Root/mm/compaction.c

1/*
2 * linux/mm/compaction.c
3 *
4 * Memory compaction for the reduction of external fragmentation. Note that
5 * this heavily depends upon page migration to do all the real heavy
6 * lifting
7 *
8 * Copyright IBM Corp. 2007-2010 Mel Gorman <mel@csn.ul.ie>
9 */
10#include <linux/swap.h>
11#include <linux/migrate.h>
12#include <linux/compaction.h>
13#include <linux/mm_inline.h>
14#include <linux/backing-dev.h>
15#include <linux/sysctl.h>
16#include <linux/sysfs.h>
17#include "internal.h"
18
19#if defined CONFIG_COMPACTION || defined CONFIG_CMA
20
21#define CREATE_TRACE_POINTS
22#include <trace/events/compaction.h>
23
24static unsigned long release_freepages(struct list_head *freelist)
25{
26    struct page *page, *next;
27    unsigned long count = 0;
28
29    list_for_each_entry_safe(page, next, freelist, lru) {
30        list_del(&page->lru);
31        __free_page(page);
32        count++;
33    }
34
35    return count;
36}
37
38static void map_pages(struct list_head *list)
39{
40    struct page *page;
41
42    list_for_each_entry(page, list, lru) {
43        arch_alloc_page(page, 0);
44        kernel_map_pages(page, 1, 1);
45    }
46}
47
48static inline bool migrate_async_suitable(int migratetype)
49{
50    return is_migrate_cma(migratetype) || migratetype == MIGRATE_MOVABLE;
51}
52
53/*
54 * Isolate free pages onto a private freelist. Caller must hold zone->lock.
55 * If @strict is true, will abort returning 0 on any invalid PFNs or non-free
56 * pages inside of the pageblock (even though it may still end up isolating
57 * some pages).
58 */
59static unsigned long isolate_freepages_block(unsigned long blockpfn,
60                unsigned long end_pfn,
61                struct list_head *freelist,
62                bool strict)
63{
64    int nr_scanned = 0, total_isolated = 0;
65    struct page *cursor;
66
67    cursor = pfn_to_page(blockpfn);
68
69    /* Isolate free pages. This assumes the block is valid */
70    for (; blockpfn < end_pfn; blockpfn++, cursor++) {
71        int isolated, i;
72        struct page *page = cursor;
73
74        if (!pfn_valid_within(blockpfn)) {
75            if (strict)
76                return 0;
77            continue;
78        }
79        nr_scanned++;
80
81        if (!PageBuddy(page)) {
82            if (strict)
83                return 0;
84            continue;
85        }
86
87        /* Found a free page, break it into order-0 pages */
88        isolated = split_free_page(page);
89        if (!isolated && strict)
90            return 0;
91        total_isolated += isolated;
92        for (i = 0; i < isolated; i++) {
93            list_add(&page->lru, freelist);
94            page++;
95        }
96
97        /* If a page was split, advance to the end of it */
98        if (isolated) {
99            blockpfn += isolated - 1;
100            cursor += isolated - 1;
101        }
102    }
103
104    trace_mm_compaction_isolate_freepages(nr_scanned, total_isolated);
105    return total_isolated;
106}
107
108/**
109 * isolate_freepages_range() - isolate free pages.
110 * @start_pfn: The first PFN to start isolating.
111 * @end_pfn: The one-past-last PFN.
112 *
113 * Non-free pages, invalid PFNs, or zone boundaries within the
114 * [start_pfn, end_pfn) range are considered errors, cause function to
115 * undo its actions and return zero.
116 *
117 * Otherwise, function returns one-past-the-last PFN of isolated page
118 * (which may be greater then end_pfn if end fell in a middle of
119 * a free page).
