroup_count_swap_user(swp_entry_t ent, struct page **pagep)
732 {
733         struct page *page;
734         struct swap_info_struct *p;
735         int count = 0;
736
737         page = find_get_page(&swapper_space, ent.val);
738         if (page)
739                 count += page_mapcount(page);
740         p = swap_info_get(ent);
741         if (p) {
742                 count += swap_count(p->swap_map[swp_offset(ent)]);
743                 spin_unlock(&swap_lock);
744         }
745
746         *pagep = page;
747         return count;
748 }
749 #endif
750
751 #ifdef CONFIG_HIBERNATION
752 /*
753  * Find the swap type that corresponds to given device (if any).
754  *
755  * @offset - number of the PAGE_SIZE-sized block of the device, starting
756  * from 0, in which the swap header is expected to be located.
757  *
758  * This is needed for the suspend to disk (aka swsusp).
759  */
760 int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)
761 {
762         struct block_device *bdev = NULL;
763         int type;
764
765         if (device)
766                 bdev = bdget(device);
767
768         spin_lock(&swap_lock);
769         for (type = 0; type < nr_swapfiles; type++) {
770                 struct swap_info_struct *sis = swap_info[type];
771
772                 if (!(sis->flags & SWP_WRITEOK))
773                         continue;
774
775                 if (!bdev) {
776                         if (bdev_p)
777                                 *bdev_p = bdgrab(sis->bdev);
778
779                         spin_unlock(&swap_lock);
780                         return type;
781                 }
782                 if (bdev == sis->bdev) {
783                         struct swap_extent *se = &sis->first_swap_extent;
784
785                         if (se->start_block == offset) {
786                                 if (bdev_p)
787                                         *bdev_p = bdgrab(sis->bdev);
788
789                                 spin_unlock(&swap_lock);
790                                 bdput(bdev);
791                                 return type;
792                         }
793                 }
794         }
795         spin_unlock(&swap_lock);
796         if (bdev)
797                 bdput(bdev);
798
799         return -ENODEV;
800 }
801
802 /*
803  * Get the (PAGE_SIZE) block corresponding to given offset on the swapdev
804  * corresponding to given index in swap_info (swap type).
805  */
806 sector_t swapdev_block(int type, pgoff_t offset)
807 {
808         struct block_device *bdev;
809
810         if ((unsigned int)type >= nr_swapfiles)
811                 return 0;
812         if (!(swap_info[type]->flags & SWP_WRITEOK))
813                 return 0;
814         return map_swap_entry(swp_entry(type, offset), &bdev);
815 }
816
817 /*
818  * Return either the total number of swap pages of given type, or the number
819  * of free pages of that type (depending on @free)
820  *
821  * This is needed for software suspend
822  */
823 unsigned int count_swap_pages(int type, int free)
824 {
825         unsigned int n = 0;
826
827         spin_lock(&swap_lock);
828         if ((unsigned int)type < nr_swapfiles) {
829                 struct swap_info_struct *sis = swap_info[type];
830
831                 if (sis->flags & SWP_WRITEOK) {
832                         n = sis->pages;
833                         if (free)
834                                 n -= sis->inuse_pages;
835                 }
836         }
837         spin_unlock(&swap_lock);
838         return n;
839 }
840 #endif /* CONFIG_HIBERNATION */
841
842 /*
843  * No need to decide whether this PTE shares the swap entry with others,
844  * just let do_wp_page work it out if a write is requested later - to
845  * force COW, vm_page_prot omits write permission from any private vma.
846  */
847 static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
848                 unsigned long addr, swp_entry_t entry, struct page *page)
849 {
850         struct mem_cgroup *memcg;
851         spinlock_t *ptl;
852         pte_t *pte;
853         int ret = 1;
854
855         if (mem_cgroup_try_charge_swapin(vma->vm_mm, page,
856                                          GFP_KERNEL, &memcg)) {
857                 ret = -ENOMEM;
858                 goto out_nolock;
859         }
860
861         pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
862         if (unlikely(!pte_same(*pte, swp_entry_to_pte(entry)))) {
863                 if (ret > 0)
864                         mem_cgroup_cancel_charge_swapin(memcg);
865                 ret = 0;
866                 goto out;
867         }
868
869         dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
870         inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
871         get_page(page);
872         set_pte_at(vma->vm_mm, addr, pte,
873                    pte_mkold(mk_pte(page, vma->vm_page_prot)));
874         page_add_anon_rmap(page, vma, addr);
875         mem_cgroup_commit_charge_swapin(page, memcg);
876         swap_free(entry);
877         /*
878          * Move the page to the active list so it is not
879          * immediately swapped out again after swapon.
880          */
881         activate_page(page);
882 out:
883         pte_unmap_unlock(pte, ptl);
884 out_nolock:
885         return ret;
886 }
887
888 static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
889                                 unsigned long addr, unsigned long end,
890                                 swp_entry_t entry, struct page *page)
891 {
892         pte_t swp_pte = swp_entry_to_pte(entry);
893         pte_t *pte;
894         int ret = 0;
895
896         /*
897          * We don't actually need pte lock while scanning for swp_pte: since
898          * we hold page lock and mmap_sem, swp_pte cannot be inserted into the
899          * page table while we're scanning; though it could get zapped, and on
900          * some architectures (e.g. x86_32 with PAE) we might catch a glimpse
901          * of unmatched parts which look like swp_pte, so unuse_pte must
902          * recheck under pte lock.  Scanning without pte lock lets it be
903          * preemptible whenever CONFIG_PREEMPT but not CONFIG_HIGHPTE.
904          */
905         pte = pte_offset_map(pmd, addr);
906         do {
907                 /*
908                  * swapoff spends a _lot_ of time in this loop!
909                  * Test inline before going to call unuse_pte.
910                  */
911                 if (unlikely(pte_same(*pte, swp_pte))) {
912                         pte_unmap(pte);
913                         ret = unuse_pte(vma, pmd, addr, entry, page);
914                         if (ret)
915                                 goto out;
916                         pte = pte_offset_map(pmd, addr);
917                 }
918         } while (pte++, addr += PAGE_SIZE, addr != end);
919         pte_unmap(pte - 1);
920 out:
921         return ret;
922 }
923
924 static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
925                                 unsigned long addr, unsigned long end,
926                                 swp_entry_t entry, struct page *page)
927 {
928         pmd_t *pmd;
929         unsigned long next;
930         int ret;
931
932         pmd = pmd_offset(pud, addr);
933         do {
934                 next = pmd_addr_end(addr, end);
935                 if (pmd_none_or_trans_huge_or_clear_bad(pmd))
936                         continue;
937                 ret = unuse_pte_range(vma, pmd, addr, next, entry, page);
938                 if (ret)
939                         return ret;
940         } while (pmd++, addr = next, addr != end);
941         return 0;
942 }
943
944 static inline int unuse_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
945                                 unsigned long addr, unsigned long end,
946                                 swp_entry_t entry, struct page *page)
947 {
948         pud_t *pud;
949         unsigned long next;
950         int ret;
951
952         pud = pud_offset(pgd, addr);
953         do {
954                 next = pud_addr_end(addr, end);
955                 if (pud_none_or_clear_bad(pud))
956                         continue;
957                 ret = unuse_pmd_range(vma, pud, addr, next, entry, page);
958                 if (ret)
959                         return ret;
960         } while (pud++, addr = next, addr != end);
961         return 0;
962 }
963
964 static int unuse_vma(struct vm_area_struct *vma,
965                                 swp_entry_t entry, struct page *page)
966 {
967         pgd_t *pgd;
968         unsigned long addr, end, next;
969         int ret;
970
971         if (page_anon_vma(page)) {
972                 addr = page_address_in_vma(page, vma);
973                 if (addr == -EFAULT)
974                         return 0;
975                 else
976                         end = addr + PAGE_SIZE;
977         } else {
978                 addr = vma->vm_start;
979                 end = vma->vm_end;
980         }
981
982         pgd = pgd_offset(vma->vm_mm, addr);
983         do {
984                 next = pgd_addr_end(addr, end);
985                 if (pgd_none_or_clear_bad(pgd))
986                         continue;
987                 ret = unuse_pud_range(vma, pgd, addr, next, entry, page);
988                 if (ret)
989                         return ret;
990         } while (pgd++, addr = next, addr != end);
991         return 0;
992 }
993
994 static int unuse_mm(struct mm_struct *mm,
995                                 swp_entry_t entry, struct page *page)
996 {
997         struct vm_area_struct *vma;
998         int ret = 0;
999
1000         if (!down_read_trylock(&mm->mmap_sem)) {
1001                 /*
1002                  * Activate page so shrink_inactive_list is unlikely to unmap
1003                  * its ptes while lock is dropped, so swapoff can make progress.
