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/shm.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
34#include <asm/pgtable.h>
35#include <asm/tlbflush.h>
36#include <linux/swapops.h>
37#include <linux/page_cgroup.h>
38
39static bool swap_count_continued(struct swap_info_struct *, pgoff_t,
40                 unsigned char);
41static void free_swap_count_continuations(struct swap_info_struct *);
42static sector_t map_swap_entry(swp_entry_t, struct block_device**);
43
44static DEFINE_SPINLOCK(swap_lock);
45static unsigned int nr_swapfiles;
46long nr_swap_pages;
47long total_swap_pages;
48static int least_priority;
49
50static const char Bad_file[] = "Bad swap file entry ";
51static const char Unused_file[] = "Unused swap file entry ";
52static const char Bad_offset[] = "Bad swap offset entry ";
53static const char Unused_offset[] = "Unused swap offset entry ";
54
55static struct swap_list_t swap_list = {-1, -1};
56
57static struct swap_info_struct *swap_info[MAX_SWAPFILES];
58
59static DEFINE_MUTEX(swapon_mutex);
60
61static inline unsigned char swap_count(unsigned char ent)
62{
63    return ent & ~SWAP_HAS_CACHE; /* may include SWAP_HAS_CONT flag */
64}
65
66/* returns 1 if swap entry is freed */
67static int
68__try_to_reclaim_swap(struct swap_info_struct *si, unsigned long offset)
69{
70    swp_entry_t entry = swp_entry(si->type, offset);
71    struct page *page;
72    int ret = 0;
73
74    page = find_get_page(&swapper_space, entry.val);
75    if (!page)
76        return 0;
77    /*
78     * This function is called from scan_swap_map() and it's called
79     * by vmscan.c at reclaiming pages. So, we hold a lock on a page, here.
80     * We have to use trylock for avoiding deadlock. This is a special
81     * case and you should use try_to_free_swap() with explicit lock_page()
82     * in usual operations.
83     */
84    if (trylock_page(page)) {
85        ret = try_to_free_swap(page);
86        unlock_page(page);
87    }
88    page_cache_release(page);
89    return ret;
90}
91
92/*
93 * We need this because the bdev->unplug_fn can sleep and we cannot
94 * hold swap_lock while calling the unplug_fn. And swap_lock
95 * cannot be turned into a mutex.
96 */
97static DECLARE_RWSEM(swap_unplug_sem);
98
99void swap_unplug_io_fn(struct backing_dev_info *unused_bdi, struct page *page)
100{
101    swp_entry_t entry;
102
103    down_read(&swap_unplug_sem);
104    entry.val = page_private(page);
105    if (PageSwapCache(page)) {
106        struct block_device *bdev = swap_info[swp_type(entry)]->bdev;
107        struct backing_dev_info *bdi;
108
109        /*
110         * If the page is removed from swapcache from under us (with a
111         * racy try_to_unuse/swapoff) we need an additional reference
112         * count to avoid reading garbage from page_private(page) above.
113         * If the WARN_ON triggers during a swapoff it maybe the race
114         * condition and it's harmless. However if it triggers without
115         * swapoff it signals a problem.
116         */
117        WARN_ON(page_count(page) <= 1);
118
119        bdi = bdev->bd_inode->i_mapping->backing_dev_info;
120        blk_run_backing_dev(bdi, page);
121    }
122    up_read(&swap_unplug_sem);
123}
124
125/*
126 * swapon tell device that all the old swap contents can be discarded,
127 * to allow the swap device to optimize its wear-levelling.
128 */
129static int discard_swap(struct swap_info_struct *si)
130{
131    struct swap_extent *se;
132    sector_t start_block;
133    sector_t nr_blocks;
134    int err = 0;
135
136    /* Do not discard the swap header page! */
137    se = &si->first_swap_extent;
138    start_block = (se->start_block + 1) << (PAGE_SHIFT - 9);
139    nr_blocks = ((sector_t)se->nr_pages - 1) << (PAGE_SHIFT - 9);
140    if (nr_blocks) {
141        err = blkdev_issue_discard(si->bdev, start_block,
142                nr_blocks, GFP_KERNEL, BLKDEV_IFL_WAIT);
143        if (err)
144            return err;
145        cond_resched();
146    }
147
148    list_for_each_entry(se, &si->first_swap_extent.list, list) {
149        start_block = se->start_block << (PAGE_SHIFT - 9);
150        nr_blocks = (sector_t)se->nr_pages << (PAGE_SHIFT - 9);
151
152        err = blkdev_issue_discard(si->bdev, start_block,
153                nr_blocks, GFP_KERNEL, BLKDEV_IFL_WAIT);
154        if (err)
155            break;
156
157        cond_resched();
158    }
159    return err; /* That will often be -EOPNOTSUPP */
160}
161
162/*
163 * swap allocation tell device that a cluster of swap can now be discarded,
164 * to allow the swap device to optimize its wear-levelling.
165 */
166static void discard_swap_cluster(struct swap_info_struct *si,
167                 pgoff_t start_page, pgoff_t nr_pages)
168{
169    struct swap_extent *se = si->curr_swap_extent;
170    int found_extent = 0;
171
172    while (nr_pages) {
173        struct list_head *lh;
174
175        if (se->start_page <= start_page &&
176            start_page < se->start_page + se->nr_pages) {
177            pgoff_t offset = start_page - se->start_page;
178            sector_t start_block = se->start_block + offset;
179            sector_t nr_blocks = se->nr_pages - offset;
180
181            if (nr_blocks > nr_pages)
182                nr_blocks = nr_pages;
183            start_page += nr_blocks;
184            nr_pages -= nr_blocks;
185
186            if (!found_extent++)
187                si->curr_swap_extent = se;
188
189            start_block <<= PAGE_SHIFT - 9;
190            nr_blocks <<= PAGE_SHIFT - 9;
191            if (blkdev_issue_discard(si->bdev, start_block,
192                    nr_blocks, GFP_NOIO, BLKDEV_IFL_WAIT))
193                break;
194        }
195
196        lh = se->list.next;
197        se = list_entry(lh, struct swap_extent, list);
198    }
199}
200
201static int wait_for_discard(void *word)
202{
203    schedule();
204    return 0;
205}
206
207#define SWAPFILE_CLUSTER 256
208#define LATENCY_LIMIT 256
209
210static inline unsigned long scan_swap_map(struct swap_info_struct *si,
211                      unsigned char usage)
212{
213    unsigned long offset;
214    unsigned long scan_base;
215    unsigned long last_in_cluster = 0;
216    int latency_ration = LATENCY_LIMIT;
217    int found_free_cluster = 0;
218
219    /*
220     * We try to cluster swap pages by allocating them sequentially
221     * in swap. Once we've allocated SWAPFILE_CLUSTER pages this
222     * way, however, we resort to first-free allocation, starting
223     * a new cluster. This prevents us from scattering swap pages
224     * all over the entire swap partition, so that we reduce
225     * overall disk seek times between swap pages. -- sct
226     * But we do now try to find an empty cluster. -Andrea
227     * And we let swap pages go all over an SSD partition. Hugh
228     */
229
230    si->flags += SWP_SCANNING;
231    scan_base = offset = si->cluster_next;
232
233    if (unlikely(!si->cluster_nr--)) {
234        if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER) {
235            si->cluster_nr = SWAPFILE_CLUSTER - 1;
236            goto checks;
237        }
238        if (si->flags & SWP_DISCARDABLE) {
239            /*
240             * Start range check on racing allocations, in case
241             * they overlap the cluster we eventually decide on
242             * (we scan without swap_lock to allow preemption).
243             * It's hardly conceivable that cluster_nr could be
244             * wrapped during our scan, but don't depend on it.
245             */
246            if (si->lowest_alloc)
247                goto checks;
248            si->lowest_alloc = si->max;
249            si->highest_alloc = 0;
250        }
251        spin_unlock(&swap_lock);
252
253        /*
254         * If seek is expensive, start searching for new cluster from
255         * start of partition, to minimize the span of allocated swap.
256         * But if seek is cheap, search from our current position, so
257         * that swap is allocated from all over the partition: if the
258         * Flash Translation Layer only remaps within limited zones,
259         * we don't want to wear out the first zone too quickly.
260         */
261        if (!(si->flags & SWP_SOLIDSTATE))
262            scan_base = offset = si->lowest_bit;
263        last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
264
265        /* Locate the first empty (unaligned) cluster */
266        for (; last_in_cluster <= si->highest_bit; offset++) {
267            if (si->swap_map[offset])
268                last_in_cluster = offset + SWAPFILE_CLUSTER;
269            else if (offset == last_in_cluster) {
270                spin_lock(&swap_lock);
271                offset -= SWAPFILE_CLUSTER - 1;
272                si->cluster_next = offset;
273                si->cluster_nr = SWAPFILE_CLUSTER - 1;
274                found_free_cluster = 1;
275                goto checks;
276            }
277            if (unlikely(--latency_ration < 0)) {
278                cond_resched();
279                latency_ration = LATENCY_LIMIT;
280            }
281        }
282
283        offset = si->lowest_bit;
284        last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
285
286        /* Locate the first empty (unaligned) cluster */
287        for (; last_in_cluster < scan_base; offset++) {
288            if (si->swap_map[offset])
289                last_in_cluster = offset + SWAPFILE_CLUSTER;
290            else if (offset == last_in_cluster) {
291                spin_lock(&swap_lock);
292                offset -= SWAPFILE_CLUSTER - 1;
293                si->cluster_next = offset;
294                si->cluster_nr = SWAPFILE_CLUSTER - 1;
295                found_free_cluster = 1;
296                goto checks;
297            }
298            if (unlikely(--latency_ration < 0)) {
299                cond_resched();
300                latency_ration = LATENCY_LIMIT;
301            }
302        }
303
304        offset = scan_base;
305        spin_lock(&swap_lock);
306        si->cluster_nr = SWAPFILE_CLUSTER - 1;
307        si->lowest_alloc = 0;
308    }
309
310checks:
311    if (!(si->flags & SWP_WRITEOK))
312        goto no_page;
313    if (!si->highest_bit)
314        goto no_page;
315    if (offset > si->highest_bit)
316        scan_base = offset = si->lowest_bit;
317
318    /* reuse swap entry of cache-only swap if not busy. */
319    if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
320        int swap_was_freed;
321        spin_unlock(&swap_lock);
322        swap_was_freed = __try_to_reclaim_swap(si, offset);
323        spin_lock(&swap_lock);
324        /* entry was freed successfully, try to use this again */
325        if (swap_was_freed)
326            goto checks;
327        goto scan; /* check next one */
328    }
329
330    if (si->swap_map[offset])
331        goto scan;
332
333    if (offset == si->lowest_bit)
334        si->lowest_bit++;
335    if (offset == si->highest_bit)
336        si->highest_bit--;
337    si->inuse_pages++;
338    if (si->inuse_pages == si->pages) {
339        si->lowest_bit = si->max;
340        si->highest_bit = 0;
341    }
342    si->swap_map[offset] = usage;
343    si->cluster_next = offset + 1;
344    si->flags -= SWP_SCANNING;
345
346    if (si->lowest_alloc) {
347        /*
348         * Only set when SWP_DISCARDABLE, and there's a scan
349         * for a free cluster in progress or just completed.