120 */
121unsigned long
122isolate_freepages_range(unsigned long start_pfn, unsigned long end_pfn)
123{
124    unsigned long isolated, pfn, block_end_pfn, flags;
125    struct zone *zone = NULL;
126    LIST_HEAD(freelist);
127
128    if (pfn_valid(start_pfn))
129        zone = page_zone(pfn_to_page(start_pfn));
130
131    for (pfn = start_pfn; pfn < end_pfn; pfn += isolated) {
132        if (!pfn_valid(pfn) || zone != page_zone(pfn_to_page(pfn)))
133            break;
134
135        /*
136         * On subsequent iterations ALIGN() is actually not needed,
137         * but we keep it that we not to complicate the code.
138         */
139        block_end_pfn = ALIGN(pfn + 1, pageblock_nr_pages);
140        block_end_pfn = min(block_end_pfn, end_pfn);
141
142        spin_lock_irqsave(&zone->lock, flags);
143        isolated = isolate_freepages_block(pfn, block_end_pfn,
144                           &freelist, true);
145        spin_unlock_irqrestore(&zone->lock, flags);
146
147        /*
148         * In strict mode, isolate_freepages_block() returns 0 if
149         * there are any holes in the block (ie. invalid PFNs or
150         * non-free pages).
151         */
152        if (!isolated)
153            break;
154
155        /*
156         * If we managed to isolate pages, it is always (1 << n) *
157         * pageblock_nr_pages for some non-negative n. (Max order
158         * page may span two pageblocks).
159         */
160    }
161
162    /* split_free_page does not map the pages */
163    map_pages(&freelist);
164
165    if (pfn < end_pfn) {
166        /* Loop terminated early, cleanup. */
167        release_freepages(&freelist);
168        return 0;
169    }
170
171    /* We don't use freelists for anything. */
172    return pfn;
173}
174
175/* Update the number of anon and file isolated pages in the zone */
176static void acct_isolated(struct zone *zone, struct compact_control *cc)
177{
178    struct page *page;
179    unsigned int count[2] = { 0, };
180
181    list_for_each_entry(page, &cc->migratepages, lru)
182        count[!!page_is_file_cache(page)]++;
183
184    __mod_zone_page_state(zone, NR_ISOLATED_ANON, count[0]);
185    __mod_zone_page_state(zone, NR_ISOLATED_FILE, count[1]);
186}
187
188/* Similar to reclaim, but different enough that they don't share logic */
189static bool too_many_isolated(struct zone *zone)
190{
191    unsigned long active, inactive, isolated;
192
193    inactive = zone_page_state(zone, NR_INACTIVE_FILE) +
194                    zone_page_state(zone, NR_INACTIVE_ANON);
195    active = zone_page_state(zone, NR_ACTIVE_FILE) +
196                    zone_page_state(zone, NR_ACTIVE_ANON);
197    isolated = zone_page_state(zone, NR_ISOLATED_FILE) +
198                    zone_page_state(zone, NR_ISOLATED_ANON);
199
200    return isolated > (inactive + active) / 2;
201}
202
203/**
204 * isolate_migratepages_range() - isolate all migrate-able pages in range.
205 * @zone: Zone pages are in.
206 * @cc: Compaction control structure.
207 * @low_pfn: The first PFN of the range.
208 * @end_pfn: The one-past-the-last PFN of the range.
209 *
210 * Isolate all pages that can be migrated from the range specified by
211 * [low_pfn, end_pfn). Returns zero if there is a fatal signal
212 * pending), otherwise PFN of the first page that was not scanned
213 * (which may be both less, equal to or more then end_pfn).
214 *
215 * Assumes that cc->migratepages is empty and cc->nr_migratepages is
216 * zero.
217 *
218 * Apart from cc->migratepages and cc->nr_migratetypes this function
219 * does not modify any cc's fields, in particular it does not modify
220 * (or read for that matter) cc->migrate_pfn.