1004                  */
1005                 activate_page(page);
1006                 unlock_page(page);
1007                 down_read(&mm->mmap_sem);
1008                 lock_page(page);
1009         }
1010         for (vma = mm->mmap; vma; vma = vma->vm_next) {
1011                 if (vma->anon_vma && (ret = unuse_vma(vma, entry, page)))
1012                         break;
1013         }
1014         up_read(&mm->mmap_sem);
1015         return (ret < 0)? ret: 0;
1016 }
1017
1018 /*
1019  * Scan swap_map from current position to next entry still in use.
1020  * Recycle to start on reaching the end, returning 0 when empty.
1021  */
1022 static unsigned int find_next_to_unuse(struct swap_info_struct *si,
1023                                         unsigned int prev)
1024 {
1025         unsigned int max = si->max;
1026         unsigned int i = prev;
1027         unsigned char count;
1028
1029         /*
1030          * No need for swap_lock here: we're just looking
1031          * for whether an entry is in use, not modifying it; false
1032          * hits are okay, and sys_swapoff() has already prevented new
1033          * allocations from this area (while holding swap_lock).
1034          */
1035         for (;;) {
1036                 if (++i >= max) {
1037                         if (!prev) {
1038                                 i = 0;
1039                                 break;
1040                         }
1041                         /*
1042                          * No entries in use at top of swap_map,
1043                          * loop back to start and recheck there.
1044                          */
1045                         max = prev + 1;
1046                         prev = 0;
1047                         i = 1;
1048                 }
1049                 count = si->swap_map[i];
1050                 if (count && swap_count(count) != SWAP_MAP_BAD)
1051                         break;
1052         }
1053         return i;
1054 }
1055
1056 /*
1057  * We completely avoid races by reading each swap page in advance,
1058  * and then search for the process using it.  All the necessary
1059  * page table adjustments can then be made atomically.
1060  */
1061 static int try_to_unuse(unsigned int type)
1062 {
1063         struct swap_info_struct *si = swap_info[type];
1064         struct mm_struct *start_mm;
1065         unsigned char *swap_map;
1066         unsigned char swcount;
1067         struct page *page;
1068         swp_entry_t entry;
1069         unsigned int i = 0;
1070         int retval = 0;
1071
1072         /*
1073          * When searching mms for an entry, a good strategy is to
1074          * start at the first mm we freed the previous entry from
1075          * (though actually we don't notice whether we or coincidence
1076          * freed the entry).  Initialize this start_mm with a hold.
1077          *
1078          * A simpler strategy would be to start at the last mm we
1079          * freed the previous entry from; but that would take less
1080          * advantage of mmlist ordering, which clusters forked mms
1081          * together, child after parent.  If we race with dup_mmap(), we
1082          * prefer to resolve parent before child, lest we miss entries
1083          * duplicated after we scanned child: using last mm would invert
1084          * that.
1085          */
1086         start_mm = &init_mm;
1087         atomic_inc(&init_mm.mm_users);
1088
1089         /*
1090          * Keep on scanning until all entries have gone.  Usually,
1091          * one pass through swap_map is enough, but not necessarily:
1092          * there are races when an instance of an entry might be missed.
1093          */
1094         while ((i = find_next_to_unuse(si, i)) != 0) {
1095                 if (signal_pending(current)) {
1096                         retval = -EINTR;
1097                         break;
1098                 }
1099
1100                 /*
1101                  * Get a page for the entry, using the existing swap
1102                  * cache page if there is one.  Otherwise, get a clean
1103                  * page and read the swap into it.
1104                  */
1105                 swap_map = &si->swap_map[i];
1106                 entry = swp_entry(type, i);
1107                 page = read_swap_cache_async(entry,
1108                                         GFP_HIGHUSER_MOVABLE, NULL, 0);
1109                 if (!page) {
1110                         /*
1111                          * Either swap_duplicate() failed because entry
1112                          * has been freed independently, and will not be
1113                          * reused since sys_swapoff() already disabled
1114                          * allocation from here, or alloc_page() failed.
1115                          */
1116                         if (!*swap_map)
1117                                 continue;
1118                         retval = -ENOMEM;
1119                         break;
1120                 }
1121
1122                 /*
1123                  * Don't hold on to start_mm if it looks like exiting.
1124                  */
1125                 if (atomic_read(&start_mm->mm_users) == 1) {
1126                         mmput(start_mm);
1127                         start_mm = &init_mm;
1128                         atomic_inc(&init_mm.mm_users);
1129                 }
1130
1131                 /*
1132                  * Wait for and lock page.  When do_swap_page races with
1133                  * try_to_unuse, do_swap_page can handle the fault much
1134                  * faster than try_to_unuse can locate the entry.  This
1135                  * apparently redundant "wait_on_page_locked" lets try_to_unuse
1136                  * defer to do_swap_page in such a case - in some tests,
1137                  * do_swap_page and try_to_unuse repeatedly compete.
1138                  */
1139                 wait_on_page_locked(page);
1140                 wait_on_page_writeback(page);
1141                 lock_page(page);
1142                 wait_on_page_writeback(page);
1143
1144                 /*
1145                  * Remove all references to entry.
1146                  */
1147                 swcount = *swap_map;
1148                 if (swap_count(swcount) == SWAP_MAP_SHMEM) {
1149                         retval = shmem_unuse(entry, page);
1150                         /* page has already been unlocked and released */
1151                         if (retval < 0)
1152                                 break;
1153                         continue;
1154                 }
1155                 if (swap_count(swcount) && start_mm != &init_mm)
1156                         retval = unuse_mm(start_mm, entry, page);
1157
1158                 if (swap_count(*swap_map)) {
1159                         int set_start_mm = (*swap_map >= swcount);
1160                         struct list_head *p = &start_mm->mmlist;
1161                         struct mm_struct *new_start_mm = start_mm;
1162                         struct mm_struct *prev_mm = start_mm;
1163                         struct mm_struct *mm;
1164
1165                         atomic_inc(&new_start_mm->mm_users);
1166                         atomic_inc(&prev_mm->mm_users);
1167                         spin_lock(&mmlist_lock);
1168                         while (swap_count(*swap_map) && !retval &&
1169                                         (p = p->next) != &start_mm->mmlist) {
1170                                 mm = list_entry(p, struct mm_struct, mmlist);
1171                                 if (!atomic_inc_not_zero(&mm->mm_users))
1172                                         continue;
1173                                 spin_unlock(&mmlist_lock);
1174                                 mmput(prev_mm);
1175                                 prev_mm = mm;
1176
1177                                 cond_resched();
1178
1179                                 swcount = *swap_map;
1180                                 if (!swap_count(swcount)) /* any usage ? */
1181                                         ;
1182                                 else if (mm == &init_mm)
1183                                         set_start_mm = 1;
1184                                 else
1185                                         retval = unuse_mm(mm, entry, page);
1186
1187                                 if (set_start_mm && *swap_map < swcount) {
1188                                         mmput(new_start_mm);
1189                                         atomic_inc(&mm->mm_users);
1190                                         new_start_mm = mm;
1191                                         set_start_mm = 0;
1192                                 }
1193                                 spin_lock(&mmlist_lock);
1194                         }
1195                         spin_unlock(&mmlist_lock);
1196                         mmput(prev_mm);
1197                         mmput(start_mm);
1198                         start_mm = new_start_mm;
1199                 }
1200                 if (retval) {
1201                         unlock_page(page);
1202                         page_cache_release(page);
1203                         break;
1204                 }
1205
1206                 /*
1207                  * If a reference remains (rare), we would like to leave
1208                  * the page in the swap cache; but try_to_unmap could
1209                  * then re-duplicate the entry once we drop page lock,
1210                  * so we might loop indefinitely; also, that page could
1211                  * not be swapped out to other storage meanwhile.  So:
1212                  * delete from cache even if there's another reference,
1213                  * after ensuring that the data has been saved to disk -
1214                  * since if the reference remains (rarer), it will be
1215                  * read from disk into another page.  Splitting into two
1216                  * pages would be incorrect if swap supported "shared
1217                  * private" pages, but they are handled by tmpfs files.
