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_PAGE_DISCARD) {
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_PAGE_DISCARD, 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
869static inline int maybe_same_pte(pte_t pte, pte_t swp_pte)
870{
871#ifdef CONFIG_MEM_SOFT_DIRTY
872    /*
873     * When pte keeps soft dirty bit the pte generated
874     * from swap entry does not has it, still it's same
875     * pte from logical point of view.
876     */
877    pte_t swp_pte_dirty = pte_swp_mksoft_dirty(swp_pte);
878    return pte_same(pte, swp_pte) || pte_same(pte, swp_pte_dirty);
879#else
880    return pte_same(pte, swp_pte);
881#endif
882}
883
884/*
885 * No need to decide whether this PTE shares the swap entry with others,
886 * just let do_wp_page work it out if a write is requested later - to
887 * force COW, vm_page_prot omits write permission from any private vma.
888 */
889static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
890        unsigned long addr, swp_entry_t entry, struct page *page)
891{
892    struct page *swapcache;
893    struct mem_cgroup *memcg;
894    spinlock_t *ptl;
895    pte_t *pte;
896    int ret = 1;
897
898    swapcache = page;
899    page = ksm_might_need_to_copy(page, vma, addr);
900    if (unlikely(!page))
901        return -ENOMEM;
902
903    if (mem_cgroup_try_charge_swapin(vma->vm_mm, page,
904                     GFP_KERNEL, &memcg)) {
905        ret = -ENOMEM;
906        goto out_nolock;
907    }
908
909    pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
910    if (unlikely(!maybe_same_pte(*pte, swp_entry_to_pte(entry)))) {
911        mem_cgroup_cancel_charge_swapin(memcg);
912        ret = 0;
913        goto out;
914    }
915
916    dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
917    inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
918    get_page(page);
919    set_pte_at(vma->vm_mm, addr, pte,
920           pte_mkold(mk_pte(page, vma->vm_page_prot)));
921    if (page == swapcache)
922        page_add_anon_rmap(page, vma, addr);
923    else /* ksm created a completely new copy */
924        page_add_new_anon_rmap(page, vma, addr);
925    mem_cgroup_commit_charge_swapin(page, memcg);
926    swap_free(entry);
927    /*
928     * Move the page to the active list so it is not
929     * immediately swapped out again after swapon.
930     */
931    activate_page(page);
932out:
933    pte_unmap_unlock(pte, ptl);
934out_nolock:
935    if (page != swapcache) {
936        unlock_page(page);
937        put_page(page);
938    }
939    return ret;
940}
941
942static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
943                unsigned long addr, unsigned long end,
944                swp_entry_t entry, struct page *page)
945{
946    pte_t swp_pte = swp_entry_to_pte(entry);
947    pte_t *pte;
948    int ret = 0;
949
950    /*
951     * We don't actually need pte lock while scanning for swp_pte: since
952     * we hold page lock and mmap_sem, swp_pte cannot be inserted into the
953     * page table while we're scanning; though it could get zapped, and on
954     * some architectures (e.g. x86_32 with PAE) we might catch a glimpse
955     * of unmatched parts which look like swp_pte, so unuse_pte must
956     * recheck under pte lock. Scanning without pte lock lets it be
957     * preemptible whenever CONFIG_PREEMPT but not CONFIG_HIGHPTE.
958     */
959    pte = pte_offset_map(pmd, addr);
960    do {
961        /*
962         * swapoff spends a _lot_ of time in this loop!
963         * Test inline before going to call unuse_pte.
964         */
965        if (unlikely(maybe_same_pte(*pte, swp_pte))) {
966            pte_unmap(pte);
967            ret = unuse_pte(vma, pmd, addr, entry, page);
968            if (ret)
969                goto out;
970            pte = pte_offset_map(pmd, addr);
971        }
972    } while (pte++, addr += PAGE_SIZE, addr != end);
973    pte_unmap(pte - 1);
974out:
975    return ret;
976}
977
978static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
979                unsigned long addr, unsigned long end,
980                swp_entry_t entry, struct page *page)
981{
982    pmd_t *pmd;
983    unsigned long next;
984    int ret;
985
986    pmd = pmd_offset(pud, addr);
987    do {
988        next = pmd_addr_end(addr, end);
989        if (pmd_none_or_trans_huge_or_clear_bad(pmd))
990            continue;
991        ret = unuse_pte_range(vma, pmd, addr, next, entry, page);
992        if (ret)
993            return ret;
994    } while (pmd++, addr = next, addr != end);
995    return 0;
996}
997
998static inline int unuse_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
999                unsigned long addr, unsigned long end,
1000                swp_entry_t entry, struct page *page)
1001{
1002    pud_t *pud;
1003    unsigned long next;
1004    int ret;
1005
1006    pud = pud_offset(pgd, addr);
1007    do {
1008        next = pud_addr_end(addr, end);
1009        if (pud_none_or_clear_bad(pud))
1010            continue;
1011        ret = unuse_pmd_range(vma, pud, addr, next, entry, page);
1012        if (ret)
1013            return ret;
1014    } while (pud++, addr = next, addr != end);
1015    return 0;
1016}
1017
1018static int unuse_vma(struct vm_area_struct *vma,
1019                swp_entry_t entry, struct page *page)
1020{
1021    pgd_t *pgd;
1022    unsigned long addr, end, next;
1023    int ret;
1024
1025    if (page_anon_vma(page)) {
1026        addr = page_address_in_vma(page, vma);
1027        if (addr == -EFAULT)
1028            return 0;
1029        else
1030            end = addr + PAGE_SIZE;
1031    } else {
1032        addr = vma->vm_start;
1033        end = vma->vm_end;
1034    }
1035
1036    pgd = pgd_offset(vma->vm_mm, addr);
1037    do {
1038        next = pgd_addr_end(addr, end);
1039        if (pgd_none_or_clear_bad(pgd))
1040            continue;
1041        ret = unuse_pud_range(vma, pgd, addr, next, entry, page);
1042        if (ret)
1043            return ret;
1044    } while (pgd++, addr = next, addr != end);
1045    return 0;
1046}
1047
1048static int unuse_mm(struct mm_struct *mm,
1049                swp_entry_t entry, struct page *page)
1050{
1051    struct vm_area_struct *vma;
1052    int ret = 0;
1053
1054    if (!down_read_trylock(&mm->mmap_sem)) {
1055        /*
1056         * Activate page so shrink_inactive_list is unlikely to unmap
1057         * its ptes while lock is dropped, so swapoff can make progress.
1058         */
1059        activate_page(page);
1060        unlock_page(page);
1061        down_read(&mm->mmap_sem);
1062        lock_page(page);
1063    }
1064    for (vma = mm->mmap; vma; vma = vma->vm_next) {
1065        if (vma->anon_vma && (ret = unuse_vma(vma, entry, page)))
1066            break;
1067    }
1068    up_read(&mm->mmap_sem);
1069    return (ret < 0)? ret: 0;
1070}
1071
1072/*
1073 * Scan swap_map (or frontswap_map if frontswap parameter is true)
1074 * from current position to next entry still in use.
1075 * Recycle to start on reaching the end, returning 0 when empty.
1076 */
1077static unsigned int find_next_to_unuse(struct swap_info_struct *si,
1078                    unsigned int prev, bool frontswap)
1079{
1080    unsigned int max = si->max;
1081    unsigned int i = prev;
1082    unsigned char count;
1083
1084    /*
1085     * No need for swap_lock here: we're just looking
1086     * for whether an entry is in use, not modifying it; false
1087     * hits are okay, and sys_swapoff() has already prevented new
1088     * allocations from this area (while holding swap_lock).
1089     */
1090    for (;;) {
1091        if (++i >= max) {
1092            if (!prev) {
1093                i = 0;
1094                break;
1095            }
1096            /*
1097             * No entries in use at top of swap_map,
1098             * loop back to start and recheck there.
