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;
50atomic_long_t nr_swap_pages;
51/* protected with swap_lock. reading in vm_swap_full() doesn't need lock */
52long total_swap_pages;
53static int least_priority;
54static atomic_t highest_priority_index = ATOMIC_INIT(-1);
55
56static const char Bad_file[] = "Bad swap file entry ";
57static const char Unused_file[] = "Unused swap file entry ";
58static const char Bad_offset[] = "Bad swap offset entry ";
59static const char Unused_offset[] = "Unused swap offset entry ";
60
61struct swap_list_t swap_list = {-1, -1};
62
63struct swap_info_struct *swap_info[MAX_SWAPFILES];
64
65static DEFINE_MUTEX(swapon_mutex);
66
67static DECLARE_WAIT_QUEUE_HEAD(proc_poll_wait);
68/* Activity counter to indicate that a swapon or swapoff has occurred */
69static atomic_t proc_poll_event = ATOMIC_INIT(0);
70
71static inline unsigned char swap_count(unsigned char ent)
72{
73    return ent & ~SWAP_HAS_CACHE; /* may include SWAP_HAS_CONT flag */
74}
75
76/* returns 1 if swap entry is freed */
77static int
78__try_to_reclaim_swap(struct swap_info_struct *si, unsigned long offset)
79{
80    swp_entry_t entry = swp_entry(si->type, offset);
81    struct page *page;
82    int ret = 0;
83
84    page = find_get_page(swap_address_space(entry), entry.val);
85    if (!page)
86        return 0;
87    /*
88     * This function is called from scan_swap_map() and it's called
89     * by vmscan.c at reclaiming pages. So, we hold a lock on a page, here.
90     * We have to use trylock for avoiding deadlock. This is a special
91     * case and you should use try_to_free_swap() with explicit lock_page()
92     * in usual operations.
93     */
94    if (trylock_page(page)) {
95        ret = try_to_free_swap(page);
96        unlock_page(page);
97    }
98    page_cache_release(page);
99    return ret;
100}
101
102/*
103 * swapon tell device that all the old swap contents can be discarded,
104 * to allow the swap device to optimize its wear-levelling.
105 */
106static int discard_swap(struct swap_info_struct *si)
107{
108    struct swap_extent *se;
109    sector_t start_block;
110    sector_t nr_blocks;
111    int err = 0;
112
113    /* Do not discard the swap header page! */
114    se = &si->first_swap_extent;
115    start_block = (se->start_block + 1) << (PAGE_SHIFT - 9);
116    nr_blocks = ((sector_t)se->nr_pages - 1) << (PAGE_SHIFT - 9);
117    if (nr_blocks) {
118        err = blkdev_issue_discard(si->bdev, start_block,
119                nr_blocks, GFP_KERNEL, 0);
120        if (err)
121            return err;
122        cond_resched();
123    }
124
125    list_for_each_entry(se, &si->first_swap_extent.list, list) {
126        start_block = se->start_block << (PAGE_SHIFT - 9);
127        nr_blocks = (sector_t)se->nr_pages << (PAGE_SHIFT - 9);
128
129        err = blkdev_issue_discard(si->bdev, start_block,
130                nr_blocks, GFP_KERNEL, 0);
131        if (err)
132            break;
133
134        cond_resched();
135    }
136    return err; /* That will often be -EOPNOTSUPP */
137}
138
139/*
140 * swap allocation tell device that a cluster of swap can now be discarded,
141 * to allow the swap device to optimize its wear-levelling.
142 */
143static void discard_swap_cluster(struct swap_info_struct *si,
144                 pgoff_t start_page, pgoff_t nr_pages)
145{
146    struct swap_extent *se = si->curr_swap_extent;
147    int found_extent = 0;
148
149    while (nr_pages) {
150        struct list_head *lh;
151
152        if (se->start_page <= start_page &&
153            start_page < se->start_page + se->nr_pages) {
154            pgoff_t offset = start_page - se->start_page;
155            sector_t start_block = se->start_block + offset;
156            sector_t nr_blocks = se->nr_pages - offset;
157
158            if (nr_blocks > nr_pages)
159                nr_blocks = nr_pages;
160            start_page += nr_blocks;
161            nr_pages -= nr_blocks;
162
163            if (!found_extent++)
164                si->curr_swap_extent = se;
165
166            start_block <<= PAGE_SHIFT - 9;
167            nr_blocks <<= PAGE_SHIFT - 9;
168            if (blkdev_issue_discard(si->bdev, start_block,
169                    nr_blocks, GFP_NOIO, 0))
170                break;
171        }
172
173        lh = se->list.next;
174        se = list_entry(lh, struct swap_extent, list);
175    }
176}
177
178static int wait_for_discard(void *word)
179{
180    schedule();
181    return 0;
182}
183
184#define SWAPFILE_CLUSTER 256
185#define LATENCY_LIMIT 256
186
187static unsigned long scan_swap_map(struct swap_info_struct *si,
188                   unsigned char usage)
189{
190    unsigned long offset;
191    unsigned long scan_base;
192    unsigned long last_in_cluster = 0;
193    int latency_ration = LATENCY_LIMIT;
194    int found_free_cluster = 0;
195
196    /*
197     * We try to cluster swap pages by allocating them sequentially
198     * in swap. Once we've allocated SWAPFILE_CLUSTER pages this
199     * way, however, we resort to first-free allocation, starting
200     * a new cluster. This prevents us from scattering swap pages
201     * all over the entire swap partition, so that we reduce
202     * overall disk seek times between swap pages. -- sct
203     * But we do now try to find an empty cluster. -Andrea
204     * And we let swap pages go all over an SSD partition. Hugh
205     */
206
207    si->flags += SWP_SCANNING;
208    scan_base = offset = si->cluster_next;
209
210    if (unlikely(!si->cluster_nr--)) {
211        if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER) {
212            si->cluster_nr = SWAPFILE_CLUSTER - 1;
213            goto checks;
214        }
215        if (si->flags & SWP_DISCARDABLE) {
216            /*
217             * Start range check on racing allocations, in case
218             * they overlap the cluster we eventually decide on
219             * (we scan without swap_lock to allow preemption).
220             * It's hardly conceivable that cluster_nr could be
221             * wrapped during our scan, but don't depend on it.
222             */
223            if (si->lowest_alloc)
224                goto checks;
225            si->lowest_alloc = si->max;
226            si->highest_alloc = 0;
227        }
228        spin_unlock(&si->lock);
229
230        /*
231         * If seek is expensive, start searching for new cluster from
232         * start of partition, to minimize the span of allocated swap.
233         * But if seek is cheap, search from our current position, so
234         * that swap is allocated from all over the partition: if the
235         * Flash Translation Layer only remaps within limited zones,
236         * we don't want to wear out the first zone too quickly.
237         */
238        if (!(si->flags & SWP_SOLIDSTATE))
239            scan_base = offset = si->lowest_bit;
240        last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
241
242        /* Locate the first empty (unaligned) cluster */
243        for (; last_in_cluster <= si->highest_bit; offset++) {
244            if (si->swap_map[offset])
245                last_in_cluster = offset + SWAPFILE_CLUSTER;
246            else if (offset == last_in_cluster) {
247                spin_lock(&si->lock);
248                offset -= SWAPFILE_CLUSTER - 1;
249                si->cluster_next = offset;
250                si->cluster_nr = SWAPFILE_CLUSTER - 1;
251                found_free_cluster = 1;
252                goto checks;
253            }
254            if (unlikely(--latency_ration < 0)) {
255                cond_resched();
256                latency_ration = LATENCY_LIMIT;
257            }
258        }
259
260        offset = si->lowest_bit;
261        last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
262
263        /* Locate the first empty (unaligned) cluster */
264        for (; last_in_cluster < scan_base; offset++) {
265            if (si->swap_map[offset])
266                last_in_cluster = offset + SWAPFILE_CLUSTER;
267            else if (offset == last_in_cluster) {
268                spin_lock(&si->lock);
269                offset -= SWAPFILE_CLUSTER - 1;
270                si->cluster_next = offset;
271                si->cluster_nr = SWAPFILE_CLUSTER - 1;
272                found_free_cluster = 1;
273                goto checks;
274            }
275            if (unlikely(--latency_ration < 0)) {
276                cond_resched();
277                latency_ration = LATENCY_LIMIT;
278            }
279        }
280
281        offset = scan_base;
282        spin_lock(&si->lock);
283        si->cluster_nr = SWAPFILE_CLUSTER - 1;
284        si->lowest_alloc = 0;
285    }
286
287checks:
288    if (!(si->flags & SWP_WRITEOK))
289        goto no_page;
290    if (!si->highest_bit)
291        goto no_page;
292    if (offset > si->highest_bit)
293        scan_base = offset = si->lowest_bit;
294
295    /* reuse swap entry of cache-only swap if not busy. */
296    if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
297        int swap_was_freed;
298        spin_unlock(&si->lock);
299        swap_was_freed = __try_to_reclaim_swap(si, offset);
300        spin_lock(&si->lock);
301        /* entry was freed successfully, try to use this again */
302        if (swap_was_freed)
303            goto checks;
304        goto scan; /* check next one */
305    }
306
307    if (si->swap_map[offset])
308        goto scan;
309
310    if (offset == si->lowest_bit)
311        si->lowest_bit++;
312    if (offset == si->highest_bit)
313        si->highest_bit--;
314    si->inuse_pages++;
315    if (si->inuse_pages == si->pages) {
316        si->lowest_bit = si->max;
317        si->highest_bit = 0;
318    }
319    si->swap_map[offset] = usage;
320    si->cluster_next = offset + 1;
321    si->flags -= SWP_SCANNING;
322
323    if (si->lowest_alloc) {
324        /*
325         * Only set when SWP_DISCARDABLE, and there's a scan
326         * for a free cluster in progress or just completed.
327         */
328        if (found_free_cluster) {
329            /*
330             * To optimize wear-levelling, discard the
331             * old data of the cluster, taking care not to
332             * discard any of its pages that have already
333             * been allocated by racing tasks (offset has
334             * already stepped over any at the beginning).
335             */
336            if (offset < si->highest_alloc &&
337                si->lowest_alloc <= last_in_cluster)
338                last_in_cluster = si->lowest_alloc - 1;
339            si->flags |= SWP_DISCARDING;
340            spin_unlock(&si->lock);
341
342            if (offset < last_in_cluster)
343                discard_swap_cluster(si, offset,
344                    last_in_cluster - offset + 1);
345
346            spin_lock(&si->lock);
347            si->lowest_alloc = 0;
348            si->flags &= ~SWP_DISCARDING;
349
350            smp_mb(); /* wake_up_bit advises this */
351            wake_up_bit(&si->flags, ilog2(SWP_DISCARDING));
352
353        } else if (si->flags & SWP_DISCARDING) {
354            /*
355             * Delay using pages allocated by racing tasks
356             * until the whole discard has been issued. We
357             * could defer that delay until swap_writepage,
358             * but it's easier to keep this self-contained.