221 */
222unsigned long
223isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
224               unsigned long low_pfn, unsigned long end_pfn)
225{
226    unsigned long last_pageblock_nr = 0, pageblock_nr;
227    unsigned long nr_scanned = 0, nr_isolated = 0;
228    struct list_head *migratelist = &cc->migratepages;
229    isolate_mode_t mode = 0;
230    struct lruvec *lruvec;
231
232    /*
233     * Ensure that there are not too many pages isolated from the LRU
234     * list by either parallel reclaimers or compaction. If there are,
235     * delay for some time until fewer pages are isolated
236     */
237    while (unlikely(too_many_isolated(zone))) {
238        /* async migration should just abort */
239        if (!cc->sync)
240            return 0;
241
242        congestion_wait(BLK_RW_ASYNC, HZ/10);
243
244        if (fatal_signal_pending(current))
245            return 0;
246    }
247
248    /* Time to isolate some pages for migration */
249    cond_resched();
250    spin_lock_irq(&zone->lru_lock);
251    for (; low_pfn < end_pfn; low_pfn++) {
252        struct page *page;
253        bool locked = true;
254
255        /* give a chance to irqs before checking need_resched() */
256        if (!((low_pfn+1) % SWAP_CLUSTER_MAX)) {
257            spin_unlock_irq(&zone->lru_lock);
258            locked = false;
259        }
260        if (need_resched() || spin_is_contended(&zone->lru_lock)) {
261            if (locked)
262                spin_unlock_irq(&zone->lru_lock);
263            cond_resched();
264            spin_lock_irq(&zone->lru_lock);
265            if (fatal_signal_pending(current))
266                break;
267        } else if (!locked)
268            spin_lock_irq(&zone->lru_lock);
269
270        /*
271         * migrate_pfn does not necessarily start aligned to a
272         * pageblock. Ensure that pfn_valid is called when moving
273         * into a new MAX_ORDER_NR_PAGES range in case of large
274         * memory holes within the zone
275         */
276        if ((low_pfn & (MAX_ORDER_NR_PAGES - 1)) == 0) {
277            if (!pfn_valid(low_pfn)) {
278                low_pfn += MAX_ORDER_NR_PAGES - 1;
279                continue;
280            }
281        }
282
283        if (!pfn_valid_within(low_pfn))
284            continue;
285        nr_scanned++;
286
287        /*
288         * Get the page and ensure the page is within the same zone.
289         * See the comment in isolate_freepages about overlapping
290         * nodes. It is deliberate that the new zone lock is not taken
291         * as memory compaction should not move pages between nodes.
292         */
293        page = pfn_to_page(low_pfn);
294        if (page_zone(page) != zone)
295            continue;
296
297        /* Skip if free */
298        if (PageBuddy(page))
299            continue;
300
301        /*
302         * For async migration, also only scan in MOVABLE blocks. Async
303         * migration is optimistic to see if the minimum amount of work
304         * satisfies the allocation
305         */
306        pageblock_nr = low_pfn >> pageblock_order;
307        if (!cc->sync && last_pageblock_nr != pageblock_nr &&
308            !migrate_async_suitable(get_pageblock_migratetype(page))) {
309            low_pfn += pageblock_nr_pages;
310            low_pfn = ALIGN(low_pfn, pageblock_nr_pages) - 1;
311            last_pageblock_nr = pageblock_nr;
312            continue;
313        }
314
315        if (!PageLRU(page))
316            continue;
317
318        /*
319         * PageLRU is set, and lru_lock excludes isolation,
320         * splitting and collapsing (collapsing has already
321         * happened if PageLRU is set).
