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/module.h>
25#include <linux/ksm.h>
26#include <linux/rmap.h>
27#include <linux/security.h>
28#include <linux/backing-dev.h>
29#include <linux/mutex.h>
30#include <linux/capability.h>
31#include <linux/syscalls.h>
32#include <linux/memcontrol.h>
33#include <linux/poll.h>
34#include <linux/oom.h>
35
36#include <asm/pgtable.h>
37#include <asm/tlbflush.h>
38#include <linux/swapops.h>
39#include <linux/page_cgroup.h>
40
41static bool swap_count_continued(struct swap_info_struct *, pgoff_t,
42                 unsigned char);
43static void free_swap_count_continuations(struct swap_info_struct *);
44static sector_t map_swap_entry(swp_entry_t, struct block_device**);
45
46static DEFINE_SPINLOCK(swap_lock);
47static unsigned int nr_swapfiles;
48long nr_swap_pages;
49long total_swap_pages;
50static int least_priority;
51
52static const char Bad_file[] = "Bad swap file entry ";
53static const char Unused_file[] = "Unused swap file entry ";
54static const char Bad_offset[] = "Bad swap offset entry ";
55static const char Unused_offset[] = "Unused swap offset entry ";
56
57static struct swap_list_t swap_list = {-1, -1};
58
59static struct swap_info_struct *swap_info[MAX_SWAPFILES];
60
61static DEFINE_MUTEX(swapon_mutex);
62
63static DECLARE_WAIT_QUEUE_HEAD(proc_poll_wait);
64/* Activity counter to indicate that a swapon or swapoff has occurred */
65static atomic_t proc_poll_event = ATOMIC_INIT(0);
66
67static inline unsigned char swap_count(unsigned char ent)
68{
69    return ent & ~SWAP_HAS_CACHE; /* may include SWAP_HAS_CONT flag */
70}
71
72/* returns 1 if swap entry is freed */
73static int
74__try_to_reclaim_swap(struct swap_info_struct *si, unsigned long offset)
75{
76    swp_entry_t entry = swp_entry(si->type, offset);
77    struct page *page;
78    int ret = 0;
79
80    page = find_get_page(&swapper_space, entry.val);
81    if (!page)
82        return 0;
83    /*
84     * This function is called from scan_swap_map() and it's called
85     * by vmscan.c at reclaiming pages. So, we hold a lock on a page, here.
86     * We have to use trylock for avoiding deadlock. This is a special
87     * case and you should use try_to_free_swap() with explicit lock_page()
88     * in usual operations.
89     */
90    if (trylock_page(page)) {
91        ret = try_to_free_swap(page);
92        unlock_page(page);
93    }
94    page_cache_release(page);
95    return ret;
96}
97
98/*
99 * swapon tell device that all the old swap contents can be discarded,
100 * to allow the swap device to optimize its wear-levelling.
101 */
102static int discard_swap(struct swap_info_struct *si)
103{
104    struct swap_extent *se;
105    sector_t start_block;
106    sector_t nr_blocks;
107    int err = 0;
108
109    /* Do not discard the swap header page! */
110    se = &si->first_swap_extent;
111    start_block = (se->start_block + 1) << (PAGE_SHIFT - 9);
112    nr_blocks = ((sector_t)se->nr_pages - 1) << (PAGE_SHIFT - 9);
113    if (nr_blocks) {
114        err = blkdev_issue_discard(si->bdev, start_block,
115                nr_blocks, GFP_KERNEL, 0);
116        if (err)
117            return err;
118        cond_resched();
119    }
120
121    list_for_each_entry(se, &si->first_swap_extent.list, list) {
122        start_block = se->start_block << (PAGE_SHIFT - 9);
123        nr_blocks = (sector_t)se->nr_pages << (PAGE_SHIFT - 9);
124
125        err = blkdev_issue_discard(si->bdev, start_block,
126                nr_blocks, GFP_KERNEL, 0);
127        if (err)
128            break;
129
130        cond_resched();
131    }
132    return err; /* That will often be -EOPNOTSUPP */
133}
134
135/*
136 * swap allocation tell device that a cluster of swap can now be discarded,
137 * to allow the swap device to optimize its wear-levelling.
138 */
139static void discard_swap_cluster(struct swap_info_struct *si,
140                 pgoff_t start_page, pgoff_t nr_pages)
141{
142    struct swap_extent *se = si->curr_swap_extent;
143    int found_extent = 0;
144
145    while (nr_pages) {
146        struct list_head *lh;
147
148        if (se->start_page <= start_page &&
149            start_page < se->start_page + se->nr_pages) {
150            pgoff_t offset = start_page - se->start_page;
151            sector_t start_block = se->start_block + offset;
152            sector_t nr_blocks = se->nr_pages - offset;
153
154            if (nr_blocks > nr_pages)
155                nr_blocks = nr_pages;
156            start_page += nr_blocks;
157            nr_pages -= nr_blocks;
158
159            if (!found_extent++)
160                si->curr_swap_extent = se;
161
162            start_block <<= PAGE_SHIFT - 9;
163            nr_blocks <<= PAGE_SHIFT - 9;
164            if (blkdev_issue_discard(si->bdev, start_block,
165                    nr_blocks, GFP_NOIO, 0))
166                break;
167        }
168
169        lh = se->list.next;
170        se = list_entry(lh, struct swap_extent, list);
171    }
172}
173
174static int wait_for_discard(void *word)
175{
176    schedule();
177    return 0;
178}
179
180#define SWAPFILE_CLUSTER 256
181#define LATENCY_LIMIT 256
182
183static unsigned long scan_swap_map(struct swap_info_struct *si,
184                   unsigned char usage)
185{
186    unsigned long offset;
187    unsigned long scan_base;
188    unsigned long last_in_cluster = 0;
189    int latency_ration = LATENCY_LIMIT;
190    int found_free_cluster = 0;
191
192    /*
193     * We try to cluster swap pages by allocating them sequentially
194     * in swap. Once we've allocated SWAPFILE_CLUSTER pages this
195     * way, however, we resort to first-free allocation, starting
196     * a new cluster. This prevents us from scattering swap pages
197     * all over the entire swap partition, so that we reduce
198     * overall disk seek times between swap pages. -- sct
199     * But we do now try to find an empty cluster. -Andrea
200     * And we let swap pages go all over an SSD partition. Hugh
201     */
202
203    si->flags += SWP_SCANNING;
204    scan_base = offset = si->cluster_next;
205
206    if (unlikely(!si->cluster_nr--)) {
207        if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER) {
208            si->cluster_nr = SWAPFILE_CLUSTER - 1;
209            goto checks;
210        }
211        if (si->flags & SWP_DISCARDABLE) {
212            /*
213             * Start range check on racing allocations, in case
214             * they overlap the cluster we eventually decide on
215             * (we scan without swap_lock to allow preemption).
216             * It's hardly conceivable that cluster_nr could be
217             * wrapped during our scan, but don't depend on it.
218             */
219            if (si->lowest_alloc)
220                goto checks;
221            si->lowest_alloc = si->max;
222            si->highest_alloc = 0;
223        }
224        spin_unlock(&swap_lock);
225
226        /*
227         * If seek is expensive, start searching for new cluster from
228         * start of partition, to minimize the span of allocated swap.
229         * But if seek is cheap, search from our current position, so
230         * that swap is allocated from all over the partition: if the
231         * Flash Translation Layer only remaps within limited zones,
232         * we don't want to wear out the first zone too quickly.
233         */
234        if (!(si->flags & SWP_SOLIDSTATE))
235            scan_base = offset = si->lowest_bit;
236        last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
237
238        /* Locate the first empty (unaligned) cluster */
239        for (; last_in_cluster <= si->highest_bit; offset++) {
240            if (si->swap_map[offset])
241                last_in_cluster = offset + SWAPFILE_CLUSTER;
242            else if (offset == last_in_cluster) {
243                spin_lock(&swap_lock);
244                offset -= SWAPFILE_CLUSTER - 1;
245                si->cluster_next = offset;
246                si->cluster_nr = SWAPFILE_CLUSTER - 1;
247                found_free_cluster = 1;
248                goto checks;
249            }
250            if (unlikely(--latency_ration < 0)) {
251                cond_resched();
252                latency_ration = LATENCY_LIMIT;
253            }
254        }
255
256        offset = si->lowest_bit;
257        last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
258
259        /* Locate the first empty (unaligned) cluster */
260        for (; last_in_cluster < scan_base; offset++) {
261            if (si->swap_map[offset])
262                last_in_cluster = offset + SWAPFILE_CLUSTER;
263            else if (offset == last_in_cluster) {
264                spin_lock(&swap_lock);
265                offset -= SWAPFILE_CLUSTER - 1;
266                si->cluster_next = offset;
267                si->cluster_nr = SWAPFILE_CLUSTER - 1;
268                found_free_cluster = 1;
269                goto checks;
270            }
271            if (unlikely(--latency_ration < 0)) {
272                cond_resched();
273                latency_ration = LATENCY_LIMIT;
274            }
275        }
276
277        offset = scan_base;
278        spin_lock(&swap_lock);
279        si->cluster_nr = SWAPFILE_CLUSTER - 1;
280        si->lowest_alloc = 0;
281    }
282
283checks:
284    if (!(si->flags & SWP_WRITEOK))
285        goto no_page;
286    if (!si->highest_bit)
287        goto no_page;
288    if (offset > si->highest_bit)
289        scan_base = offset = si->lowest_bit;
290
291    /* reuse swap entry of cache-only swap if not busy. */
292    if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
293        int swap_was_freed;
294        spin_unlock(&swap_lock);
295        swap_was_freed = __try_to_reclaim_swap(si, offset);
296        spin_lock(&swap_lock);
297        /* entry was freed successfully, try to use this again */
298        if (swap_was_freed)
299            goto checks;
300        goto scan; /* check next one */
301    }
302
303    if (si->swap_map[offset])
304        goto scan;
305
306    if (offset == si->lowest_bit)
307        si->lowest_bit++;
308    if (offset == si->highest_bit)
309        si->highest_bit--;
310    si->inuse_pages++;
311    if (si->inuse_pages == si->pages) {
312        si->lowest_bit = si->max;
313        si->highest_bit = 0;
314    }
315    si->swap_map[offset] = usage;
316    si->cluster_next = offset + 1;
317    si->flags -= SWP_SCANNING;
318
319    if (si->lowest_alloc) {
320        /*
321         * Only set when SWP_DISCARDABLE, and there's a scan
322         * for a free cluster in progress or just completed.
323         */
324        if (found_free_cluster) {
325            /*
326             * To optimize wear-levelling, discard the
327             * old data of the cluster, taking care not to
328             * discard any of its pages that have already
329             * been allocated by racing tasks (offset has
330             * already stepped over any at the beginning).