1218                  *
1219                  * Given how unuse_vma() targets one particular offset
1220                  * in an anon_vma, once the anon_vma has been determined,
1221                  * this splitting happens to be just what is needed to
1222                  * handle where KSM pages have been swapped out: re-reading
1223                  * is unnecessarily slow, but we can fix that later on.
1224                  */
1225                 if (swap_count(*swap_map) &&
1226                      PageDirty(page) && PageSwapCache(page)) {
1227                         struct writeback_control wbc = {
1228                                 .sync_mode = WB_SYNC_NONE,
1229                         };
1230
1231                         swap_writepage(page, &wbc);
1232                         lock_page(page);
1233                         wait_on_page_writeback(page);
1234                 }
1235
1236                 /*
1237                  * It is conceivable that a racing task removed this page from
1238                  * swap cache just before we acquired the page lock at the top,
1239                  * or while we dropped it in unuse_mm().  The page might even
1240                  * be back in swap cache on another swap area: that we must not
1241                  * delete, since it may not have been written out to swap yet.
1242                  */
1243                 if (PageSwapCache(page) &&
1244                     likely(page_private(page) == entry.val))
1245                         delete_from_swap_cache(page);
1246
1247                 /*
1248                  * So we could skip searching mms once swap count went
1249                  * to 1, we did not mark any present ptes as dirty: must
1250                  * mark page dirty so shrink_page_list will preserve it.
1251                  */
1252                 SetPageDirty(page);
1253                 unlock_page(page);
1254                 page_cache_release(page);
1255
1256                 /*
1257                  * Make sure that we aren't completely killing
1258                  * interactive performance.
1259                  */
1260                 cond_resched();
1261         }
1262
1263         mmput(start_mm);
1264         return retval;
1265 }
1266
1267 /*
1268  * After a successful try_to_unuse, if no swap is now in use, we know
1269  * we can empty the mmlist.  swap_lock must be held on entry and exit.
1270  * Note that mmlist_lock nests inside swap_lock, and an mm must be
1271  * added to the mmlist just after page_duplicate - before would be racy.
1272  */
1273 static void drain_mmlist(void)
1274 {
1275         struct list_head *p, *next;
1276         unsigned int type;
1277
1278         for (type = 0; type < nr_swapfiles; type++)
1279                 if (swap_info[type]->inuse_pages)
1280                         return;
1281         spin_lock(&mmlist_lock);
1282         list_for_each_safe(p, next, &init_mm.mmlist)
1283                 list_del_init(p);
1284         spin_unlock(&mmlist_lock);
1285 }
1286
1287 /*
1288  * Use this swapdev's extent info to locate the (PAGE_SIZE) block which
1289  * corresponds to page offset for the specified swap entry.
1290  * Note that the type of this function is sector_t, but it returns page offset
1291  * into the bdev, not sector offset.
1292  */
1293 static sector_t map_swap_entry(swp_entry_t entry, struct block_device **bdev)
1294 {
1295         struct swap_info_struct *sis;
1296         struct swap_extent *start_se;
1297         struct swap_extent *se;
1298         pgoff_t offset;
1299
1300         sis = swap_info[swp_type(entry)];
1301         *bdev = sis->bdev;
1302
1303         offset = swp_offset(entry);
1304         start_se = sis->curr_swap_extent;
1305         se = start_se;
1306
1307         for ( ; ; ) {
1308                 struct list_head *lh;
1309
1310                 if (se->start_page <= offset &&
1311                                 offset < (se->start_page + se->nr_pages)) {
1312                         return se->start_block + (offset - se->start_page);
1313                 }
1314                 lh = se->list.next;
1315                 se = list_entry(lh, struct swap_extent, list);
1316                 sis->curr_swap_extent = se;
1317                 BUG_ON(se == start_se);         /* It *must* be present */
1318         }
1319 }
1320
1321 /*
1322  * Returns the page offset into bdev for the specified page's swap entry.
1323  */
1324 sector_t map_swap_page(struct page *page, struct block_device **bdev)
1325 {
1326         swp_entry_t entry;
1327         entry.val = page_private(page);
1328         return map_swap_entry(entry, bdev);
1329 }
1330
1331 /*
1332  * Free all of a swapdev's extent information
1333  */
1334 static void destroy_swap_extents(struct swap_info_struct *sis)
1335 {
1336         while (!list_empty(&sis->first_swap_extent.list)) {
1337                 struct swap_extent *se;
1338
1339                 se = list_entry(sis->first_swap_extent.list.next,
1340                                 struct swap_extent, list);
1341                 list_del(&se->list);
1342                 kfree(se);
1343         }
1344 }
1345
1346 /*
1347  * Add a block range (and the corresponding page range) into this swapdev's
1348  * extent list.  The extent list is kept sorted in page order.
1349  *
1350  * This function rather assumes that it is called in ascending page order.
1351  */
1352 static int
1353 add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
1354                 unsigned long nr_pages, sector_t start_block)
1355 {
1356         struct swap_extent *se;
1357         struct swap_extent *new_se;
1358         struct list_head *lh;
1359
1360         if (start_page == 0) {
1361                 se = &sis->first_swap_extent;
1362                 sis->curr_swap_extent = se;
1363                 se->start_page = 0;
1364                 se->nr_pages = nr_pages;
1365                 se->start_block = start_block;
1366                 return 1;
1367         } else {
1368                 lh = sis->first_swap_extent.list.prev;  /* Highest extent */
1369                 se = list_entry(lh, struct swap_extent, list);
1370                 BUG_ON(se->start_page + se->nr_pages != start_page);
1371                 if (se->start_block + se->nr_pages == start_block) {
1372                         /* Merge it */
1373                         se->nr_pages += nr_pages;
1374                         return 0;
1375                 }
1376         }
1377
1378         /*
1379          * No merge.  Insert a new extent, preserving ordering.
1380          */
1381         new_se = kmalloc(sizeof(*se), GFP_KERNEL);
1382         if (new_se == NULL)
1383                 return -ENOMEM;
1384         new_se->start_page = start_page;
1385         new_se->nr_pages = nr_pages;
1386         new_se->start_block = start_block;
1387
1388         list_add_tail(&new_se->list, &sis->first_swap_extent.list);
1389         return 1;
1390 }
1391
1392 /*
1393  * A `swap extent' is a simple thing which maps a contiguous range of pages
1394  * onto a contiguous range of disk blocks.  An ordered list of swap extents
1395  * is built at swapon time and is then used at swap_writepage/swap_readpage
1396  * time for locating where on disk a page belongs.
1397  *
1398  * If the swapfile is an S_ISBLK block device, a single extent is installed.
1399  * This is done so that the main operating code can treat S_ISBLK and S_ISREG
1400  * swap files identically.
1401  *
1402  * Whether the swapdev is an S_ISREG file or an S_ISBLK blockdev, the swap
1403  * extent list operates in PAGE_SIZE disk blocks.  Both S_ISREG and S_ISBLK
1404  * swapfiles are handled *identically* after swapon time.
1405  *
1406  * For S_ISREG swapfiles, setup_swap_extents() will walk all the file's blocks
1407  * and will parse them into an ordered extent list, in PAGE_SIZE chunks.  If
1408  * some stray blocks are found which do not fall within the PAGE_SIZE alignment
1409  * requirements, they are simply tossed out - we will never use those blocks
1410  * for swapping.