1099             */
1100            max = prev + 1;
1101            prev = 0;
1102            i = 1;
1103        }
1104        if (frontswap) {
1105            if (frontswap_test(si, i))
1106                break;
1107            else
1108                continue;
1109        }
1110        count = si->swap_map[i];
1111        if (count && swap_count(count) != SWAP_MAP_BAD)
1112            break;
1113    }
1114    return i;
1115}
1116
1117/*
1118 * We completely avoid races by reading each swap page in advance,
1119 * and then search for the process using it. All the necessary
1120 * page table adjustments can then be made atomically.
1121 *
1122 * if the boolean frontswap is true, only unuse pages_to_unuse pages;
1123 * pages_to_unuse==0 means all pages; ignored if frontswap is false
1124 */
1125int try_to_unuse(unsigned int type, bool frontswap,
1126         unsigned long pages_to_unuse)
1127{
1128    struct swap_info_struct *si = swap_info[type];
1129    struct mm_struct *start_mm;
1130    unsigned char *swap_map;
1131    unsigned char swcount;
1132    struct page *page;
1133    swp_entry_t entry;
1134    unsigned int i = 0;
1135    int retval = 0;
1136
1137    /*
1138     * When searching mms for an entry, a good strategy is to
1139     * start at the first mm we freed the previous entry from
1140     * (though actually we don't notice whether we or coincidence
1141     * freed the entry). Initialize this start_mm with a hold.
1142     *
1143     * A simpler strategy would be to start at the last mm we
1144     * freed the previous entry from; but that would take less
1145     * advantage of mmlist ordering, which clusters forked mms
1146     * together, child after parent. If we race with dup_mmap(), we
1147     * prefer to resolve parent before child, lest we miss entries
1148     * duplicated after we scanned child: using last mm would invert
1149     * that.
1150     */
1151    start_mm = &init_mm;
1152    atomic_inc(&init_mm.mm_users);
1153
1154    /*
1155     * Keep on scanning until all entries have gone. Usually,
1156     * one pass through swap_map is enough, but not necessarily:
1157     * there are races when an instance of an entry might be missed.
1158     */
1159    while ((i = find_next_to_unuse(si, i, frontswap)) != 0) {
1160        if (signal_pending(current)) {
1161            retval = -EINTR;
1162            break;
1163        }
1164
1165        /*
1166         * Get a page for the entry, using the existing swap
1167         * cache page if there is one. Otherwise, get a clean
1168         * page and read the swap into it.
1169         */
1170        swap_map = &si->swap_map[i];
1171        entry = swp_entry(type, i);
1172        page = read_swap_cache_async(entry,
1173                    GFP_HIGHUSER_MOVABLE, NULL, 0);
1174        if (!page) {
1175            /*
1176             * Either swap_duplicate() failed because entry
1177             * has been freed independently, and will not be
1178             * reused since sys_swapoff() already disabled
1179             * allocation from here, or alloc_page() failed.
1180             */
1181            if (!*swap_map)
1182                continue;
1183            retval = -ENOMEM;
1184            break;
1185        }
1186
1187        /*
1188         * Don't hold on to start_mm if it looks like exiting.
1189         */
1190        if (atomic_read(&start_mm->mm_users) == 1) {
1191            mmput(start_mm);
1192            start_mm = &init_mm;
1193            atomic_inc(&init_mm.mm_users);
1194        }
1195
1196        /*
1197         * Wait for and lock page. When do_swap_page races with
1198         * try_to_unuse, do_swap_page can handle the fault much
1199         * faster than try_to_unuse can locate the entry. This
1200         * apparently redundant "wait_on_page_locked" lets try_to_unuse
1201         * defer to do_swap_page in such a case - in some tests,
1202         * do_swap_page and try_to_unuse repeatedly compete.
1203         */
1204        wait_on_page_locked(page);
1205        wait_on_page_writeback(page);
1206        lock_page(page);
1207        wait_on_page_writeback(page);
1208
1209        /*
1210         * Remove all references to entry.
1211         */
1212        swcount = *swap_map;
1213        if (swap_count(swcount) == SWAP_MAP_SHMEM) {
1214            retval = shmem_unuse(entry, page);
1215            /* page has already been unlocked and released */
1216            if (retval < 0)
1217                break;
1218            continue;
1219        }
1220        if (swap_count(swcount) && start_mm != &init_mm)
1221            retval = unuse_mm(start_mm, entry, page);
1222
1223        if (swap_count(*swap_map)) {
1224            int set_start_mm = (*swap_map >= swcount);
1225            struct list_head *p = &start_mm->mmlist;
1226            struct mm_struct *new_start_mm = start_mm;
1227            struct mm_struct *prev_mm = start_mm;
1228            struct mm_struct *mm;
1229
1230            atomic_inc(&new_start_mm->mm_users);
1231            atomic_inc(&prev_mm->mm_users);
1232            spin_lock(&mmlist_lock);
1233            while (swap_count(*swap_map) && !retval &&
1234                    (p = p->next) != &start_mm->mmlist) {
1235                mm = list_entry(p, struct mm_struct, mmlist);
1236                if (!atomic_inc_not_zero(&mm->mm_users))
1237                    continue;
1238                spin_unlock(&mmlist_lock);
1239                mmput(prev_mm);
1240                prev_mm = mm;
1241
1242                cond_resched();
1243
1244                swcount = *swap_map;
1245                if (!swap_count(swcount)) /* any usage ? */
1246                    ;
1247                else if (mm == &init_mm)
1248                    set_start_mm = 1;
1249                else
1250                    retval = unuse_mm(mm, entry, page);
1251
1252                if (set_start_mm && *swap_map < swcount) {
1253                    mmput(new_start_mm);
1254                    atomic_inc(&mm->mm_users);
1255                    new_start_mm = mm;
1256                    set_start_mm = 0;
1257                }
1258                spin_lock(&mmlist_lock);
1259            }
1260            spin_unlock(&mmlist_lock);
1261            mmput(prev_mm);
1262            mmput(start_mm);
1263            start_mm = new_start_mm;
1264        }
1265        if (retval) {
1266            unlock_page(page);
1267            page_cache_release(page);
1268            break;
1269        }
1270
1271        /*
1272         * If a reference remains (rare), we would like to leave
1273         * the page in the swap cache; but try_to_unmap could
1274         * then re-duplicate the entry once we drop page lock,
1275         * so we might loop indefinitely; also, that page could
1276         * not be swapped out to other storage meanwhile. So:
1277         * delete from cache even if there's another reference,
1278         * after ensuring that the data has been saved to disk -
1279         * since if the reference remains (rarer), it will be
1280         * read from disk into another page. Splitting into two
1281         * pages would be incorrect if swap supported "shared
1282         * private" pages, but they are handled by tmpfs files.
1283         *
1284         * Given how unuse_vma() targets one particular offset
1285         * in an anon_vma, once the anon_vma has been determined,
1286         * this splitting happens to be just what is needed to
1287         * handle where KSM pages have been swapped out: re-reading
1288         * is unnecessarily slow, but we can fix that later on.
1289         */
1290        if (swap_count(*swap_map) &&
1291             PageDirty(page) && PageSwapCache(page)) {
1292            struct writeback_control wbc = {
1293                .sync_mode = WB_SYNC_NONE,
1294            };
1295
1296            swap_writepage(page, &wbc);
1297            lock_page(page);
1298            wait_on_page_writeback(page);
1299        }
1300
1301        /*
1302         * It is conceivable that a racing task removed this page from
1303         * swap cache just before we acquired the page lock at the top,
1304         * or while we dropped it in unuse_mm(). The page might even
1305         * be back in swap cache on another swap area: that we must not
1306         * delete, since it may not have been written out to swap yet.