331             */
332            if (offset < si->highest_alloc &&
333                si->lowest_alloc <= last_in_cluster)
334                last_in_cluster = si->lowest_alloc - 1;
335            si->flags |= SWP_DISCARDING;
336            spin_unlock(&swap_lock);
337
338            if (offset < last_in_cluster)
339                discard_swap_cluster(si, offset,
340                    last_in_cluster - offset + 1);
341
342            spin_lock(&swap_lock);
343            si->lowest_alloc = 0;
344            si->flags &= ~SWP_DISCARDING;
345
346            smp_mb(); /* wake_up_bit advises this */
347            wake_up_bit(&si->flags, ilog2(SWP_DISCARDING));
348
349        } else if (si->flags & SWP_DISCARDING) {
350            /*
351             * Delay using pages allocated by racing tasks
352             * until the whole discard has been issued. We
353             * could defer that delay until swap_writepage,
354             * but it's easier to keep this self-contained.
355             */
356            spin_unlock(&swap_lock);
357            wait_on_bit(&si->flags, ilog2(SWP_DISCARDING),
358                wait_for_discard, TASK_UNINTERRUPTIBLE);
359            spin_lock(&swap_lock);
360        } else {
361            /*
362             * Note pages allocated by racing tasks while
363             * scan for a free cluster is in progress, so
364             * that its final discard can exclude them.
365             */
366            if (offset < si->lowest_alloc)
367                si->lowest_alloc = offset;
368            if (offset > si->highest_alloc)
369                si->highest_alloc = offset;
370        }
371    }
372    return offset;
373
374scan:
375    spin_unlock(&swap_lock);
376    while (++offset <= si->highest_bit) {
377        if (!si->swap_map[offset]) {
378            spin_lock(&swap_lock);
379            goto checks;
380        }
381        if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
382            spin_lock(&swap_lock);
383            goto checks;
384        }
385        if (unlikely(--latency_ration < 0)) {
386            cond_resched();
387            latency_ration = LATENCY_LIMIT;
388        }
389    }
390    offset = si->lowest_bit;
391    while (++offset < scan_base) {
392        if (!si->swap_map[offset]) {
393            spin_lock(&swap_lock);
394            goto checks;
395        }
396        if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
397            spin_lock(&swap_lock);
398            goto checks;
399        }
400        if (unlikely(--latency_ration < 0)) {
401            cond_resched();
402            latency_ration = LATENCY_LIMIT;
403        }
404    }
405    spin_lock(&swap_lock);
406
407no_page:
408    si->flags -= SWP_SCANNING;
409    return 0;
410}
411
412swp_entry_t get_swap_page(void)
413{
414    struct swap_info_struct *si;
415    pgoff_t offset;
416    int type, next;
417    int wrapped = 0;
418
419    spin_lock(&swap_lock);
420    if (nr_swap_pages <= 0)
421        goto noswap;
422    nr_swap_pages--;
423
424    for (type = swap_list.next; type >= 0 && wrapped < 2; type = next) {
425        si = swap_info[type];
426        next = si->next;
427        if (next < 0 ||
428            (!wrapped && si->prio != swap_info[next]->prio)) {
429            next = swap_list.head;
430            wrapped++;
431        }
432
433        if (!si->highest_bit)
434            continue;
435        if (!(si->flags & SWP_WRITEOK))
436            continue;
437
438        swap_list.next = next;
439        /* This is called for allocating swap entry for cache */
440        offset = scan_swap_map(si, SWAP_HAS_CACHE);
441        if (offset) {
442            spin_unlock(&swap_lock);
443            return swp_entry(type, offset);
444        }
445        next = swap_list.next;
446    }
447
448    nr_swap_pages++;
449noswap:
450    spin_unlock(&swap_lock);
451    return (swp_entry_t) {0};
452}
453
454/* The only caller of this function is now susupend routine */
455swp_entry_t get_swap_page_of_type(int type)
456{
457    struct swap_info_struct *si;
458    pgoff_t offset;
459
460    spin_lock(&swap_lock);
461    si = swap_info[type];
462    if (si && (si->flags & SWP_WRITEOK)) {
463        nr_swap_pages--;
464        /* This is called for allocating swap entry, not cache */
465        offset = scan_swap_map(si, 1);
466        if (offset) {
467            spin_unlock(&swap_lock);
468            return swp_entry(type, offset);
469        }
470        nr_swap_pages++;
471    }
472    spin_unlock(&swap_lock);
473    return (swp_entry_t) {0};
474}
475
476static struct swap_info_struct *swap_info_get(swp_entry_t entry)
477{
478    struct swap_info_struct *p;
479    unsigned long offset, type;
480
481    if (!entry.val)
482        goto out;
483    type = swp_type(entry);
484    if (type >= nr_swapfiles)
485        goto bad_nofile;
486    p = swap_info[type];
487    if (!(p->flags & SWP_USED))
488        goto bad_device;
489    offset = swp_offset(entry);
490    if (offset >= p->max)
491        goto bad_offset;
492    if (!p->swap_map[offset])
493        goto bad_free;
494    spin_lock(&swap_lock);
495    return p;
496
497bad_free:
498    printk(KERN_ERR "swap_free: %s%08lx\n", Unused_offset, entry.val);
499    goto out;
500bad_offset:
501    printk(KERN_ERR "swap_free: %s%08lx\n", Bad_offset, entry.val);
502    goto out;
503bad_device:
504    printk(KERN_ERR "swap_free: %s%08lx\n", Unused_file, entry.val);
505    goto out;
506bad_nofile:
507    printk(KERN_ERR "swap_free: %s%08lx\n", Bad_file, entry.val);
508out:
509    return NULL;
510}
511
512static unsigned char swap_entry_free(struct swap_info_struct *p,
513                     swp_entry_t entry, unsigned char usage)
514{
515    unsigned long offset = swp_offset(entry);
516    unsigned char count;
517    unsigned char has_cache;
518
519    count = p->swap_map[offset];
520    has_cache = count & SWAP_HAS_CACHE;
521    count &= ~SWAP_HAS_CACHE;
522
523    if (usage == SWAP_HAS_CACHE) {
524        VM_BUG_ON(!has_cache);
525        has_cache = 0;
526    } else if (count == SWAP_MAP_SHMEM) {
527        /*
528         * Or we could insist on shmem.c using a special
529         * swap_shmem_free() and free_shmem_swap_and_cache()...
530         */
531        count = 0;
532    } else if ((count & ~COUNT_CONTINUED) <= SWAP_MAP_MAX) {
533        if (count == COUNT_CONTINUED) {
534            if (swap_count_continued(p, offset, count))
535                count = SWAP_MAP_MAX | COUNT_CONTINUED;
536            else
537                count = SWAP_MAP_MAX;
538        } else
539            count--;
540    }
541
542    if (!count)
543        mem_cgroup_uncharge_swap(entry);
544
545    usage = count | has_cache;
546    p->swap_map[offset] = usage;
547
548    /* free if no reference */
549    if (!usage) {
550        struct gendisk *disk = p->bdev->bd_disk;
551        if (offset < p->lowest_bit)
552            p->lowest_bit = offset;
553        if (offset > p->highest_bit)
554            p->highest_bit = offset;
555        if (swap_list.next >= 0 &&
556            p->prio > swap_info[swap_list.next]->prio)
557            swap_list.next = p->type;
558        nr_swap_pages++;
559        p->inuse_pages--;
560        if ((p->flags & SWP_BLKDEV) &&
561                disk->fops->swap_slot_free_notify)
562            disk->fops->swap_slot_free_notify(p->bdev, offset);
563    }
564
565    return usage;
566}
567
568/*
569 * Caller has made sure that the swapdevice corresponding to entry
570 * is still around or has not been recycled.
571 */
572void swap_free(swp_entry_t entry)
573{
574    struct swap_info_struct *p;
575
576    p = swap_info_get(entry);
577    if (p) {
578        swap_entry_free(p, entry, 1);
579        spin_unlock(&swap_lock);
580    }
581}
582
583/*
584 * Called after dropping swapcache to decrease refcnt to swap entries.
585 */
586void swapcache_free(swp_entry_t entry, struct page *page)
587{
588    struct swap_info_struct *p;
589    unsigned char count;
590
591    p = swap_info_get(entry);
592    if (p) {
593        count = swap_entry_free(p, entry, SWAP_HAS_CACHE);
594        if (page)
595            mem_cgroup_uncharge_swapcache(page, entry, count != 0);
596        spin_unlock(&swap_lock);
597    }
598}
599
600/*
601 * How many references to page are currently swapped out?
602 * This does not give an exact answer when swap count is continued,
603 * but does include the high COUNT_CONTINUED flag to allow for that.
604 */
605static inline int page_swapcount(struct page *page)
606{
607    int count = 0;
608    struct swap_info_struct *p;
609    swp_entry_t entry;
610
611    entry.val = page_private(page);
612    p = swap_info_get(entry);
613    if (p) {
614        count = swap_count(p->swap_map[swp_offset(entry)]);
615        spin_unlock(&swap_lock);
616    }
617    return count;
618}
619
620/*
621 * We can write to an anon page without COW if there are no other references
622 * to it. And as a side-effect, free up its swap: because the old content
623 * on disk will never be read, and seeking back there to write new content
624 * later would only waste time away from clustering.
625 */
626int reuse_swap_page(struct page *page)
627{
628    int count;
629
630    VM_BUG_ON(!PageLocked(page));
631    if (unlikely(PageKsm(page)))
632        return 0;
633    count = page_mapcount(page);
634    if (count <= 1 && PageSwapCache(page)) {
635        count += page_swapcount(page);
636        if (count == 1 && !PageWriteback(page)) {
637            delete_from_swap_cache(page);
638            SetPageDirty(page);
639        }
640    }
641    return count <= 1;
642}
643
644/*
645 * If swap is getting full, or if there are no more mappings of this page,
646 * then try_to_free_swap is called to free its swap space.
647 */
648int try_to_free_swap(struct page *page)
649{
650    VM_BUG_ON(!PageLocked(page));
651
652    if (!PageSwapCache(page))
653        return 0;
654    if (PageWriteback(page))
655        return 0;
656    if (page_swapcount(page))
657        return 0;
658
659    /*
660     * Once hibernation has begun to create its image of memory,
661     * there's a danger that one of the calls to try_to_free_swap()
662     * - most probably a call from __try_to_reclaim_swap() while
663     * hibernation is allocating its own swap pages for the image,
664     * but conceivably even a call from memory reclaim - will free
665     * the swap from a page which has already been recorded in the
666     * image as a clean swapcache page, and then reuse its swap for
667     * another page of the image. On waking from hibernation, the
668     * original page might be freed under memory pressure, then
669     * later read back in from swap, now with the wrong data.
