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

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