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#define CREATE_TRACE_POINTS
20#include <trace/events/compaction.h>
21
22/*
23 * compact_control is used to track pages being migrated and the free pages
24 * they are being migrated to during memory compaction. The free_pfn starts
25 * at the end of a zone and migrate_pfn begins at the start. Movable pages
26 * are moved to the end of a zone during a compaction run and the run
27 * completes when free_pfn <= migrate_pfn
28 */
29struct compact_control {
30    struct list_head freepages; /* List of free pages to migrate to */
31    struct list_head migratepages; /* List of pages being migrated */
32    unsigned long nr_freepages; /* Number of isolated free pages */
33    unsigned long nr_migratepages; /* Number of pages to migrate */
34    unsigned long free_pfn; /* isolate_freepages search base */
35    unsigned long migrate_pfn; /* isolate_migratepages search base */
36    bool sync; /* Synchronous migration */
37
38    /* Account for isolated anon and file pages */
39    unsigned long nr_anon;
40    unsigned long nr_file;
41
42    unsigned int order; /* order a direct compactor needs */
43    int migratetype; /* MOVABLE, RECLAIMABLE etc */
44    struct zone *zone;
45};
46
47static unsigned long release_freepages(struct list_head *freelist)
48{
49    struct page *page, *next;
50    unsigned long count = 0;
51
52    list_for_each_entry_safe(page, next, freelist, lru) {
53        list_del(&page->lru);
54        __free_page(page);
55        count++;
56    }
57
58    return count;
59}
60
61/* Isolate free pages onto a private freelist. Must hold zone->lock */
62static unsigned long isolate_freepages_block(struct zone *zone,
63                unsigned long blockpfn,
64                struct list_head *freelist)
65{
66    unsigned long zone_end_pfn, end_pfn;
67    int nr_scanned = 0, total_isolated = 0;
68    struct page *cursor;
69
70    /* Get the last PFN we should scan for free pages at */
71    zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages;
72    end_pfn = min(blockpfn + pageblock_nr_pages, zone_end_pfn);
73
74    /* Find the first usable PFN in the block to initialse page cursor */
75    for (; blockpfn < end_pfn; blockpfn++) {
76        if (pfn_valid_within(blockpfn))
77            break;
78    }
79    cursor = pfn_to_page(blockpfn);
80
81    /* Isolate free pages. This assumes the block is valid */
82    for (; blockpfn < end_pfn; blockpfn++, cursor++) {
83        int isolated, i;
84        struct page *page = cursor;
85
86        if (!pfn_valid_within(blockpfn))
87            continue;
88        nr_scanned++;
89
90        if (!PageBuddy(page))
91            continue;
92
93        /* Found a free page, break it into order-0 pages */
94        isolated = split_free_page(page);
95        total_isolated += isolated;
96        for (i = 0; i < isolated; i++) {
97            list_add(&page->lru, freelist);
98            page++;
99        }
100
101        /* If a page was split, advance to the end of it */
102        if (isolated) {
103            blockpfn += isolated - 1;
104            cursor += isolated - 1;
105        }
106    }
107
108    trace_mm_compaction_isolate_freepages(nr_scanned, total_isolated);
109    return total_isolated;
110}
111
112/* Returns true if the page is within a block suitable for migration to */
113static bool suitable_migration_target(struct page *page)
114{
115
116    int migratetype = get_pageblock_migratetype(page);
117
118    /* Don't interfere with memory hot-remove or the min_free_kbytes blocks */
119    if (migratetype == MIGRATE_ISOLATE || migratetype == MIGRATE_RESERVE)
120        return false;
121
122    /* If the page is a large free page, then allow migration */
123    if (PageBuddy(page) && page_order(page) >= pageblock_order)
124        return true;
125
126    /* If the block is MIGRATE_MOVABLE, allow migration */
127    if (migratetype == MIGRATE_MOVABLE)
128        return true;
129
130    /* Otherwise skip the block */
131    return false;
132}
133
134/*
135 * Based on information in the current compact_control, find blocks
136 * suitable for isolating free pages from and then isolate them.
137 */
138static void isolate_freepages(struct zone *zone,
139                struct compact_control *cc)
140{
141    struct page *page;
142    unsigned long high_pfn, low_pfn, pfn;
143    unsigned long flags;
144    int nr_freepages = cc->nr_freepages;
145    struct list_head *freelist = &cc->freepages;
146
147    /*
148     * Initialise the free scanner. The starting point is where we last
149     * scanned from (or the end of the zone if starting). The low point
150     * is the end of the pageblock the migration scanner is using.
151     */
152    pfn = cc->free_pfn;
153    low_pfn = cc->migrate_pfn + pageblock_nr_pages;
154
155    /*
156     * Take care that if the migration scanner is at the end of the zone
157     * that the free scanner does not accidentally move to the next zone
158     * in the next isolation cycle.