670     *
671     * Hibernation clears bits from gfp_allowed_mask to prevent
672     * memory reclaim from writing to disk, so check that here.
673     */
674    if (!(gfp_allowed_mask & __GFP_IO))
675        return 0;
676
677    delete_from_swap_cache(page);
678    SetPageDirty(page);
679    return 1;
680}
681
682/*
683 * Free the swap entry like above, but also try to
684 * free the page cache entry if it is the last user.
685 */
686int free_swap_and_cache(swp_entry_t entry)
687{
688    struct swap_info_struct *p;
689    struct page *page = NULL;
690
691    if (non_swap_entry(entry))
692        return 1;
693
694    p = swap_info_get(entry);
695    if (p) {
696        if (swap_entry_free(p, entry, 1) == SWAP_HAS_CACHE) {
697            page = find_get_page(&swapper_space, entry.val);
698            if (page && !trylock_page(page)) {
699                page_cache_release(page);
700                page = NULL;
701            }
702        }
703        spin_unlock(&swap_lock);
704    }
705    if (page) {
706        /*
707         * Not mapped elsewhere, or swap space full? Free it!
708         * Also recheck PageSwapCache now page is locked (above).
709         */
710        if (PageSwapCache(page) && !PageWriteback(page) &&
711                (!page_mapped(page) || vm_swap_full())) {
712            delete_from_swap_cache(page);
713            SetPageDirty(page);
714        }
715        unlock_page(page);
716        page_cache_release(page);
717    }
718    return p != NULL;
719}
720
721#ifdef CONFIG_CGROUP_MEM_RES_CTLR
722/**
723 * mem_cgroup_count_swap_user - count the user of a swap entry
724 * @ent: the swap entry to be checked
725 * @pagep: the pointer for the swap cache page of the entry to be stored
726 *
727 * Returns the number of the user of the swap entry. The number is valid only
728 * for swaps of anonymous pages.
729 * If the entry is found on swap cache, the page is stored to pagep with
730 * refcount of it being incremented.
731 */
732int mem_cgroup_count_swap_user(swp_entry_t ent, struct page **pagep)
733{
734    struct page *page;
735    struct swap_info_struct *p;
736    int count = 0;
737
738    page = find_get_page(&swapper_space, ent.val);
739    if (page)
740        count += page_mapcount(page);
741    p = swap_info_get(ent);
742    if (p) {
743        count += swap_count(p->swap_map[swp_offset(ent)]);
744        spin_unlock(&swap_lock);
745    }
746
747    *pagep = page;
748    return count;
749}
750#endif
751
752#ifdef CONFIG_HIBERNATION
753/*
754 * Find the swap type that corresponds to given device (if any).
755 *
756 * @offset - number of the PAGE_SIZE-sized block of the device, starting
757 * from 0, in which the swap header is expected to be located.
758 *
759 * This is needed for the suspend to disk (aka swsusp).
760 */
761int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)
762{
763    struct block_device *bdev = NULL;
764    int type;
765
766    if (device)
767        bdev = bdget(device);
768
769    spin_lock(&swap_lock);
770    for (type = 0; type < nr_swapfiles; type++) {
771        struct swap_info_struct *sis = swap_info[type];
772
773        if (!(sis->flags & SWP_WRITEOK))
774            continue;
775
776        if (!bdev) {
777            if (bdev_p)
778                *bdev_p = bdgrab(sis->bdev);
779
780            spin_unlock(&swap_lock);
781            return type;
782        }
783        if (bdev == sis->bdev) {
784            struct swap_extent *se = &sis->first_swap_extent;
785
786            if (se->start_block == offset) {
787                if (bdev_p)
788                    *bdev_p = bdgrab(sis->bdev);
789
790                spin_unlock(&swap_lock);
791                bdput(bdev);
792                return type;
793            }
794        }
795    }
796    spin_unlock(&swap_lock);
797    if (bdev)
798        bdput(bdev);
799
800    return -ENODEV;
801}
802
803/*
804 * Get the (PAGE_SIZE) block corresponding to given offset on the swapdev
805 * corresponding to given index in swap_info (swap type).
806 */
807sector_t swapdev_block(int type, pgoff_t offset)
808{
809    struct block_device *bdev;
810
811    if ((unsigned int)type >= nr_swapfiles)
812        return 0;
813    if (!(swap_info[type]->flags & SWP_WRITEOK))
814        return 0;
815    return map_swap_entry(swp_entry(type, offset), &bdev);
816}
817
818/*
819 * Return either the total number of swap pages of given type, or the number
820 * of free pages of that type (depending on @free)
821 *
822 * This is needed for software suspend
823 */
824unsigned int count_swap_pages(int type, int free)
825{
826    unsigned int n = 0;
827
828    spin_lock(&swap_lock);
829    if ((unsigned int)type < nr_swapfiles) {
830        struct swap_info_struct *sis = swap_info[type];
831
832        if (sis->flags & SWP_WRITEOK) {
833            n = sis->pages;
834            if (free)
835                n -= sis->inuse_pages;
836        }
837    }
838    spin_unlock(&swap_lock);
839    return n;
840}
841#endif /* CONFIG_HIBERNATION */
842
843/*
844 * No need to decide whether this PTE shares the swap entry with others,
845 * just let do_wp_page work it out if a write is requested later - to
846 * force COW, vm_page_prot omits write permission from any private vma.
847 */
848static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
849        unsigned long addr, swp_entry_t entry, struct page *page)
850{
851    struct mem_cgroup *ptr;
852    spinlock_t *ptl;
853    pte_t *pte;
854    int ret = 1;
855
856    if (mem_cgroup_try_charge_swapin(vma->vm_mm, page, GFP_KERNEL, &ptr)) {
857        ret = -ENOMEM;
858        goto out_nolock;
859    }
860
861    pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
862    if (unlikely(!pte_same(*pte, swp_entry_to_pte(entry)))) {
863        if (ret > 0)
864            mem_cgroup_cancel_charge_swapin(ptr);
865        ret = 0;
866        goto out;
867    }
868
869    dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
870    inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
871    get_page(page);
872    set_pte_at(vma->vm_mm, addr, pte,
873           pte_mkold(mk_pte(page, vma->vm_page_prot)));
874    page_add_anon_rmap(page, vma, addr);
875    mem_cgroup_commit_charge_swapin(page, ptr);
876    swap_free(entry);
877    /*
878     * Move the page to the active list so it is not
879     * immediately swapped out again after swapon.
880     */
881    activate_page(page);
882out:
883    pte_unmap_unlock(pte, ptl);
884out_nolock:
885    return ret;
886}
887
888static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
889                unsigned long addr, unsigned long end,
890                swp_entry_t entry, struct page *page)
891{
892    pte_t swp_pte = swp_entry_to_pte(entry);
893    pte_t *pte;
894    int ret = 0;
895
896    /*
897     * We don't actually need pte lock while scanning for swp_pte: since
898     * we hold page lock and mmap_sem, swp_pte cannot be inserted into the
899     * page table while we're scanning; though it could get zapped, and on
900     * some architectures (e.g. x86_32 with PAE) we might catch a glimpse
901     * of unmatched parts which look like swp_pte, so unuse_pte must
902     * recheck under pte lock. Scanning without pte lock lets it be
903     * preemptible whenever CONFIG_PREEMPT but not CONFIG_HIGHPTE.
904     */
905    pte = pte_offset_map(pmd, addr);
906    do {
907        /*
908         * swapoff spends a _lot_ of time in this loop!
909         * Test inline before going to call unuse_pte.
910         */
911        if (unlikely(pte_same(*pte, swp_pte))) {
912            pte_unmap(pte);
913            ret = unuse_pte(vma, pmd, addr, entry, page);
914            if (ret)
915                goto out;
916            pte = pte_offset_map(pmd, addr);
917        }
918    } while (pte++, addr += PAGE_SIZE, addr != end);
919    pte_unmap(pte - 1);
920out:
921    return ret;
922}
923
924static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
925                unsigned long addr, unsigned long end,
926                swp_entry_t entry, struct page *page)
927{
928    pmd_t *pmd;
929    unsigned long next;
930    int ret;
931
932    pmd = pmd_offset(pud, addr);
933    do {
934        next = pmd_addr_end(addr, end);
935        if (unlikely(pmd_trans_huge(*pmd)))
936            continue;
937        if (pmd_none_or_clear_bad(pmd))
938            continue;
939        ret = unuse_pte_range(vma, pmd, addr, next, entry, page);
940        if (ret)
941            return ret;
942    } while (pmd++, addr = next, addr != end);
943    return 0;
944}
945
946static inline int unuse_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
947                unsigned long addr, unsigned long end,
948                swp_entry_t entry, struct page *page)
949{
950    pud_t *pud;
951    unsigned long next;
952    int ret;
953
954    pud = pud_offset(pgd, addr);
955    do {
956        next = pud_addr_end(addr, end);
957        if (pud_none_or_clear_bad(pud))
958            continue;
959        ret = unuse_pmd_range(vma, pud, addr, next, entry, page);
960        if (ret)
961            return ret;
962    } while (pud++, addr = next, addr != end);
963    return 0;
964}
965
966static int unuse_vma(struct vm_area_struct *vma,
967                swp_entry_t entry, struct page *page)
968{
969    pgd_t *pgd;
970    unsigned long addr, end, next;
971    int ret;
972
973    if (page_anon_vma(page)) {
974        addr = page_address_in_vma(page, vma);
975        if (addr == -EFAULT)
976            return 0;
977        else
978            end = addr + PAGE_SIZE;
979    } else {
980        addr = vma->vm_start;
981        end = vma->vm_end;
982    }
983
984    pgd = pgd_offset(vma->vm_mm, addr);
985    do {
986        next = pgd_addr_end(addr, end);
987        if (pgd_none_or_clear_bad(pgd))
988            continue;
989        ret = unuse_pud_range(vma, pgd, addr, next, entry, page);
990        if (ret)
991            return ret;
992    } while (pgd++, addr = next, addr != end);
993    return 0;
994}
995
996static int unuse_mm(struct mm_struct *mm,
997                swp_entry_t entry, struct page *page)
998{
999    struct vm_area_struct *vma;
1000    int ret = 0;
1001
1002    if (!down_read_trylock(&mm->mmap_sem)) {
1003        /*
1004         * Activate page so shrink_inactive_list is unlikely to unmap
1005         * its ptes while lock is dropped, so swapoff can make progress.