350         */
351        if (found_free_cluster) {
352            /*
353             * To optimize wear-levelling, discard the
354             * old data of the cluster, taking care not to
355             * discard any of its pages that have already
356             * been allocated by racing tasks (offset has
357             * already stepped over any at the beginning).
358             */
359            if (offset < si->highest_alloc &&
360                si->lowest_alloc <= last_in_cluster)
361                last_in_cluster = si->lowest_alloc - 1;
362            si->flags |= SWP_DISCARDING;
363            spin_unlock(&swap_lock);
364
365            if (offset < last_in_cluster)
366                discard_swap_cluster(si, offset,
367                    last_in_cluster - offset + 1);
368
369            spin_lock(&swap_lock);
370            si->lowest_alloc = 0;
371            si->flags &= ~SWP_DISCARDING;
372
373            smp_mb(); /* wake_up_bit advises this */
374            wake_up_bit(&si->flags, ilog2(SWP_DISCARDING));
375
376        } else if (si->flags & SWP_DISCARDING) {
377            /*
378             * Delay using pages allocated by racing tasks
379             * until the whole discard has been issued. We
380             * could defer that delay until swap_writepage,
381             * but it's easier to keep this self-contained.
382             */
383            spin_unlock(&swap_lock);
384            wait_on_bit(&si->flags, ilog2(SWP_DISCARDING),
385                wait_for_discard, TASK_UNINTERRUPTIBLE);
386            spin_lock(&swap_lock);
387        } else {
388            /*
389             * Note pages allocated by racing tasks while
390             * scan for a free cluster is in progress, so
391             * that its final discard can exclude them.
392             */
393            if (offset < si->lowest_alloc)
394                si->lowest_alloc = offset;
395            if (offset > si->highest_alloc)
396                si->highest_alloc = offset;
397        }
398    }
399    return offset;
400
401scan:
402    spin_unlock(&swap_lock);
403    while (++offset <= si->highest_bit) {
404        if (!si->swap_map[offset]) {
405            spin_lock(&swap_lock);
406            goto checks;
407        }
408        if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
409            spin_lock(&swap_lock);
410            goto checks;
411        }
412        if (unlikely(--latency_ration < 0)) {
413            cond_resched();
414            latency_ration = LATENCY_LIMIT;
415        }
416    }
417    offset = si->lowest_bit;
418    while (++offset < scan_base) {
419        if (!si->swap_map[offset]) {
420            spin_lock(&swap_lock);
421            goto checks;
422        }
423        if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
424            spin_lock(&swap_lock);
425            goto checks;
426        }
427        if (unlikely(--latency_ration < 0)) {
428            cond_resched();
429            latency_ration = LATENCY_LIMIT;
430        }
431    }
432    spin_lock(&swap_lock);
433
434no_page:
435    si->flags -= SWP_SCANNING;
436    return 0;
437}
438
439swp_entry_t get_swap_page(void)
440{
441    struct swap_info_struct *si;
442    pgoff_t offset;
443    int type, next;
444    int wrapped = 0;
445
446    spin_lock(&swap_lock);
447    if (nr_swap_pages <= 0)
448        goto noswap;
449    nr_swap_pages--;
450
451    for (type = swap_list.next; type >= 0 && wrapped < 2; type = next) {
452        si = swap_info[type];
453        next = si->next;
454        if (next < 0 ||
455            (!wrapped && si->prio != swap_info[next]->prio)) {
456            next = swap_list.head;
457            wrapped++;
458        }
459
460        if (!si->highest_bit)
461            continue;
462        if (!(si->flags & SWP_WRITEOK))
463            continue;
464
465        swap_list.next = next;
466        /* This is called for allocating swap entry for cache */
467        offset = scan_swap_map(si, SWAP_HAS_CACHE);
468        if (offset) {
469            spin_unlock(&swap_lock);
470            return swp_entry(type, offset);
471        }
472        next = swap_list.next;
473    }
474
475    nr_swap_pages++;
476noswap:
477    spin_unlock(&swap_lock);
478    return (swp_entry_t) {0};
479}
480
481/* The only caller of this function is now susupend routine */
482swp_entry_t get_swap_page_of_type(int type)
483{
484    struct swap_info_struct *si;
485    pgoff_t offset;
486
487    spin_lock(&swap_lock);
488    si = swap_info[type];
489    if (si && (si->flags & SWP_WRITEOK)) {
490        nr_swap_pages--;
491        /* This is called for allocating swap entry, not cache */
492        offset = scan_swap_map(si, 1);
493        if (offset) {
494            spin_unlock(&swap_lock);
495            return swp_entry(type, offset);
496        }
497        nr_swap_pages++;
498    }
499    spin_unlock(&swap_lock);
500    return (swp_entry_t) {0};
501}
502
503static struct swap_info_struct *swap_info_get(swp_entry_t entry)
504{
505    struct swap_info_struct *p;
506    unsigned long offset, type;
507
508    if (!entry.val)
509        goto out;
510    type = swp_type(entry);
511    if (type >= nr_swapfiles)
512        goto bad_nofile;
513    p = swap_info[type];
514    if (!(p->flags & SWP_USED))
515        goto bad_device;
516    offset = swp_offset(entry);
517    if (offset >= p->max)
518        goto bad_offset;
519    if (!p->swap_map[offset])
520        goto bad_free;
521    spin_lock(&swap_lock);
522    return p;
523
524bad_free:
525    printk(KERN_ERR "swap_free: %s%08lx\n", Unused_offset, entry.val);
526    goto out;
527bad_offset:
528    printk(KERN_ERR "swap_free: %s%08lx\n", Bad_offset, entry.val);
529    goto out;
530bad_device:
531    printk(KERN_ERR "swap_free: %s%08lx\n", Unused_file, entry.val);
532    goto out;
533bad_nofile:
534    printk(KERN_ERR "swap_free: %s%08lx\n", Bad_file, entry.val);
535out:
536    return NULL;
537}
538
539static unsigned char swap_entry_free(struct swap_info_struct *p,
540                     swp_entry_t entry, unsigned char usage)
541{
542    unsigned long offset = swp_offset(entry);
543    unsigned char count;
544    unsigned char has_cache;
545
546    count = p->swap_map[offset];
547    has_cache = count & SWAP_HAS_CACHE;
548    count &= ~SWAP_HAS_CACHE;
549
550    if (usage == SWAP_HAS_CACHE) {
551        VM_BUG_ON(!has_cache);
552        has_cache = 0;
553    } else if (count == SWAP_MAP_SHMEM) {
554        /*
555         * Or we could insist on shmem.c using a special
556         * swap_shmem_free() and free_shmem_swap_and_cache()...
557         */
558        count = 0;
559    } else if ((count & ~COUNT_CONTINUED) <= SWAP_MAP_MAX) {
560        if (count == COUNT_CONTINUED) {
561            if (swap_count_continued(p, offset, count))
562                count = SWAP_MAP_MAX | COUNT_CONTINUED;
563            else
564                count = SWAP_MAP_MAX;
565        } else
566            count--;
567    }
568
569    if (!count)
570        mem_cgroup_uncharge_swap(entry);
571
572    usage = count | has_cache;
573    p->swap_map[offset] = usage;
574
575    /* free if no reference */
576    if (!usage) {
577        struct gendisk *disk = p->bdev->bd_disk;
578        if (offset < p->lowest_bit)
579            p->lowest_bit = offset;
580        if (offset > p->highest_bit)
581            p->highest_bit = offset;
582        if (swap_list.next >= 0 &&
583            p->prio > swap_info[swap_list.next]->prio)
584            swap_list.next = p->type;
585        nr_swap_pages++;
586        p->inuse_pages--;
587        if ((p->flags & SWP_BLKDEV) &&
588                disk->fops->swap_slot_free_notify)
589            disk->fops->swap_slot_free_notify(p->bdev, offset);
590    }
591
592    return usage;
593}
594
595/*
596 * Caller has made sure that the swapdevice corresponding to entry
597 * is still around or has not been recycled.
598 */
599void swap_free(swp_entry_t entry)
600{
601    struct swap_info_struct *p;
602
603    p = swap_info_get(entry);
604    if (p) {
605        swap_entry_free(p, entry, 1);
606        spin_unlock(&swap_lock);
607    }
608}
609
610/*
611 * Called after dropping swapcache to decrease refcnt to swap entries.
612 */
613void swapcache_free(swp_entry_t entry, struct page *page)
614{
615    struct swap_info_struct *p;
616    unsigned char count;
617
618    p = swap_info_get(entry);
619    if (p) {
620        count = swap_entry_free(p, entry, SWAP_HAS_CACHE);
621        if (page)
622            mem_cgroup_uncharge_swapcache(page, entry, count != 0);
623        spin_unlock(&swap_lock);
624    }
625}
626
627/*
628 * How many references to page are currently swapped out?
629 * This does not give an exact answer when swap count is continued,
630 * but does include the high COUNT_CONTINUED flag to allow for that.
631 */
632static inline int page_swapcount(struct page *page)
633{
634    int count = 0;
635    struct swap_info_struct *p;
636    swp_entry_t entry;
637
638    entry.val = page_private(page);
639    p = swap_info_get(entry);
640    if (p) {
641        count = swap_count(p->swap_map[swp_offset(entry)]);
642        spin_unlock(&swap_lock);
643    }
644    return count;
645}
646
647/*
648 * We can write to an anon page without COW if there are no other references
649 * to it. And as a side-effect, free up its swap: because the old content
650 * on disk will never be read, and seeking back there to write new content
651 * later would only waste time away from clustering.
652 */
653int reuse_swap_page(struct page *page)
654{
655    int count;
656
657    VM_BUG_ON(!PageLocked(page));
658    if (unlikely(PageKsm(page)))
659        return 0;
660    count = page_mapcount(page);
661    if (count <= 1 && PageSwapCache(page)) {
662        count += page_swapcount(page);
663        if (count == 1 && !PageWriteback(page)) {
664            delete_from_swap_cache(page);
665            SetPageDirty(page);
666        }
667    }
668    return count <= 1;
669}
670
671/*
672 * If swap is getting full, or if there are no more mappings of this page,
673 * then try_to_free_swap is called to free its swap space.