1411  *
1412  * For S_ISREG swapfiles we set S_SWAPFILE across the life of the swapon.  This
1413  * prevents root from shooting her foot off by ftruncating an in-use swapfile,
1414  * which will scribble on the fs.
1415  *
1416  * The amount of disk space which a single swap extent represents varies.
1417  * Typically it is in the 1-4 megabyte range.  So we can have hundreds of
1418  * extents in the list.  To avoid much list walking, we cache the previous
1419  * search location in `curr_swap_extent', and start new searches from there.
1420  * This is extremely effective.  The average number of iterations in
1421  * map_swap_page() has been measured at about 0.3 per page.  - akpm.
1422  */
1423 static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
1424 {
1425         struct inode *inode;
1426         unsigned blocks_per_page;
1427         unsigned long page_no;
1428         unsigned blkbits;
1429         sector_t probe_block;
1430         sector_t last_block;
1431         sector_t lowest_block = -1;
1432         sector_t highest_block = 0;
1433         int nr_extents = 0;
1434         int ret;
1435
1436         inode = sis->swap_file->f_mapping->host;
1437         if (S_ISBLK(inode->i_mode)) {
1438                 ret = add_swap_extent(sis, 0, sis->max, 0);
1439                 *span = sis->pages;
1440                 goto out;
1441         }
1442
1443         blkbits = inode->i_blkbits;
1444         blocks_per_page = PAGE_SIZE >> blkbits;
1445
1446         /*
1447          * Map all the blocks into the extent list.  This code doesn't try
1448          * to be very smart.
1449          */
1450         probe_block = 0;
1451         page_no = 0;
1452         last_block = i_size_read(inode) >> blkbits;
1453         while ((probe_block + blocks_per_page) <= last_block &&
1454                         page_no < sis->max) {
1455                 unsigned block_in_page;
1456                 sector_t first_block;
1457
1458                 first_block = bmap(inode, probe_block);
1459                 if (first_block == 0)
1460                         goto bad_bmap;
1461
1462                 /*
1463                  * It must be PAGE_SIZE aligned on-disk
1464                  */
1465                 if (first_block & (blocks_per_page - 1)) {
1466                         probe_block++;
1467                         goto reprobe;
1468                 }
1469
1470                 for (block_in_page = 1; block_in_page < blocks_per_page;
1471                                         block_in_page++) {
1472                         sector_t block;
1473
1474                         block = bmap(inode, probe_block + block_in_page);
1475                         if (block == 0)
1476                                 goto bad_bmap;
1477                         if (block != first_block + block_in_page) {
1478                                 /* Discontiguity */
1479                                 probe_block++;
1480                                 goto reprobe;
1481                         }
1482                 }
1483
1484                 first_block >>= (PAGE_SHIFT - blkbits);
1485                 if (page_no) {  /* exclude the header page */
1486                         if (first_block < lowest_block)
1487                                 lowest_block = first_block;
1488                         if (first_block > highest_block)
1489                                 highest_block = first_block;
1490                 }
1491
1492                 /*
1493                  * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks
1494                  */
1495                 ret = add_swap_extent(sis, page_no, 1, first_block);
1496                 if (ret < 0)
1497                         goto out;
1498                 nr_extents += ret;
1499                 page_no++;
1500                 probe_block += blocks_per_page;
1501 reprobe:
1502                 continue;
1503         }
1504         ret = nr_extents;
1505         *span = 1 + highest_block - lowest_block;
1506         if (page_no == 0)
1507                 page_no = 1;    /* force Empty message */
1508         sis->max = page_no;
1509         sis->pages = page_no - 1;
1510         sis->highest_bit = page_no - 1;
1511 out:
1512         return ret;
1513 bad_bmap:
1514         printk(KERN_ERR "swapon: swapfile has holes\n");
1515         ret = -EINVAL;
1516         goto out;
1517 }
1518
1519 static void enable_swap_info(struct swap_info_struct *p, int prio,
1520                                 unsigned char *swap_map)
1521 {
1522         int i, prev;
1523
1524         spin_lock(&swap_lock);
1525         if (prio >= 0)
1526                 p->prio = prio;
1527         else
1528                 p->prio = --least_priority;
1529         p->swap_map = swap_map;
1530         p->flags |= SWP_WRITEOK;
1531         nr_swap_pages += p->pages;
1532         total_swap_pages += p->pages;
1533
1534         /* insert swap space into swap_list: */
1535         prev = -1;
1536         for (i = swap_list.head; i >= 0; i = swap_info[i]->next) {
1537                 if (p->prio >= swap_info[i]->prio)
1538                         break;
1539                 prev = i;
1540         }
1541         p->next = i;
1542         if (prev < 0)
1543                 swap_list.head = swap_list.next = p->type;
1544         else
1545                 swap_info[prev]->next = p->type;
1546         spin_unlock(&swap_lock);
1547 }
1548
1549 SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
1550 {
1551         struct swap_info_struct *p = NULL;
1552         unsigned char *swap_map;
1553         struct file *swap_file, *victim;
1554         struct address_space *mapping;
1555         struct inode *inode;
1556         char *pathname;
1557         int oom_score_adj;
1558         int i, type, prev;
1559         int err;
1560
1561         if (!capable(CAP_SYS_ADMIN))
1562                 return -EPERM;
1563
1564         pathname = getname(specialfile);
1565         err = PTR_ERR(pathname);
1566         if (IS_ERR(pathname))
1567                 goto out;
1568
1569         victim = filp_open(pathname, O_RDWR|O_LARGEFILE, 0);
1570         putname(pathname);
1571         err = PTR_ERR(victim);
1572         if (IS_ERR(victim))
1573                 goto out;
1574
1575         mapping = victim->f_mapping;
1576         prev = -1;
1577         spin_lock(&swap_lock);
1578         for (type = swap_list.head; type >= 0; type = swap_info[type]->next) {
1579                 p = swap_info[type];
1580                 if (p->flags & SWP_WRITEOK) {
1581                         if (p->swap_file->f_mapping == mapping)
1582                                 break;
1583                 }
1584                 prev = type;
1585         }
1586         if (type < 0) {
1587                 err = -EINVAL;
1588                 spin_unlock(&swap_lock);
1589                 goto out_dput;
1590         }
1591         if (!security_vm_enough_memory(p->pages))
1592                 vm_unacct_memory(p->pages);
1593         else {
1594                 err = -ENOMEM;
1595                 spin_unlock(&swap_lock);
1596                 goto out_dput;
1597         }
1598         if (prev < 0)
1599                 swap_list.head = p->next;
1600         else
1601                 swap_info[prev]->next = p->next;
1602         if (type == swap_list.next) {
1603                 /* just pick something that's safe... */
1604                 swap_list.next = swap_list.head;
1605         }
1606         if (p->prio < 0) {
1607                 for (i = p->next; i >= 0; i = swap_info[i]->next)
1608                         swap_info[i]->prio = p->prio--;
1609                 least_priority++;
1610         }
1611         nr_swap_pages -= p->pages;
1612         total_swap_pages -= p->pages;
1613         p->flags &= ~SWP_WRITEOK;
1614         spin_unlock(&swap_lock);
1615
1616         oom_score_adj = test_set_oom_score_adj(OOM_SCORE_ADJ_MAX);
1617         err = try_to_unuse(type);
1618         compare_swap_oom_score_adj(OOM_SCORE_ADJ_MAX, oom_score_adj);
1619
1620         if (err) {
1621                 /*
1622                  * reading p->prio and p->swap_map outside the lock is
1623                  * safe here because only sys_swapon and sys_swapoff
1624                  * change them, and there can be no other sys_swapon or
1625                  * sys_swapoff for this swap_info_struct at this point.