1006         */
1007        activate_page(page);
1008        unlock_page(page);
1009        down_read(&mm->mmap_sem);
1010        lock_page(page);
1011    }
1012    for (vma = mm->mmap; vma; vma = vma->vm_next) {
1013        if (vma->anon_vma && (ret = unuse_vma(vma, entry, page)))
1014            break;
1015    }
1016    up_read(&mm->mmap_sem);
1017    return (ret < 0)? ret: 0;
1018}
1019
1020/*
1021 * Scan swap_map from current position to next entry still in use.
1022 * Recycle to start on reaching the end, returning 0 when empty.
1023 */
1024static unsigned int find_next_to_unuse(struct swap_info_struct *si,
1025                    unsigned int prev)
1026{
1027    unsigned int max = si->max;
1028    unsigned int i = prev;
1029    unsigned char count;
1030
1031    /*
1032     * No need for swap_lock here: we're just looking
1033     * for whether an entry is in use, not modifying it; false
1034     * hits are okay, and sys_swapoff() has already prevented new
1035     * allocations from this area (while holding swap_lock).
1036     */
1037    for (;;) {
1038        if (++i >= max) {
1039            if (!prev) {
1040                i = 0;
1041                break;
1042            }
1043            /*
1044             * No entries in use at top of swap_map,
1045             * loop back to start and recheck there.
1046             */
1047            max = prev + 1;
1048            prev = 0;
1049            i = 1;
1050        }
1051        count = si->swap_map[i];
1052        if (count && swap_count(count) != SWAP_MAP_BAD)
1053            break;
1054    }
1055    return i;
1056}
1057
1058/*
1059 * We completely avoid races by reading each swap page in advance,
1060 * and then search for the process using it. All the necessary
1061 * page table adjustments can then be made atomically.
1062 */
1063static int try_to_unuse(unsigned int type)
1064{
1065    struct swap_info_struct *si = swap_info[type];
1066    struct mm_struct *start_mm;
1067    unsigned char *swap_map;
1068    unsigned char swcount;
1069    struct page *page;
1070    swp_entry_t entry;
1071    unsigned int i = 0;
1072    int retval = 0;
1073
1074    /*
1075     * When searching mms for an entry, a good strategy is to
1076     * start at the first mm we freed the previous entry from
1077     * (though actually we don't notice whether we or coincidence
1078     * freed the entry). Initialize this start_mm with a hold.
1079     *
1080     * A simpler strategy would be to start at the last mm we
1081     * freed the previous entry from; but that would take less
1082     * advantage of mmlist ordering, which clusters forked mms
1083     * together, child after parent. If we race with dup_mmap(), we
1084     * prefer to resolve parent before child, lest we miss entries
1085     * duplicated after we scanned child: using last mm would invert
1086     * that.
1087     */
1088    start_mm = &init_mm;
1089    atomic_inc(&init_mm.mm_users);
1090
1091    /*
1092     * Keep on scanning until all entries have gone. Usually,
1093     * one pass through swap_map is enough, but not necessarily:
1094     * there are races when an instance of an entry might be missed.
1095     */
1096    while ((i = find_next_to_unuse(si, i)) != 0) {
1097        if (signal_pending(current)) {
1098            retval = -EINTR;
1099            break;
1100        }
1101
1102        /*
1103         * Get a page for the entry, using the existing swap
1104         * cache page if there is one. Otherwise, get a clean
1105         * page and read the swap into it.
1106         */
1107        swap_map = &si->swap_map[i];
1108        entry = swp_entry(type, i);
1109        page = read_swap_cache_async(entry,
1110                    GFP_HIGHUSER_MOVABLE, NULL, 0);
1111        if (!page) {
1112            /*
1113             * Either swap_duplicate() failed because entry
1114             * has been freed independently, and will not be
1115             * reused since sys_swapoff() already disabled
1116             * allocation from here, or alloc_page() failed.
1117             */
1118            if (!*swap_map)
1119                continue;
1120            retval = -ENOMEM;
1121            break;
1122        }
1123
1124        /*
1125         * Don't hold on to start_mm if it looks like exiting.
1126         */
1127        if (atomic_read(&start_mm->mm_users) == 1) {
1128            mmput(start_mm);
1129            start_mm = &init_mm;
1130            atomic_inc(&init_mm.mm_users);
1131        }
1132
1133        /*
1134         * Wait for and lock page. When do_swap_page races with
1135         * try_to_unuse, do_swap_page can handle the fault much
1136         * faster than try_to_unuse can locate the entry. This
1137         * apparently redundant "wait_on_page_locked" lets try_to_unuse
1138         * defer to do_swap_page in such a case - in some tests,
1139         * do_swap_page and try_to_unuse repeatedly compete.
1140         */
1141        wait_on_page_locked(page);
1142        wait_on_page_writeback(page);
1143        lock_page(page);
1144        wait_on_page_writeback(page);
1145
1146        /*
1147         * Remove all references to entry.
1148         */
1149        swcount = *swap_map;
1150        if (swap_count(swcount) == SWAP_MAP_SHMEM) {
1151            retval = shmem_unuse(entry, page);
1152            /* page has already been unlocked and released */
1153            if (retval < 0)
1154                break;
1155            continue;
1156        }
1157        if (swap_count(swcount) && start_mm != &init_mm)
1158            retval = unuse_mm(start_mm, entry, page);
1159
1160        if (swap_count(*swap_map)) {
1161            int set_start_mm = (*swap_map >= swcount);
1162            struct list_head *p = &start_mm->mmlist;
1163            struct mm_struct *new_start_mm = start_mm;
1164            struct mm_struct *prev_mm = start_mm;
1165            struct mm_struct *mm;
1166
1167            atomic_inc(&new_start_mm->mm_users);
1168            atomic_inc(&prev_mm->mm_users);
1169            spin_lock(&mmlist_lock);
1170            while (swap_count(*swap_map) && !retval &&
1171                    (p = p->next) != &start_mm->mmlist) {
1172                mm = list_entry(p, struct mm_struct, mmlist);
1173                if (!atomic_inc_not_zero(&mm->mm_users))
1174                    continue;
1175                spin_unlock(&mmlist_lock);
1176                mmput(prev_mm);
1177                prev_mm = mm;
1178
1179                cond_resched();
1180
1181                swcount = *swap_map;
1182                if (!swap_count(swcount)) /* any usage ? */
1183                    ;
1184                else if (mm == &init_mm)
1185                    set_start_mm = 1;
1186                else
1187                    retval = unuse_mm(mm, entry, page);
1188
1189                if (set_start_mm && *swap_map < swcount) {
1190                    mmput(new_start_mm);
1191                    atomic_inc(&mm->mm_users);
1192                    new_start_mm = mm;
1193                    set_start_mm = 0;
1194                }
1195                spin_lock(&mmlist_lock);
1196            }
1197            spin_unlock(&mmlist_lock);
1198            mmput(prev_mm);
1199            mmput(start_mm);
1200            start_mm = new_start_mm;
1201        }
1202        if (retval) {
1203            unlock_page(page);
1204            page_cache_release(page);
1205            break;
1206        }
1207
1208        /*
1209         * If a reference remains (rare), we would like to leave
1210         * the page in the swap cache; but try_to_unmap could
1211         * then re-duplicate the entry once we drop page lock,
1212         * so we might loop indefinitely; also, that page could
1213         * not be swapped out to other storage meanwhile. So:
1214         * delete from cache even if there's another reference,
1215         * after ensuring that the data has been saved to disk -
1216         * since if the reference remains (rarer), it will be
1217         * read from disk into another page. Splitting into two
1218         * pages would be incorrect if swap supported "shared
1219         * private" pages, but they are handled by tmpfs files.
1220         *
1221         * Given how unuse_vma() targets one particular offset
1222         * in an anon_vma, once the anon_vma has been determined,
1223         * this splitting happens to be just what is needed to
1224         * handle where KSM pages have been swapped out: re-reading
1225         * is unnecessarily slow, but we can fix that later on.
1226         */
1227        if (swap_count(*swap_map) &&
1228             PageDirty(page) && PageSwapCache(page)) {
1229            struct writeback_control wbc = {
1230                .sync_mode = WB_SYNC_NONE,
1231            };
1232
1233            swap_writepage(page, &wbc);
1234            lock_page(page);
1235            wait_on_page_writeback(page);
1236        }
1237
1238        /*
1239         * It is conceivable that a racing task removed this page from
1240         * swap cache just before we acquired the page lock at the top,
1241         * or while we dropped it in unuse_mm(). The page might even
1242         * be back in swap cache on another swap area: that we must not
1243         * delete, since it may not have been written out to swap yet.
1244         */
1245        if (PageSwapCache(page) &&
1246            likely(page_private(page) == entry.val))
1247            delete_from_swap_cache(page);
1248
1249        /*
1250         * So we could skip searching mms once swap count went
1251         * to 1, we did not mark any present ptes as dirty: must
1252         * mark page dirty so shrink_page_list will preserve it.
1253         */
1254        SetPageDirty(page);
1255        unlock_page(page);
1256        page_cache_release(page);
1257
1258        /*
1259         * Make sure that we aren't completely killing
1260         * interactive performance.
1261         */
1262        cond_resched();
1263    }
1264
1265    mmput(start_mm);
1266    return retval;
1267}
1268
1269/*
1270 * After a successful try_to_unuse, if no swap is now in use, we know
1271 * we can empty the mmlist. swap_lock must be held on entry and exit.
1272 * Note that mmlist_lock nests inside swap_lock, and an mm must be
1273 * added to the mmlist just after page_duplicate - before would be racy.
1274 */
1275static void drain_mmlist(void)
1276{
1277    struct list_head *p, *next;
1278    unsigned int type;
1279
1280    for (type = 0; type < nr_swapfiles; type++)
1281        if (swap_info[type]->inuse_pages)
1282            return;
1283    spin_lock(&mmlist_lock);
1284    list_for_each_safe(p, next, &init_mm.mmlist)
1285        list_del_init(p);
1286    spin_unlock(&mmlist_lock);
1287}
1288
1289/*
1290 * Use this swapdev's extent info to locate the (PAGE_SIZE) block which
1291 * corresponds to page offset for the specified swap entry.
1292 * Note that the type of this function is sector_t, but it returns page offset
1293 * into the bdev, not sector offset.