674 */
675int try_to_free_swap(struct page *page)
676{
677    VM_BUG_ON(!PageLocked(page));
678
679    if (!PageSwapCache(page))
680        return 0;
681    if (PageWriteback(page))
682        return 0;
683    if (page_swapcount(page))
684        return 0;
685
686    /*
687     * Once hibernation has begun to create its image of memory,
688     * there's a danger that one of the calls to try_to_free_swap()
689     * - most probably a call from __try_to_reclaim_swap() while
690     * hibernation is allocating its own swap pages for the image,
691     * but conceivably even a call from memory reclaim - will free
692     * the swap from a page which has already been recorded in the
693     * image as a clean swapcache page, and then reuse its swap for
694     * another page of the image. On waking from hibernation, the
695     * original page might be freed under memory pressure, then
696     * later read back in from swap, now with the wrong data.
697     *
698     * Hibernation clears bits from gfp_allowed_mask to prevent
699     * memory reclaim from writing to disk, so check that here.
700     */
701    if (!(gfp_allowed_mask & __GFP_IO))
702        return 0;
703
704    delete_from_swap_cache(page);
705    SetPageDirty(page);
706    return 1;
707}
708
709/*
710 * Free the swap entry like above, but also try to
711 * free the page cache entry if it is the last user.
712 */
713int free_swap_and_cache(swp_entry_t entry)
714{
715    struct swap_info_struct *p;
716    struct page *page = NULL;
717
718    if (non_swap_entry(entry))
719        return 1;
720
721    p = swap_info_get(entry);
722    if (p) {
723        if (swap_entry_free(p, entry, 1) == SWAP_HAS_CACHE) {
724            page = find_get_page(&swapper_space, entry.val);
725            if (page && !trylock_page(page)) {
726                page_cache_release(page);
727                page = NULL;
728            }
729        }
730        spin_unlock(&swap_lock);
731    }
732    if (page) {
733        /*
734         * Not mapped elsewhere, or swap space full? Free it!
735         * Also recheck PageSwapCache now page is locked (above).
736         */
737        if (PageSwapCache(page) && !PageWriteback(page) &&
738                (!page_mapped(page) || vm_swap_full())) {
739            delete_from_swap_cache(page);
740            SetPageDirty(page);
741        }
742        unlock_page(page);
743        page_cache_release(page);
744    }
745    return p != NULL;
746}
747
748#ifdef CONFIG_CGROUP_MEM_RES_CTLR
749/**
750 * mem_cgroup_count_swap_user - count the user of a swap entry
751 * @ent: the swap entry to be checked
752 * @pagep: the pointer for the swap cache page of the entry to be stored
753 *
754 * Returns the number of the user of the swap entry. The number is valid only
755 * for swaps of anonymous pages.
756 * If the entry is found on swap cache, the page is stored to pagep with
757 * refcount of it being incremented.
758 */
759int mem_cgroup_count_swap_user(swp_entry_t ent, struct page **pagep)
760{
761    struct page *page;
762    struct swap_info_struct *p;
763    int count = 0;
764
765    page = find_get_page(&swapper_space, ent.val);
766    if (page)
767        count += page_mapcount(page);
768    p = swap_info_get(ent);
769    if (p) {
770        count += swap_count(p->swap_map[swp_offset(ent)]);
771        spin_unlock(&swap_lock);
772    }
773
774    *pagep = page;
775    return count;
776}
777#endif
778
779#ifdef CONFIG_HIBERNATION
780/*
781 * Find the swap type that corresponds to given device (if any).
782 *
783 * @offset - number of the PAGE_SIZE-sized block of the device, starting
784 * from 0, in which the swap header is expected to be located.
785 *
786 * This is needed for the suspend to disk (aka swsusp).
787 */
788int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)
789{
790    struct block_device *bdev = NULL;
791    int type;
792
793    if (device)
794        bdev = bdget(device);
795
796    spin_lock(&swap_lock);
797    for (type = 0; type < nr_swapfiles; type++) {
798        struct swap_info_struct *sis = swap_info[type];
799
800        if (!(sis->flags & SWP_WRITEOK))
801            continue;
802
803        if (!bdev) {
804            if (bdev_p)
805                *bdev_p = bdgrab(sis->bdev);
806
807            spin_unlock(&swap_lock);
808            return type;
809        }
810        if (bdev == sis->bdev) {
811            struct swap_extent *se = &sis->first_swap_extent;
812
813            if (se->start_block == offset) {
814                if (bdev_p)
815                    *bdev_p = bdgrab(sis->bdev);
816
817                spin_unlock(&swap_lock);
818                bdput(bdev);
819                return type;
820            }
821        }
822    }
823    spin_unlock(&swap_lock);
824    if (bdev)
825        bdput(bdev);
826
827    return -ENODEV;
828}
829
830/*
831 * Get the (PAGE_SIZE) block corresponding to given offset on the swapdev
832 * corresponding to given index in swap_info (swap type).
833 */
834sector_t swapdev_block(int type, pgoff_t offset)
835{
836    struct block_device *bdev;
837
838    if ((unsigned int)type >= nr_swapfiles)
839        return 0;
840    if (!(swap_info[type]->flags & SWP_WRITEOK))
841        return 0;
842    return map_swap_entry(swp_entry(type, offset), &bdev);
843}
844
845/*
846 * Return either the total number of swap pages of given type, or the number
847 * of free pages of that type (depending on @free)
848 *
849 * This is needed for software suspend
850 */
851unsigned int count_swap_pages(int type, int free)
852{
853    unsigned int n = 0;
854
855    spin_lock(&swap_lock);
856    if ((unsigned int)type < nr_swapfiles) {
857        struct swap_info_struct *sis = swap_info[type];
858
859        if (sis->flags & SWP_WRITEOK) {
860            n = sis->pages;
861            if (free)
862                n -= sis->inuse_pages;
863        }
864    }
865    spin_unlock(&swap_lock);
866    return n;
867}
868#endif /* CONFIG_HIBERNATION */
869
870/*
871 * No need to decide whether this PTE shares the swap entry with others,
872 * just let do_wp_page work it out if a write is requested later - to
873 * force COW, vm_page_prot omits write permission from any private vma.
874 */
875static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
876        unsigned long addr, swp_entry_t entry, struct page *page)
877{
878    struct mem_cgroup *ptr = NULL;
879    spinlock_t *ptl;
880    pte_t *pte;
881    int ret = 1;
882
883    if (mem_cgroup_try_charge_swapin(vma->vm_mm, page, GFP_KERNEL, &ptr)) {
884        ret = -ENOMEM;
885        goto out_nolock;
886    }
887
888    pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
889    if (unlikely(!pte_same(*pte, swp_entry_to_pte(entry)))) {
890        if (ret > 0)
891            mem_cgroup_cancel_charge_swapin(ptr);
892        ret = 0;
893        goto out;
894    }
895
896    dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
897    inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
898    get_page(page);
899    set_pte_at(vma->vm_mm, addr, pte,
900           pte_mkold(mk_pte(page, vma->vm_page_prot)));
901    page_add_anon_rmap(page, vma, addr);
902    mem_cgroup_commit_charge_swapin(page, ptr);
903    swap_free(entry);
904    /*
905     * Move the page to the active list so it is not
906     * immediately swapped out again after swapon.
907     */
908    activate_page(page);
909out:
910    pte_unmap_unlock(pte, ptl);
911out_nolock:
912    return ret;
913}
914
915static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
916                unsigned long addr, unsigned long end,
917                swp_entry_t entry, struct page *page)
918{
919    pte_t swp_pte = swp_entry_to_pte(entry);
920    pte_t *pte;
921    int ret = 0;
922
923    /*
924     * We don't actually need pte lock while scanning for swp_pte: since
925     * we hold page lock and mmap_sem, swp_pte cannot be inserted into the
926     * page table while we're scanning; though it could get zapped, and on
927     * some architectures (e.g. x86_32 with PAE) we might catch a glimpse
928     * of unmatched parts which look like swp_pte, so unuse_pte must
929     * recheck under pte lock. Scanning without pte lock lets it be
930     * preemptible whenever CONFIG_PREEMPT but not CONFIG_HIGHPTE.
931     */
932    pte = pte_offset_map(pmd, addr);
933    do {
934        /*
935         * swapoff spends a _lot_ of time in this loop!
936         * Test inline before going to call unuse_pte.
937         */
938        if (unlikely(pte_same(*pte, swp_pte))) {
939            pte_unmap(pte);
940            ret = unuse_pte(vma, pmd, addr, entry, page);
941            if (ret)
942                goto out;
943            pte = pte_offset_map(pmd, addr);
944        }
945    } while (pte++, addr += PAGE_SIZE, addr != end);
946    pte_unmap(pte - 1);
947out:
948    return ret;
949}
950
951static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
952                unsigned long addr, unsigned long end,
953                swp_entry_t entry, struct page *page)
954{
955    pmd_t *pmd;
956    unsigned long next;
957    int ret;
958
959    pmd = pmd_offset(pud, addr);
960    do {
961        next = pmd_addr_end(addr, end);
962        if (pmd_none_or_clear_bad(pmd))
963            continue;
964        ret = unuse_pte_range(vma, pmd, addr, next, entry, page);
965        if (ret)
966            return ret;
967    } while (pmd++, addr = next, addr != end);
968    return 0;
969}
970
971static inline int unuse_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
972                unsigned long addr, unsigned long end,
973                swp_entry_t entry, struct page *page)
974{
975    pud_t *pud;
976    unsigned long next;
977    int ret;
978
979    pud = pud_offset(pgd, addr);
980    do {
981        next = pud_addr_end(addr, end);
982        if (pud_none_or_clear_bad(pud))
983            continue;
984        ret = unuse_pmd_range(vma, pud, addr, next, entry, page);
985        if (ret)
986            return ret;
987    } while (pud++, addr = next, addr != end);
988    return 0;
989}
990
991static int unuse_vma(struct vm_area_struct *vma,
992                swp_entry_t entry, struct page *page)
993{
994    pgd_t *pgd;
995    unsigned long addr, end, next;
996    int ret;
997
998    if (page_anon_vma(page)) {
999        addr = page_address_in_vma(page, vma);
1000        if (addr == -EFAULT)
1001            return 0;
1002        else
1003            end = addr + PAGE_SIZE;
1004    } else {
1005        addr = vma->vm_start;
1006        end = vma->vm_end;
1007    }
1008
1009    pgd = pgd_offset(vma->vm_mm, addr);
1010    do {
1011        next = pgd_addr_end(addr, end);
1012        if (pgd_none_or_clear_bad(pgd))
1013            continue;
1014        ret = unuse_pud_range(vma, pgd, addr, next, entry, page);
1015        if (ret)
1016            return ret;
1017    } while (pgd++, addr = next, addr != end);
1018    return 0;
1019}
1020
1021static int unuse_mm(struct mm_struct *mm,
1022                swp_entry_t entry, struct page *page)
1023{
1024    struct vm_area_struct *vma;
1025    int ret = 0;
1026
1027    if (!down_read_trylock(&mm->mmap_sem)) {
1028        /*
1029         * Activate page so shrink_inactive_list is unlikely to unmap
1030         * its ptes while lock is dropped, so swapoff can make progress.