1307         */
1308        if (PageSwapCache(page) &&
1309            likely(page_private(page) == entry.val))
1310            delete_from_swap_cache(page);
1311
1312        /*
1313         * So we could skip searching mms once swap count went
1314         * to 1, we did not mark any present ptes as dirty: must
1315         * mark page dirty so shrink_page_list will preserve it.
1316         */
1317        SetPageDirty(page);
1318        unlock_page(page);
1319        page_cache_release(page);
1320
1321        /*
1322         * Make sure that we aren't completely killing
1323         * interactive performance.
1324         */
1325        cond_resched();
1326        if (frontswap && pages_to_unuse > 0) {
1327            if (!--pages_to_unuse)
1328                break;
1329        }
1330    }
1331
1332    mmput(start_mm);
1333    return retval;
1334}
1335
1336/*
1337 * After a successful try_to_unuse, if no swap is now in use, we know
1338 * we can empty the mmlist. swap_lock must be held on entry and exit.
1339 * Note that mmlist_lock nests inside swap_lock, and an mm must be
1340 * added to the mmlist just after page_duplicate - before would be racy.
1341 */
1342static void drain_mmlist(void)
1343{
1344    struct list_head *p, *next;
1345    unsigned int type;
1346
1347    for (type = 0; type < nr_swapfiles; type++)
1348        if (swap_info[type]->inuse_pages)
1349            return;
1350    spin_lock(&mmlist_lock);
1351    list_for_each_safe(p, next, &init_mm.mmlist)
1352        list_del_init(p);
1353    spin_unlock(&mmlist_lock);
1354}
1355
1356/*
1357 * Use this swapdev's extent info to locate the (PAGE_SIZE) block which
1358 * corresponds to page offset for the specified swap entry.
1359 * Note that the type of this function is sector_t, but it returns page offset
1360 * into the bdev, not sector offset.
1361 */
1362static sector_t map_swap_entry(swp_entry_t entry, struct block_device **bdev)
1363{
1364    struct swap_info_struct *sis;
1365    struct swap_extent *start_se;
1366    struct swap_extent *se;
1367    pgoff_t offset;
1368
1369    sis = swap_info[swp_type(entry)];
1370    *bdev = sis->bdev;
1371
1372    offset = swp_offset(entry);
1373    start_se = sis->curr_swap_extent;
1374    se = start_se;
1375
1376    for ( ; ; ) {
1377        struct list_head *lh;
1378
1379        if (se->start_page <= offset &&
1380                offset < (se->start_page + se->nr_pages)) {
1381            return se->start_block + (offset - se->start_page);
1382        }
1383        lh = se->list.next;
1384        se = list_entry(lh, struct swap_extent, list);
1385        sis->curr_swap_extent = se;
1386        BUG_ON(se == start_se); /* It *must* be present */
1387    }
1388}
1389
1390/*
1391 * Returns the page offset into bdev for the specified page's swap entry.
1392 */
1393sector_t map_swap_page(struct page *page, struct block_device **bdev)
1394{
1395    swp_entry_t entry;
1396    entry.val = page_private(page);
1397    return map_swap_entry(entry, bdev);
1398}
1399
1400/*
1401 * Free all of a swapdev's extent information
1402 */
1403static void destroy_swap_extents(struct swap_info_struct *sis)
1404{
1405    while (!list_empty(&sis->first_swap_extent.list)) {
1406        struct swap_extent *se;
1407
1408        se = list_entry(sis->first_swap_extent.list.next,
1409                struct swap_extent, list);
1410        list_del(&se->list);
1411        kfree(se);
1412    }
1413
1414    if (sis->flags & SWP_FILE) {
1415        struct file *swap_file = sis->swap_file;
1416        struct address_space *mapping = swap_file->f_mapping;
1417
1418        sis->flags &= ~SWP_FILE;
1419        mapping->a_ops->swap_deactivate(swap_file);
1420    }
1421}
1422
1423/*
1424 * Add a block range (and the corresponding page range) into this swapdev's
1425 * extent list. The extent list is kept sorted in page order.
1426 *
1427 * This function rather assumes that it is called in ascending page order.
1428 */
1429int
1430add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
1431        unsigned long nr_pages, sector_t start_block)
1432{
1433    struct swap_extent *se;
1434    struct swap_extent *new_se;
1435    struct list_head *lh;
1436
1437    if (start_page == 0) {
1438        se = &sis->first_swap_extent;
1439        sis->curr_swap_extent = se;
1440        se->start_page = 0;
1441        se->nr_pages = nr_pages;
1442        se->start_block = start_block;
1443        return 1;
1444    } else {
1445        lh = sis->first_swap_extent.list.prev; /* Highest extent */
1446        se = list_entry(lh, struct swap_extent, list);
1447        BUG_ON(se->start_page + se->nr_pages != start_page);
1448        if (se->start_block + se->nr_pages == start_block) {
1449            /* Merge it */
1450            se->nr_pages += nr_pages;
1451            return 0;
1452        }
1453    }
1454
1455    /*
1456     * No merge. Insert a new extent, preserving ordering.
1457     */
1458    new_se = kmalloc(sizeof(*se), GFP_KERNEL);
1459    if (new_se == NULL)
1460        return -ENOMEM;
1461    new_se->start_page = start_page;
1462    new_se->nr_pages = nr_pages;
1463    new_se->start_block = start_block;
1464
1465    list_add_tail(&new_se->list, &sis->first_swap_extent.list);
1466    return 1;
1467}
1468
1469/*
1470 * A `swap extent' is a simple thing which maps a contiguous range of pages
1471 * onto a contiguous range of disk blocks. An ordered list of swap extents
1472 * is built at swapon time and is then used at swap_writepage/swap_readpage
1473 * time for locating where on disk a page belongs.
1474 *
1475 * If the swapfile is an S_ISBLK block device, a single extent is installed.
1476 * This is done so that the main operating code can treat S_ISBLK and S_ISREG
1477 * swap files identically.
1478 *
1479 * Whether the swapdev is an S_ISREG file or an S_ISBLK blockdev, the swap
1480 * extent list operates in PAGE_SIZE disk blocks. Both S_ISREG and S_ISBLK
1481 * swapfiles are handled *identically* after swapon time.
1482 *
1483 * For S_ISREG swapfiles, setup_swap_extents() will walk all the file's blocks
1484 * and will parse them into an ordered extent list, in PAGE_SIZE chunks. If
1485 * some stray blocks are found which do not fall within the PAGE_SIZE alignment
1486 * requirements, they are simply tossed out - we will never use those blocks
1487 * for swapping.
1488 *
1489 * For S_ISREG swapfiles we set S_SWAPFILE across the life of the swapon. This
1490 * prevents root from shooting her foot off by ftruncating an in-use swapfile,
1491 * which will scribble on the fs.
1492 *
1493 * The amount of disk space which a single swap extent represents varies.
1494 * Typically it is in the 1-4 megabyte range. So we can have hundreds of
1495 * extents in the list. To avoid much list walking, we cache the previous
1496 * search location in `curr_swap_extent', and start new searches from there.
1497 * This is extremely effective. The average number of iterations in
1498 * map_swap_page() has been measured at about 0.3 per page. - akpm.