1294 */
1295static sector_t map_swap_entry(swp_entry_t entry, struct block_device **bdev)
1296{
1297    struct swap_info_struct *sis;
1298    struct swap_extent *start_se;
1299    struct swap_extent *se;
1300    pgoff_t offset;
1301
1302    sis = swap_info[swp_type(entry)];
1303    *bdev = sis->bdev;
1304
1305    offset = swp_offset(entry);
1306    start_se = sis->curr_swap_extent;
1307    se = start_se;
1308
1309    for ( ; ; ) {
1310        struct list_head *lh;
1311
1312        if (se->start_page <= offset &&
1313                offset < (se->start_page + se->nr_pages)) {
1314            return se->start_block + (offset - se->start_page);
1315        }
1316        lh = se->list.next;
1317        se = list_entry(lh, struct swap_extent, list);
1318        sis->curr_swap_extent = se;
1319        BUG_ON(se == start_se); /* It *must* be present */
1320    }
1321}
1322
1323/*
1324 * Returns the page offset into bdev for the specified page's swap entry.
1325 */
1326sector_t map_swap_page(struct page *page, struct block_device **bdev)
1327{
1328    swp_entry_t entry;
1329    entry.val = page_private(page);
1330    return map_swap_entry(entry, bdev);
1331}
1332
1333/*
1334 * Free all of a swapdev's extent information
1335 */
1336static void destroy_swap_extents(struct swap_info_struct *sis)
1337{
1338    while (!list_empty(&sis->first_swap_extent.list)) {
1339        struct swap_extent *se;
1340
1341        se = list_entry(sis->first_swap_extent.list.next,
1342                struct swap_extent, list);
1343        list_del(&se->list);
1344        kfree(se);
1345    }
1346}
1347
1348/*
1349 * Add a block range (and the corresponding page range) into this swapdev's
1350 * extent list. The extent list is kept sorted in page order.
1351 *
1352 * This function rather assumes that it is called in ascending page order.
1353 */
1354static int
1355add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
1356        unsigned long nr_pages, sector_t start_block)
1357{
1358    struct swap_extent *se;
1359    struct swap_extent *new_se;
1360    struct list_head *lh;
1361
1362    if (start_page == 0) {
1363        se = &sis->first_swap_extent;
1364        sis->curr_swap_extent = se;
1365        se->start_page = 0;
1366        se->nr_pages = nr_pages;
1367        se->start_block = start_block;
1368        return 1;
1369    } else {
1370        lh = sis->first_swap_extent.list.prev; /* Highest extent */
1371        se = list_entry(lh, struct swap_extent, list);
1372        BUG_ON(se->start_page + se->nr_pages != start_page);
1373        if (se->start_block + se->nr_pages == start_block) {
1374            /* Merge it */
1375            se->nr_pages += nr_pages;
1376            return 0;
1377        }
1378    }
1379
1380    /*
1381     * No merge. Insert a new extent, preserving ordering.
1382     */
1383    new_se = kmalloc(sizeof(*se), GFP_KERNEL);
1384    if (new_se == NULL)
1385        return -ENOMEM;
1386    new_se->start_page = start_page;
1387    new_se->nr_pages = nr_pages;
1388    new_se->start_block = start_block;
1389
1390    list_add_tail(&new_se->list, &sis->first_swap_extent.list);
1391    return 1;
1392}
1393
1394/*
1395 * A `swap extent' is a simple thing which maps a contiguous range of pages
1396 * onto a contiguous range of disk blocks. An ordered list of swap extents
1397 * is built at swapon time and is then used at swap_writepage/swap_readpage
1398 * time for locating where on disk a page belongs.
1399 *
1400 * If the swapfile is an S_ISBLK block device, a single extent is installed.
1401 * This is done so that the main operating code can treat S_ISBLK and S_ISREG
1402 * swap files identically.
1403 *
1404 * Whether the swapdev is an S_ISREG file or an S_ISBLK blockdev, the swap
1405 * extent list operates in PAGE_SIZE disk blocks. Both S_ISREG and S_ISBLK
1406 * swapfiles are handled *identically* after swapon time.
1407 *
1408 * For S_ISREG swapfiles, setup_swap_extents() will walk all the file's blocks
1409 * and will parse them into an ordered extent list, in PAGE_SIZE chunks. If
1410 * some stray blocks are found which do not fall within the PAGE_SIZE alignment
1411 * requirements, they are simply tossed out - we will never use those blocks
1412 * for swapping.
1413 *
1414 * For S_ISREG swapfiles we set S_SWAPFILE across the life of the swapon. This
1415 * prevents root from shooting her foot off by ftruncating an in-use swapfile,
1416 * which will scribble on the fs.
1417 *
1418 * The amount of disk space which a single swap extent represents varies.
1419 * Typically it is in the 1-4 megabyte range. So we can have hundreds of
1420 * extents in the list. To avoid much list walking, we cache the previous
1421 * search location in `curr_swap_extent', and start new searches from there.
1422 * This is extremely effective. The average number of iterations in
1423 * map_swap_page() has been measured at about 0.3 per page. - akpm.
1424 */
1425static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
1426{
1427    struct inode *inode;
1428    unsigned blocks_per_page;
1429    unsigned long page_no;
1430    unsigned blkbits;
1431    sector_t probe_block;
1432    sector_t last_block;
1433    sector_t lowest_block = -1;
1434    sector_t highest_block = 0;
1435    int nr_extents = 0;
1436    int ret;
1437
1438    inode = sis->swap_file->f_mapping->host;
1439    if (S_ISBLK(inode->i_mode)) {
1440        ret = add_swap_extent(sis, 0, sis->max, 0);
1441        *span = sis->pages;
1442        goto out;
1443    }
1444
1445    blkbits = inode->i_blkbits;
1446    blocks_per_page = PAGE_SIZE >> blkbits;
1447
1448    /*
1449     * Map all the blocks into the extent list. This code doesn't try
1450     * to be very smart.
1451     */
1452    probe_block = 0;
1453    page_no = 0;
1454    last_block = i_size_read(inode) >> blkbits;
1455    while ((probe_block + blocks_per_page) <= last_block &&
1456            page_no < sis->max) {
1457        unsigned block_in_page;
1458        sector_t first_block;
1459
1460        first_block = bmap(inode, probe_block);
1461        if (first_block == 0)
1462            goto bad_bmap;
1463
1464        /*
1465         * It must be PAGE_SIZE aligned on-disk
1466         */
1467        if (first_block & (blocks_per_page - 1)) {
1468            probe_block++;
1469            goto reprobe;
1470        }
1471
1472        for (block_in_page = 1; block_in_page < blocks_per_page;
1473                    block_in_page++) {
1474            sector_t block;
1475
1476            block = bmap(inode, probe_block + block_in_page);
1477            if (block == 0)
1478                goto bad_bmap;
1479            if (block != first_block + block_in_page) {
1480                /* Discontiguity */
1481                probe_block++;
1482                goto reprobe;
1483            }
1484        }
1485
1486        first_block >>= (PAGE_SHIFT - blkbits);
1487        if (page_no) { /* exclude the header page */
1488            if (first_block < lowest_block)
1489                lowest_block = first_block;
1490            if (first_block > highest_block)
1491                highest_block = first_block;
1492        }
1493
1494        /*
1495         * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks
1496         */
1497        ret = add_swap_extent(sis, page_no, 1, first_block);
1498        if (ret < 0)
1499            goto out;
1500        nr_extents += ret;
1501        page_no++;
1502        probe_block += blocks_per_page;
1503reprobe:
1504        continue;
1505    }
1506    ret = nr_extents;
1507    *span = 1 + highest_block - lowest_block;
1508    if (page_no == 0)
1509        page_no = 1; /* force Empty message */
1510    sis->max = page_no;
1511    sis->pages = page_no - 1;
1512    sis->highest_bit = page_no - 1;
1513out:
1514    return ret;
1515bad_bmap:
1516    printk(KERN_ERR "swapon: swapfile has holes\n");
1517    ret = -EINVAL;
1518    goto out;
1519}
1520
1521static void enable_swap_info(struct swap_info_struct *p, int prio,
1522                unsigned char *swap_map)
1523{
1524    int i, prev;
1525
1526    spin_lock(&swap_lock);
1527    if (prio >= 0)
1528        p->prio = prio;
1529    else
1530        p->prio = --least_priority;
1531    p->swap_map = swap_map;
1532    p->flags |= SWP_WRITEOK;
1533    nr_swap_pages += p->pages;
1534    total_swap_pages += p->pages;
1535
1536    /* insert swap space into swap_list: */
1537    prev = -1;
1538    for (i = swap_list.head; i >= 0; i = swap_info[i]->next) {
1539        if (p->prio >= swap_info[i]->prio)
1540            break;
1541        prev = i;
1542    }
1543    p->next = i;
1544    if (prev < 0)
1545        swap_list.head = swap_list.next = p->type;
1546    else
1547        swap_info[prev]->next = p->type;
1548    spin_unlock(&swap_lock);
1549}
1550
1551SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
1552{
1553    struct swap_info_struct *p = NULL;
1554    unsigned char *swap_map;
1555    struct file *swap_file, *victim;
1556    struct address_space *mapping;
1557    struct inode *inode;
1558    char *pathname;
1559    int oom_score_adj;
1560    int i, type, prev;
1561    int err;
1562
1563    if (!capable(CAP_SYS_ADMIN))
1564        return -EPERM;
1565
1566    pathname = getname(specialfile);
1567    err = PTR_ERR(pathname);
1568    if (IS_ERR(pathname))
1569        goto out;
1570
1571    victim = filp_open(pathname, O_RDWR|O_LARGEFILE, 0);
1572    putname(pathname);
1573    err = PTR_ERR(victim);
1574    if (IS_ERR(victim))
1575        goto out;
1576
1577    mapping = victim->f_mapping;
1578    prev = -1;
1579    spin_lock(&swap_lock);
1580    for (type = swap_list.head; type >= 0; type = swap_info[type]->next) {
1581        p = swap_info[type];
1582        if (p->flags & SWP_WRITEOK) {
1583            if (p->swap_file->f_mapping == mapping)
1584                break;
1585        }
1586        prev = type;
1587    }
1588    if (type < 0) {
1589        err = -EINVAL;
1590        spin_unlock(&swap_lock);
1591        goto out_dput;
1592    }
1593    if (!security_vm_enough_memory(p->pages))
1594        vm_unacct_memory(p->pages);
1595    else {
1596        err = -ENOMEM;
1597        spin_unlock(&swap_lock);
1598        goto out_dput;
1599    }
1600    if (prev < 0)
1601        swap_list.head = p->next;
1602    else
1603        swap_info[prev]->next = p->next;
1604    if (type == swap_list.next) {
1605        /* just pick something that's safe... */
1606        swap_list.next = swap_list.head;
1607    }
1608    if (p->prio < 0) {
1609        for (i = p->next; i >= 0; i = swap_info[i]->next)
1610            swap_info[i]->prio = p->prio--;
1611        least_priority++;
1612    }
1613    nr_swap_pages -= p->pages;
1614    total_swap_pages -= p->pages;
1615    p->flags &= ~SWP_WRITEOK;
1616    spin_unlock(&swap_lock);
1617
1618    oom_score_adj = test_set_oom_score_adj(OOM_SCORE_ADJ_MAX);
1619    err = try_to_unuse(type);
1620    test_set_oom_score_adj(oom_score_adj);
1621
1622    if (err) {
1623        /*
1624         * reading p->prio and p->swap_map outside the lock is
1625         * safe here because only sys_swapon and sys_swapoff
1626         * change them, and there can be no other sys_swapon or
1627         * sys_swapoff for this swap_info_struct at this point.