1031         */
1032        activate_page(page);
1033        unlock_page(page);
1034        down_read(&mm->mmap_sem);
1035        lock_page(page);
1036    }
1037    for (vma = mm->mmap; vma; vma = vma->vm_next) {
1038        if (vma->anon_vma && (ret = unuse_vma(vma, entry, page)))
1039            break;
1040    }
1041    up_read(&mm->mmap_sem);
1042    return (ret < 0)? ret: 0;
1043}
1044
1045/*
1046 * Scan swap_map from current position to next entry still in use.
1047 * Recycle to start on reaching the end, returning 0 when empty.
1048 */
1049static unsigned int find_next_to_unuse(struct swap_info_struct *si,
1050                    unsigned int prev)
1051{
1052    unsigned int max = si->max;
1053    unsigned int i = prev;
1054    unsigned char count;
1055
1056    /*
1057     * No need for swap_lock here: we're just looking
1058     * for whether an entry is in use, not modifying it; false
1059     * hits are okay, and sys_swapoff() has already prevented new
1060     * allocations from this area (while holding swap_lock).
1061     */
1062    for (;;) {
1063        if (++i >= max) {
1064            if (!prev) {
1065                i = 0;
1066                break;
1067            }
1068            /*
1069             * No entries in use at top of swap_map,
1070             * loop back to start and recheck there.
1071             */
1072            max = prev + 1;
1073            prev = 0;
1074            i = 1;
1075        }
1076        count = si->swap_map[i];
1077        if (count && swap_count(count) != SWAP_MAP_BAD)
1078            break;
1079    }
1080    return i;
1081}
1082
1083/*
1084 * We completely avoid races by reading each swap page in advance,
1085 * and then search for the process using it. All the necessary
1086 * page table adjustments can then be made atomically.
1087 */
1088static int try_to_unuse(unsigned int type)
1089{
1090    struct swap_info_struct *si = swap_info[type];
1091    struct mm_struct *start_mm;
1092    unsigned char *swap_map;
1093    unsigned char swcount;
1094    struct page *page;
1095    swp_entry_t entry;
1096    unsigned int i = 0;
1097    int retval = 0;
1098
1099    /*
1100     * When searching mms for an entry, a good strategy is to
1101     * start at the first mm we freed the previous entry from
1102     * (though actually we don't notice whether we or coincidence
1103     * freed the entry). Initialize this start_mm with a hold.
1104     *
1105     * A simpler strategy would be to start at the last mm we
1106     * freed the previous entry from; but that would take less
1107     * advantage of mmlist ordering, which clusters forked mms
1108     * together, child after parent. If we race with dup_mmap(), we
1109     * prefer to resolve parent before child, lest we miss entries
1110     * duplicated after we scanned child: using last mm would invert
1111     * that.
1112     */
1113    start_mm = &init_mm;
1114    atomic_inc(&init_mm.mm_users);
1115
1116    /*
1117     * Keep on scanning until all entries have gone. Usually,
1118     * one pass through swap_map is enough, but not necessarily:
1119     * there are races when an instance of an entry might be missed.
1120     */
1121    while ((i = find_next_to_unuse(si, i)) != 0) {
1122        if (signal_pending(current)) {
1123            retval = -EINTR;
1124            break;
1125        }
1126
1127        /*
1128         * Get a page for the entry, using the existing swap
1129         * cache page if there is one. Otherwise, get a clean
1130         * page and read the swap into it.
1131         */
1132        swap_map = &si->swap_map[i];
1133        entry = swp_entry(type, i);
1134        page = read_swap_cache_async(entry,
1135                    GFP_HIGHUSER_MOVABLE, NULL, 0);
1136        if (!page) {
1137            /*
1138             * Either swap_duplicate() failed because entry
1139             * has been freed independently, and will not be
1140             * reused since sys_swapoff() already disabled
1141             * allocation from here, or alloc_page() failed.
1142             */
1143            if (!*swap_map)
1144                continue;
1145            retval = -ENOMEM;
1146            break;
1147        }
1148
1149        /*
1150         * Don't hold on to start_mm if it looks like exiting.
1151         */
1152        if (atomic_read(&start_mm->mm_users) == 1) {
1153            mmput(start_mm);
1154            start_mm = &init_mm;
1155            atomic_inc(&init_mm.mm_users);
1156        }
1157
1158        /*
1159         * Wait for and lock page. When do_swap_page races with
1160         * try_to_unuse, do_swap_page can handle the fault much
1161         * faster than try_to_unuse can locate the entry. This
1162         * apparently redundant "wait_on_page_locked" lets try_to_unuse
1163         * defer to do_swap_page in such a case - in some tests,
1164         * do_swap_page and try_to_unuse repeatedly compete.
1165         */
1166        wait_on_page_locked(page);
1167        wait_on_page_writeback(page);
1168        lock_page(page);
1169        wait_on_page_writeback(page);
1170
1171        /*
1172         * Remove all references to entry.
1173         */
1174        swcount = *swap_map;
1175        if (swap_count(swcount) == SWAP_MAP_SHMEM) {
1176            retval = shmem_unuse(entry, page);
1177            /* page has already been unlocked and released */
1178            if (retval < 0)
1179                break;
1180            continue;
1181        }
1182        if (swap_count(swcount) && start_mm != &init_mm)
1183            retval = unuse_mm(start_mm, entry, page);
1184
1185        if (swap_count(*swap_map)) {
1186            int set_start_mm = (*swap_map >= swcount);
1187            struct list_head *p = &start_mm->mmlist;
1188            struct mm_struct *new_start_mm = start_mm;
1189            struct mm_struct *prev_mm = start_mm;
1190            struct mm_struct *mm;
1191
1192            atomic_inc(&new_start_mm->mm_users);
1193            atomic_inc(&prev_mm->mm_users);
1194            spin_lock(&mmlist_lock);
1195            while (swap_count(*swap_map) && !retval &&
1196                    (p = p->next) != &start_mm->mmlist) {
1197                mm = list_entry(p, struct mm_struct, mmlist);
1198                if (!atomic_inc_not_zero(&mm->mm_users))
1199                    continue;
1200                spin_unlock(&mmlist_lock);
1201                mmput(prev_mm);
1202                prev_mm = mm;
1203
1204                cond_resched();
1205
1206                swcount = *swap_map;
1207                if (!swap_count(swcount)) /* any usage ? */
1208                    ;
1209                else if (mm == &init_mm)
1210                    set_start_mm = 1;
1211                else
1212                    retval = unuse_mm(mm, entry, page);
1213
1214                if (set_start_mm && *swap_map < swcount) {
1215                    mmput(new_start_mm);
1216                    atomic_inc(&mm->mm_users);
1217                    new_start_mm = mm;
1218                    set_start_mm = 0;
1219                }
1220                spin_lock(&mmlist_lock);
1221            }
1222            spin_unlock(&mmlist_lock);
1223            mmput(prev_mm);
1224            mmput(start_mm);
1225            start_mm = new_start_mm;
1226        }
1227        if (retval) {
1228            unlock_page(page);
1229            page_cache_release(page);
1230            break;
1231        }
1232
1233        /*
1234         * If a reference remains (rare), we would like to leave
1235         * the page in the swap cache; but try_to_unmap could
1236         * then re-duplicate the entry once we drop page lock,
1237         * so we might loop indefinitely; also, that page could
1238         * not be swapped out to other storage meanwhile. So:
1239         * delete from cache even if there's another reference,
1240         * after ensuring that the data has been saved to disk -
1241         * since if the reference remains (rarer), it will be
1242         * read from disk into another page. Splitting into two
1243         * pages would be incorrect if swap supported "shared
1244         * private" pages, but they are handled by tmpfs files.
1245         *
1246         * Given how unuse_vma() targets one particular offset
1247         * in an anon_vma, once the anon_vma has been determined,
1248         * this splitting happens to be just what is needed to
1249         * handle where KSM pages have been swapped out: re-reading
1250         * is unnecessarily slow, but we can fix that later on.
1251         */
1252        if (swap_count(*swap_map) &&
1253             PageDirty(page) && PageSwapCache(page)) {
1254            struct writeback_control wbc = {
1255                .sync_mode = WB_SYNC_NONE,
1256            };
1257
1258            swap_writepage(page, &wbc);
1259            lock_page(page);
1260            wait_on_page_writeback(page);
1261        }
1262
1263        /*
1264         * It is conceivable that a racing task removed this page from
1265         * swap cache just before we acquired the page lock at the top,
1266         * or while we dropped it in unuse_mm(). The page might even
1267         * be back in swap cache on another swap area: that we must not
1268         * delete, since it may not have been written out to swap yet.
1269         */
1270        if (PageSwapCache(page) &&
1271            likely(page_private(page) == entry.val))
1272            delete_from_swap_cache(page);
1273
1274        /*
1275         * So we could skip searching mms once swap count went
1276         * to 1, we did not mark any present ptes as dirty: must
1277         * mark page dirty so shrink_page_list will preserve it.
1278         */
1279        SetPageDirty(page);
1280        unlock_page(page);
1281        page_cache_release(page);
1282
1283        /*
1284         * Make sure that we aren't completely killing
1285         * interactive performance.
1286         */
1287        cond_resched();
1288    }
1289
1290    mmput(start_mm);
1291    return retval;
1292}
1293
1294/*
1295 * After a successful try_to_unuse, if no swap is now in use, we know
1296 * we can empty the mmlist. swap_lock must be held on entry and exit.
1297 * Note that mmlist_lock nests inside swap_lock, and an mm must be
1298 * added to the mmlist just after page_duplicate - before would be racy.
1299 */
1300static void drain_mmlist(void)
1301{
1302    struct list_head *p, *next;
1303    unsigned int type;
1304
1305    for (type = 0; type < nr_swapfiles; type++)
1306        if (swap_info[type]->inuse_pages)
1307            return;
1308    spin_lock(&mmlist_lock);
1309    list_for_each_safe(p, next, &init_mm.mmlist)
1310        list_del_init(p);
1311    spin_unlock(&mmlist_lock);
1312}
1313
1314/*
1315 * Use this swapdev's extent info to locate the (PAGE_SIZE) block which
1316 * corresponds to page offset for the specified swap entry.
1317 * Note that the type of this function is sector_t, but it returns page offset
1318 * into the bdev, not sector offset.