359             */
360            spin_unlock(&si->lock);
361            wait_on_bit(&si->flags, ilog2(SWP_DISCARDING),
362                wait_for_discard, TASK_UNINTERRUPTIBLE);
363            spin_lock(&si->lock);
364        } else {
365            /*
366             * Note pages allocated by racing tasks while
367             * scan for a free cluster is in progress, so
368             * that its final discard can exclude them.
369             */
370            if (offset < si->lowest_alloc)
371                si->lowest_alloc = offset;
372            if (offset > si->highest_alloc)
373                si->highest_alloc = offset;
374        }
375    }
376    return offset;
377
378scan:
379    spin_unlock(&si->lock);
380    while (++offset <= si->highest_bit) {
381        if (!si->swap_map[offset]) {
382            spin_lock(&si->lock);
383            goto checks;
384        }
385        if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
386            spin_lock(&si->lock);
387            goto checks;
388        }
389        if (unlikely(--latency_ration < 0)) {
390            cond_resched();
391            latency_ration = LATENCY_LIMIT;
392        }
393    }
394    offset = si->lowest_bit;
395    while (++offset < scan_base) {
396        if (!si->swap_map[offset]) {
397            spin_lock(&si->lock);
398            goto checks;
399        }
400        if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
401            spin_lock(&si->lock);
402            goto checks;
403        }
404        if (unlikely(--latency_ration < 0)) {
405            cond_resched();
406            latency_ration = LATENCY_LIMIT;
407        }
408    }
409    spin_lock(&si->lock);
410
411no_page:
412    si->flags -= SWP_SCANNING;
413    return 0;
414}
415
416swp_entry_t get_swap_page(void)
417{
418    struct swap_info_struct *si;
419    pgoff_t offset;
420    int type, next;
421    int wrapped = 0;
422    int hp_index;
423
424    spin_lock(&swap_lock);
425    if (atomic_long_read(&nr_swap_pages) <= 0)
426        goto noswap;
427    atomic_long_dec(&nr_swap_pages);
428
429    for (type = swap_list.next; type >= 0 && wrapped < 2; type = next) {
430        hp_index = atomic_xchg(&highest_priority_index, -1);
431        /*
432         * highest_priority_index records current highest priority swap
433         * type which just frees swap entries. If its priority is
434         * higher than that of swap_list.next swap type, we use it. It
435         * isn't protected by swap_lock, so it can be an invalid value
436         * if the corresponding swap type is swapoff. We double check
437         * the flags here. It's even possible the swap type is swapoff
438         * and swapon again and its priority is changed. In such rare
439         * case, low prority swap type might be used, but eventually
440         * high priority swap will be used after several rounds of
441         * swap.
442         */
443        if (hp_index != -1 && hp_index != type &&
444            swap_info[type]->prio < swap_info[hp_index]->prio &&
445            (swap_info[hp_index]->flags & SWP_WRITEOK)) {
446            type = hp_index;
447            swap_list.next = type;
448        }
449
450        si = swap_info[type];
451        next = si->next;
452        if (next < 0 ||
453            (!wrapped && si->prio != swap_info[next]->prio)) {
454            next = swap_list.head;
455            wrapped++;
456        }
457
458        spin_lock(&si->lock);
459        if (!si->highest_bit) {
460            spin_unlock(&si->lock);
461            continue;
462        }
463        if (!(si->flags & SWP_WRITEOK)) {
464            spin_unlock(&si->lock);
465            continue;
466        }
467
468        swap_list.next = next;
469
470        spin_unlock(&swap_lock);
471        /* This is called for allocating swap entry for cache */
472        offset = scan_swap_map(si, SWAP_HAS_CACHE);
473        spin_unlock(&si->lock);
474        if (offset)
475            return swp_entry(type, offset);
476        spin_lock(&swap_lock);
477        next = swap_list.next;
478    }
479
480    atomic_long_inc(&nr_swap_pages);
481noswap:
482    spin_unlock(&swap_lock);
483    return (swp_entry_t) {0};
484}
485
486/* The only caller of this function is now susupend routine */
487swp_entry_t get_swap_page_of_type(int type)
488{
489    struct swap_info_struct *si;
490    pgoff_t offset;
491
492    si = swap_info[type];
493    spin_lock(&si->lock);
494    if (si && (si->flags & SWP_WRITEOK)) {
495        atomic_long_dec(&nr_swap_pages);
496        /* This is called for allocating swap entry, not cache */
497        offset = scan_swap_map(si, 1);
498        if (offset) {
499            spin_unlock(&si->lock);
500            return swp_entry(type, offset);
501        }
502        atomic_long_inc(&nr_swap_pages);
503    }
504    spin_unlock(&si->lock);
505    return (swp_entry_t) {0};
506}
507
508static struct swap_info_struct *swap_info_get(swp_entry_t entry)
509{
510    struct swap_info_struct *p;
511    unsigned long offset, type;
512
513    if (!entry.val)
514        goto out;
515    type = swp_type(entry);
516    if (type >= nr_swapfiles)
517        goto bad_nofile;
518    p = swap_info[type];
519    if (!(p->flags & SWP_USED))
520        goto bad_device;
521    offset = swp_offset(entry);
522    if (offset >= p->max)
523        goto bad_offset;
524    if (!p->swap_map[offset])
525        goto bad_free;
526    spin_lock(&p->lock);
527    return p;
528
529bad_free:
530    printk(KERN_ERR "swap_free: %s%08lx\n", Unused_offset, entry.val);
531    goto out;
532bad_offset:
533    printk(KERN_ERR "swap_free: %s%08lx\n", Bad_offset, entry.val);
534    goto out;
535bad_device:
536    printk(KERN_ERR "swap_free: %s%08lx\n", Unused_file, entry.val);
537    goto out;
538bad_nofile:
539    printk(KERN_ERR "swap_free: %s%08lx\n", Bad_file, entry.val);
540out:
541    return NULL;
542}
543
544/*
545 * This swap type frees swap entry, check if it is the highest priority swap
546 * type which just frees swap entry. get_swap_page() uses
547 * highest_priority_index to search highest priority swap type. The
548 * swap_info_struct.lock can't protect us if there are multiple swap types
549 * active, so we use atomic_cmpxchg.
550 */
551static void set_highest_priority_index(int type)
552{
553    int old_hp_index, new_hp_index;
554
555    do {
556        old_hp_index = atomic_read(&highest_priority_index);
557        if (old_hp_index != -1 &&
558            swap_info[old_hp_index]->prio >= swap_info[type]->prio)
559            break;
560        new_hp_index = type;
561    } while (atomic_cmpxchg(&highest_priority_index,
562        old_hp_index, new_hp_index) != old_hp_index);
563}
564
565static unsigned char swap_entry_free(struct swap_info_struct *p,
566                     swp_entry_t entry, unsigned char usage)
567{
568    unsigned long offset = swp_offset(entry);
569    unsigned char count;
570    unsigned char has_cache;
571
572    count = p->swap_map[offset];
573    has_cache = count & SWAP_HAS_CACHE;
574    count &= ~SWAP_HAS_CACHE;
575
576    if (usage == SWAP_HAS_CACHE) {
577        VM_BUG_ON(!has_cache);
578        has_cache = 0;
579    } else if (count == SWAP_MAP_SHMEM) {
580        /*
581         * Or we could insist on shmem.c using a special
582         * swap_shmem_free() and free_shmem_swap_and_cache()...
583         */
584        count = 0;
585    } else if ((count & ~COUNT_CONTINUED) <= SWAP_MAP_MAX) {
586        if (count == COUNT_CONTINUED) {
587            if (swap_count_continued(p, offset, count))
588                count = SWAP_MAP_MAX | COUNT_CONTINUED;
589            else
590                count = SWAP_MAP_MAX;
591        } else
592            count--;
593    }
594
595    if (!count)
596        mem_cgroup_uncharge_swap(entry);
597
598    usage = count | has_cache;
599    p->swap_map[offset] = usage;
600
601    /* free if no reference */
602    if (!usage) {
603        if (offset < p->lowest_bit)
604            p->lowest_bit = offset;
605        if (offset > p->highest_bit)
606            p->highest_bit = offset;
607        set_highest_priority_index(p->type);
608        atomic_long_inc(&nr_swap_pages);
609        p->inuse_pages--;
610        frontswap_invalidate_page(p->type, offset);
611        if (p->flags & SWP_BLKDEV) {
612            struct gendisk *disk = p->bdev->bd_disk;
613            if (disk->fops->swap_slot_free_notify)
614                disk->fops->swap_slot_free_notify(p->bdev,
615                                  offset);
616        }
617    }
618
619    return usage;
620}
621
622/*
623 * Caller has made sure that the swapdevice corresponding to entry
624 * is still around or has not been recycled.
625 */
626void swap_free(swp_entry_t entry)
627{
628    struct swap_info_struct *p;
629
630    p = swap_info_get(entry);
631    if (p) {
632        swap_entry_free(p, entry, 1);
633        spin_unlock(&p->lock);
634    }
635}
636
637/*
638 * Called after dropping swapcache to decrease refcnt to swap entries.
639 */
640void swapcache_free(swp_entry_t entry, struct page *page)
641{
642    struct swap_info_struct *p;
643    unsigned char count;
644
645    p = swap_info_get(entry);
646    if (p) {
647        count = swap_entry_free(p, entry, SWAP_HAS_CACHE);
648        if (page)
649            mem_cgroup_uncharge_swapcache(page, entry, count != 0);
650        spin_unlock(&p->lock);
651    }
652}
653
654/*
655 * How many references to page are currently swapped out?
656 * This does not give an exact answer when swap count is continued,
657 * but does include the high COUNT_CONTINUED flag to allow for that.
658 */
659int page_swapcount(struct page *page)
660{
661    int count = 0;
662    struct swap_info_struct *p;
663    swp_entry_t entry;
664
665    entry.val = page_private(page);
666    p = swap_info_get(entry);
667    if (p) {
668        count = swap_count(p->swap_map[swp_offset(entry)]);
669        spin_unlock(&p->lock);
670    }
671    return count;
672}
673
674/*
675 * We can write to an anon page without COW if there are no other references
676 * to it. And as a side-effect, free up its swap: because the old content
677 * on disk will never be read, and seeking back there to write new content
678 * later would only waste time away from clustering.
679 */
680int reuse_swap_page(struct page *page)
681{
682    int count;
683
684    VM_BUG_ON(!PageLocked(page));
685    if (unlikely(PageKsm(page)))
686        return 0;
687    count = page_mapcount(page);
688    if (count <= 1 && PageSwapCache(page)) {
689        count += page_swapcount(page);
690        if (count == 1 && !PageWriteback(page)) {
691            delete_from_swap_cache(page);
692            SetPageDirty(page);
693        }
694    }
695    return count <= 1;
696}
697
698/*
699 * If swap is getting full, or if there are no more mappings of this page,
700 * then try_to_free_swap is called to free its swap space.