322         */
323        if (PageTransHuge(page)) {
324            low_pfn += (1 << compound_order(page)) - 1;
325            continue;
326        }
327
328        if (!cc->sync)
329            mode |= ISOLATE_ASYNC_MIGRATE;
330
331        lruvec = mem_cgroup_page_lruvec(page, zone);
332
333        /* Try isolate the page */
334        if (__isolate_lru_page(page, mode) != 0)
335            continue;
336
337        VM_BUG_ON(PageTransCompound(page));
338
339        /* Successfully isolated */
340        del_page_from_lru_list(page, lruvec, page_lru(page));
341        list_add(&page->lru, migratelist);
342        cc->nr_migratepages++;
343        nr_isolated++;
344
345        /* Avoid isolating too much */
346        if (cc->nr_migratepages == COMPACT_CLUSTER_MAX) {
347            ++low_pfn;
348            break;
349        }
350    }
351
352    acct_isolated(zone, cc);
353
354    spin_unlock_irq(&zone->lru_lock);
355
356    trace_mm_compaction_isolate_migratepages(nr_scanned, nr_isolated);
357
358    return low_pfn;
359}
360
361#endif /* CONFIG_COMPACTION || CONFIG_CMA */
362#ifdef CONFIG_COMPACTION
363
364/* Returns true if the page is within a block suitable for migration to */
365static bool suitable_migration_target(struct page *page)
366{
367
368    int migratetype = get_pageblock_migratetype(page);
369
370    /* Don't interfere with memory hot-remove or the min_free_kbytes blocks */
371    if (migratetype == MIGRATE_ISOLATE || migratetype == MIGRATE_RESERVE)
372        return false;
373
374    /* If the page is a large free page, then allow migration */
375    if (PageBuddy(page) && page_order(page) >= pageblock_order)
376        return true;
377
378    /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
379    if (migrate_async_suitable(migratetype))
380        return true;
381
382    /* Otherwise skip the block */
383    return false;
384}
385
386/*
387 * Based on information in the current compact_control, find blocks
388 * suitable for isolating free pages from and then isolate them.
389 */
390static void isolate_freepages(struct zone *zone,
391                struct compact_control *cc)
392{
393    struct page *page;
394    unsigned long high_pfn, low_pfn, pfn, zone_end_pfn, end_pfn;
395    unsigned long flags;
396    int nr_freepages = cc->nr_freepages;
397    struct list_head *freelist = &cc->freepages;
398
399    /*
400     * Initialise the free scanner. The starting point is where we last
401     * scanned from (or the end of the zone if starting). The low point
402     * is the end of the pageblock the migration scanner is using.
403     */
404    pfn = cc->free_pfn;
405    low_pfn = cc->migrate_pfn + pageblock_nr_pages;
406
407    /*
408     * Take care that if the migration scanner is at the end of the zone
409     * that the free scanner does not accidentally move to the next zone
410     * in the next isolation cycle.
411     */
412    high_pfn = min(low_pfn, pfn);
413
414    zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages;
415
416    /*
417     * Isolate free pages until enough are available to migrate the
418     * pages on cc->migratepages. We stop searching if the migrate
419     * and free page scanners meet or enough free pages are isolated.
420     */
421    for (; pfn > low_pfn && cc->nr_migratepages > nr_freepages;
422                    pfn -= pageblock_nr_pages) {
423        unsigned long isolated;
424
425        /*
426         * Skip ahead if another thread is compacting in the area
427         * simultaneously. If we wrapped around, we can only skip
428         * ahead if zone->compact_cached_free_pfn also wrapped to
429         * above our starting point.
430         */
431        if (cc->order > 0 && (!cc->wrapped ||
432                      zone->compact_cached_free_pfn >
433                      cc->start_free_pfn))
434            pfn = min(pfn, zone->compact_cached_free_pfn);
435
436        if (!pfn_valid(pfn))
437            continue;
438
439        /*
440         * Check for overlapping nodes/zones. It's possible on some
441         * configurations to have a setup like
442         * node0 node1 node0
443         * i.e. it's possible that all pages within a zones range of
444         * pages do not belong to a single zone.
445         */
446        page = pfn_to_page(pfn);
447        if (page_zone(page) != zone)
448            continue;
449
450        /* Check the block is suitable for migration */
451        if (!suitable_migration_target(page))
452            continue;
453
454        /*
455         * Found a block suitable for isolating free pages from. Now
456         * we disabled interrupts, double check things are ok and
457         * isolate the pages. This is to minimise the time IRQs
458         * are disabled
459         */
460        isolated = 0;
461        spin_lock_irqsave(&zone->lock, flags);
462        if (suitable_migration_target(page)) {
463            end_pfn = min(pfn + pageblock_nr_pages, zone_end_pfn);
464            isolated = isolate_freepages_block(pfn, end_pfn,
465                               freelist, false);
466            nr_freepages += isolated;
467        }
468        spin_unlock_irqrestore(&zone->lock, flags);
469
470        /*
471         * Record the highest PFN we isolated pages from. When next
472         * looking for free pages, the search will restart here as
473         * page migration may have returned some pages to the allocator
474         */
475        if (isolated) {
476            high_pfn = max(high_pfn, pfn);
477            if (cc->order > 0)
478                zone->compact_cached_free_pfn = high_pfn;
479        }
480    }
481
482    /* split_free_page does not map the pages */
483    map_pages(freelist);
484
485    cc->free_pfn = high_pfn;
486    cc->nr_freepages = nr_freepages;
487}
488
489/*
490 * This is a migrate-callback that "allocates" freepages by taking pages
491 * from the isolated freelists in the block we are migrating to.