1628         */
1629        /* re-insert swap space back into swap_list */
1630        enable_swap_info(p, p->prio, p->swap_map);
1631        goto out_dput;
1632    }
1633
1634    destroy_swap_extents(p);
1635    if (p->flags & SWP_CONTINUED)
1636        free_swap_count_continuations(p);
1637
1638    mutex_lock(&swapon_mutex);
1639    spin_lock(&swap_lock);
1640    drain_mmlist();
1641
1642    /* wait for anyone still in scan_swap_map */
1643    p->highest_bit = 0; /* cuts scans short */
1644    while (p->flags >= SWP_SCANNING) {
1645        spin_unlock(&swap_lock);
1646        schedule_timeout_uninterruptible(1);
1647        spin_lock(&swap_lock);
1648    }
1649
1650    swap_file = p->swap_file;
1651    p->swap_file = NULL;
1652    p->max = 0;
1653    swap_map = p->swap_map;
1654    p->swap_map = NULL;
1655    p->flags = 0;
1656    spin_unlock(&swap_lock);
1657    mutex_unlock(&swapon_mutex);
1658    vfree(swap_map);
1659    /* Destroy swap account informatin */
1660    swap_cgroup_swapoff(type);
1661
1662    inode = mapping->host;
1663    if (S_ISBLK(inode->i_mode)) {
1664        struct block_device *bdev = I_BDEV(inode);
1665        set_blocksize(bdev, p->old_block_size);
1666        blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
1667    } else {
1668        mutex_lock(&inode->i_mutex);
1669        inode->i_flags &= ~S_SWAPFILE;
1670        mutex_unlock(&inode->i_mutex);
1671    }
1672    filp_close(swap_file, NULL);
1673    err = 0;
1674    atomic_inc(&proc_poll_event);
1675    wake_up_interruptible(&proc_poll_wait);
1676
1677out_dput:
1678    filp_close(victim, NULL);
1679out:
1680    return err;
1681}
1682
1683#ifdef CONFIG_PROC_FS
1684struct proc_swaps {
1685    struct seq_file seq;
1686    int event;
1687};
1688
1689static unsigned swaps_poll(struct file *file, poll_table *wait)
1690{
1691    struct proc_swaps *s = file->private_data;
1692
1693    poll_wait(file, &proc_poll_wait, wait);
1694
1695    if (s->event != atomic_read(&proc_poll_event)) {
1696        s->event = atomic_read(&proc_poll_event);
1697        return POLLIN | POLLRDNORM | POLLERR | POLLPRI;
1698    }
1699
1700    return POLLIN | POLLRDNORM;
1701}
1702
1703/* iterator */
1704static void *swap_start(struct seq_file *swap, loff_t *pos)
1705{
1706    struct swap_info_struct *si;
1707    int type;
1708    loff_t l = *pos;
1709
1710    mutex_lock(&swapon_mutex);
1711
1712    if (!l)
1713        return SEQ_START_TOKEN;
1714
1715    for (type = 0; type < nr_swapfiles; type++) {
1716        smp_rmb(); /* read nr_swapfiles before swap_info[type] */
1717        si = swap_info[type];
1718        if (!(si->flags & SWP_USED) || !si->swap_map)
1719            continue;
1720        if (!--l)
1721            return si;
1722    }
1723
1724    return NULL;
1725}
1726
1727static void *swap_next(struct seq_file *swap, void *v, loff_t *pos)
1728{
1729    struct swap_info_struct *si = v;
1730    int type;
1731
1732    if (v == SEQ_START_TOKEN)
1733        type = 0;
1734    else
1735        type = si->type + 1;
1736
1737    for (; type < nr_swapfiles; type++) {
1738        smp_rmb(); /* read nr_swapfiles before swap_info[type] */
1739        si = swap_info[type];
1740        if (!(si->flags & SWP_USED) || !si->swap_map)
1741            continue;
1742        ++*pos;
1743        return si;
1744    }
1745
1746    return NULL;
1747}
1748
1749static void swap_stop(struct seq_file *swap, void *v)
1750{
1751    mutex_unlock(&swapon_mutex);
1752}
1753
1754static int swap_show(struct seq_file *swap, void *v)
1755{
1756    struct swap_info_struct *si = v;
1757    struct file *file;
1758    int len;
1759
1760    if (si == SEQ_START_TOKEN) {
1761        seq_puts(swap,"Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n");
1762        return 0;
1763    }
1764
1765    file = si->swap_file;
1766    len = seq_path(swap, &file->f_path, " \t\n\\");
1767    seq_printf(swap, "%*s%s\t%u\t%u\t%d\n",
1768            len < 40 ? 40 - len : 1, " ",
1769            S_ISBLK(file->f_path.dentry->d_inode->i_mode) ?
1770                "partition" : "file\t",
1771            si->pages << (PAGE_SHIFT - 10),
1772            si->inuse_pages << (PAGE_SHIFT - 10),
1773            si->prio);
1774    return 0;
1775}
1776
1777static const struct seq_operations swaps_op = {
1778    .start = swap_start,
1779    .next = swap_next,
1780    .stop = swap_stop,
1781    .show = swap_show
1782};
1783
1784static int swaps_open(struct inode *inode, struct file *file)
1785{
1786    struct proc_swaps *s;
1787    int ret;
1788
1789    s = kmalloc(sizeof(struct proc_swaps), GFP_KERNEL);
1790    if (!s)
1791        return -ENOMEM;
1792
1793    file->private_data = s;
1794
1795    ret = seq_open(file, &swaps_op);
1796    if (ret) {
1797        kfree(s);
1798        return ret;
1799    }
1800
1801    s->seq.private = s;
1802    s->event = atomic_read(&proc_poll_event);
1803    return ret;
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
1873    return p;
1874}
1875
1876static int claim_swapfile(struct swap_info_struct *p, struct inode *inode)
1877{
1878    int error;
1879
1880    if (S_ISBLK(inode->i_mode)) {
1881        p->bdev = bdgrab(I_BDEV(inode));
1882        error = blkdev_get(p->bdev,
1883                   FMODE_READ | FMODE_WRITE | FMODE_EXCL,
1884                   sys_swapon);
1885        if (error < 0) {
1886            p->bdev = NULL;
1887            return -EINVAL;
1888        }
1889        p->old_block_size = block_size(p->bdev);
1890        error = set_blocksize(p->bdev, PAGE_SIZE);
1891        if (error < 0)
1892            return error;
1893        p->flags |= SWP_BLKDEV;
1894    } else if (S_ISREG(inode->i_mode)) {
1895        p->bdev = inode->i_sb->s_bdev;
1896        mutex_lock(&inode->i_mutex);
1897        if (IS_SWAPFILE(inode))
1898            return -EBUSY;
1899    } else
1900        return -EINVAL;
1901
1902    return 0;
1903}
1904
1905static unsigned long read_swap_header(struct swap_info_struct *p,
1906                    union swap_header *swap_header,
1907                    struct inode *inode)
1908{
1909    int i;
1910    unsigned long maxpages;
1911    unsigned long swapfilepages;
1912
1913    if (memcmp("SWAPSPACE2", swap_header->magic.magic, 10)) {
1914        printk(KERN_ERR "Unable to find swap-space signature\n");
1915        return 0;
1916    }
1917
1918    /* swap partition endianess hack... */
1919    if (swab32(swap_header->info.version) == 1) {
1920        swab32s(&swap_header->info.version);
1921        swab32s(&swap_header->info.last_page);
1922        swab32s(&swap_header->info.nr_badpages);
1923        for (i = 0; i < swap_header->info.nr_badpages; i++)
1924            swab32s(&swap_header->info.badpages[i]);
1925    }
1926    /* Check the swap header's sub-version */
1927    if (swap_header->info.version != 1) {
1928        printk(KERN_WARNING
1929               "Unable to handle swap header version %d\n",
1930               swap_header->info.version);
1931        return 0;
1932    }
1933
1934    p->lowest_bit = 1;
1935    p->cluster_next = 1;
1936    p->cluster_nr = 0;
1937
1938    /*
1939     * Find out how many pages are allowed for a single swap
1940     * device. There are two limiting factors: 1) the number of
1941     * bits for the swap offset in the swp_entry_t type and
1942     * 2) the number of bits in the a swap pte as defined by
1943     * the different architectures. In order to find the
1944     * largest possible bit mask a swap entry with swap type 0
1945     * and swap offset ~0UL is created, encoded to a swap pte,
1946     * decoded to a swp_entry_t again and finally the swap
1947     * offset is extracted. This will mask all the bits from
1948     * the initial ~0UL mask that can't be encoded in either
1949     * the swp_entry_t or the architecture definition of a
1950     * swap pte.