1319 */
1320static sector_t map_swap_entry(swp_entry_t entry, struct block_device **bdev)
1321{
1322    struct swap_info_struct *sis;
1323    struct swap_extent *start_se;
1324    struct swap_extent *se;
1325    pgoff_t offset;
1326
1327    sis = swap_info[swp_type(entry)];
1328    *bdev = sis->bdev;
1329
1330    offset = swp_offset(entry);
1331    start_se = sis->curr_swap_extent;
1332    se = start_se;
1333
1334    for ( ; ; ) {
1335        struct list_head *lh;
1336
1337        if (se->start_page <= offset &&
1338                offset < (se->start_page + se->nr_pages)) {
1339            return se->start_block + (offset - se->start_page);
1340        }
1341        lh = se->list.next;
1342        se = list_entry(lh, struct swap_extent, list);
1343        sis->curr_swap_extent = se;
1344        BUG_ON(se == start_se); /* It *must* be present */
1345    }
1346}
1347
1348/*
1349 * Returns the page offset into bdev for the specified page's swap entry.
1350 */
1351sector_t map_swap_page(struct page *page, struct block_device **bdev)
1352{
1353    swp_entry_t entry;
1354    entry.val = page_private(page);
1355    return map_swap_entry(entry, bdev);
1356}
1357
1358/*
1359 * Free all of a swapdev's extent information
1360 */
1361static void destroy_swap_extents(struct swap_info_struct *sis)
1362{
1363    while (!list_empty(&sis->first_swap_extent.list)) {
1364        struct swap_extent *se;
1365
1366        se = list_entry(sis->first_swap_extent.list.next,
1367                struct swap_extent, list);
1368        list_del(&se->list);
1369        kfree(se);
1370    }
1371}
1372
1373/*
1374 * Add a block range (and the corresponding page range) into this swapdev's
1375 * extent list. The extent list is kept sorted in page order.
1376 *
1377 * This function rather assumes that it is called in ascending page order.
1378 */
1379static int
1380add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
1381        unsigned long nr_pages, sector_t start_block)
1382{
1383    struct swap_extent *se;
1384    struct swap_extent *new_se;
1385    struct list_head *lh;
1386
1387    if (start_page == 0) {
1388        se = &sis->first_swap_extent;
1389        sis->curr_swap_extent = se;
1390        se->start_page = 0;
1391        se->nr_pages = nr_pages;
1392        se->start_block = start_block;
1393        return 1;
1394    } else {
1395        lh = sis->first_swap_extent.list.prev; /* Highest extent */
1396        se = list_entry(lh, struct swap_extent, list);
1397        BUG_ON(se->start_page + se->nr_pages != start_page);
1398        if (se->start_block + se->nr_pages == start_block) {
1399            /* Merge it */
1400            se->nr_pages += nr_pages;
1401            return 0;
1402        }
1403    }
1404
1405    /*
1406     * No merge. Insert a new extent, preserving ordering.
1407     */
1408    new_se = kmalloc(sizeof(*se), GFP_KERNEL);
1409    if (new_se == NULL)
1410        return -ENOMEM;
1411    new_se->start_page = start_page;
1412    new_se->nr_pages = nr_pages;
1413    new_se->start_block = start_block;
1414
1415    list_add_tail(&new_se->list, &sis->first_swap_extent.list);
1416    return 1;
1417}
1418
1419/*
1420 * A `swap extent' is a simple thing which maps a contiguous range of pages
1421 * onto a contiguous range of disk blocks. An ordered list of swap extents
1422 * is built at swapon time and is then used at swap_writepage/swap_readpage
1423 * time for locating where on disk a page belongs.
1424 *
1425 * If the swapfile is an S_ISBLK block device, a single extent is installed.
1426 * This is done so that the main operating code can treat S_ISBLK and S_ISREG
1427 * swap files identically.
1428 *
1429 * Whether the swapdev is an S_ISREG file or an S_ISBLK blockdev, the swap
1430 * extent list operates in PAGE_SIZE disk blocks. Both S_ISREG and S_ISBLK
1431 * swapfiles are handled *identically* after swapon time.
1432 *
1433 * For S_ISREG swapfiles, setup_swap_extents() will walk all the file's blocks
1434 * and will parse them into an ordered extent list, in PAGE_SIZE chunks. If
1435 * some stray blocks are found which do not fall within the PAGE_SIZE alignment
1436 * requirements, they are simply tossed out - we will never use those blocks
1437 * for swapping.
1438 *
1439 * For S_ISREG swapfiles we set S_SWAPFILE across the life of the swapon. This
1440 * prevents root from shooting her foot off by ftruncating an in-use swapfile,
1441 * which will scribble on the fs.
1442 *
1443 * The amount of disk space which a single swap extent represents varies.
1444 * Typically it is in the 1-4 megabyte range. So we can have hundreds of
1445 * extents in the list. To avoid much list walking, we cache the previous
1446 * search location in `curr_swap_extent', and start new searches from there.
1447 * This is extremely effective. The average number of iterations in
1448 * map_swap_page() has been measured at about 0.3 per page. - akpm.
1449 */
1450static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
1451{
1452    struct inode *inode;
1453    unsigned blocks_per_page;
1454    unsigned long page_no;
1455    unsigned blkbits;
1456    sector_t probe_block;
1457    sector_t last_block;
1458    sector_t lowest_block = -1;
1459    sector_t highest_block = 0;
1460    int nr_extents = 0;
1461    int ret;
1462
1463    inode = sis->swap_file->f_mapping->host;
1464    if (S_ISBLK(inode->i_mode)) {
1465        ret = add_swap_extent(sis, 0, sis->max, 0);
1466        *span = sis->pages;
1467        goto out;
1468    }
1469
1470    blkbits = inode->i_blkbits;
1471    blocks_per_page = PAGE_SIZE >> blkbits;
1472
1473    /*
1474     * Map all the blocks into the extent list. This code doesn't try
1475     * to be very smart.
1476     */
1477    probe_block = 0;
1478    page_no = 0;
1479    last_block = i_size_read(inode) >> blkbits;
1480    while ((probe_block + blocks_per_page) <= last_block &&
1481            page_no < sis->max) {
1482        unsigned block_in_page;
1483        sector_t first_block;
1484
1485        first_block = bmap(inode, probe_block);
1486        if (first_block == 0)
1487            goto bad_bmap;
1488
1489        /*
1490         * It must be PAGE_SIZE aligned on-disk
1491         */
1492        if (first_block & (blocks_per_page - 1)) {
1493            probe_block++;
1494            goto reprobe;
1495        }
1496
1497        for (block_in_page = 1; block_in_page < blocks_per_page;
1498                    block_in_page++) {
1499            sector_t block;
1500
1501            block = bmap(inode, probe_block + block_in_page);
1502            if (block == 0)
1503                goto bad_bmap;
1504            if (block != first_block + block_in_page) {
1505                /* Discontiguity */
1506                probe_block++;
1507                goto reprobe;
1508            }
1509        }
1510
1511        first_block >>= (PAGE_SHIFT - blkbits);
1512        if (page_no) { /* exclude the header page */
1513            if (first_block < lowest_block)
1514                lowest_block = first_block;
1515            if (first_block > highest_block)
1516                highest_block = first_block;
1517        }
1518
1519        /*
1520         * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks
1521         */
1522        ret = add_swap_extent(sis, page_no, 1, first_block);
1523        if (ret < 0)
1524            goto out;
1525        nr_extents += ret;
1526        page_no++;
1527        probe_block += blocks_per_page;
1528reprobe:
1529        continue;
1530    }
1531    ret = nr_extents;
1532    *span = 1 + highest_block - lowest_block;
1533    if (page_no == 0)
1534        page_no = 1; /* force Empty message */
1535    sis->max = page_no;
1536    sis->pages = page_no - 1;
1537    sis->highest_bit = page_no - 1;
1538out:
1539    return ret;
1540bad_bmap:
1541    printk(KERN_ERR "swapon: swapfile has holes\n");
1542    ret = -EINVAL;
1543    goto out;
1544}
1545
1546SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
1547{
1548    struct swap_info_struct *p = NULL;
1549    unsigned char *swap_map;
1550    struct file *swap_file, *victim;
1551    struct address_space *mapping;
1552    struct inode *inode;
1553    char *pathname;
1554    int i, type, prev;
1555    int err;
1556
1557    if (!capable(CAP_SYS_ADMIN))
1558        return -EPERM;
1559
1560    pathname = getname(specialfile);
1561    err = PTR_ERR(pathname);
1562    if (IS_ERR(pathname))
1563        goto out;
1564
1565    victim = filp_open(pathname, O_RDWR|O_LARGEFILE, 0);
1566    putname(pathname);
1567    err = PTR_ERR(victim);
1568    if (IS_ERR(victim))
1569        goto out;
1570
1571    mapping = victim->f_mapping;
1572    prev = -1;
1573    spin_lock(&swap_lock);
1574    for (type = swap_list.head; type >= 0; type = swap_info[type]->next) {
1575        p = swap_info[type];
1576        if (p->flags & SWP_WRITEOK) {
1577            if (p->swap_file->f_mapping == mapping)
1578                break;
1579        }
1580        prev = type;
1581    }
1582    if (type < 0) {
1583        err = -EINVAL;
1584        spin_unlock(&swap_lock);
1585        goto out_dput;
1586    }
1587    if (!security_vm_enough_memory(p->pages))
1588        vm_unacct_memory(p->pages);
1589    else {
1590        err = -ENOMEM;
1591        spin_unlock(&swap_lock);
1592        goto out_dput;
1593    }
1594    if (prev < 0)
1595        swap_list.head = p->next;
1596    else
1597        swap_info[prev]->next = p->next;
1598    if (type == swap_list.next) {