1626                  */
1627                 /* re-insert swap space back into swap_list */
1628                 enable_swap_info(p, p->prio, p->swap_map);
1629                 goto out_dput;
1630         }
1631
1632         destroy_swap_extents(p);
1633         if (p->flags & SWP_CONTINUED)
1634                 free_swap_count_continuations(p);
1635
1636         mutex_lock(&swapon_mutex);
1637         spin_lock(&swap_lock);
1638         drain_mmlist();
1639
1640         /* wait for anyone still in scan_swap_map */
1641         p->highest_bit = 0;             /* cuts scans short */
1642         while (p->flags >= SWP_SCANNING) {
1643                 spin_unlock(&swap_lock);
1644                 schedule_timeout_uninterruptible(1);
1645                 spin_lock(&swap_lock);
1646         }
1647
1648         swap_file = p->swap_file;
1649         p->swap_file = NULL;
1650         p->max = 0;
1651         swap_map = p->swap_map;
1652         p->swap_map = NULL;
1653         p->flags = 0;
1654         spin_unlock(&swap_lock);
1655         mutex_unlock(&swapon_mutex);
1656         vfree(swap_map);
1657         /* Destroy swap account informatin */
1658         swap_cgroup_swapoff(type);
1659
1660         inode = mapping->host;
1661         if (S_ISBLK(inode->i_mode)) {
1662                 struct block_device *bdev = I_BDEV(inode);
1663                 set_blocksize(bdev, p->old_block_size);
1664                 blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
1665         } else {
1666                 mutex_lock(&inode->i_mutex);
1667                 inode->i_flags &= ~S_SWAPFILE;
1668                 mutex_unlock(&inode->i_mutex);
1669         }
1670         filp_close(swap_file, NULL);
1671         err = 0;
1672         atomic_inc(&proc_poll_event);
1673         wake_up_interruptible(&proc_poll_wait);
1674
1675 out_dput:
1676         filp_close(victim, NULL);
1677 out:
1678         return err;
1679 }
1680
1681 #ifdef CONFIG_PROC_FS
1682 static unsigned swaps_poll(struct file *file, poll_table *wait)
1683 {
1684         struct seq_file *seq = file->private_data;
1685
1686         poll_wait(file, &proc_poll_wait, wait);
1687
1688         if (seq->poll_event != atomic_read(&proc_poll_event)) {
1689                 seq->poll_event = atomic_read(&proc_poll_event);
1690                 return POLLIN | POLLRDNORM | POLLERR | POLLPRI;
1691         }
1692
1693         return POLLIN | POLLRDNORM;
1694 }
1695
1696 /* iterator */
1697 static void *swap_start(struct seq_file *swap, loff_t *pos)
1698 {
1699         struct swap_info_struct *si;
1700         int type;
1701         loff_t l = *pos;
1702
1703         mutex_lock(&swapon_mutex);
1704
1705         if (!l)
1706                 return SEQ_START_TOKEN;
1707
1708         for (type = 0; type < nr_swapfiles; type++) {
1709                 smp_rmb();      /* read nr_swapfiles before swap_info[type] */
1710                 si = swap_info[type];
1711                 if (!(si->flags & SWP_USED) || !si->swap_map)
1712                         continue;
1713                 if (!--l)
1714                         return si;
1715         }
1716
1717         return NULL;
1718 }
1719
1720 static void *swap_next(struct seq_file *swap, void *v, loff_t *pos)
1721 {
1722         struct swap_info_struct *si = v;
1723         int type;
1724
1725         if (v == SEQ_START_TOKEN)
1726                 type = 0;
1727         else
1728                 type = si->type + 1;
1729
1730         for (; type < nr_swapfiles; type++) {
1731                 smp_rmb();      /* read nr_swapfiles before swap_info[type] */
1732                 si = swap_info[type];
1733                 if (!(si->flags & SWP_USED) || !si->swap_map)
1734                         continue;
1735                 ++*pos;
1736                 return si;
1737         }
1738
1739         return NULL;
1740 }
1741
1742 static void swap_stop(struct seq_file *swap, void *v)
1743 {
1744         mutex_unlock(&swapon_mutex);
1745 }
1746
1747 static int swap_show(struct seq_file *swap, void *v)
1748 {
1749         struct swap_info_struct *si = v;
1750         struct file *file;
1751         int len;
1752
1753         if (si == SEQ_START_TOKEN) {
1754                 seq_puts(swap,"Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n");
1755                 return 0;
1756         }
1757
1758         file = si->swap_file;
1759         len = seq_path(swap, &file->f_path, " \t\n\\");
1760         seq_printf(swap, "%*s%s\t%u\t%u\t%d\n",
1761                         len < 40 ? 40 - len : 1, " ",
1762                         S_ISBLK(file->f_path.dentry->d_inode->i_mode) ?
1763                                 "partition" : "file\t",
1764                         si->pages << (PAGE_SHIFT - 10),
1765                         si->inuse_pages << (PAGE_SHIFT - 10),
1766                         si->prio);
1767         return 0;
1768 }
1769
1770 static const struct seq_operations swaps_op = {
1771         .start =        swap_start,
1772         .next =         swap_next,
1773         .stop =         swap_stop,
1774         .show =         swap_show
1775 };
1776
1777 static int swaps_open(struct inode *inode, struct file *file)
1778 {
1779         struct seq_file *seq;
1780         int ret;
1781
1782         ret = seq_open(file, &swaps_op);
1783         if (ret)
1784                 return ret;
1785
1786         seq = file->private_data;
1787         seq->poll_event = atomic_read(&proc_poll_event);
1788         return 0;
1789 }
1790
1791 static const struct file_operations proc_swaps_operations = {
1792         .open           = swaps_open,
1793         .read           = seq_read,
1794         .llseek         = seq_lseek,
1795         .release        = seq_release,
1796         .poll           = swaps_poll,
1797 };
1798
1799 static int __init procswaps_init(void)
1800 {
1801         proc_create("swaps", 0, NULL, &proc_swaps_operations);
1802         return 0;
1803 }
1804 __initcall(procswaps_init);
1805 #endif /* CONFIG_PROC_FS */
1806
1807 #ifdef MAX_SWAPFILES_CHECK
1808 static int __init max_swapfiles_check(void)
1809 {
1810         MAX_SWAPFILES_CHECK();
1811         return 0;
1812 }
1813 late_initcall(max_swapfiles_check);
1814 #endif
1815
1816 static struct swap_info_struct *alloc_swap_info(void)
1817 {
1818         struct swap_info_struct *p;
1819         unsigned int type;
1820
1821         p = kzalloc(sizeof(*p), GFP_KERNEL);
1822         if (!p)
1823                 return ERR_PTR(-ENOMEM);
1824
1825         spin_lock(&swap_lock);
1826         for (type = 0; type < nr_swapfiles; type++) {
1827                 if (!(swap_info[type]->flags & SWP_USED))
1828                         break;
1829         }
1830         if (type >= MAX_SWAPFILES) {
1831                 spin_unlock(&swap_lock);
1832                 kfree(p);
1833                 return ERR_PTR(-EPERM);
1834         }
1835         if (type >= nr_swapfiles) {
1836                 p->type = type;
1837                 swap_info[type] = p;
1838                 /*
1839                  * Write swap_info[type] before nr_swapfiles, in case a
1840                  * racing procfs swap_start() or swap_next() is reading them.
1841                  * (We never shrink nr_swapfiles, we never free this entry.)
1842                  */
1843                 smp_wmb();
1844                 nr_swapfiles++;
1845         } else {
1846                 kfree(p);
1847                 p = swap_info[type];
1848                 /*
1849                  * Do not memset this entry: a racing procfs swap_next()
1850                  * would be relying on p->type to remain valid.