1951     */
1952    maxpages = swp_offset(pte_to_swp_entry(
1953            swp_entry_to_pte(swp_entry(0, ~0UL)))) + 1;
1954    if (maxpages > swap_header->info.last_page) {
1955        maxpages = swap_header->info.last_page + 1;
1956        /* p->max is an unsigned int: don't overflow it */
1957        if ((unsigned int)maxpages == 0)
1958            maxpages = UINT_MAX;
1959    }
1960    p->highest_bit = maxpages - 1;
1961
1962    if (!maxpages)
1963        return 0;
1964    swapfilepages = i_size_read(inode) >> PAGE_SHIFT;
1965    if (swapfilepages && maxpages > swapfilepages) {
1966        printk(KERN_WARNING
1967               "Swap area shorter than signature indicates\n");
1968        return 0;
1969    }
1970    if (swap_header->info.nr_badpages && S_ISREG(inode->i_mode))
1971        return 0;
1972    if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
1973        return 0;
1974
1975    return maxpages;
1976}
1977
1978static int setup_swap_map_and_extents(struct swap_info_struct *p,
1979                    union swap_header *swap_header,
1980                    unsigned char *swap_map,
1981                    unsigned long maxpages,
1982                    sector_t *span)
1983{
1984    int i;
1985    unsigned int nr_good_pages;
1986    int nr_extents;
1987
1988    nr_good_pages = maxpages - 1; /* omit header page */
1989
1990    for (i = 0; i < swap_header->info.nr_badpages; i++) {
1991        unsigned int page_nr = swap_header->info.badpages[i];
1992        if (page_nr == 0 || page_nr > swap_header->info.last_page)
1993            return -EINVAL;
1994        if (page_nr < maxpages) {
1995            swap_map[page_nr] = SWAP_MAP_BAD;
1996            nr_good_pages--;
1997        }
1998    }
1999
2000    if (nr_good_pages) {
2001        swap_map[0] = SWAP_MAP_BAD;
2002        p->max = maxpages;
2003        p->pages = nr_good_pages;
2004        nr_extents = setup_swap_extents(p, span);
2005        if (nr_extents < 0)
2006            return nr_extents;
2007        nr_good_pages = p->pages;
2008    }
2009    if (!nr_good_pages) {
2010        printk(KERN_WARNING "Empty swap-file\n");
2011        return -EINVAL;
2012    }
2013
2014    return nr_extents;
2015}
2016
2017SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
2018{
2019    struct swap_info_struct *p;
2020    char *name;
2021    struct file *swap_file = NULL;
2022    struct address_space *mapping;
2023    int i;
2024    int prio;
2025    int error;
2026    union swap_header *swap_header;
2027    int nr_extents;
2028    sector_t span;
2029    unsigned long maxpages;
2030    unsigned char *swap_map = NULL;
2031    struct page *page = NULL;
2032    struct inode *inode = NULL;
2033
2034    if (!capable(CAP_SYS_ADMIN))
2035        return -EPERM;
2036
2037    p = alloc_swap_info();
2038    if (IS_ERR(p))
2039        return PTR_ERR(p);
2040
2041    name = getname(specialfile);
2042    if (IS_ERR(name)) {
2043        error = PTR_ERR(name);
2044        name = NULL;
2045        goto bad_swap;
2046    }
2047    swap_file = filp_open(name, O_RDWR|O_LARGEFILE, 0);
2048    if (IS_ERR(swap_file)) {
2049        error = PTR_ERR(swap_file);
2050        swap_file = NULL;
2051        goto bad_swap;
2052    }
2053
2054    p->swap_file = swap_file;
2055    mapping = swap_file->f_mapping;
2056
2057    for (i = 0; i < nr_swapfiles; i++) {
2058        struct swap_info_struct *q = swap_info[i];
2059
2060        if (q == p || !q->swap_file)
2061            continue;
2062        if (mapping == q->swap_file->f_mapping) {
2063            error = -EBUSY;
2064            goto bad_swap;
2065        }
2066    }
2067
2068    inode = mapping->host;
2069    /* If S_ISREG(inode->i_mode) will do mutex_lock(&inode->i_mutex); */
2070    error = claim_swapfile(p, inode);
2071    if (unlikely(error))
2072        goto bad_swap;
2073
2074    /*
2075     * Read the swap header.
2076     */
2077    if (!mapping->a_ops->readpage) {
2078        error = -EINVAL;
2079        goto bad_swap;
2080    }
2081    page = read_mapping_page(mapping, 0, swap_file);
2082    if (IS_ERR(page)) {
2083        error = PTR_ERR(page);
2084        goto bad_swap;
2085    }
2086    swap_header = kmap(page);
2087
2088    maxpages = read_swap_header(p, swap_header, inode);
2089    if (unlikely(!maxpages)) {
2090        error = -EINVAL;
2091        goto bad_swap;
2092    }
2093
2094    /* OK, set up the swap map and apply the bad block list */
2095    swap_map = vzalloc(maxpages);
2096    if (!swap_map) {
2097        error = -ENOMEM;
2098        goto bad_swap;
2099    }
2100
2101    error = swap_cgroup_swapon(p->type, maxpages);
2102    if (error)
2103        goto bad_swap;
2104
2105    nr_extents = setup_swap_map_and_extents(p, swap_header, swap_map,
2106        maxpages, &span);
2107    if (unlikely(nr_extents < 0)) {
2108        error = nr_extents;
2109        goto bad_swap;
2110    }
2111
2112    if (p->bdev) {
2113        if (blk_queue_nonrot(bdev_get_queue(p->bdev))) {
2114            p->flags |= SWP_SOLIDSTATE;
2115            p->cluster_next = 1 + (random32() % p->highest_bit);
2116        }
2117        if (discard_swap(p) == 0 && (swap_flags & SWAP_FLAG_DISCARD))
2118            p->flags |= SWP_DISCARDABLE;
2119    }
2120
2121    mutex_lock(&swapon_mutex);
2122    prio = -1;
2123    if (swap_flags & SWAP_FLAG_PREFER)
2124        prio =
2125          (swap_flags & SWAP_FLAG_PRIO_MASK) >> SWAP_FLAG_PRIO_SHIFT;
2126    enable_swap_info(p, prio, swap_map);
2127
2128    printk(KERN_INFO "Adding %uk swap on %s. "
2129            "Priority:%d extents:%d across:%lluk %s%s\n",
2130        p->pages<<(PAGE_SHIFT-10), name, p->prio,
2131        nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10),
2132        (p->flags & SWP_SOLIDSTATE) ? "SS" : "",
2133        (p->flags & SWP_DISCARDABLE) ? "D" : "");
2134
2135    mutex_unlock(&swapon_mutex);
2136    atomic_inc(&proc_poll_event);
2137    wake_up_interruptible(&proc_poll_wait);
2138
2139    if (S_ISREG(inode->i_mode))
2140        inode->i_flags |= S_SWAPFILE;
2141    error = 0;
2142    goto out;
2143bad_swap:
2144    if (inode && S_ISBLK(inode->i_mode) && p->bdev) {
2145        set_blocksize(p->bdev, p->old_block_size);
2146        blkdev_put(p->bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
2147    }
2148    destroy_swap_extents(p);
2149    swap_cgroup_swapoff(p->type);
2150    spin_lock(&swap_lock);
2151    p->swap_file = NULL;
2152    p->flags = 0;
2153    spin_unlock(&swap_lock);
2154    vfree(swap_map);
2155    if (swap_file) {
2156        if (inode && S_ISREG(inode->i_mode)) {
2157            mutex_unlock(&inode->i_mutex);
2158            inode = NULL;
2159        }
2160        filp_close(swap_file, NULL);
2161    }
2162out:
2163    if (page && !IS_ERR(page)) {
2164        kunmap(page);
2165        page_cache_release(page);
2166    }
2167    if (name)
2168        putname(name);
2169    if (inode && S_ISREG(inode->i_mode))
2170        mutex_unlock(&inode->i_mutex);
2171    return error;
2172}
2173
2174void si_swapinfo(struct sysinfo *val)
2175{
2176    unsigned int type;
2177    unsigned long nr_to_be_unused = 0;
2178
2179    spin_lock(&swap_lock);
2180    for (type = 0; type < nr_swapfiles; type++) {
2181        struct swap_info_struct *si = swap_info[type];
2182
2183        if ((si->flags & SWP_USED) && !(si->flags & SWP_WRITEOK))
2184            nr_to_be_unused += si->inuse_pages;
2185    }
2186    val->freeswap = nr_swap_pages + nr_to_be_unused;
2187    val->totalswap = total_swap_pages + nr_to_be_unused;
2188    spin_unlock(&swap_lock);
2189}
2190
2191/*
2192 * Verify that a swap entry is valid and increment its swap map count.
2193 *
2194 * Returns error code in following case.
2195 * - success -> 0
2196 * - swp_entry is invalid -> EINVAL
2197 * - swp_entry is migration entry -> EINVAL
2198 * - swap-cache reference is requested but there is already one. -> EEXIST
2199 * - swap-cache reference is requested but the entry is not used. -> ENOENT
2200 * - swap-mapped reference requested but needs continued swap count. -> ENOMEM
2201 */
2202static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
2203{
2204    struct swap_info_struct *p;
2205    unsigned long offset, type;
2206    unsigned char count;
2207    unsigned char has_cache;
2208    int err = -EINVAL;
2209
2210    if (non_swap_entry(entry))
2211        goto out;
2212
2213    type = swp_type(entry);
2214    if (type >= nr_swapfiles)
2215        goto bad_file;
2216    p = swap_info[type];
2217    offset = swp_offset(entry);
2218
2219    spin_lock(&swap_lock);
2220    if (unlikely(offset >= p->max))
2221        goto unlock_out;
2222
2223    count = p->swap_map[offset];
2224    has_cache = count & SWAP_HAS_CACHE;
2225    count &= ~SWAP_HAS_CACHE;
2226    err = 0;
2227
2228    if (usage == SWAP_HAS_CACHE) {
2229
2230        /* set SWAP_HAS_CACHE if there is no cache and entry is used */
2231        if (!has_cache && count)
2232            has_cache = SWAP_HAS_CACHE;
2233        else if (has_cache) /* someone else added cache */
2234            err = -EEXIST;
2235        else /* no users remaining */
2236            err = -ENOENT;
2237
2238    } else if (count || has_cache) {
2239
2240        if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
2241            count += usage;
2242        else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX)
2243            err = -EINVAL;
2244        else if (swap_count_continued(p, offset, count))
2245            count = COUNT_CONTINUED;
2246        else
2247            err = -ENOMEM;
2248    } else
2249        err = -ENOENT; /* unused swap entry */
2250
2251    p->swap_map[offset] = count | has_cache;
2252
2253unlock_out:
2254    spin_unlock(&swap_lock);
2255out:
2256    return err;
2257
2258bad_file:
2259    printk(KERN_ERR "swap_dup: %s%08lx\n", Bad_file, entry.val);
2260    goto out;
2261}
2262
2263/*
2264 * Help swapoff by noting that swap entry belongs to shmem/tmpfs
2265 * (in which case its reference count is never incremented).
2266 */
2267void swap_shmem_alloc(swp_entry_t entry)
2268{
2269    __swap_duplicate(entry, SWAP_MAP_SHMEM);
2270}
2271
2272/*
2273 * Increase reference count of swap entry by 1.
2274 * Returns 0 for success, or -ENOMEM if a swap_count_continuation is required
2275 * but could not be atomically allocated. Returns 0, just as if it succeeded,
2276 * if __swap_duplicate() fails for another reason (-EINVAL or -ENOENT), which
2277 * might occur if a page table entry has got corrupted.
2278 */
2279int swap_duplicate(swp_entry_t entry)
2280{
2281    int err = 0;
2282
2283    while (!err && __swap_duplicate(entry, 1) == -ENOMEM)
2284        err = add_swap_count_continuation(entry, GFP_ATOMIC);
2285    return err;
2286}
2287
2288/*
2289 * @entry: swap entry for which we allocate swap cache.