1499 */
1500static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
1501{
1502    struct file *swap_file = sis->swap_file;
1503    struct address_space *mapping = swap_file->f_mapping;
1504    struct inode *inode = mapping->host;
1505    int ret;
1506
1507    if (S_ISBLK(inode->i_mode)) {
1508        ret = add_swap_extent(sis, 0, sis->max, 0);
1509        *span = sis->pages;
1510        return ret;
1511    }
1512
1513    if (mapping->a_ops->swap_activate) {
1514        ret = mapping->a_ops->swap_activate(sis, swap_file, span);
1515        if (!ret) {
1516            sis->flags |= SWP_FILE;
1517            ret = add_swap_extent(sis, 0, sis->max, 0);
1518            *span = sis->pages;
1519        }
1520        return ret;
1521    }
1522
1523    return generic_swapfile_activate(sis, swap_file, span);
1524}
1525
1526static void _enable_swap_info(struct swap_info_struct *p, int prio,
1527                unsigned char *swap_map)
1528{
1529    int i, prev;
1530
1531    if (prio >= 0)
1532        p->prio = prio;
1533    else
1534        p->prio = --least_priority;
1535    p->swap_map = swap_map;
1536    p->flags |= SWP_WRITEOK;
1537    atomic_long_add(p->pages, &nr_swap_pages);
1538    total_swap_pages += p->pages;
1539
1540    /* insert swap space into swap_list: */
1541    prev = -1;
1542    for (i = swap_list.head; i >= 0; i = swap_info[i]->next) {
1543        if (p->prio >= swap_info[i]->prio)
1544            break;
1545        prev = i;
1546    }
1547    p->next = i;
1548    if (prev < 0)
1549        swap_list.head = swap_list.next = p->type;
1550    else
1551        swap_info[prev]->next = p->type;
1552}
1553
1554static void enable_swap_info(struct swap_info_struct *p, int prio,
1555                unsigned char *swap_map,
1556                unsigned long *frontswap_map)
1557{
1558    frontswap_init(p->type, frontswap_map);
1559    spin_lock(&swap_lock);
1560    spin_lock(&p->lock);
1561     _enable_swap_info(p, prio, swap_map);
1562    spin_unlock(&p->lock);
1563    spin_unlock(&swap_lock);
1564}
1565
1566static void reinsert_swap_info(struct swap_info_struct *p)
1567{
1568    spin_lock(&swap_lock);
1569    spin_lock(&p->lock);
1570    _enable_swap_info(p, p->prio, p->swap_map);
1571    spin_unlock(&p->lock);
1572    spin_unlock(&swap_lock);
1573}
1574
1575SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
1576{
1577    struct swap_info_struct *p = NULL;
1578    unsigned char *swap_map;
1579    unsigned long *frontswap_map;
1580    struct file *swap_file, *victim;
1581    struct address_space *mapping;
1582    struct inode *inode;
1583    struct filename *pathname;
1584    int i, type, prev;
1585    int err;
1586
1587    if (!capable(CAP_SYS_ADMIN))
1588        return -EPERM;
1589
1590    BUG_ON(!current->mm);
1591
1592    pathname = getname(specialfile);
1593    if (IS_ERR(pathname))
1594        return PTR_ERR(pathname);
1595
1596    victim = file_open_name(pathname, O_RDWR|O_LARGEFILE, 0);
1597    err = PTR_ERR(victim);
1598    if (IS_ERR(victim))
1599        goto out;
1600
1601    mapping = victim->f_mapping;
1602    prev = -1;
1603    spin_lock(&swap_lock);
1604    for (type = swap_list.head; type >= 0; type = swap_info[type]->next) {
1605        p = swap_info[type];
1606        if (p->flags & SWP_WRITEOK) {
1607            if (p->swap_file->f_mapping == mapping)
1608                break;
1609        }
1610        prev = type;
1611    }
1612    if (type < 0) {
1613        err = -EINVAL;
1614        spin_unlock(&swap_lock);
1615        goto out_dput;
1616    }
1617    if (!security_vm_enough_memory_mm(current->mm, p->pages))
1618        vm_unacct_memory(p->pages);
1619    else {
1620        err = -ENOMEM;
1621        spin_unlock(&swap_lock);
1622        goto out_dput;
1623    }
1624    if (prev < 0)
1625        swap_list.head = p->next;
1626    else
1627        swap_info[prev]->next = p->next;
1628    if (type == swap_list.next) {
1629        /* just pick something that's safe... */
1630        swap_list.next = swap_list.head;
1631    }
1632    spin_lock(&p->lock);
1633    if (p->prio < 0) {
1634        for (i = p->next; i >= 0; i = swap_info[i]->next)
1635            swap_info[i]->prio = p->prio--;
1636        least_priority++;
1637    }
1638    atomic_long_sub(p->pages, &nr_swap_pages);
1639    total_swap_pages -= p->pages;
1640    p->flags &= ~SWP_WRITEOK;
1641    spin_unlock(&p->lock);
1642    spin_unlock(&swap_lock);
1643
1644    set_current_oom_origin();
1645    err = try_to_unuse(type, false, 0); /* force all pages to be unused */
1646    clear_current_oom_origin();
1647
1648    if (err) {
1649        /* re-insert swap space back into swap_list */
1650        reinsert_swap_info(p);
1651        goto out_dput;
1652    }
1653
1654    destroy_swap_extents(p);
1655    if (p->flags & SWP_CONTINUED)
1656        free_swap_count_continuations(p);
1657
1658    mutex_lock(&swapon_mutex);
1659    spin_lock(&swap_lock);
1660    spin_lock(&p->lock);
1661    drain_mmlist();
1662
1663    /* wait for anyone still in scan_swap_map */
1664    p->highest_bit = 0; /* cuts scans short */
1665    while (p->flags >= SWP_SCANNING) {
1666        spin_unlock(&p->lock);
1667        spin_unlock(&swap_lock);
1668        schedule_timeout_uninterruptible(1);
1669        spin_lock(&swap_lock);
1670        spin_lock(&p->lock);
1671    }
1672
1673    swap_file = p->swap_file;
1674    p->swap_file = NULL;
1675    p->max = 0;
1676    swap_map = p->swap_map;
1677    p->swap_map = NULL;
1678    p->flags = 0;
1679    frontswap_map = frontswap_map_get(p);
1680    frontswap_map_set(p, NULL);
1681    spin_unlock(&p->lock);
1682    spin_unlock(&swap_lock);
1683    frontswap_invalidate_area(type);
1684    mutex_unlock(&swapon_mutex);
1685    vfree(swap_map);
1686    vfree(frontswap_map);
1687    /* Destroy swap account informatin */
1688    swap_cgroup_swapoff(type);
1689
1690    inode = mapping->host;
1691    if (S_ISBLK(inode->i_mode)) {
1692        struct block_device *bdev = I_BDEV(inode);
1693        set_blocksize(bdev, p->old_block_size);
1694        blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
1695    } else {
1696        mutex_lock(&inode->i_mutex);
1697        inode->i_flags &= ~S_SWAPFILE;
1698        mutex_unlock(&inode->i_mutex);
1699    }
1700    filp_close(swap_file, NULL);
1701    err = 0;
1702    atomic_inc(&proc_poll_event);
1703    wake_up_interruptible(&proc_poll_wait);
1704
1705out_dput:
1706    filp_close(victim, NULL);
1707out:
1708    putname(pathname);
1709    return err;
1710}
1711
1712#ifdef CONFIG_PROC_FS
1713static unsigned swaps_poll(struct file *file, poll_table *wait)
1714{
1715    struct seq_file *seq = file->private_data;
1716
1717    poll_wait(file, &proc_poll_wait, wait);
1718
1719    if (seq->poll_event != atomic_read(&proc_poll_event)) {
1720        seq->poll_event = atomic_read(&proc_poll_event);
1721        return POLLIN | POLLRDNORM | POLLERR | POLLPRI;
1722    }
1723
1724    return POLLIN | POLLRDNORM;
1725}
1726
1727/* iterator */
1728static void *swap_start(struct seq_file *swap, loff_t *pos)
1729{
1730    struct swap_info_struct *si;
1731    int type;
1732    loff_t l = *pos;
1733
1734    mutex_lock(&swapon_mutex);
1735
1736    if (!l)
1737        return SEQ_START_TOKEN;
1738
1739    for (type = 0; type < nr_swapfiles; type++) {
1740        smp_rmb(); /* read nr_swapfiles before swap_info[type] */
1741        si = swap_info[type];
1742        if (!(si->flags & SWP_USED) || !si->swap_map)
1743            continue;
1744        if (!--l)
1745            return si;
1746    }
1747
1748    return NULL;
1749}
1750
1751static void *swap_next(struct seq_file *swap, void *v, loff_t *pos)
1752{
1753    struct swap_info_struct *si = v;
1754    int type;
1755
1756    if (v == SEQ_START_TOKEN)
1757        type = 0;
1758    else
1759        type = si->type + 1;
1760
1761    for (; type < nr_swapfiles; type++) {
1762        smp_rmb(); /* read nr_swapfiles before swap_info[type] */
1763        si = swap_info[type];
1764        if (!(si->flags & SWP_USED) || !si->swap_map)
1765            continue;
1766        ++*pos;
1767        return si;
1768    }
1769
1770    return NULL;
1771}
1772
1773static void swap_stop(struct seq_file *swap, void *v)
1774{
1775    mutex_unlock(&swapon_mutex);
1776}
1777
1778static int swap_show(struct seq_file *swap, void *v)
1779{
1780    struct swap_info_struct *si = v;
1781    struct file *file;
1782    int len;
1783
1784    if (si == SEQ_START_TOKEN) {
1785        seq_puts(swap,"Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n");
1786        return 0;
1787    }
1788
1789    file = si->swap_file;
1790    len = seq_path(swap, &file->f_path, " \t\n\\");