701 */
702int try_to_free_swap(struct page *page)
703{
704    VM_BUG_ON(!PageLocked(page));
705
706    if (!PageSwapCache(page))
707        return 0;
708    if (PageWriteback(page))
709        return 0;
710    if (page_swapcount(page))
711        return 0;
712
713    /*
714     * Once hibernation has begun to create its image of memory,
715     * there's a danger that one of the calls to try_to_free_swap()
716     * - most probably a call from __try_to_reclaim_swap() while
717     * hibernation is allocating its own swap pages for the image,
718     * but conceivably even a call from memory reclaim - will free
719     * the swap from a page which has already been recorded in the
720     * image as a clean swapcache page, and then reuse its swap for
721     * another page of the image. On waking from hibernation, the
722     * original page might be freed under memory pressure, then
723     * later read back in from swap, now with the wrong data.
724     *
725     * Hibration suspends storage while it is writing the image
726     * to disk so check that here.
727     */
728    if (pm_suspended_storage())
729        return 0;
730
731    delete_from_swap_cache(page);
732    SetPageDirty(page);
733    return 1;
734}
735
736/*
737 * Free the swap entry like above, but also try to
738 * free the page cache entry if it is the last user.
739 */
740int free_swap_and_cache(swp_entry_t entry)
741{
742    struct swap_info_struct *p;
743    struct page *page = NULL;
744
745    if (non_swap_entry(entry))
746        return 1;
747
748    p = swap_info_get(entry);
749    if (p) {
750        if (swap_entry_free(p, entry, 1) == SWAP_HAS_CACHE) {
751            page = find_get_page(swap_address_space(entry),
752                        entry.val);
753            if (page && !trylock_page(page)) {
754                page_cache_release(page);
755                page = NULL;
756            }
757        }
758        spin_unlock(&p->lock);
759    }
760    if (page) {
761        /*
762         * Not mapped elsewhere, or swap space full? Free it!
763         * Also recheck PageSwapCache now page is locked (above).
764         */
765        if (PageSwapCache(page) && !PageWriteback(page) &&
766                (!page_mapped(page) || vm_swap_full())) {
767            delete_from_swap_cache(page);
768            SetPageDirty(page);
769        }
770        unlock_page(page);
771        page_cache_release(page);
772    }
773    return p != NULL;
774}
775
776#ifdef CONFIG_HIBERNATION
777/*
778 * Find the swap type that corresponds to given device (if any).
779 *
780 * @offset - number of the PAGE_SIZE-sized block of the device, starting
781 * from 0, in which the swap header is expected to be located.
782 *
783 * This is needed for the suspend to disk (aka swsusp).
784 */
785int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)
786{
787    struct block_device *bdev = NULL;
788    int type;
789
790    if (device)
791        bdev = bdget(device);
792
793    spin_lock(&swap_lock);
794    for (type = 0; type < nr_swapfiles; type++) {
795        struct swap_info_struct *sis = swap_info[type];
796
797        if (!(sis->flags & SWP_WRITEOK))
798            continue;
799
800        if (!bdev) {
801            if (bdev_p)
802                *bdev_p = bdgrab(sis->bdev);
803
804            spin_unlock(&swap_lock);
805            return type;
806        }
807        if (bdev == sis->bdev) {
808            struct swap_extent *se = &sis->first_swap_extent;
809
810            if (se->start_block == offset) {
811                if (bdev_p)
812                    *bdev_p = bdgrab(sis->bdev);
813
814                spin_unlock(&swap_lock);
815                bdput(bdev);
816                return type;
817            }
818        }
819    }
820    spin_unlock(&swap_lock);
821    if (bdev)
822        bdput(bdev);
823
824    return -ENODEV;
825}
826
827/*
828 * Get the (PAGE_SIZE) block corresponding to given offset on the swapdev
829 * corresponding to given index in swap_info (swap type).
830 */
831sector_t swapdev_block(int type, pgoff_t offset)
832{
833    struct block_device *bdev;
834
835    if ((unsigned int)type >= nr_swapfiles)
836        return 0;
837    if (!(swap_info[type]->flags & SWP_WRITEOK))
838        return 0;
839    return map_swap_entry(swp_entry(type, offset), &bdev);
840}
841
842/*
843 * Return either the total number of swap pages of given type, or the number
844 * of free pages of that type (depending on @free)
845 *
846 * This is needed for software suspend
847 */
848unsigned int count_swap_pages(int type, int free)
849{
850    unsigned int n = 0;
851
852    spin_lock(&swap_lock);
853    if ((unsigned int)type < nr_swapfiles) {
854        struct swap_info_struct *sis = swap_info[type];
855
856        spin_lock(&sis->lock);
857        if (sis->flags & SWP_WRITEOK) {
858            n = sis->pages;
859            if (free)
860                n -= sis->inuse_pages;
861        }
862        spin_unlock(&sis->lock);
863    }
864    spin_unlock(&swap_lock);
865    return n;
866}
867#endif /* CONFIG_HIBERNATION */
868
869/*
870 * No need to decide whether this PTE shares the swap entry with others,
871 * just let do_wp_page work it out if a write is requested later - to
872 * force COW, vm_page_prot omits write permission from any private vma.
873 */
874static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
875        unsigned long addr, swp_entry_t entry, struct page *page)
876{
877    struct page *swapcache;
878    struct mem_cgroup *memcg;
879    spinlock_t *ptl;
880    pte_t *pte;
881    int ret = 1;
882
883    swapcache = page;
884    page = ksm_might_need_to_copy(page, vma, addr);
885    if (unlikely(!page))
886        return -ENOMEM;
887
888    if (mem_cgroup_try_charge_swapin(vma->vm_mm, page,
889                     GFP_KERNEL, &memcg)) {
890        ret = -ENOMEM;
891        goto out_nolock;
892    }
893
894    pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
895    if (unlikely(!pte_same(*pte, swp_entry_to_pte(entry)))) {
896        mem_cgroup_cancel_charge_swapin(memcg);
897        ret = 0;
898        goto out;
899    }
900
901    dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
902    inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
903    get_page(page);
904    set_pte_at(vma->vm_mm, addr, pte,
905           pte_mkold(mk_pte(page, vma->vm_page_prot)));
906    if (page == swapcache)
907        page_add_anon_rmap(page, vma, addr);
908    else /* ksm created a completely new copy */
909        page_add_new_anon_rmap(page, vma, addr);
910    mem_cgroup_commit_charge_swapin(page, memcg);
911    swap_free(entry);
912    /*
913     * Move the page to the active list so it is not
914     * immediately swapped out again after swapon.
915     */
916    activate_page(page);
917out:
918    pte_unmap_unlock(pte, ptl);
919out_nolock:
920    if (page != swapcache) {
921        unlock_page(page);
922        put_page(page);
923    }
924    return ret;
925}
926
927static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
928                unsigned long addr, unsigned long end,
929                swp_entry_t entry, struct page *page)
930{
931    pte_t swp_pte = swp_entry_to_pte(entry);
932    pte_t *pte;
933    int ret = 0;
934
935    /*
936     * We don't actually need pte lock while scanning for swp_pte: since
937     * we hold page lock and mmap_sem, swp_pte cannot be inserted into the
938     * page table while we're scanning; though it could get zapped, and on
939     * some architectures (e.g. x86_32 with PAE) we might catch a glimpse
940     * of unmatched parts which look like swp_pte, so unuse_pte must
941     * recheck under pte lock. Scanning without pte lock lets it be
942     * preemptible whenever CONFIG_PREEMPT but not CONFIG_HIGHPTE.
943     */
944    pte = pte_offset_map(pmd, addr);
945    do {
946        /*
947         * swapoff spends a _lot_ of time in this loop!
948         * Test inline before going to call unuse_pte.
949         */
950        if (unlikely(pte_same(*pte, swp_pte))) {
951            pte_unmap(pte);
952            ret = unuse_pte(vma, pmd, addr, entry, page);
953            if (ret)
954                goto out;
955            pte = pte_offset_map(pmd, addr);
956        }
957    } while (pte++, addr += PAGE_SIZE, addr != end);
958    pte_unmap(pte - 1);
959out:
960    return ret;
961}
962
963static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
964                unsigned long addr, unsigned long end,
965                swp_entry_t entry, struct page *page)
966{
967    pmd_t *pmd;
968    unsigned long next;
969    int ret;
970
971    pmd = pmd_offset(pud, addr);
972    do {
973        next = pmd_addr_end(addr, end);
974        if (pmd_none_or_trans_huge_or_clear_bad(pmd))
975            continue;
976        ret = unuse_pte_range(vma, pmd, addr, next, entry, page);
977        if (ret)
978            return ret;
979    } while (pmd++, addr = next, addr != end);
980    return 0;
981}
982
983static inline int unuse_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
984                unsigned long addr, unsigned long end,
985                swp_entry_t entry, struct page *page)
986{
987    pud_t *pud;
988    unsigned long next;
989    int ret;
990
991    pud = pud_offset(pgd, addr);
992    do {
993        next = pud_addr_end(addr, end);
994        if (pud_none_or_clear_bad(pud))
995            continue;
996        ret = unuse_pmd_range(vma, pud, addr, next, entry, page);
997        if (ret)
998            return ret;
999    } while (pud++, addr = next, addr != end);
1000    return 0;
1001}
1002
1003static int unuse_vma(struct vm_area_struct *vma,
1004                swp_entry_t entry, struct page *page)
1005{
1006    pgd_t *pgd;
1007    unsigned long addr, end, next;
1008    int ret;
1009
1010    if (page_anon_vma(page)) {
1011        addr = page_address_in_vma(page, vma);
1012        if (addr == -EFAULT)
1013            return 0;
1014        else
1015            end = addr + PAGE_SIZE;
1016    } else {
1017        addr = vma->vm_start;
1018        end = vma->vm_end;
1019    }
1020
1021    pgd = pgd_offset(vma->vm_mm, addr);
1022    do {
1023        next = pgd_addr_end(addr, end);
1024        if (pgd_none_or_clear_bad(pgd))
1025            continue;
1026        ret = unuse_pud_range(vma, pgd, addr, next, entry, page);
1027        if (ret)
1028            return ret;
1029    } while (pgd++, addr = next, addr != end);
1030    return 0;
1031}
1032
1033static int unuse_mm(struct mm_struct *mm,
1034                swp_entry_t entry, struct page *page)
1035{
1036    struct vm_area_struct *vma;
1037    int ret = 0;
1038
1039    if (!down_read_trylock(&mm->mmap_sem)) {
1040        /*
1041         * Activate page so shrink_inactive_list is unlikely to unmap
1042         * its ptes while lock is dropped, so swapoff can make progress.