1599        /* just pick something that's safe... */
1600        swap_list.next = swap_list.head;
1601    }
1602    if (p->prio < 0) {
1603        for (i = p->next; i >= 0; i = swap_info[i]->next)
1604            swap_info[i]->prio = p->prio--;
1605        least_priority++;
1606    }
1607    nr_swap_pages -= p->pages;
1608    total_swap_pages -= p->pages;
1609    p->flags &= ~SWP_WRITEOK;
1610    spin_unlock(&swap_lock);
1611
1612    current->flags |= PF_OOM_ORIGIN;
1613    err = try_to_unuse(type);
1614    current->flags &= ~PF_OOM_ORIGIN;
1615
1616    if (err) {
1617        /* re-insert swap space back into swap_list */
1618        spin_lock(&swap_lock);
1619        if (p->prio < 0)
1620            p->prio = --least_priority;
1621        prev = -1;
1622        for (i = swap_list.head; i >= 0; i = swap_info[i]->next) {
1623            if (p->prio >= swap_info[i]->prio)
1624                break;
1625            prev = i;
1626        }
1627        p->next = i;
1628        if (prev < 0)
1629            swap_list.head = swap_list.next = type;
1630        else
1631            swap_info[prev]->next = type;
1632        nr_swap_pages += p->pages;
1633        total_swap_pages += p->pages;
1634        p->flags |= SWP_WRITEOK;
1635        spin_unlock(&swap_lock);
1636        goto out_dput;
1637    }
1638
1639    /* wait for any unplug function to finish */
1640    down_write(&swap_unplug_sem);
1641    up_write(&swap_unplug_sem);
1642
1643    destroy_swap_extents(p);
1644    if (p->flags & SWP_CONTINUED)
1645        free_swap_count_continuations(p);
1646
1647    mutex_lock(&swapon_mutex);
1648    spin_lock(&swap_lock);
1649    drain_mmlist();
1650
1651    /* wait for anyone still in scan_swap_map */
1652    p->highest_bit = 0; /* cuts scans short */
1653    while (p->flags >= SWP_SCANNING) {
1654        spin_unlock(&swap_lock);
1655        schedule_timeout_uninterruptible(1);
1656        spin_lock(&swap_lock);
1657    }
1658
1659    swap_file = p->swap_file;
1660    p->swap_file = NULL;
1661    p->max = 0;
1662    swap_map = p->swap_map;
1663    p->swap_map = NULL;
1664    p->flags = 0;
1665    spin_unlock(&swap_lock);
1666    mutex_unlock(&swapon_mutex);
1667    vfree(swap_map);
1668    /* Destroy swap account informatin */
1669    swap_cgroup_swapoff(type);
1670
1671    inode = mapping->host;
1672    if (S_ISBLK(inode->i_mode)) {
1673        struct block_device *bdev = I_BDEV(inode);
1674        set_blocksize(bdev, p->old_block_size);
1675        bd_release(bdev);
1676    } else {
1677        mutex_lock(&inode->i_mutex);
1678        inode->i_flags &= ~S_SWAPFILE;
1679        mutex_unlock(&inode->i_mutex);
1680    }
1681    filp_close(swap_file, NULL);
1682    err = 0;
1683
1684out_dput:
1685    filp_close(victim, NULL);
1686out:
1687    return err;
1688}
1689
1690#ifdef CONFIG_PROC_FS
1691/* iterator */
1692static void *swap_start(struct seq_file *swap, loff_t *pos)
1693{
1694    struct swap_info_struct *si;
1695    int type;
1696    loff_t l = *pos;
1697
1698    mutex_lock(&swapon_mutex);
1699
1700    if (!l)
1701        return SEQ_START_TOKEN;
1702
1703    for (type = 0; type < nr_swapfiles; type++) {
1704        smp_rmb(); /* read nr_swapfiles before swap_info[type] */
1705        si = swap_info[type];
1706        if (!(si->flags & SWP_USED) || !si->swap_map)
1707            continue;
1708        if (!--l)
1709            return si;
1710    }
1711
1712    return NULL;
1713}
1714
1715static void *swap_next(struct seq_file *swap, void *v, loff_t *pos)
1716{
1717    struct swap_info_struct *si = v;
1718    int type;
1719
1720    if (v == SEQ_START_TOKEN)
1721        type = 0;
1722    else
1723        type = si->type + 1;
1724
1725    for (; type < nr_swapfiles; type++) {
1726        smp_rmb(); /* read nr_swapfiles before swap_info[type] */
1727        si = swap_info[type];
1728        if (!(si->flags & SWP_USED) || !si->swap_map)
1729            continue;
1730        ++*pos;
1731        return si;
1732    }
1733
1734    return NULL;
1735}
1736
1737static void swap_stop(struct seq_file *swap, void *v)
1738{
1739    mutex_unlock(&swapon_mutex);
1740}
1741
1742static int swap_show(struct seq_file *swap, void *v)
1743{
1744    struct swap_info_struct *si = v;
1745    struct file *file;
1746    int len;
1747
1748    if (si == SEQ_START_TOKEN) {
1749        seq_puts(swap,"Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n");
1750        return 0;
1751    }
1752
1753    file = si->swap_file;
1754    len = seq_path(swap, &file->f_path, " \t\n\\");
1755    seq_printf(swap, "%*s%s\t%u\t%u\t%d\n",
1756            len < 40 ? 40 - len : 1, " ",
1757            S_ISBLK(file->f_path.dentry->d_inode->i_mode) ?
1758                "partition" : "file\t",
1759            si->pages << (PAGE_SHIFT - 10),
1760            si->inuse_pages << (PAGE_SHIFT - 10),
1761            si->prio);
1762    return 0;
1763}
1764
1765static const struct seq_operations swaps_op = {
1766    .start = swap_start,
1767    .next = swap_next,
1768    .stop = swap_stop,
1769    .show = swap_show
1770};
1771
1772static int swaps_open(struct inode *inode, struct file *file)
1773{
1774    return seq_open(file, &swaps_op);
1775}
1776
1777static const struct file_operations proc_swaps_operations = {
1778    .open = swaps_open,
1779    .read = seq_read,
1780    .llseek = seq_lseek,
1781    .release = seq_release,
1782};
1783
1784static int __init procswaps_init(void)
1785{
1786    proc_create("swaps", 0, NULL, &proc_swaps_operations);
1787    return 0;
1788}
1789__initcall(procswaps_init);
1790#endif /* CONFIG_PROC_FS */
1791
1792#ifdef MAX_SWAPFILES_CHECK
1793static int __init max_swapfiles_check(void)
1794{
1795    MAX_SWAPFILES_CHECK();
1796    return 0;
1797}
1798late_initcall(max_swapfiles_check);
1799#endif
1800
1801/*
1802 * Written 01/25/92 by Simmule Turner, heavily changed by Linus.
1803 *
1804 * The swapon system call
1805 */
1806SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
1807{
1808    struct swap_info_struct *p;
1809    char *name = NULL;
1810    struct block_device *bdev = NULL;
1811    struct file *swap_file = NULL;
1812    struct address_space *mapping;
1813    unsigned int type;
1814    int i, prev;
1815    int error;
1816    union swap_header *swap_header;
1817    unsigned int nr_good_pages;
1818    int nr_extents = 0;
1819    sector_t span;
1820    unsigned long maxpages;
1821    unsigned long swapfilepages;
1822    unsigned char *swap_map = NULL;
1823    struct page *page = NULL;
1824    struct inode *inode = NULL;
1825    int did_down = 0;
1826
1827    if (!capable(CAP_SYS_ADMIN))
1828        return -EPERM;
1829
1830    p = kzalloc(sizeof(*p), GFP_KERNEL);
1831    if (!p)
1832        return -ENOMEM;
1833
1834    spin_lock(&swap_lock);
1835    for (type = 0; type < nr_swapfiles; type++) {
1836        if (!(swap_info[type]->flags & SWP_USED))
1837            break;
1838    }
1839    error = -EPERM;
1840    if (type >= MAX_SWAPFILES) {
1841        spin_unlock(&swap_lock);
1842        kfree(p);
1843        goto out;
1844    }
1845    if (type >= nr_swapfiles) {
1846        p->type = type;
1847        swap_info[type] = p;
1848        /*
1849         * Write swap_info[type] before nr_swapfiles, in case a
1850         * racing procfs swap_start() or swap_next() is reading them.
1851         * (We never shrink nr_swapfiles, we never free this entry.)
1852         */
1853        smp_wmb();
1854        nr_swapfiles++;
1855    } else {
1856        kfree(p);
1857        p = swap_info[type];
1858        /*
1859         * Do not memset this entry: a racing procfs swap_next()
1860         * would be relying on p->type to remain valid.
1861         */
1862    }
1863    INIT_LIST_HEAD(&p->first_swap_extent.list);
1864    p->flags = SWP_USED;
1865    p->next = -1;
1866    spin_unlock(&swap_lock);
1867
1868    name = getname(specialfile);
1869    error = PTR_ERR(name);
1870    if (IS_ERR(name)) {
1871        name = NULL;
1872        goto bad_swap_2;
1873    }
1874    swap_file = filp_open(name, O_RDWR|O_LARGEFILE, 0);
1875    error = PTR_ERR(swap_file);
1876    if (IS_ERR(swap_file)) {
1877        swap_file = NULL;
1878        goto bad_swap_2;
1879    }
1880
1881    p->swap_file = swap_file;
1882    mapping = swap_file->f_mapping;
1883    inode = mapping->host;
1884
1885    error = -EBUSY;
1886    for (i = 0; i < nr_swapfiles; i++) {
1887        struct swap_info_struct *q = swap_info[i];
1888
1889        if (i == type || !q->swap_file)
1890            continue;
1891        if (mapping == q->swap_file->f_mapping)
1892            goto bad_swap;
1893    }
1894
1895    error = -EINVAL;
1896    if (S_ISBLK(inode->i_mode)) {
1897        bdev = I_BDEV(inode);
1898        error = bd_claim(bdev, sys_swapon);
1899        if (error < 0) {
1900            bdev = NULL;
1901            error = -EINVAL;
1902            goto bad_swap;
1903        }
1904        p->old_block_size = block_size(bdev);
1905        error = set_blocksize(bdev, PAGE_SIZE);
1906        if (error < 0)
1907            goto bad_swap;
1908        p->bdev = bdev;
1909        p->flags |= SWP_BLKDEV;
1910    } else if (S_ISREG(inode->i_mode)) {
1911        p->bdev = inode->i_sb->s_bdev;
1912        mutex_lock(&inode->i_mutex);
1913        did_down = 1;
1914        if (IS_SWAPFILE(inode)) {
1915            error = -EBUSY;
1916            goto bad_swap;
1917        }
1918    } else {
1919        goto bad_swap;
1920    }
1921
1922    swapfilepages = i_size_read(inode) >> PAGE_SHIFT;
1923
1924    /*
1925     * Read the swap header.