492 */
493static struct page *compaction_alloc(struct page *migratepage,
494                    unsigned long data,
495                    int **result)
496{
497    struct compact_control *cc = (struct compact_control *)data;
498    struct page *freepage;
499
500    /* Isolate free pages if necessary */
501    if (list_empty(&cc->freepages)) {
502        isolate_freepages(cc->zone, cc);
503
504        if (list_empty(&cc->freepages))
505            return NULL;
506    }
507
508    freepage = list_entry(cc->freepages.next, struct page, lru);
509    list_del(&freepage->lru);
510    cc->nr_freepages--;
511
512    return freepage;
513}
514
515/*
516 * We cannot control nr_migratepages and nr_freepages fully when migration is
517 * running as migrate_pages() has no knowledge of compact_control. When
518 * migration is complete, we count the number of pages on the lists by hand.
519 */
520static void update_nr_listpages(struct compact_control *cc)
521{
522    int nr_migratepages = 0;
523    int nr_freepages = 0;
524    struct page *page;
525
526    list_for_each_entry(page, &cc->migratepages, lru)
527        nr_migratepages++;
528    list_for_each_entry(page, &cc->freepages, lru)
529        nr_freepages++;
530
531    cc->nr_migratepages = nr_migratepages;
532    cc->nr_freepages = nr_freepages;
533}
534
535/* possible outcome of isolate_migratepages */
536typedef enum {
537    ISOLATE_ABORT, /* Abort compaction now */
538    ISOLATE_NONE, /* No pages isolated, continue scanning */
539    ISOLATE_SUCCESS, /* Pages isolated, migrate */
540} isolate_migrate_t;
541
542/*
543 * Isolate all pages that can be migrated from the block pointed to by
544 * the migrate scanner within compact_control.
545 */
546static isolate_migrate_t isolate_migratepages(struct zone *zone,
547                    struct compact_control *cc)
548{
549    unsigned long low_pfn, end_pfn;
550
551    /* Do not scan outside zone boundaries */
552    low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);
553
554    /* Only scan within a pageblock boundary */
555    end_pfn = ALIGN(low_pfn + pageblock_nr_pages, pageblock_nr_pages);
556
557    /* Do not cross the free scanner or scan within a memory hole */
558    if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
559        cc->migrate_pfn = end_pfn;
560        return ISOLATE_NONE;
561    }
562
563    /* Perform the isolation */
564    low_pfn = isolate_migratepages_range(zone, cc, low_pfn, end_pfn);
565    if (!low_pfn)
566        return ISOLATE_ABORT;
567
568    cc->migrate_pfn = low_pfn;
569
570    return ISOLATE_SUCCESS;
571}
572
573/*
574 * Returns the start pfn of the last page block in a zone. This is the starting
575 * point for full compaction of a zone. Compaction searches for free pages from
576 * the end of each zone, while isolate_freepages_block scans forward inside each
577 * page block.
578 */
579static unsigned long start_free_pfn(struct zone *zone)
580{
581    unsigned long free_pfn;
582    free_pfn = zone->zone_start_pfn + zone->spanned_pages;
583    free_pfn &= ~(pageblock_nr_pages-1);
584    return free_pfn;
585}
586
587static int compact_finished(struct zone *zone,
588                struct compact_control *cc)
589{
590    unsigned int order;
591    unsigned long watermark;
592
593    if (fatal_signal_pending(current))
594        return COMPACT_PARTIAL;
595
596    /*
597     * A full (order == -1) compaction run starts at the beginning and
598     * end of a zone; it completes when the migrate and free scanner meet.