1043         */
1044        activate_page(page);
1045        unlock_page(page);
1046        down_read(&mm->mmap_sem);
1047        lock_page(page);
1048    }
1049    for (vma = mm->mmap; vma; vma = vma->vm_next) {
1050        if (vma->anon_vma && (ret = unuse_vma(vma, entry, page)))
1051            break;
1052    }
1053    up_read(&mm->mmap_sem);
1054    return (ret < 0)? ret: 0;
1055}
1056
1057/*
1058 * Scan swap_map (or frontswap_map if frontswap parameter is true)
1059 * from current position to next entry still in use.
1060 * Recycle to start on reaching the end, returning 0 when empty.
1061 */
1062static unsigned int find_next_to_unuse(struct swap_info_struct *si,
1063                    unsigned int prev, bool frontswap)
1064{
1065    unsigned int max = si->max;
1066    unsigned int i = prev;
1067    unsigned char count;
1068
1069    /*
1070     * No need for swap_lock here: we're just looking
1071     * for whether an entry is in use, not modifying it; false
1072     * hits are okay, and sys_swapoff() has already prevented new
1073     * allocations from this area (while holding swap_lock).
1074     */
1075    for (;;) {
1076        if (++i >= max) {
1077            if (!prev) {
1078                i = 0;
1079                break;
1080            }
1081            /*
1082             * No entries in use at top of swap_map,
1083             * loop back to start and recheck there.
1084             */
1085            max = prev + 1;
1086            prev = 0;
1087            i = 1;
1088        }
1089        if (frontswap) {
1090            if (frontswap_test(si, i))
1091                break;
1092            else
1093                continue;
1094        }
1095        count = si->swap_map[i];
1096        if (count && swap_count(count) != SWAP_MAP_BAD)
1097            break;
1098    }
1099    return i;
1100}
1101
1102/*
1103 * We completely avoid races by reading each swap page in advance,
1104 * and then search for the process using it. All the necessary
1105 * page table adjustments can then be made atomically.
1106 *
1107 * if the boolean frontswap is true, only unuse pages_to_unuse pages;
1108 * pages_to_unuse==0 means all pages; ignored if frontswap is false
1109 */
1110int try_to_unuse(unsigned int type, bool frontswap,
1111         unsigned long pages_to_unuse)
1112{
1113    struct swap_info_struct *si = swap_info[type];
1114    struct mm_struct *start_mm;
1115    unsigned char *swap_map;
1116    unsigned char swcount;
1117    struct page *page;
1118    swp_entry_t entry;
1119    unsigned int i = 0;
1120    int retval = 0;
1121
1122    /*
1123     * When searching mms for an entry, a good strategy is to
1124     * start at the first mm we freed the previous entry from
1125     * (though actually we don't notice whether we or coincidence
1126     * freed the entry). Initialize this start_mm with a hold.
1127     *
1128     * A simpler strategy would be to start at the last mm we
1129     * freed the previous entry from; but that would take less
1130     * advantage of mmlist ordering, which clusters forked mms
1131     * together, child after parent. If we race with dup_mmap(), we
1132     * prefer to resolve parent before child, lest we miss entries
1133     * duplicated after we scanned child: using last mm would invert
1134     * that.
1135     */
1136    start_mm = &init_mm;
1137    atomic_inc(&init_mm.mm_users);
1138
1139    /*
1140     * Keep on scanning until all entries have gone. Usually,
1141     * one pass through swap_map is enough, but not necessarily:
1142     * there are races when an instance of an entry might be missed.
1143     */
1144    while ((i = find_next_to_unuse(si, i, frontswap)) != 0) {
1145        if (signal_pending(current)) {
1146            retval = -EINTR;
1147            break;
1148        }
1149
1150        /*
1151         * Get a page for the entry, using the existing swap
1152         * cache page if there is one. Otherwise, get a clean
1153         * page and read the swap into it.
1154         */
1155        swap_map = &si->swap_map[i];
1156        entry = swp_entry(type, i);
1157        page = read_swap_cache_async(entry,
1158                    GFP_HIGHUSER_MOVABLE, NULL, 0);
1159        if (!page) {
1160            /*
1161             * Either swap_duplicate() failed because entry
1162             * has been freed independently, and will not be
1163             * reused since sys_swapoff() already disabled
1164             * allocation from here, or alloc_page() failed.
1165             */
1166            if (!*swap_map)
1167                continue;
1168            retval = -ENOMEM;
1169            break;
1170        }
1171
1172        /*
1173         * Don't hold on to start_mm if it looks like exiting.
1174         */
1175        if (atomic_read(&start_mm->mm_users) == 1) {
1176            mmput(start_mm);
1177            start_mm = &init_mm;
1178            atomic_inc(&init_mm.mm_users);
1179        }
1180
1181        /*
1182         * Wait for and lock page. When do_swap_page races with
1183         * try_to_unuse, do_swap_page can handle the fault much
1184         * faster than try_to_unuse can locate the entry. This
1185         * apparently redundant "wait_on_page_locked" lets try_to_unuse
1186         * defer to do_swap_page in such a case - in some tests,
1187         * do_swap_page and try_to_unuse repeatedly compete.
1188         */
1189        wait_on_page_locked(page);
1190        wait_on_page_writeback(page);
1191        lock_page(page);
1192        wait_on_page_writeback(page);
1193
1194        /*
1195         * Remove all references to entry.
1196         */
1197        swcount = *swap_map;
1198        if (swap_count(swcount) == SWAP_MAP_SHMEM) {
1199            retval = shmem_unuse(entry, page);
1200            /* page has already been unlocked and released */
1201            if (retval < 0)
1202                break;
1203            continue;
1204        }
1205        if (swap_count(swcount) && start_mm != &init_mm)
1206            retval = unuse_mm(start_mm, entry, page);
1207
1208        if (swap_count(*swap_map)) {
1209            int set_start_mm = (*swap_map >= swcount);
1210            struct list_head *p = &start_mm->mmlist;
1211            struct mm_struct *new_start_mm = start_mm;
1212            struct mm_struct *prev_mm = start_mm;
1213            struct mm_struct *mm;
1214
1215            atomic_inc(&new_start_mm->mm_users);
1216            atomic_inc(&prev_mm->mm_users);
1217            spin_lock(&mmlist_lock);
1218            while (swap_count(*swap_map) && !retval &&
1219                    (p = p->next) != &start_mm->mmlist) {
1220                mm = list_entry(p, struct mm_struct, mmlist);
1221                if (!atomic_inc_not_zero(&mm->mm_users))
1222                    continue;
1223                spin_unlock(&mmlist_lock);
1224                mmput(prev_mm);
1225                prev_mm = mm;
1226
1227                cond_resched();
1228
1229                swcount = *swap_map;
1230                if (!swap_count(swcount)) /* any usage ? */
1231                    ;
1232                else if (mm == &init_mm)
1233                    set_start_mm = 1;
1234                else
1235                    retval = unuse_mm(mm, entry, page);
1236
1237                if (set_start_mm && *swap_map < swcount) {
1238                    mmput(new_start_mm);
1239                    atomic_inc(&mm->mm_users);
1240                    new_start_mm = mm;
1241                    set_start_mm = 0;
1242                }
1243                spin_lock(&mmlist_lock);
1244            }
1245            spin_unlock(&mmlist_lock);
1246            mmput(prev_mm);
1247            mmput(start_mm);
1248            start_mm = new_start_mm;
1249        }
1250        if (retval) {
1251            unlock_page(page);
1252            page_cache_release(page);
1253            break;
1254        }
1255
1256        /*
1257         * If a reference remains (rare), we would like to leave
1258         * the page in the swap cache; but try_to_unmap could
1259         * then re-duplicate the entry once we drop page lock,
1260         * so we might loop indefinitely; also, that page could
1261         * not be swapped out to other storage meanwhile. So:
1262         * delete from cache even if there's another reference,
1263         * after ensuring that the data has been saved to disk -
1264         * since if the reference remains (rarer), it will be
1265         * read from disk into another page. Splitting into two
1266         * pages would be incorrect if swap supported "shared
1267         * private" pages, but they are handled by tmpfs files.
1268         *
1269         * Given how unuse_vma() targets one particular offset
1270         * in an anon_vma, once the anon_vma has been determined,
1271         * this splitting happens to be just what is needed to
1272         * handle where KSM pages have been swapped out: re-reading
1273         * is unnecessarily slow, but we can fix that later on.
1274         */
1275        if (swap_count(*swap_map) &&
1276             PageDirty(page) && PageSwapCache(page)) {
1277            struct writeback_control wbc = {
1278                .sync_mode = WB_SYNC_NONE,
1279            };
1280
1281            swap_writepage(page, &wbc);
1282            lock_page(page);
1283            wait_on_page_writeback(page);
1284        }
1285
1286        /*
1287         * It is conceivable that a racing task removed this page from
1288         * swap cache just before we acquired the page lock at the top,
1289         * or while we dropped it in unuse_mm(). The page might even
1290         * be back in swap cache on another swap area: that we must not
1291         * delete, since it may not have been written out to swap yet.
1292         */
1293        if (PageSwapCache(page) &&
1294            likely(page_private(page) == entry.val))
1295            delete_from_swap_cache(page);
1296
1297        /*
1298         * So we could skip searching mms once swap count went
1299         * to 1, we did not mark any present ptes as dirty: must
1300         * mark page dirty so shrink_page_list will preserve it.
1301         */
1302        SetPageDirty(page);
1303        unlock_page(page);
1304        page_cache_release(page);
1305
1306        /*
1307         * Make sure that we aren't completely killing
1308         * interactive performance.
1309         */
1310        cond_resched();
1311        if (frontswap && pages_to_unuse > 0) {
1312            if (!--pages_to_unuse)
1313                break;
1314        }
1315    }
1316
1317    mmput(start_mm);
1318    return retval;
1319}
1320
1321/*
1322 * After a successful try_to_unuse, if no swap is now in use, we know
1323 * we can empty the mmlist. swap_lock must be held on entry and exit.
1324 * Note that mmlist_lock nests inside swap_lock, and an mm must be
1325 * added to the mmlist just after page_duplicate - before would be racy.
1326 */
1327static void drain_mmlist(void)
1328{
1329    struct list_head *p, *next;
1330    unsigned int type;
1331
1332    for (type = 0; type < nr_swapfiles; type++)
1333        if (swap_info[type]->inuse_pages)
1334            return;
1335    spin_lock(&mmlist_lock);
1336    list_for_each_safe(p, next, &init_mm.mmlist)
1337        list_del_init(p);
1338    spin_unlock(&mmlist_lock);
1339}
1340
1341/*
1342 * Use this swapdev's extent info to locate the (PAGE_SIZE) block which
1343 * corresponds to page offset for the specified swap entry.
1344 * Note that the type of this function is sector_t, but it returns page offset
1345 * into the bdev, not sector offset.