1791    seq_printf(swap, "%*s%s\t%u\t%u\t%d\n",
1792            len < 40 ? 40 - len : 1, " ",
1793            S_ISBLK(file_inode(file)->i_mode) ?
1794                "partition" : "file\t",
1795            si->pages << (PAGE_SHIFT - 10),
1796            si->inuse_pages << (PAGE_SHIFT - 10),
1797            si->prio);
1798    return 0;
1799}
1800
1801static const struct seq_operations swaps_op = {
1802    .start = swap_start,
1803    .next = swap_next,
1804    .stop = swap_stop,
1805    .show = swap_show
1806};
1807
1808static int swaps_open(struct inode *inode, struct file *file)
1809{
1810    struct seq_file *seq;
1811    int ret;
1812
1813    ret = seq_open(file, &swaps_op);
1814    if (ret)
1815        return ret;
1816
1817    seq = file->private_data;
1818    seq->poll_event = atomic_read(&proc_poll_event);
1819    return 0;
1820}
1821
1822static const struct file_operations proc_swaps_operations = {
1823    .open = swaps_open,
1824    .read = seq_read,
1825    .llseek = seq_lseek,
1826    .release = seq_release,
1827    .poll = swaps_poll,
1828};
1829
1830static int __init procswaps_init(void)
1831{
1832    proc_create("swaps", 0, NULL, &proc_swaps_operations);
1833    return 0;
1834}
1835__initcall(procswaps_init);
1836#endif /* CONFIG_PROC_FS */
1837
1838#ifdef MAX_SWAPFILES_CHECK
1839static int __init max_swapfiles_check(void)
1840{
1841    MAX_SWAPFILES_CHECK();
1842    return 0;
1843}
1844late_initcall(max_swapfiles_check);
1845#endif
1846
1847static struct swap_info_struct *alloc_swap_info(void)
1848{
1849    struct swap_info_struct *p;
1850    unsigned int type;
1851
1852    p = kzalloc(sizeof(*p), GFP_KERNEL);
1853    if (!p)
1854        return ERR_PTR(-ENOMEM);
1855
1856    spin_lock(&swap_lock);
1857    for (type = 0; type < nr_swapfiles; type++) {
1858        if (!(swap_info[type]->flags & SWP_USED))
1859            break;
1860    }
1861    if (type >= MAX_SWAPFILES) {
1862        spin_unlock(&swap_lock);
1863        kfree(p);
1864        return ERR_PTR(-EPERM);
1865    }
1866    if (type >= nr_swapfiles) {
1867        p->type = type;
1868        swap_info[type] = p;
1869        /*
1870         * Write swap_info[type] before nr_swapfiles, in case a
1871         * racing procfs swap_start() or swap_next() is reading them.
1872         * (We never shrink nr_swapfiles, we never free this entry.)
1873         */
1874        smp_wmb();
1875        nr_swapfiles++;
1876    } else {
1877        kfree(p);
1878        p = swap_info[type];
1879        /*
1880         * Do not memset this entry: a racing procfs swap_next()
1881         * would be relying on p->type to remain valid.
1882         */
1883    }
1884    INIT_LIST_HEAD(&p->first_swap_extent.list);
1885    p->flags = SWP_USED;
1886    p->next = -1;
1887    spin_unlock(&swap_lock);
1888    spin_lock_init(&p->lock);
1889
1890    return p;
1891}
1892
1893static int claim_swapfile(struct swap_info_struct *p, struct inode *inode)
1894{
1895    int error;
1896
1897    if (S_ISBLK(inode->i_mode)) {
1898        p->bdev = bdgrab(I_BDEV(inode));
1899        error = blkdev_get(p->bdev,
1900                   FMODE_READ | FMODE_WRITE | FMODE_EXCL,
1901                   sys_swapon);
1902        if (error < 0) {
1903            p->bdev = NULL;
1904            return -EINVAL;
1905        }
1906        p->old_block_size = block_size(p->bdev);
1907        error = set_blocksize(p->bdev, PAGE_SIZE);
1908        if (error < 0)
1909            return error;
1910        p->flags |= SWP_BLKDEV;
1911    } else if (S_ISREG(inode->i_mode)) {
1912        p->bdev = inode->i_sb->s_bdev;
1913        mutex_lock(&inode->i_mutex);
1914        if (IS_SWAPFILE(inode))
1915            return -EBUSY;
1916    } else
1917        return -EINVAL;
1918
1919    return 0;
1920}
1921
1922static unsigned long read_swap_header(struct swap_info_struct *p,
1923                    union swap_header *swap_header,
1924                    struct inode *inode)
1925{
1926    int i;
1927    unsigned long maxpages;
1928    unsigned long swapfilepages;
1929
1930    if (memcmp("SWAPSPACE2", swap_header->magic.magic, 10)) {
1931        printk(KERN_ERR "Unable to find swap-space signature\n");
1932        return 0;
1933    }
1934
1935    /* swap partition endianess hack... */
1936    if (swab32(swap_header->info.version) == 1) {
1937        swab32s(&swap_header->info.version);
1938        swab32s(&swap_header->info.last_page);
1939        swab32s(&swap_header->info.nr_badpages);
1940        for (i = 0; i < swap_header->info.nr_badpages; i++)
1941            swab32s(&swap_header->info.badpages[i]);
1942    }
1943    /* Check the swap header's sub-version */
1944    if (swap_header->info.version != 1) {
1945        printk(KERN_WARNING
1946               "Unable to handle swap header version %d\n",
1947               swap_header->info.version);
1948        return 0;
1949    }
1950
1951    p->lowest_bit = 1;
1952    p->cluster_next = 1;
1953    p->cluster_nr = 0;
1954
1955    /*
1956     * Find out how many pages are allowed for a single swap
1957     * device. There are two limiting factors: 1) the number
1958     * of bits for the swap offset in the swp_entry_t type, and
1959     * 2) the number of bits in the swap pte as defined by the
1960     * different architectures. In order to find the
1961     * largest possible bit mask, a swap entry with swap type 0
1962     * and swap offset ~0UL is created, encoded to a swap pte,
1963     * decoded to a swp_entry_t again, and finally the swap
1964     * offset is extracted. This will mask all the bits from
1965     * the initial ~0UL mask that can't be encoded in either
1966     * the swp_entry_t or the architecture definition of a
1967     * swap pte.