599     * A partial (order > 0) compaction can start with the free scanner
600     * at a random point in the zone, and may have to restart.
601     */
602    if (cc->free_pfn <= cc->migrate_pfn) {
603        if (cc->order > 0 && !cc->wrapped) {
604            /* We started partway through; restart at the end. */
605            unsigned long free_pfn = start_free_pfn(zone);
606            zone->compact_cached_free_pfn = free_pfn;
607            cc->free_pfn = free_pfn;
608            cc->wrapped = 1;
609            return COMPACT_CONTINUE;
610        }
611        return COMPACT_COMPLETE;
612    }
613
614    /* We wrapped around and ended up where we started. */
615    if (cc->wrapped && cc->free_pfn <= cc->start_free_pfn)
616        return COMPACT_COMPLETE;
617
618    /*
619     * order == -1 is expected when compacting via
620     * /proc/sys/vm/compact_memory
621     */
622    if (cc->order == -1)
623        return COMPACT_CONTINUE;
624
625    /* Compaction run is not finished if the watermark is not met */
626    watermark = low_wmark_pages(zone);
627    watermark += (1 << cc->order);
628
629    if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0))
630        return COMPACT_CONTINUE;
631
632    /* Direct compactor: Is a suitable page free? */
633    for (order = cc->order; order < MAX_ORDER; order++) {
634        /* Job done if page is free of the right migratetype */
635        if (!list_empty(&zone->free_area[order].free_list[cc->migratetype]))
636            return COMPACT_PARTIAL;
637
638        /* Job done if allocation would set block type */
639        if (order >= pageblock_order && zone->free_area[order].nr_free)
640            return COMPACT_PARTIAL;
641    }
642
643    return COMPACT_CONTINUE;
644}
645
646/*
647 * compaction_suitable: Is this suitable to run compaction on this zone now?
648 * Returns
649 * COMPACT_SKIPPED - If there are too few free pages for compaction
650 * COMPACT_PARTIAL - If the allocation would succeed without compaction
651 * COMPACT_CONTINUE - If compaction should run now
652 */
653unsigned long compaction_suitable(struct zone *zone, int order)
654{
655    int fragindex;
656    unsigned long watermark;
657
658    /*
659     * order == -1 is expected when compacting via
660     * /proc/sys/vm/compact_memory
661     */
662    if (order == -1)
663        return COMPACT_CONTINUE;
664
665    /*
666     * Watermarks for order-0 must be met for compaction. Note the 2UL.
667     * This is because during migration, copies of pages need to be
668     * allocated and for a short time, the footprint is higher
669     */
670    watermark = low_wmark_pages(zone) + (2UL << order);
671    if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
672        return COMPACT_SKIPPED;
673
674    /*
675     * fragmentation index determines if allocation failures are due to
676     * low memory or external fragmentation
677     *
678     * index of -1000 implies allocations might succeed depending on
679     * watermarks
680     * index towards 0 implies failure is due to lack of memory
681     * index towards 1000 implies failure is due to fragmentation
682     *
683     * Only compact if a failure would be due to fragmentation.