159     */
160    high_pfn = min(low_pfn, pfn);
161
162    /*
163     * Isolate free pages until enough are available to migrate the
164     * pages on cc->migratepages. We stop searching if the migrate
165     * and free page scanners meet or enough free pages are isolated.
166     */
167    for (; pfn > low_pfn && cc->nr_migratepages > nr_freepages;
168                    pfn -= pageblock_nr_pages) {
169        unsigned long isolated;
170
171        if (!pfn_valid(pfn))
172            continue;
173
174        /*
175         * Check for overlapping nodes/zones. It's possible on some
176         * configurations to have a setup like
177         * node0 node1 node0
178         * i.e. it's possible that all pages within a zones range of
179         * pages do not belong to a single zone.
180         */
181        page = pfn_to_page(pfn);
182        if (page_zone(page) != zone)
183            continue;
184
185        /* Check the block is suitable for migration */
186        if (!suitable_migration_target(page))
187            continue;
188
189        /*
190         * Found a block suitable for isolating free pages from. Now
191         * we disabled interrupts, double check things are ok and
192         * isolate the pages. This is to minimise the time IRQs
193         * are disabled
194         */
195        isolated = 0;
196        spin_lock_irqsave(&zone->lock, flags);
197        if (suitable_migration_target(page)) {
198            isolated = isolate_freepages_block(zone, pfn, freelist);
199            nr_freepages += isolated;
200        }
201        spin_unlock_irqrestore(&zone->lock, flags);
202
203        /*
204         * Record the highest PFN we isolated pages from. When next
205         * looking for free pages, the search will restart here as
206         * page migration may have returned some pages to the allocator
207         */
208        if (isolated)
209            high_pfn = max(high_pfn, pfn);
210    }
211
212    /* split_free_page does not map the pages */
213    list_for_each_entry(page, freelist, lru) {
214        arch_alloc_page(page, 0);
215        kernel_map_pages(page, 1, 1);
216    }
217
218    cc->free_pfn = high_pfn;
219    cc->nr_freepages = nr_freepages;
220}
221
222/* Update the number of anon and file isolated pages in the zone */
223static void acct_isolated(struct zone *zone, struct compact_control *cc)
224{
225    struct page *page;
226    unsigned int count[NR_LRU_LISTS] = { 0, };
227
228    list_for_each_entry(page, &cc->migratepages, lru) {
229        int lru = page_lru_base_type(page);
230        count[lru]++;
231    }
232
233    cc->nr_anon = count[LRU_ACTIVE_ANON] + count[LRU_INACTIVE_ANON];
234    cc->nr_file = count[LRU_ACTIVE_FILE] + count[LRU_INACTIVE_FILE];
235    __mod_zone_page_state(zone, NR_ISOLATED_ANON, cc->nr_anon);
236    __mod_zone_page_state(zone, NR_ISOLATED_FILE, cc->nr_file);
237}
238
239/* Similar to reclaim, but different enough that they don't share logic */
240static bool too_many_isolated(struct zone *zone)
241{
242    unsigned long active, inactive, isolated;
243
244    inactive = zone_page_state(zone, NR_INACTIVE_FILE) +
245                    zone_page_state(zone, NR_INACTIVE_ANON);
246    active = zone_page_state(zone, NR_ACTIVE_FILE) +
247                    zone_page_state(zone, NR_ACTIVE_ANON);
248    isolated = zone_page_state(zone, NR_ISOLATED_FILE) +
249                    zone_page_state(zone, NR_ISOLATED_ANON);
250
251    return isolated > (inactive + active) / 2;
252}
253
254/* possible outcome of isolate_migratepages */
255typedef enum {
256    ISOLATE_ABORT, /* Abort compaction now */
257    ISOLATE_NONE, /* No pages isolated, continue scanning */
258    ISOLATE_SUCCESS, /* Pages isolated, migrate */
259} isolate_migrate_t;
260
261/*
262 * Isolate all pages that can be migrated from the block pointed to by
263 * the migrate scanner within compact_control.