1851                  */
1852         }
1853         INIT_LIST_HEAD(&p->first_swap_extent.list);
1854         p->flags = SWP_USED;
1855         p->next = -1;
1856         spin_unlock(&swap_lock);
1857
1858         return p;
1859 }
1860
1861 static int claim_swapfile(struct swap_info_struct *p, struct inode *inode)
1862 {
1863         int error;
1864
1865         if (S_ISBLK(inode->i_mode)) {
1866                 p->bdev = bdgrab(I_BDEV(inode));
1867                 error = blkdev_get(p->bdev,
1868                                    FMODE_READ | FMODE_WRITE | FMODE_EXCL,
1869                                    sys_swapon);
1870                 if (error < 0) {
1871                         p->bdev = NULL;
1872                         return -EINVAL;
1873                 }
1874                 p->old_block_size = block_size(p->bdev);
1875                 error = set_blocksize(p->bdev, PAGE_SIZE);
1876                 if (error < 0)
1877                         return error;
1878                 p->flags |= SWP_BLKDEV;
1879         } else if (S_ISREG(inode->i_mode)) {
1880                 p->bdev = inode->i_sb->s_bdev;
1881                 mutex_lock(&inode->i_mutex);
1882                 if (IS_SWAPFILE(inode))
1883                         return -EBUSY;
1884         } else
1885                 return -EINVAL;
1886
1887         return 0;
1888 }
1889
1890 static unsigned long read_swap_header(struct swap_info_struct *p,
1891                                         union swap_header *swap_header,
1892                                         struct inode *inode)
1893 {
1894         int i;
1895         unsigned long maxpages;
1896         unsigned long swapfilepages;
1897
1898         if (memcmp("SWAPSPACE2", swap_header->magic.magic, 10)) {
1899                 printk(KERN_ERR "Unable to find swap-space signature\n");
1900                 return 0;
1901         }
1902
1903         /* swap partition endianess hack... */
1904         if (swab32(swap_header->info.version) == 1) {
1905                 swab32s(&swap_header->info.version);
1906                 swab32s(&swap_header->info.last_page);
1907                 swab32s(&swap_header->info.nr_badpages);
1908                 for (i = 0; i < swap_header->info.nr_badpages; i++)
1909                         swab32s(&swap_header->info.badpages[i]);
1910         }
1911         /* Check the swap header's sub-version */
1912         if (swap_header->info.version != 1) {
1913                 printk(KERN_WARNING
1914                        "Unable to handle swap header version %d\n",
1915                        swap_header->info.version);
1916                 return 0;
1917         }
1918
1919         p->lowest_bit  = 1;
1920         p->cluster_next = 1;
1921         p->cluster_nr = 0;
1922
1923         /*
1924          * Find out how many pages are allowed for a single swap
1925          * device. There are three limiting factors: 1) the number
1926          * of bits for the swap offset in the swp_entry_t type, and
1927          * 2) the number of bits in the swap pte as defined by the
1928          * the different architectures, and 3) the number of free bits
1929          * in an exceptional radix_tree entry. In order to find the
1930          * largest possible bit mask, a swap entry with swap type 0
1931          * and swap offset ~0UL is created, encoded to a swap pte,
1932          * decoded to a swp_entry_t again, and finally the swap
1933          * offset is extracted. This will mask all the bits from
1934          * the initial ~0UL mask that can't be encoded in either
1935          * the swp_entry_t or the architecture definition of a
1936          * swap pte.  Then the same is done for a radix_tree entry.
1937          */
1938         maxpages = swp_offset(pte_to_swp_entry(
1939                         swp_entry_to_pte(swp_entry(0, ~0UL))));
1940         maxpages = swp_offset(radix_to_swp_entry(
1941                         swp_to_radix_entry(swp_entry(0, maxpages)))) + 1;
1942
1943         if (maxpages > swap_header->info.last_page) {
1944                 maxpages = swap_header->info.last_page + 1;
1945                 /* p->max is an unsigned int: don't overflow it */
1946                 if ((unsigned int)maxpages == 0)
1947                         maxpages = UINT_MAX;
1948         }
1949         p->highest_bit = maxpages - 1;
1950
1951         if (!maxpages)
1952                 return 0;
1953         swapfilepages = i_size_read(inode) >> PAGE_SHIFT;
1954         if (swapfilepages && maxpages > swapfilepages) {
1955                 printk(KERN_WARNING
1956                        "Swap area shorter than signature indicates\n");
1957                 return 0;
1958         }
1959         if (swap_header->info.nr_badpages && S_ISREG(inode->i_mode))
1960                 return 0;
1961         if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
1962                 return 0;
1963
1964         return maxpages;
1965 }
1966
1967 static int setup_swap_map_and_extents(struct swap_info_struct *p,
1968                                         union swap_header *swap_header,
1969                                         unsigned char *swap_map,
1970                                         unsigned long maxpages,
1971                                         sector_t *span)
1972 {
1973         int i;
1974         unsigned int nr_good_pages;
1975         int nr_extents;
1976
1977         nr_good_pages = maxpages - 1;   /* omit header page */
1978
1979         for (i = 0; i < swap_header->info.nr_badpages; i++) {
1980                 unsigned int page_nr = swap_header->info.badpages[i];
1981                 if (page_nr == 0 || page_nr > swap_header->info.last_page)
1982                         return -EINVAL;
1983                 if (page_nr < maxpages) {
1984                         swap_map[page_nr] = SWAP_MAP_BAD;
1985                         nr_good_pages--;
1986                 }
1987         }
1988
1989         if (nr_good_pages) {
1990                 swap_map[0] = SWAP_MAP_BAD;
1991                 p->max = maxpages;
1992                 p->pages = nr_good_pages;
1993                 nr_extents = setup_swap_extents(p, span);
1994                 if (nr_extents < 0)
1995                         return nr_extents;
1996                 nr_good_pages = p->pages;
1997         }
1998         if (!nr_good_pages) {
1999                 printk(KERN_WARNING "Empty swap-file\n");
2000                 return -EINVAL;
2001         }
2002
2003         return nr_extents;
2004 }
2005
2006 SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
2007 {
2008         struct swap_info_struct *p;
2009         char *name;
2010         struct file *swap_file = NULL;
2011         struct address_space *mapping;
2012         int i;
2013         int prio;
2014         int error;
2015         union swap_header *swap_header;
2016         int nr_extents;
2017         sector_t span;
2018         unsigned long maxpages;
2019         unsigned char *swap_map = NULL;
2020         struct page *page = NULL;
2021         struct inode *inode = NULL;
2022
2023         if (!capable(CAP_SYS_ADMIN))
2024                 return -EPERM;
2025
2026         p = alloc_swap_info();
2027         if (IS_ERR(p))
2028                 return PTR_ERR(p);
2029
2030         name = getname(specialfile);
2031         if (IS_ERR(name)) {
2032                 error = PTR_ERR(name);
2033                 name = NULL;
2034                 goto bad_swap;
2035         }
2036         swap_file = filp_open(name, O_RDWR|O_LARGEFILE, 0);
2037         if (IS_ERR(swap_file)) {
2038                 error = PTR_ERR(swap_file);
2039                 swap_file = NULL;
2040                 goto bad_swap;
2041         }
2042
2043         p->swap_file = swap_file;
2044         mapping = swap_file->f_mapping;
2045
2046         for (i = 0; i < nr_swapfiles; i++) {
2047                 struct swap_info_struct *q = swap_info[i];
2048
2049                 if (q == p || !q->swap_file)
2050                         continue;
2051                 if (mapping == q->swap_file->f_mapping) {
2052                         error = -EBUSY;
2053                         goto bad_swap;
2054                 }
2055         }
2056
2057         inode = mapping->host;
2058         /* If S_ISREG(inode->i_mode) will do mutex_lock(&inode->i_mutex); */
2059         error = claim_swapfile(p, inode);
2060         if (unlikely(error))
2061                 goto bad_swap;
2062
2063         /*
2064          * Read the swap header.