684     */
685    fragindex = fragmentation_index(zone, order);
686    if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
687        return COMPACT_SKIPPED;
688
689    if (fragindex == -1000 && zone_watermark_ok(zone, order, watermark,
690        0, 0))
691        return COMPACT_PARTIAL;
692
693    return COMPACT_CONTINUE;
694}
695
696static int compact_zone(struct zone *zone, struct compact_control *cc)
697{
698    int ret;
699
700    ret = compaction_suitable(zone, cc->order);
701    switch (ret) {
702    case COMPACT_PARTIAL:
703    case COMPACT_SKIPPED:
704        /* Compaction is likely to fail */
705        return ret;
706    case COMPACT_CONTINUE:
707        /* Fall through to compaction */
708        ;
709    }
710
711    /* Setup to move all movable pages to the end of the zone */
712    cc->migrate_pfn = zone->zone_start_pfn;
713
714    if (cc->order > 0) {
715        /* Incremental compaction. Start where the last one stopped. */
716        cc->free_pfn = zone->compact_cached_free_pfn;
717        cc->start_free_pfn = cc->free_pfn;
718    } else {
719        /* Order == -1 starts at the end of the zone. */
720        cc->free_pfn = start_free_pfn(zone);
721    }
722
723    migrate_prep_local();
724
725    while ((ret = compact_finished(zone, cc)) == COMPACT_CONTINUE) {
726        unsigned long nr_migrate, nr_remaining;
727        int err;
728
729        switch (isolate_migratepages(zone, cc)) {
730        case ISOLATE_ABORT:
731            ret = COMPACT_PARTIAL;
732            goto out;
733        case ISOLATE_NONE:
734            continue;
735        case ISOLATE_SUCCESS:
736            ;
737        }
738
739        nr_migrate = cc->nr_migratepages;
740        err = migrate_pages(&cc->migratepages, compaction_alloc,
741                (unsigned long)cc, false,
742                cc->sync ? MIGRATE_SYNC_LIGHT : MIGRATE_ASYNC);
743        update_nr_listpages(cc);
744        nr_remaining = cc->nr_migratepages;
745
746        count_vm_event(COMPACTBLOCKS);
747        count_vm_events(COMPACTPAGES, nr_migrate - nr_remaining);
748        if (nr_remaining)
749            count_vm_events(COMPACTPAGEFAILED, nr_remaining);
750        trace_mm_compaction_migratepages(nr_migrate - nr_remaining,
751                        nr_remaining);
752
753        /* Release LRU pages not migrated */
754        if (err) {
755            putback_lru_pages(&cc->migratepages);
756            cc->nr_migratepages = 0;
757            if (err == -ENOMEM) {
758                ret = COMPACT_PARTIAL;
759                goto out;
760            }
761        }
762    }
763
764out:
765    /* Release free pages and check accounting */
766    cc->nr_freepages -= release_freepages(&cc->freepages);
767    VM_BUG_ON(cc->nr_freepages != 0);
768
769    return ret;
770}
771
772static unsigned long compact_zone_order(struct zone *zone,
773                 int order, gfp_t gfp_mask,
774                 bool sync)
775{
776    struct compact_control cc = {
777        .nr_freepages = 0,
778        .nr_migratepages = 0,
779        .order = order,
780        .migratetype = allocflags_to_migratetype(gfp_mask),
781        .zone = zone,
782        .sync = sync,
783    };
784    INIT_LIST_HEAD(&cc.freepages);
785    INIT_LIST_HEAD(&cc.migratepages);
786
787    return compact_zone(zone, &cc);
788}
789
790int sysctl_extfrag_threshold = 500;
791
792/**
793 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
794 * @zonelist: The zonelist used for the current allocation
795 * @order: The order of the current allocation
796 * @gfp_mask: The GFP mask of the current allocation
797 * @nodemask: The allowed nodes to allocate from
798 * @sync: Whether migration is synchronous or not
799 *
800 * This is the main entry point for direct page compaction.