2290 *
2291 * Called when allocating swap cache for existing swap entry,
2292 * This can return error codes. Returns 0 at success.
2293 * -EBUSY means there is a swap cache.
2294 * Note: return code is different from swap_duplicate().
2295 */
2296int swapcache_prepare(swp_entry_t entry)
2297{
2298    return __swap_duplicate(entry, SWAP_HAS_CACHE);
2299}
2300
2301/*
2302 * swap_lock prevents swap_map being freed. Don't grab an extra
2303 * reference on the swaphandle, it doesn't matter if it becomes unused.
2304 */
2305int valid_swaphandles(swp_entry_t entry, unsigned long *offset)
2306{
2307    struct swap_info_struct *si;
2308    int our_page_cluster = page_cluster;
2309    pgoff_t target, toff;
2310    pgoff_t base, end;
2311    int nr_pages = 0;
2312
2313    if (!our_page_cluster) /* no readahead */
2314        return 0;
2315
2316    si = swap_info[swp_type(entry)];
2317    target = swp_offset(entry);
2318    base = (target >> our_page_cluster) << our_page_cluster;
2319    end = base + (1 << our_page_cluster);
2320    if (!base) /* first page is swap header */
2321        base++;
2322
2323    spin_lock(&swap_lock);
2324    if (end > si->max) /* don't go beyond end of map */
2325        end = si->max;
2326
2327    /* Count contiguous allocated slots above our target */
2328    for (toff = target; ++toff < end; nr_pages++) {
2329        /* Don't read in free or bad pages */
2330        if (!si->swap_map[toff])
2331            break;
2332        if (swap_count(si->swap_map[toff]) == SWAP_MAP_BAD)
2333            break;
2334    }
2335    /* Count contiguous allocated slots below our target */
2336    for (toff = target; --toff >= base; nr_pages++) {
2337        /* Don't read in free or bad pages */
2338        if (!si->swap_map[toff])
2339            break;
2340        if (swap_count(si->swap_map[toff]) == SWAP_MAP_BAD)
2341            break;
2342    }
2343    spin_unlock(&swap_lock);
2344
2345    /*
2346     * Indicate starting offset, and return number of pages to get:
2347     * if only 1, say 0, since there's then no readahead to be done.
2348     */
2349    *offset = ++toff;
2350    return nr_pages? ++nr_pages: 0;
2351}
2352
2353/*
2354 * add_swap_count_continuation - called when a swap count is duplicated
2355 * beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's
2356 * page of the original vmalloc'ed swap_map, to hold the continuation count
2357 * (for that entry and for its neighbouring PAGE_SIZE swap entries). Called
2358 * again when count is duplicated beyond SWAP_MAP_MAX * SWAP_CONT_MAX, etc.
2359 *
2360 * These continuation pages are seldom referenced: the common paths all work
2361 * on the original swap_map, only referring to a continuation page when the
2362 * low "digit" of a count is incremented or decremented through SWAP_MAP_MAX.
2363 *
2364 * add_swap_count_continuation(, GFP_ATOMIC) can be called while holding
2365 * page table locks; if it fails, add_swap_count_continuation(, GFP_KERNEL)
2366 * can be called after dropping locks.
2367 */
2368int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask)
2369{
2370    struct swap_info_struct *si;
2371    struct page *head;
2372    struct page *page;
2373    struct page *list_page;
2374    pgoff_t offset;
2375    unsigned char count;
2376
2377    /*
2378     * When debugging, it's easier to use __GFP_ZERO here; but it's better
2379     * for latency not to zero a page while GFP_ATOMIC and holding locks.
2380     */
2381    page = alloc_page(gfp_mask | __GFP_HIGHMEM);
2382
2383    si = swap_info_get(entry);
2384    if (!si) {
2385        /*
2386         * An acceptable race has occurred since the failing
2387         * __swap_duplicate(): the swap entry has been freed,
2388         * perhaps even the whole swap_map cleared for swapoff.
2389         */
2390        goto outer;
2391    }
2392
2393    offset = swp_offset(entry);
2394    count = si->swap_map[offset] & ~SWAP_HAS_CACHE;
2395
2396    if ((count & ~COUNT_CONTINUED) != SWAP_MAP_MAX) {
2397        /*
2398         * The higher the swap count, the more likely it is that tasks
2399         * will race to add swap count continuation: we need to avoid
2400         * over-provisioning.
2401         */
2402        goto out;
2403    }
2404
2405    if (!page) {
2406        spin_unlock(&swap_lock);
2407        return -ENOMEM;
2408    }
2409
2410    /*
2411     * We are fortunate that although vmalloc_to_page uses pte_offset_map,
2412     * no architecture is using highmem pages for kernel pagetables: so it
2413     * will not corrupt the GFP_ATOMIC caller's atomic pagetable kmaps.
2414     */
2415    head = vmalloc_to_page(si->swap_map + offset);
2416    offset &= ~PAGE_MASK;
2417
2418    /*
2419     * Page allocation does not initialize the page's lru field,
2420     * but it does always reset its private field.
2421     */
2422    if (!page_private(head)) {
2423        BUG_ON(count & COUNT_CONTINUED);
2424        INIT_LIST_HEAD(&head->lru);
2425        set_page_private(head, SWP_CONTINUED);
2426        si->flags |= SWP_CONTINUED;
2427    }
2428
2429    list_for_each_entry(list_page, &head->lru, lru) {
2430        unsigned char *map;
2431
2432        /*
2433         * If the previous map said no continuation, but we've found
2434         * a continuation page, free our allocation and use this one.
2435         */
2436        if (!(count & COUNT_CONTINUED))
2437            goto out;
2438
2439        map = kmap_atomic(list_page, KM_USER0) + offset;
2440        count = *map;
2441        kunmap_atomic(map, KM_USER0);
2442
2443        /*
2444         * If this continuation count now has some space in it,
2445         * free our allocation and use this one.
2446         */
2447        if ((count & ~COUNT_CONTINUED) != SWAP_CONT_MAX)
2448            goto out;
2449    }
2450
2451    list_add_tail(&page->lru, &head->lru);
2452    page = NULL; /* now it's attached, don't free it */
2453out:
2454    spin_unlock(&swap_lock);
2455outer:
2456    if (page)
2457        __free_page(page);
2458    return 0;
2459}
2460
2461/*
2462 * swap_count_continued - when the original swap_map count is incremented
2463 * from SWAP_MAP_MAX, check if there is already a continuation page to carry
2464 * into, carry if so, or else fail until a new continuation page is allocated;
2465 * when the original swap_map count is decremented from 0 with continuation,
2466 * borrow from the continuation and report whether it still holds more.
2467 * Called while __swap_duplicate() or swap_entry_free() holds swap_lock.
2468 */
2469static bool swap_count_continued(struct swap_info_struct *si,
2470                 pgoff_t offset, unsigned char count)
2471{
2472    struct page *head;
2473    struct page *page;
2474    unsigned char *map;
2475
2476    head = vmalloc_to_page(si->swap_map + offset);
2477    if (page_private(head) != SWP_CONTINUED) {
2478        BUG_ON(count & COUNT_CONTINUED);
2479        return false; /* need to add count continuation */
2480    }
2481
2482    offset &= ~PAGE_MASK;
2483    page = list_entry(head->lru.next, struct page, lru);
2484    map = kmap_atomic(page, KM_USER0) + offset;
2485
2486    if (count == SWAP_MAP_MAX) /* initial increment from swap_map */
2487        goto init_map; /* jump over SWAP_CONT_MAX checks */
2488
2489    if (count == (SWAP_MAP_MAX | COUNT_CONTINUED)) { /* incrementing */
2490        /*
2491         * Think of how you add 1 to 999
2492         */
2493        while (*map == (SWAP_CONT_MAX | COUNT_CONTINUED)) {
2494            kunmap_atomic(map, KM_USER0);
2495            page = list_entry(page->lru.next, struct page, lru);
2496            BUG_ON(page == head);
2497            map = kmap_atomic(page, KM_USER0) + offset;
2498        }
2499        if (*map == SWAP_CONT_MAX) {
2500            kunmap_atomic(map, KM_USER0);
2501            page = list_entry(page->lru.next, struct page, lru);
2502            if (page == head)
2503                return false; /* add count continuation */
2504            map = kmap_atomic(page, KM_USER0) + offset;
2505init_map: *map = 0; /* we didn't zero the page */
2506        }
2507        *map += 1;
2508        kunmap_atomic(map, KM_USER0);
2509        page = list_entry(page->lru.prev, struct page, lru);
2510        while (page != head) {
2511            map = kmap_atomic(page, KM_USER0) + offset;
2512            *map = COUNT_CONTINUED;
2513            kunmap_atomic(map, KM_USER0);
2514            page = list_entry(page->lru.prev, struct page, lru);
2515        }
2516        return true; /* incremented */
2517
2518    } else { /* decrementing */
2519        /*
2520         * Think of how you subtract 1 from 1000
2521         */
2522        BUG_ON(count != COUNT_CONTINUED);
2523        while (*map == COUNT_CONTINUED) {
2524            kunmap_atomic(map, KM_USER0);
2525            page = list_entry(page->lru.next, struct page, lru);
2526            BUG_ON(page == head);
2527            map = kmap_atomic(page, KM_USER0) + offset;
2528        }
2529        BUG_ON(*map == 0);
2530        *map -= 1;
2531        if (*map == 0)
2532            count = 0;
2533        kunmap_atomic(map, KM_USER0);
2534        page = list_entry(page->lru.prev, struct page, lru);
2535        while (page != head) {
2536            map = kmap_atomic(page, KM_USER0) + offset;
2537            *map = SWAP_CONT_MAX | count;
2538            count = COUNT_CONTINUED;
2539            kunmap_atomic(map, KM_USER0);
2540            page = list_entry(page->lru.prev, struct page, lru);
2541        }
2542        return count == COUNT_CONTINUED;
2543    }
2544}
2545
2546/*
2547 * free_swap_count_continuations - swapoff free all the continuation pages
2548 * appended to the swap_map, after swap_map is quiesced, before vfree'ing it.
2549 */
2550static void free_swap_count_continuations(struct swap_info_struct *si)
2551{
2552    pgoff_t offset;
2553
2554    for (offset = 0; offset < si->max; offset += PAGE_SIZE) {
2555        struct page *head;
2556        head = vmalloc_to_page(si->swap_map + offset);
2557        if (page_private(head)) {
2558            struct list_head *this, *next;
2559            list_for_each_safe(this, next, &head->lru) {
2560                struct page *page;
2561                page = list_entry(this, struct page, lru);
2562                list_del(this);
2563                __free_page(page);
2564            }
2565        }
2566    }
2567}
2568

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