1926     */
1927    if (!mapping->a_ops->readpage) {
1928        error = -EINVAL;
1929        goto bad_swap;
1930    }
1931    page = read_mapping_page(mapping, 0, swap_file);
1932    if (IS_ERR(page)) {
1933        error = PTR_ERR(page);
1934        goto bad_swap;
1935    }
1936    swap_header = kmap(page);
1937
1938    if (memcmp("SWAPSPACE2", swap_header->magic.magic, 10)) {
1939        printk(KERN_ERR "Unable to find swap-space signature\n");
1940        error = -EINVAL;
1941        goto bad_swap;
1942    }
1943
1944    /* swap partition endianess hack... */
1945    if (swab32(swap_header->info.version) == 1) {
1946        swab32s(&swap_header->info.version);
1947        swab32s(&swap_header->info.last_page);
1948        swab32s(&swap_header->info.nr_badpages);
1949        for (i = 0; i < swap_header->info.nr_badpages; i++)
1950            swab32s(&swap_header->info.badpages[i]);
1951    }
1952    /* Check the swap header's sub-version */
1953    if (swap_header->info.version != 1) {
1954        printk(KERN_WARNING
1955               "Unable to handle swap header version %d\n",
1956               swap_header->info.version);
1957        error = -EINVAL;
1958        goto bad_swap;
1959    }
1960
1961    p->lowest_bit = 1;
1962    p->cluster_next = 1;
1963    p->cluster_nr = 0;
1964
1965    /*
1966     * Find out how many pages are allowed for a single swap
1967     * device. There are two limiting factors: 1) the number of
1968     * bits for the swap offset in the swp_entry_t type and
1969     * 2) the number of bits in the a swap pte as defined by
1970     * the different architectures. In order to find the
1971     * largest possible bit mask a swap entry with swap type 0
1972     * and swap offset ~0UL is created, encoded to a swap pte,
1973     * decoded to a swp_entry_t again and finally the swap
1974     * offset is extracted. This will mask all the bits from
1975     * the initial ~0UL mask that can't be encoded in either
1976     * the swp_entry_t or the architecture definition of a
1977     * swap pte.
1978     */
1979    maxpages = swp_offset(pte_to_swp_entry(
1980            swp_entry_to_pte(swp_entry(0, ~0UL)))) + 1;
1981    if (maxpages > swap_header->info.last_page) {
1982        maxpages = swap_header->info.last_page + 1;
1983        /* p->max is an unsigned int: don't overflow it */
1984        if ((unsigned int)maxpages == 0)
1985            maxpages = UINT_MAX;
1986    }
1987    p->highest_bit = maxpages - 1;
1988
1989    error = -EINVAL;
1990    if (!maxpages)
1991        goto bad_swap;
1992    if (swapfilepages && maxpages > swapfilepages) {
1993        printk(KERN_WARNING
1994               "Swap area shorter than signature indicates\n");
1995        goto bad_swap;
1996    }
1997    if (swap_header->info.nr_badpages && S_ISREG(inode->i_mode))
1998        goto bad_swap;
1999    if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
2000        goto bad_swap;
2001
2002    /* OK, set up the swap map and apply the bad block list */
2003    swap_map = vmalloc(maxpages);
2004    if (!swap_map) {
2005        error = -ENOMEM;
2006        goto bad_swap;
2007    }
2008
2009    memset(swap_map, 0, maxpages);
2010    nr_good_pages = maxpages - 1; /* omit header page */
2011
2012    for (i = 0; i < swap_header->info.nr_badpages; i++) {
2013        unsigned int page_nr = swap_header->info.badpages[i];
2014        if (page_nr == 0 || page_nr > swap_header->info.last_page) {
2015            error = -EINVAL;
2016            goto bad_swap;
2017        }
2018        if (page_nr < maxpages) {
2019            swap_map[page_nr] = SWAP_MAP_BAD;
2020            nr_good_pages--;
2021        }
2022    }
2023
2024    error = swap_cgroup_swapon(type, maxpages);
2025    if (error)
2026        goto bad_swap;
2027
2028    if (nr_good_pages) {
2029        swap_map[0] = SWAP_MAP_BAD;
2030        p->max = maxpages;
2031        p->pages = nr_good_pages;
2032        nr_extents = setup_swap_extents(p, &span);
2033        if (nr_extents < 0) {
2034            error = nr_extents;
2035            goto bad_swap;
2036        }
2037        nr_good_pages = p->pages;
2038    }
2039    if (!nr_good_pages) {
2040        printk(KERN_WARNING "Empty swap-file\n");
2041        error = -EINVAL;
2042        goto bad_swap;
2043    }
2044
2045    if (p->bdev) {
2046        if (blk_queue_nonrot(bdev_get_queue(p->bdev))) {
2047            p->flags |= SWP_SOLIDSTATE;
2048            p->cluster_next = 1 + (random32() % p->highest_bit);
2049        }
2050        if (discard_swap(p) == 0 && (swap_flags & SWAP_FLAG_DISCARD))
2051            p->flags |= SWP_DISCARDABLE;
2052    }
2053
2054    mutex_lock(&swapon_mutex);
2055    spin_lock(&swap_lock);
2056    if (swap_flags & SWAP_FLAG_PREFER)
2057        p->prio =
2058          (swap_flags & SWAP_FLAG_PRIO_MASK) >> SWAP_FLAG_PRIO_SHIFT;
2059    else
2060        p->prio = --least_priority;
2061    p->swap_map = swap_map;
2062    p->flags |= SWP_WRITEOK;
2063    nr_swap_pages += nr_good_pages;
2064    total_swap_pages += nr_good_pages;
2065
2066    printk(KERN_INFO "Adding %uk swap on %s. "
2067            "Priority:%d extents:%d across:%lluk %s%s\n",
2068        nr_good_pages<<(PAGE_SHIFT-10), name, p->prio,
2069        nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10),
2070        (p->flags & SWP_SOLIDSTATE) ? "SS" : "",
2071        (p->flags & SWP_DISCARDABLE) ? "D" : "");
2072
2073    /* insert swap space into swap_list: */
2074    prev = -1;
2075    for (i = swap_list.head; i >= 0; i = swap_info[i]->next) {
2076        if (p->prio >= swap_info[i]->prio)
2077            break;
2078        prev = i;
2079    }
2080    p->next = i;
2081    if (prev < 0)
2082        swap_list.head = swap_list.next = type;
2083    else
2084        swap_info[prev]->next = type;
2085    spin_unlock(&swap_lock);
2086    mutex_unlock(&swapon_mutex);
2087    error = 0;
2088    goto out;
2089bad_swap:
2090    if (bdev) {
2091        set_blocksize(bdev, p->old_block_size);
2092        bd_release(bdev);
2093    }
2094    destroy_swap_extents(p);
2095    swap_cgroup_swapoff(type);
2096bad_swap_2:
2097    spin_lock(&swap_lock);
2098    p->swap_file = NULL;
2099    p->flags = 0;
2100    spin_unlock(&swap_lock);
2101    vfree(swap_map);
2102    if (swap_file)
2103        filp_close(swap_file, NULL);
2104out:
2105    if (page && !IS_ERR(page)) {
2106        kunmap(page);
2107        page_cache_release(page);
2108    }
2109    if (name)
2110        putname(name);
2111    if (did_down) {
2112        if (!error)
2113            inode->i_flags |= S_SWAPFILE;
2114        mutex_unlock(&inode->i_mutex);
2115    }
2116    return error;
2117}
2118
2119void si_swapinfo(struct sysinfo *val)
2120{
2121    unsigned int type;
2122    unsigned long nr_to_be_unused = 0;
2123
2124    spin_lock(&swap_lock);
2125    for (type = 0; type < nr_swapfiles; type++) {
2126        struct swap_info_struct *si = swap_info[type];
2127
2128        if ((si->flags & SWP_USED) && !(si->flags & SWP_WRITEOK))
2129            nr_to_be_unused += si->inuse_pages;
2130    }
2131    val->freeswap = nr_swap_pages + nr_to_be_unused;
2132    val->totalswap = total_swap_pages + nr_to_be_unused;
2133    spin_unlock(&swap_lock);
2134}
2135
2136/*
2137 * Verify that a swap entry is valid and increment its swap map count.
2138 *
2139 * Returns error code in following case.
2140 * - success -> 0
2141 * - swp_entry is invalid -> EINVAL
2142 * - swp_entry is migration entry -> EINVAL
2143 * - swap-cache reference is requested but there is already one. -> EEXIST
2144 * - swap-cache reference is requested but the entry is not used. -> ENOENT
2145 * - swap-mapped reference requested but needs continued swap count. -> ENOMEM
2146 */
2147static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
2148{
2149    struct swap_info_struct *p;
2150    unsigned long offset, type;
2151    unsigned char count;
2152    unsigned char has_cache;
2153    int err = -EINVAL;
2154
2155    if (non_swap_entry(entry))
2156        goto out;
2157
2158    type = swp_type(entry);
2159    if (type >= nr_swapfiles)
2160        goto bad_file;
2161    p = swap_info[type];
2162    offset = swp_offset(entry);
2163
2164    spin_lock(&swap_lock);
2165    if (unlikely(offset >= p->max))
2166        goto unlock_out;
2167
2168    count = p->swap_map[offset];
2169    has_cache = count & SWAP_HAS_CACHE;
2170    count &= ~SWAP_HAS_CACHE;
2171    err = 0;
2172
2173    if (usage == SWAP_HAS_CACHE) {
2174
2175        /* set SWAP_HAS_CACHE if there is no cache and entry is used */
2176        if (!has_cache && count)
2177            has_cache = SWAP_HAS_CACHE;
2178        else if (has_cache) /* someone else added cache */
2179            err = -EEXIST;
2180        else /* no users remaining */
2181            err = -ENOENT;
2182
2183    } else if (count || has_cache) {
2184
2185        if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
2186            count += usage;
2187        else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX)
2188            err = -EINVAL;
2189        else if (swap_count_continued(p, offset, count))
2190            count = COUNT_CONTINUED;
2191        else
2192            err = -ENOMEM;
2193    } else
2194        err = -ENOENT; /* unused swap entry */
2195
2196    p->swap_map[offset] = count | has_cache;
2197
2198unlock_out:
2199    spin_unlock(&swap_lock);
2200out:
2201    return err;
2202
2203bad_file:
2204    printk(KERN_ERR "swap_dup: %s%08lx\n", Bad_file, entry.val);
2205    goto out;
2206}
2207
2208/*
2209 * Help swapoff by noting that swap entry belongs to shmem/tmpfs
2210 * (in which case its reference count is never incremented).
2211 */
2212void swap_shmem_alloc(swp_entry_t entry)
2213{
2214    __swap_duplicate(entry, SWAP_MAP_SHMEM);
2215}
2216
2217/*
2218 * Increase reference count of swap entry by 1.
2219 * Returns 0 for success, or -ENOMEM if a swap_count_continuation is required
2220 * but could not be atomically allocated. Returns 0, just as if it succeeded,
2221 * if __swap_duplicate() fails for another reason (-EINVAL or -ENOENT), which
2222 * might occur if a page table entry has got corrupted.
2223 */
2224int swap_duplicate(swp_entry_t entry)
2225{
2226    int err = 0;
2227
2228    while (!err && __swap_duplicate(entry, 1) == -ENOMEM)
2229        err = add_swap_count_continuation(entry, GFP_ATOMIC);
2230    return err;
2231}
2232
2233/*
2234 * @entry: swap entry for which we allocate swap cache.