1968     */
1969    maxpages = swp_offset(pte_to_swp_entry(
1970            swp_entry_to_pte(swp_entry(0, ~0UL)))) + 1;
1971    if (maxpages > swap_header->info.last_page) {
1972        maxpages = swap_header->info.last_page + 1;
1973        /* p->max is an unsigned int: don't overflow it */
1974        if ((unsigned int)maxpages == 0)
1975            maxpages = UINT_MAX;
1976    }
1977    p->highest_bit = maxpages - 1;
1978
1979    if (!maxpages)
1980        return 0;
1981    swapfilepages = i_size_read(inode) >> PAGE_SHIFT;
1982    if (swapfilepages && maxpages > swapfilepages) {
1983        printk(KERN_WARNING
1984               "Swap area shorter than signature indicates\n");
1985        return 0;
1986    }
1987    if (swap_header->info.nr_badpages && S_ISREG(inode->i_mode))
1988        return 0;
1989    if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
1990        return 0;
1991
1992    return maxpages;
1993}
1994
1995static int setup_swap_map_and_extents(struct swap_info_struct *p,
1996                    union swap_header *swap_header,
1997                    unsigned char *swap_map,
1998                    unsigned long maxpages,
1999                    sector_t *span)
2000{
2001    int i;
2002    unsigned int nr_good_pages;
2003    int nr_extents;
2004
2005    nr_good_pages = maxpages - 1; /* omit header page */
2006
2007    for (i = 0; i < swap_header->info.nr_badpages; i++) {
2008        unsigned int page_nr = swap_header->info.badpages[i];
2009        if (page_nr == 0 || page_nr > swap_header->info.last_page)
2010            return -EINVAL;
2011        if (page_nr < maxpages) {
2012            swap_map[page_nr] = SWAP_MAP_BAD;
2013            nr_good_pages--;
2014        }
2015    }
2016
2017    if (nr_good_pages) {
2018        swap_map[0] = SWAP_MAP_BAD;
2019        p->max = maxpages;
2020        p->pages = nr_good_pages;
2021        nr_extents = setup_swap_extents(p, span);
2022        if (nr_extents < 0)
2023            return nr_extents;
2024        nr_good_pages = p->pages;
2025    }
2026    if (!nr_good_pages) {
2027        printk(KERN_WARNING "Empty swap-file\n");
2028        return -EINVAL;
2029    }
2030
2031    return nr_extents;
2032}
2033
2034/*
2035 * Helper to sys_swapon determining if a given swap
2036 * backing device queue supports DISCARD operations.
2037 */
2038static bool swap_discardable(struct swap_info_struct *si)
2039{
2040    struct request_queue *q = bdev_get_queue(si->bdev);
2041
2042    if (!q || !blk_queue_discard(q))
2043        return false;
2044
2045    return true;
2046}
2047
2048SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
2049{
2050    struct swap_info_struct *p;
2051    struct filename *name;
2052    struct file *swap_file = NULL;
2053    struct address_space *mapping;
2054    int i;
2055    int prio;
2056    int error;
2057    union swap_header *swap_header;
2058    int nr_extents;
2059    sector_t span;
2060    unsigned long maxpages;
2061    unsigned char *swap_map = NULL;
2062    unsigned long *frontswap_map = NULL;
2063    struct page *page = NULL;
2064    struct inode *inode = NULL;
2065
2066    if (swap_flags & ~SWAP_FLAGS_VALID)
2067        return -EINVAL;
2068
2069    if (!capable(CAP_SYS_ADMIN))
2070        return -EPERM;
2071
2072    p = alloc_swap_info();
2073    if (IS_ERR(p))
2074        return PTR_ERR(p);
2075
2076    name = getname(specialfile);
2077    if (IS_ERR(name)) {
2078        error = PTR_ERR(name);
2079        name = NULL;
2080        goto bad_swap;
2081    }
2082    swap_file = file_open_name(name, O_RDWR|O_LARGEFILE, 0);
2083    if (IS_ERR(swap_file)) {
2084        error = PTR_ERR(swap_file);
2085        swap_file = NULL;
2086        goto bad_swap;
2087    }
2088
2089    p->swap_file = swap_file;
2090    mapping = swap_file->f_mapping;
2091
2092    for (i = 0; i < nr_swapfiles; i++) {
2093        struct swap_info_struct *q = swap_info[i];
2094
2095        if (q == p || !q->swap_file)
2096            continue;
2097        if (mapping == q->swap_file->f_mapping) {
2098            error = -EBUSY;
2099            goto bad_swap;
2100        }
2101    }
2102
2103    inode = mapping->host;
2104    /* If S_ISREG(inode->i_mode) will do mutex_lock(&inode->i_mutex); */
2105    error = claim_swapfile(p, inode);
2106    if (unlikely(error))
2107        goto bad_swap;
2108
2109    /*
2110     * Read the swap header.
2111     */
2112    if (!mapping->a_ops->readpage) {
2113        error = -EINVAL;
2114        goto bad_swap;
2115    }
2116    page = read_mapping_page(mapping, 0, swap_file);
2117    if (IS_ERR(page)) {
2118        error = PTR_ERR(page);
2119        goto bad_swap;
2120    }
2121    swap_header = kmap(page);
2122
2123    maxpages = read_swap_header(p, swap_header, inode);
2124    if (unlikely(!maxpages)) {
2125        error = -EINVAL;
2126        goto bad_swap;
2127    }
2128
2129    /* OK, set up the swap map and apply the bad block list */
2130    swap_map = vzalloc(maxpages);
2131    if (!swap_map) {
2132        error = -ENOMEM;
2133        goto bad_swap;
2134    }
2135
2136    error = swap_cgroup_swapon(p->type, maxpages);
2137    if (error)
2138        goto bad_swap;
2139
2140    nr_extents = setup_swap_map_and_extents(p, swap_header, swap_map,
2141        maxpages, &span);
2142    if (unlikely(nr_extents < 0)) {
2143        error = nr_extents;
2144        goto bad_swap;
2145    }
2146    /* frontswap enabled? set up bit-per-page map for frontswap */
2147    if (frontswap_enabled)
2148        frontswap_map = vzalloc(BITS_TO_LONGS(maxpages) * sizeof(long));
2149
2150    if (p->bdev) {
2151        if (blk_queue_nonrot(bdev_get_queue(p->bdev))) {
2152            p->flags |= SWP_SOLIDSTATE;
2153            p->cluster_next = 1 + (prandom_u32() % p->highest_bit);
2154        }
2155
2156        if ((swap_flags & SWAP_FLAG_DISCARD) && swap_discardable(p)) {
2157            /*
2158             * When discard is enabled for swap with no particular
2159             * policy flagged, we set all swap discard flags here in
2160             * order to sustain backward compatibility with older
2161             * swapon(8) releases.
2162             */
2163            p->flags |= (SWP_DISCARDABLE | SWP_AREA_DISCARD |
2164                     SWP_PAGE_DISCARD);
2165
2166            /*
2167             * By flagging sys_swapon, a sysadmin can tell us to
2168             * either do single-time area discards only, or to just
2169             * perform discards for released swap page-clusters.
2170             * Now it's time to adjust the p->flags accordingly.