2065          */
2066         if (!mapping->a_ops->readpage) {
2067                 error = -EINVAL;
2068                 goto bad_swap;
2069         }
2070         page = read_mapping_page(mapping, 0, swap_file);
2071         if (IS_ERR(page)) {
2072                 error = PTR_ERR(page);
2073                 goto bad_swap;
2074         }
2075         swap_header = kmap(page);
2076
2077         maxpages = read_swap_header(p, swap_header, inode);
2078         if (unlikely(!maxpages)) {
2079                 error = -EINVAL;
2080                 goto bad_swap;
2081         }
2082
2083         /* OK, set up the swap map and apply the bad block list */
2084         swap_map = vzalloc(maxpages);
2085         if (!swap_map) {
2086                 error = -ENOMEM;
2087                 goto bad_swap;
2088         }
2089
2090         error = swap_cgroup_swapon(p->type, maxpages);
2091         if (error)
2092                 goto bad_swap;
2093
2094         nr_extents = setup_swap_map_and_extents(p, swap_header, swap_map,
2095                 maxpages, &span);
2096         if (unlikely(nr_extents < 0)) {
2097                 error = nr_extents;
2098                 goto bad_swap;
2099         }
2100
2101         if (p->bdev) {
2102                 if (blk_queue_nonrot(bdev_get_queue(p->bdev))) {
2103                         p->flags |= SWP_SOLIDSTATE;
2104                         p->cluster_next = 1 + (random32() % p->highest_bit);
2105                 }
2106                 if (discard_swap(p) == 0 && (swap_flags & SWAP_FLAG_DISCARD))
2107                         p->flags |= SWP_DISCARDABLE;
2108         }
2109
2110         mutex_lock(&swapon_mutex);
2111         prio = -1;
2112         if (swap_flags & SWAP_FLAG_PREFER)
2113                 prio =
2114                   (swap_flags & SWAP_FLAG_PRIO_MASK) >> SWAP_FLAG_PRIO_SHIFT;
2115         enable_swap_info(p, prio, swap_map);
2116
2117         printk(KERN_INFO "Adding %uk swap on %s.  "
2118                         "Priority:%d extents:%d across:%lluk %s%s\n",
2119                 p->pages<<(PAGE_SHIFT-10), name, p->prio,
2120                 nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10),
2121                 (p->flags & SWP_SOLIDSTATE) ? "SS" : "",
2122                 (p->flags & SWP_DISCARDABLE) ? "D" : "");
2123
2124         mutex_unlock(&swapon_mutex);
2125         atomic_inc(&proc_poll_event);
2126         wake_up_interruptible(&proc_poll_wait);
2127
2128         if (S_ISREG(inode->i_mode))
2129                 inode->i_flags |= S_SWAPFILE;
2130         error = 0;
2131         goto out;
2132 bad_swap:
2133         if (inode && S_ISBLK(inode->i_mode) && p->bdev) {
2134                 set_blocksize(p->bdev, p->old_block_size);
2135                 blkdev_put(p->bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
2136         }
2137         destroy_swap_extents(p);
2138         swap_cgroup_swapoff(p->type);
2139         spin_lock(&swap_lock);
2140         p->swap_file = NULL;
2141         p->flags = 0;
2142         spin_unlock(&swap_lock);
2143         vfree(swap_map);
2144         if (swap_file) {
2145                 if (inode && S_ISREG(inode->i_mode)) {
2146                         mutex_unlock(&inode->i_mutex);
2147                         inode = NULL;
2148                 }
2149                 filp_close(swap_file, NULL);
2150         }
2151 out:
2152         if (page && !IS_ERR(page)) {
2153                 kunmap(page);
2154                 page_cache_release(page);
2155         }
2156         if (name)
2157                 putname(name);
2158         if (inode && S_ISREG(inode->i_mode))
2159                 mutex_unlock(&inode->i_mutex);
2160         return error;
2161 }
2162
2163 void si_swapinfo(struct sysinfo *val)
2164 {
2165         unsigned int type;
2166         unsigned long nr_to_be_unused = 0;
2167
2168         spin_lock(&swap_lock);
2169         for (type = 0; type < nr_swapfiles; type++) {
2170                 struct swap_info_struct *si = swap_info[type];
2171
2172                 if ((si->flags & SWP_USED) && !(si->flags & SWP_WRITEOK))
2173                         nr_to_be_unused += si->inuse_pages;
2174         }
2175         val->freeswap = nr_swap_pages + nr_to_be_unused;
2176         val->totalswap = total_swap_pages + nr_to_be_unused;
2177         spin_unlock(&swap_lock);
2178 }
2179
2180 /*
2181  * Verify that a swap entry is valid and increment its swap map count.
2182  *
2183  * Returns error code in following case.
2184  * - success -> 0
2185  * - swp_entry is invalid -> EINVAL
2186  * - swp_entry is migration entry -> EINVAL
2187  * - swap-cache reference is requested but there is already one. -> EEXIST
2188  * - swap-cache reference is requested but the entry is not used. -> ENOENT
2189  * - swap-mapped reference requested but needs continued swap count. -> ENOMEM
2190  */
2191 static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
2192 {
2193         struct swap_info_struct *p;
2194         unsigned long offset, type;
2195         unsigned char count;
2196         unsigned char has_cache;
2197         int err = -EINVAL;
2198
2199         if (non_swap_entry(entry))
2200                 goto out;
2201
2202         type = swp_type(entry);
2203         if (type >= nr_swapfiles)
2204                 goto bad_file;
2205         p = swap_info[type];
2206         offset = swp_offset(entry);
2207
2208         spin_lock(&swap_lock);
2209         if (unlikely(offset >= p->max))
2210                 goto unlock_out;
2211
2212         count = p->swap_map[offset];
2213         has_cache = count & SWAP_HAS_CACHE;
2214         count &= ~SWAP_HAS_CACHE;
2215         err = 0;
2216
2217         if (usage == SWAP_HAS_CACHE) {
2218
2219                 /* set SWAP_HAS_CACHE if there is no cache and entry is used */
2220                 if (!has_cache && count)
2221                         has_cache = SWAP_HAS_CACHE;
2222                 else if (has_cache)             /* someone else added cache */
2223                         err = -EEXIST;
2224                 else                            /* no users remaining */
2225                         err = -ENOENT;
2226
2227         } else if (count || has_cache) {
2228
2229                 if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
2230                         count += usage;
2231                 else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX)
2232                         err = -EINVAL;
2233                 else if (swap_count_continued(p, offset, count))
2234                         count = COUNT_CONTINUED;
2235                 else
2236                         err = -ENOMEM;
2237         } else
2238                 err = -ENOENT;                  /* unused swap entry */
2239
2240         p->swap_map[offset] = count | has_cache;
2241
2242 unlock_out:
2243         spin_unlock(&swap_lock);
2244 out:
2245         return err;
2246
2247 bad_file:
2248         printk(KERN_ERR "swap_dup: %s%08lx\n", Bad_file, entry.val);
2249         goto out;
2250 }
2251
2252 /*
2253  * Help swapoff by noting that swap entry belongs to shmem/tmpfs
2254  * (in which case its reference count is never incremented).
2255  */
2256 void swap_shmem_alloc(swp_entry_t entry)
2257 {
2258         __swap_duplicate(entry, SWAP_MAP_SHMEM);
2259 }
2260
2261 /*
2262  * Increase reference count of swap entry by 1.
2263  * Returns 0 for success, or -ENOMEM if a swap_count_continuation is required
2264  * but could not be atomically allocated.  Returns 0, just as if it succeeded,
2265  * if __swap_duplicate() fails for another reason (-EINVAL or -ENOENT), which
2266  * might occur if a page table entry has got corrupted.
2267  */
2268 int swap_duplicate(swp_entry_t entry)
2269 {
2270         int err = 0;
2271
2272         while (!err && __swap_duplicate(entry, 1) == -ENOMEM)
2273                 err = add_swap_count_continuation(entry, GFP_ATOMIC);
2274         return err;
2275 }
2276
2277 /*
2278  * @entry: swap entry for which we allocate swap cache.
2279  *
2280  * Called when allocating swap cache for existing swap entry,
2281  * This can return error codes. Returns 0 at success.
2282  * -EBUSY means there is a swap cache.
2283  * Note: return code is different from swap_duplicate().
2284  */
2285 int swapcache_prepare(swp_entry_t entry)
2286 {
2287         return __swap_duplicate(entry, SWAP_HAS_CACHE);
2288 }
2289
2290 /*
2291  * add_swap_count_continuation - called when a swap count is duplicated
2292  * beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's
2293  * page of the original vmalloc'ed swap_map, to hold the continuation count
2294  * (for that entry and for its neighbouring PAGE_SIZE swap entries).  Called
2295  * again when count is duplicated beyond SWAP_MAP_MAX * SWAP_CONT_MAX, etc.