264 */
265static isolate_migrate_t isolate_migratepages(struct zone *zone,
266                    struct compact_control *cc)
267{
268    unsigned long low_pfn, end_pfn;
269    unsigned long last_pageblock_nr = 0, pageblock_nr;
270    unsigned long nr_scanned = 0, nr_isolated = 0;
271    struct list_head *migratelist = &cc->migratepages;
272
273    /* Do not scan outside zone boundaries */
274    low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);
275
276    /* Only scan within a pageblock boundary */
277    end_pfn = ALIGN(low_pfn + pageblock_nr_pages, pageblock_nr_pages);
278
279    /* Do not cross the free scanner or scan within a memory hole */
280    if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
281        cc->migrate_pfn = end_pfn;
282        return ISOLATE_NONE;
283    }
284
285    /*
286     * Ensure that there are not too many pages isolated from the LRU
287     * list by either parallel reclaimers or compaction. If there are,
288     * delay for some time until fewer pages are isolated
289     */
290    while (unlikely(too_many_isolated(zone))) {
291        /* async migration should just abort */
292        if (!cc->sync)
293            return ISOLATE_ABORT;
294
295        congestion_wait(BLK_RW_ASYNC, HZ/10);
296
297        if (fatal_signal_pending(current))
298            return ISOLATE_ABORT;
299    }
300
301    /* Time to isolate some pages for migration */
302    cond_resched();
303    spin_lock_irq(&zone->lru_lock);
304    for (; low_pfn < end_pfn; low_pfn++) {
305        struct page *page;
306        bool locked = true;
307
308        /* give a chance to irqs before checking need_resched() */
309        if (!((low_pfn+1) % SWAP_CLUSTER_MAX)) {
310            spin_unlock_irq(&zone->lru_lock);
311            locked = false;
312        }
313        if (need_resched() || spin_is_contended(&zone->lru_lock)) {
314            if (locked)
315                spin_unlock_irq(&zone->lru_lock);
316            cond_resched();
317            spin_lock_irq(&zone->lru_lock);
318            if (fatal_signal_pending(current))
319                break;
320        } else if (!locked)
321            spin_lock_irq(&zone->lru_lock);
322
323        if (!pfn_valid_within(low_pfn))
324            continue;
325        nr_scanned++;
326
327        /* Get the page and skip if free */
328        page = pfn_to_page(low_pfn);
329        if (PageBuddy(page))
330            continue;
331
332        /*
333         * For async migration, also only scan in MOVABLE blocks. Async
334         * migration is optimistic to see if the minimum amount of work
335         * satisfies the allocation
336         */
337        pageblock_nr = low_pfn >> pageblock_order;
338        if (!cc->sync && last_pageblock_nr != pageblock_nr &&
339                get_pageblock_migratetype(page) != MIGRATE_MOVABLE) {
340            low_pfn += pageblock_nr_pages;
341            low_pfn = ALIGN(low_pfn, pageblock_nr_pages) - 1;
342            last_pageblock_nr = pageblock_nr;
343            continue;
344        }
345
346        if (!PageLRU(page))
347            continue;
348
349        /*
350         * PageLRU is set, and lru_lock excludes isolation,
351         * splitting and collapsing (collapsing has already
352         * happened if PageLRU is set).
353         */
354        if (PageTransHuge(page)) {
355            low_pfn += (1 << compound_order(page)) - 1;
356            continue;
357        }
358
359        /* Try isolate the page */
360        if (__isolate_lru_page(page, ISOLATE_BOTH, 0) != 0)
361            continue;
362
363        VM_BUG_ON(PageTransCompound(page));
364
365        /* Successfully isolated */
366        del_page_from_lru_list(zone, page, page_lru(page));
367        list_add(&page->lru, migratelist);
368        cc->nr_migratepages++;
369        nr_isolated++;
370
371        /* Avoid isolating too much */
372        if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
373            break;
374    }
375
376    acct_isolated(zone, cc);
377
378    spin_unlock_irq(&zone->lru_lock);
379    cc->migrate_pfn = low_pfn;
380
381    trace_mm_compaction_isolate_migratepages(nr_scanned, nr_isolated);
382
383    return ISOLATE_SUCCESS;
384}
385
386/*
387 * This is a migrate-callback that "allocates" freepages by taking pages
388 * from the isolated freelists in the block we are migrating to.
389 */
390static struct page *compaction_alloc(struct page *migratepage,
391                    unsigned long data,
392                    int **result)
393{
394    struct compact_control *cc = (struct compact_control *)data;
395    struct page *freepage;
396
397    /* Isolate free pages if necessary */
398    if (list_empty(&cc->freepages)) {
399        isolate_freepages(cc->zone, cc);
400
401        if (list_empty(&cc->freepages))
402            return NULL;
403    }
404
405    freepage = list_entry(cc->freepages.next, struct page, lru);
406    list_del(&freepage->lru);
407    cc->nr_freepages--;
408
409    return freepage;
410}
411
412/*
413 * We cannot control nr_migratepages and nr_freepages fully when migration is
414 * running as migrate_pages() has no knowledge of compact_control. When
415 * migration is complete, we count the number of pages on the lists by hand.