801 */
802unsigned long try_to_compact_pages(struct zonelist *zonelist,
803            int order, gfp_t gfp_mask, nodemask_t *nodemask,
804            bool sync)
805{
806    enum zone_type high_zoneidx = gfp_zone(gfp_mask);
807    int may_enter_fs = gfp_mask & __GFP_FS;
808    int may_perform_io = gfp_mask & __GFP_IO;
809    struct zoneref *z;
810    struct zone *zone;
811    int rc = COMPACT_SKIPPED;
812
813    /*
814     * Check whether it is worth even starting compaction. The order check is
815     * made because an assumption is made that the page allocator can satisfy
816     * the "cheaper" orders without taking special steps
817     */
818    if (!order || !may_enter_fs || !may_perform_io)
819        return rc;
820
821    count_vm_event(COMPACTSTALL);
822
823    /* Compact each zone in the list */
824    for_each_zone_zonelist_nodemask(zone, z, zonelist, high_zoneidx,
825                                nodemask) {
826        int status;
827
828        status = compact_zone_order(zone, order, gfp_mask, sync);
829        rc = max(status, rc);
830
831        /* If a normal allocation would succeed, stop compacting */
832        if (zone_watermark_ok(zone, order, low_wmark_pages(zone), 0, 0))
833            break;
834    }
835
836    return rc;
837}
838
839
840/* Compact all zones within a node */
841static int __compact_pgdat(pg_data_t *pgdat, struct compact_control *cc)
842{
843    int zoneid;
844    struct zone *zone;
845
846    for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
847
848        zone = &pgdat->node_zones[zoneid];
849        if (!populated_zone(zone))
850            continue;
851
852        cc->nr_freepages = 0;
853        cc->nr_migratepages = 0;
854        cc->zone = zone;
855        INIT_LIST_HEAD(&cc->freepages);
856        INIT_LIST_HEAD(&cc->migratepages);
857
858        if (cc->order == -1 || !compaction_deferred(zone, cc->order))
859            compact_zone(zone, cc);
860
861        if (cc->order > 0) {
862            int ok = zone_watermark_ok(zone, cc->order,
863                        low_wmark_pages(zone), 0, 0);
864            if (ok && cc->order > zone->compact_order_failed)
865                zone->compact_order_failed = cc->order + 1;
866            /* Currently async compaction is never deferred. */
867            else if (!ok && cc->sync)
868                defer_compaction(zone, cc->order);
869        }
870
871        VM_BUG_ON(!list_empty(&cc->freepages));
872        VM_BUG_ON(!list_empty(&cc->migratepages));
873    }
874
875    return 0;
876}
877
878int compact_pgdat(pg_data_t *pgdat, int order)
879{
880    struct compact_control cc = {
881        .order = order,
882        .sync = false,
883    };
884
885    return __compact_pgdat(pgdat, &cc);
886}
887
888static int compact_node(int nid)
889{
890    struct compact_control cc = {
891        .order = -1,
892        .sync = true,
893    };
894
895    return __compact_pgdat(NODE_DATA(nid), &cc);
896}
897
898/* Compact all nodes in the system */
899static int compact_nodes(void)
900{
901    int nid;
902
903    /* Flush pending updates to the LRU lists */
904    lru_add_drain_all();
905
906    for_each_online_node(nid)
907        compact_node(nid);
908
909    return COMPACT_COMPLETE;
910}
911
912/* The written value is actually unused, all memory is compacted */
913int sysctl_compact_memory;
914
915/* This is the entry point for compacting all nodes via /proc/sys/vm */
916int sysctl_compaction_handler(struct ctl_table *table, int write,
917            void __user *buffer, size_t *length, loff_t *ppos)
918{
919    if (write)
920        return compact_nodes();
921
922    return 0;
923}
924
925int sysctl_extfrag_handler(struct ctl_table *table, int write,
926            void __user *buffer, size_t *length, loff_t *ppos)
927{
928    proc_dointvec_minmax(table, write, buffer, length, ppos);
929
930    return 0;
931}
932
933#if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
934ssize_t sysfs_compact_node(struct device *dev,
935            struct device_attribute *attr,
936            const char *buf, size_t count)
937{
938    int nid = dev->id;
939
940    if (nid >= 0 && nid < nr_node_ids && node_online(nid)) {
941        /* Flush pending updates to the LRU lists */
942        lru_add_drain_all();
943
944        compact_node(nid);
945    }
946
947    return count;
948}
949static DEVICE_ATTR(compact, S_IWUSR, NULL, sysfs_compact_node);
950
951int compaction_register_node(struct node *node)
952{
953    return device_create_file(&node->dev, &dev_attr_compact);
954}
955
956void compaction_unregister_node(struct node *node)
957{
958    return device_remove_file(&node->dev, &dev_attr_compact);
959}
960#endif /* CONFIG_SYSFS && CONFIG_NUMA */
961
962#endif /* CONFIG_COMPACTION */
963

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