2171             */
2172            if (swap_flags & SWAP_FLAG_DISCARD_ONCE)
2173                p->flags &= ~SWP_PAGE_DISCARD;
2174            else if (swap_flags & SWAP_FLAG_DISCARD_PAGES)
2175                p->flags &= ~SWP_AREA_DISCARD;
2176
2177            /* issue a swapon-time discard if it's still required */
2178            if (p->flags & SWP_AREA_DISCARD) {
2179                int err = discard_swap(p);
2180                if (unlikely(err))
2181                    printk(KERN_ERR
2182                           "swapon: discard_swap(%p): %d\n",
2183                        p, err);
2184            }
2185        }
2186    }
2187
2188    mutex_lock(&swapon_mutex);
2189    prio = -1;
2190    if (swap_flags & SWAP_FLAG_PREFER)
2191        prio =
2192          (swap_flags & SWAP_FLAG_PRIO_MASK) >> SWAP_FLAG_PRIO_SHIFT;
2193    enable_swap_info(p, prio, swap_map, frontswap_map);
2194
2195    printk(KERN_INFO "Adding %uk swap on %s. "
2196            "Priority:%d extents:%d across:%lluk %s%s%s%s%s\n",
2197        p->pages<<(PAGE_SHIFT-10), name->name, p->prio,
2198        nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10),
2199        (p->flags & SWP_SOLIDSTATE) ? "SS" : "",
2200        (p->flags & SWP_DISCARDABLE) ? "D" : "",
2201        (p->flags & SWP_AREA_DISCARD) ? "s" : "",
2202        (p->flags & SWP_PAGE_DISCARD) ? "c" : "",
2203        (frontswap_map) ? "FS" : "");
2204
2205    mutex_unlock(&swapon_mutex);
2206    atomic_inc(&proc_poll_event);
2207    wake_up_interruptible(&proc_poll_wait);
2208
2209    if (S_ISREG(inode->i_mode))
2210        inode->i_flags |= S_SWAPFILE;
2211    error = 0;
2212    goto out;
2213bad_swap:
2214    if (inode && S_ISBLK(inode->i_mode) && p->bdev) {
2215        set_blocksize(p->bdev, p->old_block_size);
2216        blkdev_put(p->bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
2217    }
2218    destroy_swap_extents(p);
2219    swap_cgroup_swapoff(p->type);
2220    spin_lock(&swap_lock);
2221    p->swap_file = NULL;
2222    p->flags = 0;
2223    spin_unlock(&swap_lock);
2224    vfree(swap_map);
2225    if (swap_file) {
2226        if (inode && S_ISREG(inode->i_mode)) {
2227            mutex_unlock(&inode->i_mutex);
2228            inode = NULL;
2229        }
2230        filp_close(swap_file, NULL);
2231    }
2232out:
2233    if (page && !IS_ERR(page)) {
2234        kunmap(page);
2235        page_cache_release(page);
2236    }
2237    if (name)
2238        putname(name);
2239    if (inode && S_ISREG(inode->i_mode))
2240        mutex_unlock(&inode->i_mutex);
2241    return error;
2242}
2243
2244void si_swapinfo(struct sysinfo *val)
2245{
2246    unsigned int type;
2247    unsigned long nr_to_be_unused = 0;
2248
2249    spin_lock(&swap_lock);
2250    for (type = 0; type < nr_swapfiles; type++) {
2251        struct swap_info_struct *si = swap_info[type];
2252
2253        if ((si->flags & SWP_USED) && !(si->flags & SWP_WRITEOK))
2254            nr_to_be_unused += si->inuse_pages;
2255    }
2256    val->freeswap = atomic_long_read(&nr_swap_pages) + nr_to_be_unused;
2257    val->totalswap = total_swap_pages + nr_to_be_unused;
2258    spin_unlock(&swap_lock);
2259}
2260
2261/*
2262 * Verify that a swap entry is valid and increment its swap map count.
2263 *
2264 * Returns error code in following case.
2265 * - success -> 0
2266 * - swp_entry is invalid -> EINVAL
2267 * - swp_entry is migration entry -> EINVAL
2268 * - swap-cache reference is requested but there is already one. -> EEXIST
2269 * - swap-cache reference is requested but the entry is not used. -> ENOENT
2270 * - swap-mapped reference requested but needs continued swap count. -> ENOMEM
2271 */
2272static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
2273{
2274    struct swap_info_struct *p;
2275    unsigned long offset, type;
2276    unsigned char count;
2277    unsigned char has_cache;
2278    int err = -EINVAL;
2279
2280    if (non_swap_entry(entry))
2281        goto out;
2282
2283    type = swp_type(entry);
2284    if (type >= nr_swapfiles)
2285        goto bad_file;
2286    p = swap_info[type];
2287    offset = swp_offset(entry);
2288
2289    spin_lock(&p->lock);
2290    if (unlikely(offset >= p->max))
2291        goto unlock_out;
2292
2293    count = p->swap_map[offset];
2294    has_cache = count & SWAP_HAS_CACHE;
2295    count &= ~SWAP_HAS_CACHE;
2296    err = 0;
2297
2298    if (usage == SWAP_HAS_CACHE) {
2299
2300        /* set SWAP_HAS_CACHE if there is no cache and entry is used */
2301        if (!has_cache && count)
2302            has_cache = SWAP_HAS_CACHE;
2303        else if (has_cache) /* someone else added cache */
2304            err = -EEXIST;
2305        else /* no users remaining */
2306            err = -ENOENT;
2307
2308    } else if (count || has_cache) {
2309
2310        if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
2311            count += usage;
2312        else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX)
2313            err = -EINVAL;
2314        else if (swap_count_continued(p, offset, count))
2315            count = COUNT_CONTINUED;
2316        else
2317            err = -ENOMEM;
2318    } else
2319        err = -ENOENT; /* unused swap entry */
2320
2321    p->swap_map[offset] = count | has_cache;
2322
2323unlock_out:
2324    spin_unlock(&p->lock);
2325out:
2326    return err;
2327
2328bad_file:
2329    printk(KERN_ERR "swap_dup: %s%08lx\n", Bad_file, entry.val);
2330    goto out;
2331}
2332
2333/*
2334 * Help swapoff by noting that swap entry belongs to shmem/tmpfs
2335 * (in which case its reference count is never incremented).
2336 */
2337void swap_shmem_alloc(swp_entry_t entry)
2338{
2339    __swap_duplicate(entry, SWAP_MAP_SHMEM);
2340}
2341
2342/*
2343 * Increase reference count of swap entry by 1.
2344 * Returns 0 for success, or -ENOMEM if a swap_count_continuation is required
2345 * but could not be atomically allocated. Returns 0, just as if it succeeded,
2346 * if __swap_duplicate() fails for another reason (-EINVAL or -ENOENT), which
2347 * might occur if a page table entry has got corrupted.
2348 */
2349int swap_duplicate(swp_entry_t entry)
2350{
2351    int err = 0;
2352
2353    while (!err && __swap_duplicate(entry, 1) == -ENOMEM)
2354        err = add_swap_count_continuation(entry, GFP_ATOMIC);
2355    return err;
2356}
2357
2358/*
2359 * @entry: swap entry for which we allocate swap cache.
2360 *
2361 * Called when allocating swap cache for existing swap entry,
2362 * This can return error codes. Returns 0 at success.
2363 * -EBUSY means there is a swap cache.
2364 * Note: return code is different from swap_duplicate().
2365 */
2366int swapcache_prepare(swp_entry_t entry)
2367{
2368    return __swap_duplicate(entry, SWAP_HAS_CACHE);
2369}
2370
2371struct swap_info_struct *page_swap_info(struct page *page)
2372{
2373    swp_entry_t swap = { .val = page_private(page) };
2374    BUG_ON(!PageSwapCache(page));
2375    return swap_info[swp_type(swap)];
2376}
2377
2378/*
2379 * out-of-line __page_file_ methods to avoid include hell.
2380 */
2381struct address_space *__page_file_mapping(struct page *page)
2382{
2383    VM_BUG_ON(!PageSwapCache(page));
2384    return page_swap_info(page)->swap_file->f_mapping;
2385}
2386EXPORT_SYMBOL_GPL(__page_file_mapping);
2387
2388pgoff_t __page_file_index(struct page *page)
2389{
2390    swp_entry_t swap = { .val = page_private(page) };
2391    VM_BUG_ON(!PageSwapCache(page));
2392    return swp_offset(swap);
2393}
2394EXPORT_SYMBOL_GPL(__page_file_index);
2395
2396/*
2397 * add_swap_count_continuation - called when a swap count is duplicated
2398 * beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's
2399 * page of the original vmalloc'ed swap_map, to hold the continuation count
2400 * (for that entry and for its neighbouring PAGE_SIZE swap entries). Called
2401 * again when count is duplicated beyond SWAP_MAP_MAX * SWAP_CONT_MAX, etc.