2296  *
2297  * These continuation pages are seldom referenced: the common paths all work
2298  * on the original swap_map, only referring to a continuation page when the
2299  * low "digit" of a count is incremented or decremented through SWAP_MAP_MAX.
2300  *
2301  * add_swap_count_continuation(, GFP_ATOMIC) can be called while holding
2302  * page table locks; if it fails, add_swap_count_continuation(, GFP_KERNEL)
2303  * can be called after dropping locks.
2304  */
2305 int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask)
2306 {
2307         struct swap_info_struct *si;
2308         struct page *head;
2309         struct page *page;
2310         struct page *list_page;
2311         pgoff_t offset;
2312         unsigned char count;
2313
2314         /*
2315          * When debugging, it's easier to use __GFP_ZERO here; but it's better
2316          * for latency not to zero a page while GFP_ATOMIC and holding locks.
2317          */
2318         page = alloc_page(gfp_mask | __GFP_HIGHMEM);
2319
2320         si = swap_info_get(entry);
2321         if (!si) {
2322                 /*
2323                  * An acceptable race has occurred since the failing
2324                  * __swap_duplicate(): the swap entry has been freed,
2325                  * perhaps even the whole swap_map cleared for swapoff.
2326                  */
2327                 goto outer;
2328         }
2329
2330         offset = swp_offset(entry);
2331         count = si->swap_map[offset] & ~SWAP_HAS_CACHE;
2332
2333         if ((count & ~COUNT_CONTINUED) != SWAP_MAP_MAX) {
2334                 /*
2335                  * The higher the swap count, the more likely it is that tasks
2336                  * will race to add swap count continuation: we need to avoid
2337                  * over-provisioning.
2338                  */
2339                 goto out;
2340         }
2341
2342         if (!page) {
2343                 spin_unlock(&swap_lock);
2344                 return -ENOMEM;
2345         }
2346
2347         /*
2348          * We are fortunate that although vmalloc_to_page uses pte_offset_map,
2349          * no architecture is using highmem pages for kernel pagetables: so it
2350          * will not corrupt the GFP_ATOMIC caller's atomic pagetable kmaps.
2351          */
2352         head = vmalloc_to_page(si->swap_map + offset);
2353         offset &= ~PAGE_MASK;
2354
2355         /*
2356          * Page allocation does not initialize the page's lru field,
2357          * but it does always reset its private field.
2358          */
2359         if (!page_private(head)) {
2360                 BUG_ON(count & COUNT_CONTINUED);
2361                 INIT_LIST_HEAD(&head->lru);
2362                 set_page_private(head, SWP_CONTINUED);
2363                 si->flags |= SWP_CONTINUED;
2364         }
2365
2366         list_for_each_entry(list_page, &head->lru, lru) {
2367                 unsigned char *map;
2368
2369                 /*
2370                  * If the previous map said no continuation, but we've found
2371                  * a continuation page, free our allocation and use this one.
2372                  */
2373                 if (!(count & COUNT_CONTINUED))
2374                         goto out;
2375
2376                 map = kmap_atomic(list_page) + offset;
2377                 count = *map;
2378                 kunmap_atomic(map);
2379
2380                 /*
2381                  * If this continuation count now has some space in it,
2382                  * free our allocation and use this one.
2383                  */
2384                 if ((count & ~COUNT_CONTINUED) != SWAP_CONT_MAX)
2385                         goto out;
2386         }
2387
2388         list_add_tail(&page->lru, &head->lru);
2389         page = NULL;                    /* now it's attached, don't free it */
2390 out:
2391         spin_unlock(&swap_lock);
2392 outer:
2393         if (page)
2394                 __free_page(page);
2395         return 0;
2396 }
2397
2398 /*
2399  * swap_count_continued - when the original swap_map count is incremented
2400  * from SWAP_MAP_MAX, check if there is already a continuation page to carry
2401  * into, carry if so, or else fail until a new continuation page is allocated;
2402  * when the original swap_map count is decremented from 0 with continuation,
2403  * borrow from the continuation and report whether it still holds more.
2404  * Called while __swap_duplicate() or swap_entry_free() holds swap_lock.
2405  */
2406 static bool swap_count_continued(struct swap_info_struct *si,
2407                                  pgoff_t offset, unsigned char count)
2408 {
2409         struct page *head;
2410         struct page *page;
2411         unsigned char *map;
2412
2413         head = vmalloc_to_page(si->swap_map + offset);
2414         if (page_private(head) != SWP_CONTINUED) {
2415                 BUG_ON(count & COUNT_CONTINUED);
2416                 return false;           /* need to add count continuation */
2417         }
2418
2419         offset &= ~PAGE_MASK;
2420         page = list_entry(head->lru.next, struct page, lru);
2421         map = kmap_atomic(page) + offset;
2422
2423         if (count == SWAP_MAP_MAX)      /* initial increment from swap_map */
2424                 goto init_map;          /* jump over SWAP_CONT_MAX checks */
2425
2426         if (count == (SWAP_MAP_MAX | COUNT_CONTINUED)) { /* incrementing */
2427                 /*
2428                  * Think of how you add 1 to 999
2429                  */
2430                 while (*map == (SWAP_CONT_MAX | COUNT_CONTINUED)) {
2431                         kunmap_atomic(map);
2432                         page = list_entry(page->lru.next, struct page, lru);
2433                         BUG_ON(page == head);
2434                         map = kmap_atomic(page) + offset;
2435                 }
2436                 if (*map == SWAP_CONT_MAX) {
2437                         kunmap_atomic(map);
2438                         page = list_entry(page->lru.next, struct page, lru);
2439                         if (page == head)
2440                                 return false;   /* add count continuation */
2441                         map = kmap_atomic(page) + offset;
2442 init_map:               *map = 0;               /* we didn't zero the page */
2443                 }
2444                 *map += 1;
2445                 kunmap_atomic(map);
2446                 page = list_entry(page->lru.prev, struct page, lru);
2447                 while (page != head) {
2448                         map = kmap_atomic(page) + offset;
2449                         *map = COUNT_CONTINUED;
2450                         kunmap_atomic(map);
2451                         page = list_entry(page->lru.prev, struct page, lru);
2452                 }
2453                 return true;                    /* incremented */
2454
2455         } else {                                /* decrementing */
2456                 /*
2457                  * Think of how you subtract 1 from 1000
2458                  */
2459                 BUG_ON(count != COUNT_CONTINUED);
2460                 while (*map == COUNT_CONTINUED) {
2461                         kunmap_atomic(map);
2462                         page = list_entry(page->lru.next, struct page, lru);
2463                         BUG_ON(page == head);
2464                         map = kmap_atomic(page) + offset;
2465                 }
2466                 BUG_ON(*map == 0);
2467                 *map -= 1;
2468                 if (*map == 0)
2469                         count = 0;
2470                 kunmap_atomic(map);
2471                 page = list_entry(page->lru.prev, struct page, lru);
2472                 while (page != head) {
2473                         map = kmap_atomic(page) + offset;
2474                         *map = SWAP_CONT_MAX | count;
2475                         count = COUNT_CONTINUED;
2476                         kunmap_atomic(map);
2477                         page = list_entry(page->lru.prev, struct page, lru);
2478                 }
2479                 return count == COUNT_CONTINUED;
2480         }
2481 }
2482
2483 /*
2484  * free_swap_count_continuations - swapoff free all the continuation pages
2485  * appended to the swap_map, after swap_map is quiesced, before vfree'ing it.
2486  */
2487 static void free_swap_count_continuations(struct swap_info_struct *si)
2488 {
2489         pgoff_t offset;
2490
2491         for (offset = 0; offset < si->max; offset += PAGE_SIZE) {
2492                 struct page *head;
2493                 head = vmalloc_to_page(si->swap_map + offset);
2494                 if (page_private(head)) {
2495                         struct list_head *this, *next;
2496                         list_for_each_safe(this, next, &head->lru) {
2497                                 struct page *page;
2498                                 page = list_entry(this, struct page, lru);
2499                                 list_del(this);
2500                                 __free_page(page);
2501                         }
2502                 }
2503         }
2504 }