1346 */
1347static sector_t map_swap_entry(swp_entry_t entry, struct block_device **bdev)
1348{
1349    struct swap_info_struct *sis;
1350    struct swap_extent *start_se;
1351    struct swap_extent *se;
1352    pgoff_t offset;
1353
1354    sis = swap_info[swp_type(entry)];
1355    *bdev = sis->bdev;
1356
1357    offset = swp_offset(entry);
1358    start_se = sis->curr_swap_extent;
1359    se = start_se;
1360
1361    for ( ; ; ) {
1362        struct list_head *lh;
1363
1364        if (se->start_page <= offset &&
1365                offset < (se->start_page + se->nr_pages)) {
1366            return se->start_block + (offset - se->start_page);
1367        }
1368        lh = se->list.next;
1369        se = list_entry(lh, struct swap_extent, list);
1370        sis->curr_swap_extent = se;
1371        BUG_ON(se == start_se); /* It *must* be present */
1372    }
1373}
1374
1375/*
1376 * Returns the page offset into bdev for the specified page's swap entry.
1377 */
1378sector_t map_swap_page(struct page *page, struct block_device **bdev)
1379{
1380    swp_entry_t entry;
1381    entry.val = page_private(page);
1382    return map_swap_entry(entry, bdev);
1383}
1384
1385/*
1386 * Free all of a swapdev's extent information
1387 */
1388static void destroy_swap_extents(struct swap_info_struct *sis)
1389{
1390    while (!list_empty(&sis->first_swap_extent.list)) {
1391        struct swap_extent *se;
1392
1393        se = list_entry(sis->first_swap_extent.list.next,
1394                struct swap_extent, list);
1395        list_del(&se->list);
1396        kfree(se);
1397    }
1398
1399    if (sis->flags & SWP_FILE) {
1400        struct file *swap_file = sis->swap_file;
1401        struct address_space *mapping = swap_file->f_mapping;
1402
1403        sis->flags &= ~SWP_FILE;
1404        mapping->a_ops->swap_deactivate(swap_file);
1405    }
1406}
1407
1408/*
1409 * Add a block range (and the corresponding page range) into this swapdev's
1410 * extent list. The extent list is kept sorted in page order.
1411 *
1412 * This function rather assumes that it is called in ascending page order.
1413 */
1414int
1415add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
1416        unsigned long nr_pages, sector_t start_block)
1417{
1418    struct swap_extent *se;
1419    struct swap_extent *new_se;
1420    struct list_head *lh;
1421
1422    if (start_page == 0) {
1423        se = &sis->first_swap_extent;
1424        sis->curr_swap_extent = se;
1425        se->start_page = 0;
1426        se->nr_pages = nr_pages;
1427        se->start_block = start_block;
1428        return 1;
1429    } else {
1430        lh = sis->first_swap_extent.list.prev; /* Highest extent */
1431        se = list_entry(lh, struct swap_extent, list);
1432        BUG_ON(se->start_page + se->nr_pages != start_page);
1433        if (se->start_block + se->nr_pages == start_block) {
1434            /* Merge it */
1435            se->nr_pages += nr_pages;
1436            return 0;
1437        }
1438    }
1439
1440    /*
1441     * No merge. Insert a new extent, preserving ordering.
1442     */
1443    new_se = kmalloc(sizeof(*se), GFP_KERNEL);
1444    if (new_se == NULL)
1445        return -ENOMEM;
1446    new_se->start_page = start_page;
1447    new_se->nr_pages = nr_pages;
1448    new_se->start_block = start_block;
1449
1450    list_add_tail(&new_se->list, &sis->first_swap_extent.list);
1451    return 1;
1452}
1453
1454/*
1455 * A `swap extent' is a simple thing which maps a contiguous range of pages
1456 * onto a contiguous range of disk blocks. An ordered list of swap extents
1457 * is built at swapon time and is then used at swap_writepage/swap_readpage
1458 * time for locating where on disk a page belongs.
1459 *
1460 * If the swapfile is an S_ISBLK block device, a single extent is installed.
1461 * This is done so that the main operating code can treat S_ISBLK and S_ISREG
1462 * swap files identically.
1463 *
1464 * Whether the swapdev is an S_ISREG file or an S_ISBLK blockdev, the swap
1465 * extent list operates in PAGE_SIZE disk blocks. Both S_ISREG and S_ISBLK
1466 * swapfiles are handled *identically* after swapon time.
1467 *
1468 * For S_ISREG swapfiles, setup_swap_extents() will walk all the file's blocks
1469 * and will parse them into an ordered extent list, in PAGE_SIZE chunks. If
1470 * some stray blocks are found which do not fall within the PAGE_SIZE alignment
1471 * requirements, they are simply tossed out - we will never use those blocks
1472 * for swapping.
1473 *
1474 * For S_ISREG swapfiles we set S_SWAPFILE across the life of the swapon. This
1475 * prevents root from shooting her foot off by ftruncating an in-use swapfile,
1476 * which will scribble on the fs.
1477 *
1478 * The amount of disk space which a single swap extent represents varies.
1479 * Typically it is in the 1-4 megabyte range. So we can have hundreds of
1480 * extents in the list. To avoid much list walking, we cache the previous
1481 * search location in `curr_swap_extent', and start new searches from there.
1482 * This is extremely effective. The average number of iterations in
1483 * map_swap_page() has been measured at about 0.3 per page. - akpm.
1484 */
1485static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
1486{
1487    struct file *swap_file = sis->swap_file;
1488    struct address_space *mapping = swap_file->f_mapping;
1489    struct inode *inode = mapping->host;
1490    int ret;
1491
1492    if (S_ISBLK(inode->i_mode)) {
1493        ret = add_swap_extent(sis, 0, sis->max, 0);
1494        *span = sis->pages;
1495        return ret;
1496    }
1497
1498    if (mapping->a_ops->swap_activate) {
1499        ret = mapping->a_ops->swap_activate(sis, swap_file, span);
1500        if (!ret) {
1501            sis->flags |= SWP_FILE;
1502            ret = add_swap_extent(sis, 0, sis->max, 0);
1503            *span = sis->pages;
1504        }
1505        return ret;
1506    }
1507
1508    return generic_swapfile_activate(sis, swap_file, span);
1509}
1510
1511static void _enable_swap_info(struct swap_info_struct *p, int prio,
1512                unsigned char *swap_map,
1513                unsigned long *frontswap_map)
1514{
1515    int i, prev;
1516
1517    if (prio >= 0)
1518        p->prio = prio;
1519    else
1520        p->prio = --least_priority;
1521    p->swap_map = swap_map;
1522    frontswap_map_set(p, frontswap_map);
1523    p->flags |= SWP_WRITEOK;
1524    atomic_long_add(p->pages, &nr_swap_pages);
1525    total_swap_pages += p->pages;
1526
1527    /* insert swap space into swap_list: */
1528    prev = -1;
1529    for (i = swap_list.head; i >= 0; i = swap_info[i]->next) {
1530        if (p->prio >= swap_info[i]->prio)
1531            break;
1532        prev = i;
1533    }
1534    p->next = i;
1535    if (prev < 0)
1536        swap_list.head = swap_list.next = p->type;
1537    else
1538        swap_info[prev]->next = p->type;
1539}
1540
1541static void enable_swap_info(struct swap_info_struct *p, int prio,
1542                unsigned char *swap_map,
1543                unsigned long *frontswap_map)
1544{
1545    spin_lock(&swap_lock);
1546    spin_lock(&p->lock);
1547    _enable_swap_info(p, prio, swap_map, frontswap_map);
1548    frontswap_init(p->type);
1549    spin_unlock(&p->lock);
1550    spin_unlock(&swap_lock);
1551}
1552
1553static void reinsert_swap_info(struct swap_info_struct *p)
1554{
1555    spin_lock(&swap_lock);
1556    spin_lock(&p->lock);
1557    _enable_swap_info(p, p->prio, p->swap_map, frontswap_map_get(p));
1558    spin_unlock(&p->lock);
1559    spin_unlock(&swap_lock);
1560}
1561
1562SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
1563{
1564    struct swap_info_struct *p = NULL;
1565    unsigned char *swap_map;
1566    struct file *swap_file, *victim;
1567    struct address_space *mapping;
1568    struct inode *inode;
1569    struct filename *pathname;
1570    int i, type, prev;
1571    int err;
1572
1573    if (!capable(CAP_SYS_ADMIN))
1574        return -EPERM;
1575
1576    BUG_ON(!current->mm);
1577
1578    pathname = getname(specialfile);
1579    if (IS_ERR(pathname))
1580        return PTR_ERR(pathname);
1581
1582    victim = file_open_name(pathname, O_RDWR|O_LARGEFILE, 0);
1583    err = PTR_ERR(victim);
1584    if (IS_ERR(victim))
1585        goto out;
1586
1587    mapping = victim->f_mapping;
1588    prev = -1;
1589    spin_lock(&swap_lock);
1590    for (type = swap_list.head; type >= 0; type = swap_info[type]->next) {
1591        p = swap_info[type];
1592        if (p->flags & SWP_WRITEOK) {
1593            if (p->swap_file->f_mapping == mapping)
1594                break;
1595        }
1596        prev = type;
1597    }
1598    if (type < 0) {
1599        err = -EINVAL;
1600        spin_unlock(&swap_lock);
1601        goto out_dput;
1602    }
1603    if (!security_vm_enough_memory_mm(current->mm, p->pages))
1604        vm_unacct_memory(p->pages);
1605    else {
1606        err = -ENOMEM;
1607        spin_unlock(&swap_lock);
1608        goto out_dput;
1609    }
1610    if (prev < 0)
1611        swap_list.head = p->next;
1612    else
1613        swap_info[prev]->next = p->next;
1614    if (type == swap_list.next) {
1615        /* just pick something that's safe... */
1616        swap_list.next = swap_list.head;
1617    }
1618    spin_lock(&p->lock);
1619    if (p->prio < 0) {
1620        for (i = p->next; i >= 0; i = swap_info[i]->next)
1621            swap_info[i]->prio = p->prio--;
1622        least_priority++;
1623    }
1624    atomic_long_sub(p->pages, &nr_swap_pages);
1625    total_swap_pages -= p->pages;
1626    p->flags &= ~SWP_WRITEOK;
1627    spin_unlock(&p->lock);
1628    spin_unlock(&swap_lock);
1629
1630    set_current_oom_origin();
1631    err = try_to_unuse(type, false, 0); /* force all pages to be unused */