2402 *
2403 * These continuation pages are seldom referenced: the common paths all work
2404 * on the original swap_map, only referring to a continuation page when the
2405 * low "digit" of a count is incremented or decremented through SWAP_MAP_MAX.
2406 *
2407 * add_swap_count_continuation(, GFP_ATOMIC) can be called while holding
2408 * page table locks; if it fails, add_swap_count_continuation(, GFP_KERNEL)
2409 * can be called after dropping locks.
2410 */
2411int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask)
2412{
2413    struct swap_info_struct *si;
2414    struct page *head;
2415    struct page *page;
2416    struct page *list_page;
2417    pgoff_t offset;
2418    unsigned char count;
2419
2420    /*
2421     * When debugging, it's easier to use __GFP_ZERO here; but it's better
2422     * for latency not to zero a page while GFP_ATOMIC and holding locks.
2423     */
2424    page = alloc_page(gfp_mask | __GFP_HIGHMEM);
2425
2426    si = swap_info_get(entry);
2427    if (!si) {
2428        /*
2429         * An acceptable race has occurred since the failing
2430         * __swap_duplicate(): the swap entry has been freed,
2431         * perhaps even the whole swap_map cleared for swapoff.
2432         */
2433        goto outer;
2434    }
2435
2436    offset = swp_offset(entry);
2437    count = si->swap_map[offset] & ~SWAP_HAS_CACHE;
2438
2439    if ((count & ~COUNT_CONTINUED) != SWAP_MAP_MAX) {
2440        /*
2441         * The higher the swap count, the more likely it is that tasks
2442         * will race to add swap count continuation: we need to avoid
2443         * over-provisioning.
2444         */
2445        goto out;
2446    }
2447
2448    if (!page) {
2449        spin_unlock(&si->lock);
2450        return -ENOMEM;
2451    }
2452
2453    /*
2454     * We are fortunate that although vmalloc_to_page uses pte_offset_map,
2455     * no architecture is using highmem pages for kernel pagetables: so it
2456     * will not corrupt the GFP_ATOMIC caller's atomic pagetable kmaps.
2457     */
2458    head = vmalloc_to_page(si->swap_map + offset);
2459    offset &= ~PAGE_MASK;
2460
2461    /*
2462     * Page allocation does not initialize the page's lru field,
2463     * but it does always reset its private field.
2464     */
2465    if (!page_private(head)) {
2466        BUG_ON(count & COUNT_CONTINUED);
2467        INIT_LIST_HEAD(&head->lru);
2468        set_page_private(head, SWP_CONTINUED);
2469        si->flags |= SWP_CONTINUED;
2470    }
2471
2472    list_for_each_entry(list_page, &head->lru, lru) {
2473        unsigned char *map;
2474
2475        /*
2476         * If the previous map said no continuation, but we've found
2477         * a continuation page, free our allocation and use this one.
2478         */
2479        if (!(count & COUNT_CONTINUED))
2480            goto out;
2481
2482        map = kmap_atomic(list_page) + offset;
2483        count = *map;
2484        kunmap_atomic(map);
2485
2486        /*
2487         * If this continuation count now has some space in it,
2488         * free our allocation and use this one.
2489         */
2490        if ((count & ~COUNT_CONTINUED) != SWAP_CONT_MAX)
2491            goto out;
2492    }
2493
2494    list_add_tail(&page->lru, &head->lru);
2495    page = NULL; /* now it's attached, don't free it */
2496out:
2497    spin_unlock(&si->lock);
2498outer:
2499    if (page)
2500        __free_page(page);
2501    return 0;
2502}
2503
2504/*
2505 * swap_count_continued - when the original swap_map count is incremented
2506 * from SWAP_MAP_MAX, check if there is already a continuation page to carry
2507 * into, carry if so, or else fail until a new continuation page is allocated;
2508 * when the original swap_map count is decremented from 0 with continuation,
2509 * borrow from the continuation and report whether it still holds more.
2510 * Called while __swap_duplicate() or swap_entry_free() holds swap_lock.
2511 */
2512static bool swap_count_continued(struct swap_info_struct *si,
2513                 pgoff_t offset, unsigned char count)
2514{
2515    struct page *head;
2516    struct page *page;
2517    unsigned char *map;
2518
2519    head = vmalloc_to_page(si->swap_map + offset);
2520    if (page_private(head) != SWP_CONTINUED) {
2521        BUG_ON(count & COUNT_CONTINUED);
2522        return false; /* need to add count continuation */
2523    }
2524
2525    offset &= ~PAGE_MASK;
2526    page = list_entry(head->lru.next, struct page, lru);
2527    map = kmap_atomic(page) + offset;
2528
2529    if (count == SWAP_MAP_MAX) /* initial increment from swap_map */
2530        goto init_map; /* jump over SWAP_CONT_MAX checks */
2531
2532    if (count == (SWAP_MAP_MAX | COUNT_CONTINUED)) { /* incrementing */
2533        /*
2534         * Think of how you add 1 to 999
2535         */
2536        while (*map == (SWAP_CONT_MAX | COUNT_CONTINUED)) {
2537            kunmap_atomic(map);
2538            page = list_entry(page->lru.next, struct page, lru);
2539            BUG_ON(page == head);
2540            map = kmap_atomic(page) + offset;
2541        }
2542        if (*map == SWAP_CONT_MAX) {
2543            kunmap_atomic(map);
2544            page = list_entry(page->lru.next, struct page, lru);
2545            if (page == head)
2546                return false; /* add count continuation */
2547            map = kmap_atomic(page) + offset;
2548init_map: *map = 0; /* we didn't zero the page */
2549        }
2550        *map += 1;
2551        kunmap_atomic(map);
2552        page = list_entry(page->lru.prev, struct page, lru);
2553        while (page != head) {
2554            map = kmap_atomic(page) + offset;
2555            *map = COUNT_CONTINUED;
2556            kunmap_atomic(map);
2557            page = list_entry(page->lru.prev, struct page, lru);
2558        }
2559        return true; /* incremented */
2560
2561    } else { /* decrementing */
2562        /*
2563         * Think of how you subtract 1 from 1000
2564         */
2565        BUG_ON(count != COUNT_CONTINUED);
2566        while (*map == COUNT_CONTINUED) {
2567            kunmap_atomic(map);
2568            page = list_entry(page->lru.next, struct page, lru);
2569            BUG_ON(page == head);
2570            map = kmap_atomic(page) + offset;
2571        }
2572        BUG_ON(*map == 0);
2573        *map -= 1;
2574        if (*map == 0)
2575            count = 0;
2576        kunmap_atomic(map);
2577        page = list_entry(page->lru.prev, struct page, lru);
2578        while (page != head) {
2579            map = kmap_atomic(page) + offset;
2580            *map = SWAP_CONT_MAX | count;
2581            count = COUNT_CONTINUED;
2582            kunmap_atomic(map);
2583            page = list_entry(page->lru.prev, struct page, lru);
2584        }
2585        return count == COUNT_CONTINUED;
2586    }
2587}
2588
2589/*
2590 * free_swap_count_continuations - swapoff free all the continuation pages
2591 * appended to the swap_map, after swap_map is quiesced, before vfree'ing it.
2592 */
2593static void free_swap_count_continuations(struct swap_info_struct *si)
2594{
2595    pgoff_t offset;
2596
2597    for (offset = 0; offset < si->max; offset += PAGE_SIZE) {
2598        struct page *head;
2599        head = vmalloc_to_page(si->swap_map + offset);
2600        if (page_private(head)) {
2601            struct list_head *this, *next;
2602            list_for_each_safe(this, next, &head->lru) {
2603                struct page *page;
2604                page = list_entry(this, struct page, lru);
2605                list_del(this);
2606                __free_page(page);
2607            }
2608        }
2609    }
2610}
2611

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