2235 *
2236 * Called when allocating swap cache for existing swap entry,
2237 * This can return error codes. Returns 0 at success.
2238 * -EBUSY means there is a swap cache.
2239 * Note: return code is different from swap_duplicate().
2240 */
2241int swapcache_prepare(swp_entry_t entry)
2242{
2243    return __swap_duplicate(entry, SWAP_HAS_CACHE);
2244}
2245
2246/*
2247 * swap_lock prevents swap_map being freed. Don't grab an extra
2248 * reference on the swaphandle, it doesn't matter if it becomes unused.
2249 */
2250int valid_swaphandles(swp_entry_t entry, unsigned long *offset)
2251{
2252    struct swap_info_struct *si;
2253    int our_page_cluster = page_cluster;
2254    pgoff_t target, toff;
2255    pgoff_t base, end;
2256    int nr_pages = 0;
2257
2258    if (!our_page_cluster) /* no readahead */
2259        return 0;
2260
2261    si = swap_info[swp_type(entry)];
2262    target = swp_offset(entry);
2263    base = (target >> our_page_cluster) << our_page_cluster;
2264    end = base + (1 << our_page_cluster);
2265    if (!base) /* first page is swap header */
2266        base++;
2267
2268    spin_lock(&swap_lock);
2269    if (end > si->max) /* don't go beyond end of map */
2270        end = si->max;
2271
2272    /* Count contiguous allocated slots above our target */
2273    for (toff = target; ++toff < end; nr_pages++) {
2274        /* Don't read in free or bad pages */
2275        if (!si->swap_map[toff])
2276            break;
2277        if (swap_count(si->swap_map[toff]) == SWAP_MAP_BAD)
2278            break;
2279    }
2280    /* Count contiguous allocated slots below our target */
2281    for (toff = target; --toff >= base; nr_pages++) {
2282        /* Don't read in free or bad pages */
2283        if (!si->swap_map[toff])
2284            break;
2285        if (swap_count(si->swap_map[toff]) == SWAP_MAP_BAD)
2286            break;
2287    }
2288    spin_unlock(&swap_lock);
2289
2290    /*
2291     * Indicate starting offset, and return number of pages to get:
2292     * if only 1, say 0, since there's then no readahead to be done.
2293     */
2294    *offset = ++toff;
2295    return nr_pages? ++nr_pages: 0;
2296}
2297
2298/*
2299 * add_swap_count_continuation - called when a swap count is duplicated
2300 * beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's
2301 * page of the original vmalloc'ed swap_map, to hold the continuation count
2302 * (for that entry and for its neighbouring PAGE_SIZE swap entries). Called
2303 * again when count is duplicated beyond SWAP_MAP_MAX * SWAP_CONT_MAX, etc.
2304 *
2305 * These continuation pages are seldom referenced: the common paths all work
2306 * on the original swap_map, only referring to a continuation page when the
2307 * low "digit" of a count is incremented or decremented through SWAP_MAP_MAX.
2308 *
2309 * add_swap_count_continuation(, GFP_ATOMIC) can be called while holding
2310 * page table locks; if it fails, add_swap_count_continuation(, GFP_KERNEL)
2311 * can be called after dropping locks.
2312 */
2313int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask)
2314{
2315    struct swap_info_struct *si;
2316    struct page *head;
2317    struct page *page;
2318    struct page *list_page;
2319    pgoff_t offset;
2320    unsigned char count;
2321
2322    /*
2323     * When debugging, it's easier to use __GFP_ZERO here; but it's better
2324     * for latency not to zero a page while GFP_ATOMIC and holding locks.
2325     */
2326    page = alloc_page(gfp_mask | __GFP_HIGHMEM);
2327
2328    si = swap_info_get(entry);
2329    if (!si) {
2330        /*
2331         * An acceptable race has occurred since the failing
2332         * __swap_duplicate(): the swap entry has been freed,
2333         * perhaps even the whole swap_map cleared for swapoff.
2334         */
2335        goto outer;
2336    }
2337
2338    offset = swp_offset(entry);
2339    count = si->swap_map[offset] & ~SWAP_HAS_CACHE;
2340
2341    if ((count & ~COUNT_CONTINUED) != SWAP_MAP_MAX) {
2342        /*
2343         * The higher the swap count, the more likely it is that tasks
2344         * will race to add swap count continuation: we need to avoid
2345         * over-provisioning.
2346         */
2347        goto out;
2348    }
2349
2350    if (!page) {
2351        spin_unlock(&swap_lock);
2352        return -ENOMEM;
2353    }
2354
2355    /*
2356     * We are fortunate that although vmalloc_to_page uses pte_offset_map,
2357     * no architecture is using highmem pages for kernel pagetables: so it
2358     * will not corrupt the GFP_ATOMIC caller's atomic pagetable kmaps.
2359     */
2360    head = vmalloc_to_page(si->swap_map + offset);
2361    offset &= ~PAGE_MASK;
2362
2363    /*
2364     * Page allocation does not initialize the page's lru field,
2365     * but it does always reset its private field.
2366     */
2367    if (!page_private(head)) {
2368        BUG_ON(count & COUNT_CONTINUED);
2369        INIT_LIST_HEAD(&head->lru);
2370        set_page_private(head, SWP_CONTINUED);
2371        si->flags |= SWP_CONTINUED;
2372    }
2373
2374    list_for_each_entry(list_page, &head->lru, lru) {
2375        unsigned char *map;
2376
2377        /*
2378         * If the previous map said no continuation, but we've found
2379         * a continuation page, free our allocation and use this one.
2380         */
2381        if (!(count & COUNT_CONTINUED))
2382            goto out;
2383
2384        map = kmap_atomic(list_page, KM_USER0) + offset;
2385        count = *map;
2386        kunmap_atomic(map, KM_USER0);
2387
2388        /*
2389         * If this continuation count now has some space in it,
2390         * free our allocation and use this one.
2391         */
2392        if ((count & ~COUNT_CONTINUED) != SWAP_CONT_MAX)
2393            goto out;
2394    }
2395
2396    list_add_tail(&page->lru, &head->lru);
2397    page = NULL; /* now it's attached, don't free it */
2398out:
2399    spin_unlock(&swap_lock);
2400outer:
2401    if (page)
2402        __free_page(page);
2403    return 0;
2404}
2405
2406/*
2407 * swap_count_continued - when the original swap_map count is incremented
2408 * from SWAP_MAP_MAX, check if there is already a continuation page to carry
2409 * into, carry if so, or else fail until a new continuation page is allocated;
2410 * when the original swap_map count is decremented from 0 with continuation,
2411 * borrow from the continuation and report whether it still holds more.
2412 * Called while __swap_duplicate() or swap_entry_free() holds swap_lock.
2413 */
2414static bool swap_count_continued(struct swap_info_struct *si,
2415                 pgoff_t offset, unsigned char count)
2416{
2417    struct page *head;
2418    struct page *page;
2419    unsigned char *map;
2420
2421    head = vmalloc_to_page(si->swap_map + offset);
2422    if (page_private(head) != SWP_CONTINUED) {
2423        BUG_ON(count & COUNT_CONTINUED);
2424        return false; /* need to add count continuation */
2425    }
2426
2427    offset &= ~PAGE_MASK;
2428    page = list_entry(head->lru.next, struct page, lru);
2429    map = kmap_atomic(page, KM_USER0) + offset;
2430
2431    if (count == SWAP_MAP_MAX) /* initial increment from swap_map */
2432        goto init_map; /* jump over SWAP_CONT_MAX checks */
2433
2434    if (count == (SWAP_MAP_MAX | COUNT_CONTINUED)) { /* incrementing */
2435        /*
2436         * Think of how you add 1 to 999
2437         */
2438        while (*map == (SWAP_CONT_MAX | COUNT_CONTINUED)) {
2439            kunmap_atomic(map, KM_USER0);
2440            page = list_entry(page->lru.next, struct page, lru);
2441            BUG_ON(page == head);
2442            map = kmap_atomic(page, KM_USER0) + offset;
2443        }
2444        if (*map == SWAP_CONT_MAX) {
2445            kunmap_atomic(map, KM_USER0);
2446            page = list_entry(page->lru.next, struct page, lru);
2447            if (page == head)
2448                return false; /* add count continuation */
2449            map = kmap_atomic(page, KM_USER0) + offset;
2450init_map: *map = 0; /* we didn't zero the page */
2451        }
2452        *map += 1;
2453        kunmap_atomic(map, KM_USER0);
2454        page = list_entry(page->lru.prev, struct page, lru);
2455        while (page != head) {
2456            map = kmap_atomic(page, KM_USER0) + offset;
2457            *map = COUNT_CONTINUED;
2458            kunmap_atomic(map, KM_USER0);
2459            page = list_entry(page->lru.prev, struct page, lru);
2460        }
2461        return true; /* incremented */
2462
2463    } else { /* decrementing */
2464        /*
2465         * Think of how you subtract 1 from 1000
2466         */
2467        BUG_ON(count != COUNT_CONTINUED);
2468        while (*map == COUNT_CONTINUED) {
2469            kunmap_atomic(map, KM_USER0);
2470            page = list_entry(page->lru.next, struct page, lru);
2471            BUG_ON(page == head);
2472            map = kmap_atomic(page, KM_USER0) + offset;
2473        }
2474        BUG_ON(*map == 0);
2475        *map -= 1;
2476        if (*map == 0)
2477            count = 0;
2478        kunmap_atomic(map, KM_USER0);
2479        page = list_entry(page->lru.prev, struct page, lru);
2480        while (page != head) {
2481            map = kmap_atomic(page, KM_USER0) + offset;
2482            *map = SWAP_CONT_MAX | count;
2483            count = COUNT_CONTINUED;
2484            kunmap_atomic(map, KM_USER0);
2485            page = list_entry(page->lru.prev, struct page, lru);
2486        }
2487        return count == COUNT_CONTINUED;
2488    }
2489}
2490
2491/*
2492 * free_swap_count_continuations - swapoff free all the continuation pages
2493 * appended to the swap_map, after swap_map is quiesced, before vfree'ing it.
2494 */
2495static void free_swap_count_continuations(struct swap_info_struct *si)
2496{
2497    pgoff_t offset;
2498
2499    for (offset = 0; offset < si->max; offset += PAGE_SIZE) {
2500        struct page *head;
2501        head = vmalloc_to_page(si->swap_map + offset);
2502        if (page_private(head)) {
2503            struct list_head *this, *next;
2504            list_for_each_safe(this, next, &head->lru) {
2505                struct page *page;
2506                page = list_entry(this, struct page, lru);
2507                list_del(this);
2508                __free_page(page);
2509            }
2510        }
2511    }
2512}
2513

Archive Download this file



interactive