1632    clear_current_oom_origin();
1633
1634    if (err) {
1635        /* re-insert swap space back into swap_list */
1636        reinsert_swap_info(p);
1637        goto out_dput;
1638    }
1639
1640    destroy_swap_extents(p);
1641    if (p->flags & SWP_CONTINUED)
1642        free_swap_count_continuations(p);
1643
1644    mutex_lock(&swapon_mutex);
1645    spin_lock(&swap_lock);
1646    spin_lock(&p->lock);
1647    drain_mmlist();
1648
1649    /* wait for anyone still in scan_swap_map */
1650    p->highest_bit = 0; /* cuts scans short */
1651    while (p->flags >= SWP_SCANNING) {
1652        spin_unlock(&p->lock);
1653        spin_unlock(&swap_lock);
1654        schedule_timeout_uninterruptible(1);
1655        spin_lock(&swap_lock);
1656        spin_lock(&p->lock);
1657    }
1658
1659    swap_file = p->swap_file;
1660    p->swap_file = NULL;
1661    p->max = 0;
1662    swap_map = p->swap_map;
1663    p->swap_map = NULL;
1664    p->flags = 0;
1665    frontswap_invalidate_area(type);
1666    spin_unlock(&p->lock);
1667    spin_unlock(&swap_lock);
1668    mutex_unlock(&swapon_mutex);
1669    vfree(swap_map);
1670    vfree(frontswap_map_get(p));
1671    /* Destroy swap account informatin */
1672    swap_cgroup_swapoff(type);
1673
1674    inode = mapping->host;
1675    if (S_ISBLK(inode->i_mode)) {
1676        struct block_device *bdev = I_BDEV(inode);
1677        set_blocksize(bdev, p->old_block_size);
1678        blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
1679    } else {
1680        mutex_lock(&inode->i_mutex);
1681        inode->i_flags &= ~S_SWAPFILE;
1682        mutex_unlock(&inode->i_mutex);
1683    }
1684    filp_close(swap_file, NULL);
1685    err = 0;
1686    atomic_inc(&proc_poll_event);
1687    wake_up_interruptible(&proc_poll_wait);
1688
1689out_dput:
1690    filp_close(victim, NULL);
1691out:
1692    putname(pathname);
1693    return err;
1694}
1695
1696#ifdef CONFIG_PROC_FS
1697static unsigned swaps_poll(struct file *file, poll_table *wait)
1698{
1699    struct seq_file *seq = file->private_data;
1700
1701    poll_wait(file, &proc_poll_wait, wait);
1702
1703    if (seq->poll_event != atomic_read(&proc_poll_event)) {
1704        seq->poll_event = atomic_read(&proc_poll_event);
1705        return POLLIN | POLLRDNORM | POLLERR | POLLPRI;
1706    }
1707
1708    return POLLIN | POLLRDNORM;
1709}
1710
1711/* iterator */
1712static void *swap_start(struct seq_file *swap, loff_t *pos)
1713{
1714    struct swap_info_struct *si;
1715    int type;
1716    loff_t l = *pos;
1717
1718    mutex_lock(&swapon_mutex);
1719
1720    if (!l)
1721        return SEQ_START_TOKEN;
1722
1723    for (type = 0; type < nr_swapfiles; type++) {
1724        smp_rmb(); /* read nr_swapfiles before swap_info[type] */
1725        si = swap_info[type];
1726        if (!(si->flags & SWP_USED) || !si->swap_map)
1727            continue;
1728        if (!--l)
1729            return si;
1730    }
1731
1732    return NULL;
1733}
1734
1735static void *swap_next(struct seq_file *swap, void *v, loff_t *pos)
1736{
1737    struct swap_info_struct *si = v;
1738    int type;
1739
1740    if (v == SEQ_START_TOKEN)
1741        type = 0;
1742    else
1743        type = si->type + 1;
1744
1745    for (; type < nr_swapfiles; type++) {
1746        smp_rmb(); /* read nr_swapfiles before swap_info[type] */
1747        si = swap_info[type];
1748        if (!(si->flags & SWP_USED) || !si->swap_map)
1749            continue;
1750        ++*pos;
1751        return si;
1752    }
1753
1754    return NULL;
1755}
1756
1757static void swap_stop(struct seq_file *swap, void *v)
1758{
1759    mutex_unlock(&swapon_mutex);
1760}
1761
1762static int swap_show(struct seq_file *swap, void *v)
1763{
1764    struct swap_info_struct *si = v;
1765    struct file *file;
1766    int len;
1767
1768    if (si == SEQ_START_TOKEN) {
1769        seq_puts(swap,"Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n");
1770        return 0;
1771    }
1772
1773    file = si->swap_file;
1774    len = seq_path(swap, &file->f_path, " \t\n\\");
1775    seq_printf(swap, "%*s%s\t%u\t%u\t%d\n",
1776            len < 40 ? 40 - len : 1, " ",
1777            S_ISBLK(file_inode(file)->i_mode) ?
1778                "partition" : "file\t",
1779            si->pages << (PAGE_SHIFT - 10),
1780            si->inuse_pages << (PAGE_SHIFT - 10),
1781            si->prio);
1782    return 0;
1783}
1784
1785static const struct seq_operations swaps_op = {
1786    .start = swap_start,
1787    .next = swap_next,
1788    .stop = swap_stop,
1789    .show = swap_show
1790};
1791
1792static int swaps_open(struct inode *inode, struct file *file)
1793{
1794    struct seq_file *seq;
1795    int ret;
1796
1797    ret = seq_open(file, &swaps_op);
1798    if (ret)
1799        return ret;
1800
1801    seq = file->private_data;
1802    seq->poll_event = atomic_read(&proc_poll_event);
1803    return 0;
1804}
1805
1806static const struct file_operations proc_swaps_operations = {
1807    .open = swaps_open,
1808    .read = seq_read,
1809    .llseek = seq_lseek,
1810    .release = seq_release,
1811    .poll = swaps_poll,
1812};
1813
1814static int __init procswaps_init(void)
1815{
1816    proc_create("swaps", 0, NULL, &proc_swaps_operations);
1817    return 0;
1818}
1819__initcall(procswaps_init);
1820#endif /* CONFIG_PROC_FS */
1821
1822#ifdef MAX_SWAPFILES_CHECK
1823static int __init max_swapfiles_check(void)
1824{
1825    MAX_SWAPFILES_CHECK();
1826    return 0;
1827}
1828late_initcall(max_swapfiles_check);
1829#endif
1830
1831static struct swap_info_struct *alloc_swap_info(void)
1832{
1833    struct swap_info_struct *p;
1834    unsigned int type;
1835
1836    p = kzalloc(sizeof(*p), GFP_KERNEL);
1837    if (!p)
1838        return ERR_PTR(-ENOMEM);
1839
1840    spin_lock(&swap_lock);
1841    for (type = 0; type < nr_swapfiles; type++) {
1842        if (!(swap_info[type]->flags & SWP_USED))
1843            break;
1844    }
1845    if (type >= MAX_SWAPFILES) {
1846        spin_unlock(&swap_lock);
1847        kfree(p);
1848        return ERR_PTR(-EPERM);
1849    }
1850    if (type >= nr_swapfiles) {
1851        p->type = type;
1852        swap_info[type] = p;
1853        /*
1854         * Write swap_info[type] before nr_swapfiles, in case a
1855         * racing procfs swap_start() or swap_next() is reading them.
1856         * (We never shrink nr_swapfiles, we never free this entry.)
1857         */
1858        smp_wmb();
1859        nr_swapfiles++;
1860    } else {
1861        kfree(p);
1862        p = swap_info[type];
1863        /*
1864         * Do not memset this entry: a racing procfs swap_next()
1865         * would be relying on p->type to remain valid.
1866         */
1867    }
1868    INIT_LIST_HEAD(&p->first_swap_extent.list);
1869    p->flags = SWP_USED;
1870    p->next = -1;
1871    spin_unlock(&swap_lock);
1872    spin_lock_init(&p->lock);
1873
1874    return p;
1875}
1876
1877static int claim_swapfile(struct swap_info_struct *p, struct inode *inode)
1878{
1879    int error;
1880
1881    if (S_ISBLK(inode->i_mode)) {
1882        p->bdev = bdgrab(I_BDEV(inode));
1883        error = blkdev_get(p->bdev,
1884                   FMODE_READ | FMODE_WRITE | FMODE_EXCL,
1885                   sys_swapon);
1886        if (error < 0) {
1887            p->bdev = NULL;
1888            return -EINVAL;
1889        }
1890        p->old_block_size = block_size(p->bdev);
1891        error = set_blocksize(p->bdev, PAGE_SIZE);
1892        if (error < 0)
1893            return error;
1894        p->flags |= SWP_BLKDEV;
1895    } else if (S_ISREG(inode->i_mode)) {
1896        p->bdev = inode->i_sb->s_bdev;
1897        mutex_lock(&inode->i_mutex);
1898        if (IS_SWAPFILE(inode))
1899            return -EBUSY;
1900    } else
1901        return -EINVAL;
1902
1903    return 0;
1904}
1905
1906static unsigned long read_swap_header(struct swap_info_struct *p,
1907                    union swap_header *swap_header,
1908                    struct inode *inode)
1909{
1910    int i;
1911    unsigned long maxpages;
1912    unsigned long swapfilepages;
1913
1914    if (memcmp("SWAPSPACE2", swap_header->magic.magic, 10)) {
1915        printk(KERN_ERR "Unable to find swap-space signature\n");
1916        return 0;
1917    }
1918
1919    /* swap partition endianess hack... */
1920    if (swab32(swap_header->info.version) == 1) {
1921        swab32s(&swap_header->info.version);
1922        swab32s(&swap_header->info.last_page);
1923        swab32s(&swap_header->info.nr_badpages);
1924        for (i = 0; i < swap_header->info.nr_badpages; i++)
1925            swab32s(&swap_header->info.badpages[i]);
1926    }
1927    /* Check the swap header's sub-version */
1928    if (swap_header->info.version != 1) {
1929        printk(KERN_WARNING
1930               "Unable to handle swap header version %d\n",
1931               swap_header->info.version);
1932        return 0;
1933    }
1934
1935    p->lowest_bit = 1;
1936    p->cluster_next = 1;
1937    p->cluster_nr = 0;
1938
1939    /*
1940     * Find out how many pages are allowed for a single swap
1941     * device. There are two limiting factors: 1) the number
1942     * of bits for the swap offset in the swp_entry_t type, and
1943     * 2) the number of bits in the swap pte as defined by the
1944     * different architectures. In order to find the
1945     * largest possible bit mask, a swap entry with swap type 0
1946     * and swap offset ~0UL is created, encoded to a swap pte,
1947     * decoded to a swp_entry_t again, and finally the swap
1948     * offset is extracted. This will mask all the bits from
1949     * the initial ~0UL mask that can't be encoded in either
1950     * the swp_entry_t or the architecture definition of a
1951     * swap pte.
1952     */
1953    maxpages = swp_offset(pte_to_swp_entry(
1954            swp_entry_to_pte(swp_entry(0, ~0UL)))) + 1;
1955    if (maxpages > swap_header->info.last_page) {
1956        maxpages = swap_header->info.last_page + 1;
1957        /* p->max is an unsigned int: don't overflow it */
1958        if ((unsigned int)maxpages == 0)
1959            maxpages = UINT_MAX;
1960    }
1961    p->highest_bit = maxpages - 1;
1962
1963    if (!maxpages)
1964        return 0;
1965    swapfilepages = i_size_read(inode) >> PAGE_SHIFT;
1966    if (swapfilepages && maxpages > swapfilepages) {
1967        printk(KERN_WARNING
1968               "Swap area shorter than signature indicates\n");
1969        return 0;
1970    }
1971    if (swap_header->info.nr_badpages && S_ISREG(inode->i_mode))
1972        return 0;
1973    if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
1974        return 0;
1975
1976    return maxpages;
1977}
1978
1979static int setup_swap_map_and_extents(struct swap_info_struct *p,
1980                    union swap_header *swap_header,
1981                    unsigned char *swap_map,
1982                    unsigned long maxpages,
1983                    sector_t *span)
1984{
1985    int i;
1986    unsigned int nr_good_pages;
1987    int nr_extents;
1988
1989    nr_good_pages = maxpages - 1; /* omit header page */
1990
1991    for (i = 0; i < swap_header->info.nr_badpages; i++) {
1992        unsigned int page_nr = swap_header->info.badpages[i];
1993        if (page_nr == 0 || page_nr > swap_header->info.last_page)
1994            return -EINVAL;
1995        if (page_nr < maxpages) {
1996            swap_map[page_nr] = SWAP_MAP_BAD;
1997            nr_good_pages--;
1998        }
1999    }
2000
2001    if (nr_good_pages) {
2002        swap_map[0] = SWAP_MAP_BAD;
2003        p->max = maxpages;
2004        p->pages = nr_good_pages;
2005        nr_extents = setup_swap_extents(p, span);
2006        if (nr_extents < 0)
2007            return nr_extents;
2008        nr_good_pages = p->pages;
2009    }
2010    if (!nr_good_pages) {
2011        printk(KERN_WARNING "Empty swap-file\n");
2012        return -EINVAL;
2013    }
2014
2015    return nr_extents;
2016}
2017
2018SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
2019{
2020    struct swap_info_struct *p;
2021    struct filename *name;
2022    struct file *swap_file = NULL;
2023    struct address_space *mapping;
2024    int i;
2025    int prio;
2026    int error;
2027    union swap_header *swap_header;
2028    int nr_extents;
2029    sector_t span;
2030    unsigned long maxpages;
2031    unsigned char *swap_map = NULL;
2032    unsigned long *frontswap_map = NULL;
2033    struct page *page = NULL;
2034    struct inode *inode = NULL;
2035
2036    if (swap_flags & ~SWAP_FLAGS_VALID)
2037        return -EINVAL;
2038
2039    if (!capable(CAP_SYS_ADMIN))
2040        return -EPERM;
2041
2042    p = alloc_swap_info();
2043    if (IS_ERR(p))
2044        return PTR_ERR(p);
2045
2046    name = getname(specialfile);
2047    if (IS_ERR(name)) {
2048        error = PTR_ERR(name);
2049        name = NULL;
2050        goto bad_swap;
2051    }
2052    swap_file = file_open_name(name, O_RDWR|O_LARGEFILE, 0);
2053    if (IS_ERR(swap_file)) {
2054        error = PTR_ERR(swap_file);
2055        swap_file = NULL;
2056        goto bad_swap;
2057    }
2058
2059    p->swap_file = swap_file;
2060    mapping = swap_file->f_mapping;
2061
2062    for (i = 0; i < nr_swapfiles; i++) {
2063        struct swap_info_struct *q = swap_info[i];
2064
2065        if (q == p || !q->swap_file)
2066            continue;
2067        if (mapping == q->swap_file->f_mapping) {
2068            error = -EBUSY;
2069            goto bad_swap;
2070        }
2071    }
2072
2073    inode = mapping->host;
2074    /* If S_ISREG(inode->i_mode) will do mutex_lock(&inode->i_mutex); */
2075    error = claim_swapfile(p, inode);
2076    if (unlikely(error))
2077        goto bad_swap;
2078
2079    /*
2080     * Read the swap header.
2081     */
2082    if (!mapping->a_ops->readpage) {
2083        error = -EINVAL;
2084        goto bad_swap;
2085    }
2086    page = read_mapping_page(mapping, 0, swap_file);
2087    if (IS_ERR(page)) {
2088        error = PTR_ERR(page);
2089        goto bad_swap;
2090    }
2091    swap_header = kmap(page);
2092
2093    maxpages = read_swap_header(p, swap_header, inode);
2094    if (unlikely(!maxpages)) {
2095        error = -EINVAL;
2096        goto bad_swap;
2097    }
2098
2099    /* OK, set up the swap map and apply the bad block list */
2100    swap_map = vzalloc(maxpages);
2101    if (!swap_map) {
2102        error = -ENOMEM;
2103        goto bad_swap;
2104    }
2105
2106    error = swap_cgroup_swapon(p->type, maxpages);
2107    if (error)
2108        goto bad_swap;
2109
2110    nr_extents = setup_swap_map_and_extents(p, swap_header, swap_map,
2111        maxpages, &span);
2112    if (unlikely(nr_extents < 0)) {
2113        error = nr_extents;
2114        goto bad_swap;
2115    }
2116    /* frontswap enabled? set up bit-per-page map for frontswap */
2117    if (frontswap_enabled)
2118        frontswap_map = vzalloc(maxpages / sizeof(long));
2119
2120    if (p->bdev) {
2121        if (blk_queue_nonrot(bdev_get_queue(p->bdev))) {
2122            p->flags |= SWP_SOLIDSTATE;
2123            p->cluster_next = 1 + (random32() % p->highest_bit);
2124        }
2125        if ((swap_flags & SWAP_FLAG_DISCARD) && discard_swap(p) == 0)
2126            p->flags |= SWP_DISCARDABLE;
2127    }
2128
2129    mutex_lock(&swapon_mutex);
2130    prio = -1;
2131    if (swap_flags & SWAP_FLAG_PREFER)
2132        prio =
2133          (swap_flags & SWAP_FLAG_PRIO_MASK) >> SWAP_FLAG_PRIO_SHIFT;
2134    enable_swap_info(p, prio, swap_map, frontswap_map);
2135
2136    printk(KERN_INFO "Adding %uk swap on %s. "
2137            "Priority:%d extents:%d across:%lluk %s%s%s\n",
2138        p->pages<<(PAGE_SHIFT-10), name->name, p->prio,
2139        nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10),
2140        (p->flags & SWP_SOLIDSTATE) ? "SS" : "",
2141        (p->flags & SWP_DISCARDABLE) ? "D" : "",
2142        (frontswap_map) ? "FS" : "");
2143
2144    mutex_unlock(&swapon_mutex);
2145    atomic_inc(&proc_poll_event);
2146    wake_up_interruptible(&proc_poll_wait);
2147
2148    if (S_ISREG(inode->i_mode))
2149        inode->i_flags |= S_SWAPFILE;
2150    error = 0;
2151    goto out;
2152bad_swap:
2153    if (inode && S_ISBLK(inode->i_mode) && p->bdev) {
2154        set_blocksize(p->bdev, p->old_block_size);
2155        blkdev_put(p->bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
2156    }
2157    destroy_swap_extents(p);
2158    swap_cgroup_swapoff(p->type);
2159    spin_lock(&swap_lock);
2160    p->swap_file = NULL;
2161    p->flags = 0;
2162    spin_unlock(&swap_lock);
2163    vfree(swap_map);
2164    if (swap_file) {
2165        if (inode && S_ISREG(inode->i_mode)) {
2166            mutex_unlock(&inode->i_mutex);
2167            inode = NULL;
2168        }
2169        filp_close(swap_file, NULL);
2170    }
2171out:
2172    if (page && !IS_ERR(page)) {
2173        kunmap(page);
2174        page_cache_release(page);
2175    }
2176    if (name)
2177        putname(name);
2178    if (inode && S_ISREG(inode->i_mode))
2179        mutex_unlock(&inode->i_mutex);
2180    return error;
2181}
2182
2183void si_swapinfo(struct sysinfo *val)
2184{
2185    unsigned int type;
2186    unsigned long nr_to_be_unused = 0;
2187
2188    spin_lock(&swap_lock);
2189    for (type = 0; type < nr_swapfiles; type++) {
2190        struct swap_info_struct *si = swap_info[type];
2191
2192        if ((si->flags & SWP_USED) && !(si->flags & SWP_WRITEOK))
2193            nr_to_be_unused += si->inuse_pages;
2194    }
2195    val->freeswap = atomic_long_read(&nr_swap_pages) + nr_to_be_unused;
2196    val->totalswap = total_swap_pages + nr_to_be_unused;
2197    spin_unlock(&swap_lock);
2198}
2199
2200/*
2201 * Verify that a swap entry is valid and increment its swap map count.
2202 *
2203 * Returns error code in following case.
2204 * - success -> 0
2205 * - swp_entry is invalid -> EINVAL
2206 * - swp_entry is migration entry -> EINVAL
2207 * - swap-cache reference is requested but there is already one. -> EEXIST
2208 * - swap-cache reference is requested but the entry is not used. -> ENOENT
2209 * - swap-mapped reference requested but needs continued swap count. -> ENOMEM
2210 */
2211static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
2212{
2213    struct swap_info_struct *p;
2214    unsigned long offset, type;
2215    unsigned char count;
2216    unsigned char has_cache;
2217    int err = -EINVAL;
2218
2219    if (non_swap_entry(entry))
2220        goto out;
2221
2222    type = swp_type(entry);
2223    if (type >= nr_swapfiles)
2224        goto bad_file;
2225    p = swap_info[type];
2226    offset = swp_offset(entry);
2227
2228    spin_lock(&p->lock);
2229    if (unlikely(offset >= p->max))
2230        goto unlock_out;
2231
2232    count = p->swap_map[offset];
2233    has_cache = count & SWAP_HAS_CACHE;
2234    count &= ~SWAP_HAS_CACHE;
2235    err = 0;
2236
2237    if (usage == SWAP_HAS_CACHE) {
2238
2239        /* set SWAP_HAS_CACHE if there is no cache and entry is used */
2240        if (!has_cache && count)
2241            has_cache = SWAP_HAS_CACHE;
2242        else if (has_cache) /* someone else added cache */
2243            err = -EEXIST;
2244        else /* no users remaining */
2245            err = -ENOENT;
2246
2247    } else if (count || has_cache) {
2248
2249        if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
2250            count += usage;
2251        else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX)
2252            err = -EINVAL;
2253        else if (swap_count_continued(p, offset, count))
2254            count = COUNT_CONTINUED;
2255        else
2256            err = -ENOMEM;
2257    } else
2258        err = -ENOENT; /* unused swap entry */
2259
2260    p->swap_map[offset] = count | has_cache;
2261
2262unlock_out:
2263    spin_unlock(&p->lock);
2264out:
2265    return err;
2266
2267bad_file:
2268    printk(KERN_ERR "swap_dup: %s%08lx\n", Bad_file, entry.val);
2269    goto out;
2270}
2271
2272/*
2273 * Help swapoff by noting that swap entry belongs to shmem/tmpfs
2274 * (in which case its reference count is never incremented).
2275 */
2276void swap_shmem_alloc(swp_entry_t entry)
2277{
2278    __swap_duplicate(entry, SWAP_MAP_SHMEM);
2279}
2280
2281/*
2282 * Increase reference count of swap entry by 1.
2283 * Returns 0 for success, or -ENOMEM if a swap_count_continuation is required
2284 * but could not be atomically allocated. Returns 0, just as if it succeeded,
2285 * if __swap_duplicate() fails for another reason (-EINVAL or -ENOENT), which
2286 * might occur if a page table entry has got corrupted.
2287 */
2288int swap_duplicate(swp_entry_t entry)
2289{
2290    int err = 0;
2291
2292    while (!err && __swap_duplicate(entry, 1) == -ENOMEM)
2293        err = add_swap_count_continuation(entry, GFP_ATOMIC);
2294    return err;
2295}
2296
2297/*
2298 * @entry: swap entry for which we allocate swap cache.
2299 *
2300 * Called when allocating swap cache for existing swap entry,
2301 * This can return error codes. Returns 0 at success.
2302 * -EBUSY means there is a swap cache.
2303 * Note: return code is different from swap_duplicate().
2304 */
2305int swapcache_prepare(swp_entry_t entry)
2306{
2307    return __swap_duplicate(entry, SWAP_HAS_CACHE);
2308}
2309
2310struct swap_info_struct *page_swap_info(struct page *page)
2311{
2312    swp_entry_t swap = { .val = page_private(page) };
2313    BUG_ON(!PageSwapCache(page));
2314    return swap_info[swp_type(swap)];
2315}
2316
2317/*
2318 * out-of-line __page_file_ methods to avoid include hell.
2319 */
2320struct address_space *__page_file_mapping(struct page *page)
2321{
2322    VM_BUG_ON(!PageSwapCache(page));
2323    return page_swap_info(page)->swap_file->f_mapping;
2324}
2325EXPORT_SYMBOL_GPL(__page_file_mapping);
2326
2327pgoff_t __page_file_index(struct page *page)
2328{
2329    swp_entry_t swap = { .val = page_private(page) };
2330    VM_BUG_ON(!PageSwapCache(page));
2331    return swp_offset(swap);
2332}
2333EXPORT_SYMBOL_GPL(__page_file_index);
2334
2335/*
2336 * add_swap_count_continuation - called when a swap count is duplicated
2337 * beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's
2338 * page of the original vmalloc'ed swap_map, to hold the continuation count
2339 * (for that entry and for its neighbouring PAGE_SIZE swap entries). Called
2340 * again when count is duplicated beyond SWAP_MAP_MAX * SWAP_CONT_MAX, etc.
2341 *
2342 * These continuation pages are seldom referenced: the common paths all work
2343 * on the original swap_map, only referring to a continuation page when the
2344 * low "digit" of a count is incremented or decremented through SWAP_MAP_MAX.
2345 *
2346 * add_swap_count_continuation(, GFP_ATOMIC) can be called while holding
2347 * page table locks; if it fails, add_swap_count_continuation(, GFP_KERNEL)
2348 * can be called after dropping locks.
2349 */
2350int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask)
2351{
2352    struct swap_info_struct *si;
2353    struct page *head;
2354    struct page *page;
2355    struct page *list_page;
2356    pgoff_t offset;
2357    unsigned char count;
2358
2359    /*
2360     * When debugging, it's easier to use __GFP_ZERO here; but it's better
2361     * for latency not to zero a page while GFP_ATOMIC and holding locks.
2362     */
2363    page = alloc_page(gfp_mask | __GFP_HIGHMEM);
2364
2365    si = swap_info_get(entry);
2366    if (!si) {
2367        /*
2368         * An acceptable race has occurred since the failing
2369         * __swap_duplicate(): the swap entry has been freed,
2370         * perhaps even the whole swap_map cleared for swapoff.
2371         */
2372        goto outer;
2373    }
2374
2375    offset = swp_offset(entry);
2376    count = si->swap_map[offset] & ~SWAP_HAS_CACHE;
2377
2378    if ((count & ~COUNT_CONTINUED) != SWAP_MAP_MAX) {
2379        /*
2380         * The higher the swap count, the more likely it is that tasks
2381         * will race to add swap count continuation: we need to avoid
2382         * over-provisioning.
2383         */
2384        goto out;
2385    }
2386
2387    if (!page) {
2388        spin_unlock(&si->lock);
2389        return -ENOMEM;
2390    }
2391
2392    /*
2393     * We are fortunate that although vmalloc_to_page uses pte_offset_map,
2394     * no architecture is using highmem pages for kernel pagetables: so it
2395     * will not corrupt the GFP_ATOMIC caller's atomic pagetable kmaps.
2396     */
2397    head = vmalloc_to_page(si->swap_map + offset);
2398    offset &= ~PAGE_MASK;
2399
2400    /*
2401     * Page allocation does not initialize the page's lru field,
2402     * but it does always reset its private field.
2403     */
2404    if (!page_private(head)) {
2405        BUG_ON(count & COUNT_CONTINUED);
2406        INIT_LIST_HEAD(&head->lru);
2407        set_page_private(head, SWP_CONTINUED);
2408        si->flags |= SWP_CONTINUED;
2409    }
2410
2411    list_for_each_entry(list_page, &head->lru, lru) {
2412        unsigned char *map;
2413
2414        /*
2415         * If the previous map said no continuation, but we've found
2416         * a continuation page, free our allocation and use this one.
2417         */
2418        if (!(count & COUNT_CONTINUED))
2419            goto out;
2420
2421        map = kmap_atomic(list_page) + offset;
2422        count = *map;
2423        kunmap_atomic(map);
2424
2425        /*
2426         * If this continuation count now has some space in it,
2427         * free our allocation and use this one.
2428         */
2429        if ((count & ~COUNT_CONTINUED) != SWAP_CONT_MAX)
2430            goto out;
2431    }
2432
2433    list_add_tail(&page->lru, &head->lru);
2434    page = NULL; /* now it's attached, don't free it */
2435out:
2436    spin_unlock(&si->lock);
2437outer:
2438    if (page)
2439        __free_page(page);
2440    return 0;
2441}
2442
2443/*
2444 * swap_count_continued - when the original swap_map count is incremented
2445 * from SWAP_MAP_MAX, check if there is already a continuation page to carry
2446 * into, carry if so, or else fail until a new continuation page is allocated;
2447 * when the original swap_map count is decremented from 0 with continuation,
2448 * borrow from the continuation and report whether it still holds more.
2449 * Called while __swap_duplicate() or swap_entry_free() holds swap_lock.
2450 */
2451static bool swap_count_continued(struct swap_info_struct *si,
2452                 pgoff_t offset, unsigned char count)
2453{
2454    struct page *head;
2455    struct page *page;
2456    unsigned char *map;
2457
2458    head = vmalloc_to_page(si->swap_map + offset);
2459    if (page_private(head) != SWP_CONTINUED) {
2460        BUG_ON(count & COUNT_CONTINUED);
2461        return false; /* need to add count continuation */
2462    }
2463
2464    offset &= ~PAGE_MASK;
2465    page = list_entry(head->lru.next, struct page, lru);
2466    map = kmap_atomic(page) + offset;
2467
2468    if (count == SWAP_MAP_MAX) /* initial increment from swap_map */
2469        goto init_map; /* jump over SWAP_CONT_MAX checks */
2470
2471    if (count == (SWAP_MAP_MAX | COUNT_CONTINUED)) { /* incrementing */
2472        /*
2473         * Think of how you add 1 to 999
2474         */
2475        while (*map == (SWAP_CONT_MAX | COUNT_CONTINUED)) {
2476            kunmap_atomic(map);
2477            page = list_entry(page->lru.next, struct page, lru);
2478            BUG_ON(page == head);
2479            map = kmap_atomic(page) + offset;
2480        }
2481        if (*map == SWAP_CONT_MAX) {
2482            kunmap_atomic(map);
2483            page = list_entry(page->lru.next, struct page, lru);
2484            if (page == head)
2485                return false; /* add count continuation */
2486            map = kmap_atomic(page) + offset;
2487init_map: *map = 0; /* we didn't zero the page */
2488        }
2489        *map += 1;
2490        kunmap_atomic(map);
2491        page = list_entry(page->lru.prev, struct page, lru);
2492        while (page != head) {
2493            map = kmap_atomic(page) + offset;
2494            *map = COUNT_CONTINUED;
2495            kunmap_atomic(map);
2496            page = list_entry(page->lru.prev, struct page, lru);
2497        }
2498        return true; /* incremented */
2499
2500    } else { /* decrementing */
2501        /*
2502         * Think of how you subtract 1 from 1000
2503         */
2504        BUG_ON(count != COUNT_CONTINUED);
2505        while (*map == COUNT_CONTINUED) {
2506            kunmap_atomic(map);
2507            page = list_entry(page->lru.next, struct page, lru);
2508            BUG_ON(page == head);
2509            map = kmap_atomic(page) + offset;
2510        }
2511        BUG_ON(*map == 0);
2512        *map -= 1;
2513        if (*map == 0)
2514            count = 0;
2515        kunmap_atomic(map);
2516        page = list_entry(page->lru.prev, struct page, lru);
2517        while (page != head) {
2518            map = kmap_atomic(page) + offset;
2519            *map = SWAP_CONT_MAX | count;
2520            count = COUNT_CONTINUED;
2521            kunmap_atomic(map);
2522            page = list_entry(page->lru.prev, struct page, lru);
2523        }
2524        return count == COUNT_CONTINUED;
2525    }
2526}
2527
2528/*
2529 * free_swap_count_continuations - swapoff free all the continuation pages
2530 * appended to the swap_map, after swap_map is quiesced, before vfree'ing it.
2531 */
2532static void free_swap_count_continuations(struct swap_info_struct *si)
2533{
2534    pgoff_t offset;
2535
2536    for (offset = 0; offset < si->max; offset += PAGE_SIZE) {
2537        struct page *head;
2538        head = vmalloc_to_page(si->swap_map + offset);
2539        if (page_private(head)) {
2540            struct list_head *this, *next;
2541            list_for_each_safe(this, next, &head->lru) {
2542                struct page *page;
2543                page = list_entry(this, struct page, lru);
2544                list_del(this);
2545                __free_page(page);
2546            }
2547        }
2548    }
2549}
2550

Archive Download this file



interactive