416 */
417static void update_nr_listpages(struct compact_control *cc)
418{
419    int nr_migratepages = 0;
420    int nr_freepages = 0;
421    struct page *page;
422
423    list_for_each_entry(page, &cc->migratepages, lru)
424        nr_migratepages++;
425    list_for_each_entry(page, &cc->freepages, lru)
426        nr_freepages++;
427
428    cc->nr_migratepages = nr_migratepages;
429    cc->nr_freepages = nr_freepages;
430}
431
432static int compact_finished(struct zone *zone,
433                struct compact_control *cc)
434{
435    unsigned int order;
436    unsigned long watermark;
437
438    if (fatal_signal_pending(current))
439        return COMPACT_PARTIAL;
440
441    /* Compaction run completes if the migrate and free scanner meet */
442    if (cc->free_pfn <= cc->migrate_pfn)
443        return COMPACT_COMPLETE;
444
445    /*
446     * order == -1 is expected when compacting via
447     * /proc/sys/vm/compact_memory
448     */
449    if (cc->order == -1)
450        return COMPACT_CONTINUE;
451
452    /* Compaction run is not finished if the watermark is not met */
453    watermark = low_wmark_pages(zone);
454    watermark += (1 << cc->order);
455
456    if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0))
457        return COMPACT_CONTINUE;
458
459    /* Direct compactor: Is a suitable page free? */
460    for (order = cc->order; order < MAX_ORDER; order++) {
461        /* Job done if page is free of the right migratetype */
462        if (!list_empty(&zone->free_area[order].free_list[cc->migratetype]))
463            return COMPACT_PARTIAL;
464
465        /* Job done if allocation would set block type */
466        if (order >= pageblock_order && zone->free_area[order].nr_free)
467            return COMPACT_PARTIAL;
468    }
469
470    return COMPACT_CONTINUE;
471}
472
473/*
474 * compaction_suitable: Is this suitable to run compaction on this zone now?
475 * Returns
476 * COMPACT_SKIPPED - If there are too few free pages for compaction
477 * COMPACT_PARTIAL - If the allocation would succeed without compaction
478 * COMPACT_CONTINUE - If compaction should run now
479 */
480unsigned long compaction_suitable(struct zone *zone, int order)
481{
482    int fragindex;
483    unsigned long watermark;
484
485    /*
486     * order == -1 is expected when compacting via
487     * /proc/sys/vm/compact_memory
488     */
489    if (order == -1)
490        return COMPACT_CONTINUE;
491
492    /*
493     * Watermarks for order-0 must be met for compaction. Note the 2UL.
494     * This is because during migration, copies of pages need to be
495     * allocated and for a short time, the footprint is higher
496     */
497    watermark = low_wmark_pages(zone) + (2UL << order);
498    if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
499        return COMPACT_SKIPPED;
500
501    /*
502     * fragmentation index determines if allocation failures are due to
503     * low memory or external fragmentation
504     *
505     * index of -1000 implies allocations might succeed depending on
506     * watermarks
507     * index towards 0 implies failure is due to lack of memory
508     * index towards 1000 implies failure is due to fragmentation
509     *
510     * Only compact if a failure would be due to fragmentation.
511     */
512    fragindex = fragmentation_index(zone, order);
513    if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
514        return COMPACT_SKIPPED;
515
516    if (fragindex == -1000 && zone_watermark_ok(zone, order, watermark,
517        0, 0))
518        return COMPACT_PARTIAL;
519
520    return COMPACT_CONTINUE;
521}
522
523static int compact_zone(struct zone *zone, struct compact_control *cc)
524{
525    int ret;
526
527    ret = compaction_suitable(zone, cc->order);
528    switch (ret) {
529    case COMPACT_PARTIAL:
530    case COMPACT_SKIPPED:
531        /* Compaction is likely to fail */
532        return ret;
533    case COMPACT_CONTINUE:
534        /* Fall through to compaction */
535        ;
536    }
537
538    /* Setup to move all movable pages to the end of the zone */
539    cc->migrate_pfn = zone->zone_start_pfn;
540    cc->free_pfn = cc->migrate_pfn + zone->spanned_pages;
541    cc->free_pfn &= ~(pageblock_nr_pages-1);
542
543    migrate_prep_local();
544
545    while ((ret = compact_finished(zone, cc)) == COMPACT_CONTINUE) {
546        unsigned long nr_migrate, nr_remaining;
547        int err;
548
549        switch (isolate_migratepages(zone, cc)) {
550        case ISOLATE_ABORT:
551            ret = COMPACT_PARTIAL;
552            goto out;
553        case ISOLATE_NONE:
554            continue;
555        case ISOLATE_SUCCESS:
556            ;
557        }
558
559        nr_migrate = cc->nr_migratepages;
560        err = migrate_pages(&cc->migratepages, compaction_alloc,
561                (unsigned long)cc, false,
562                cc->sync);
563        update_nr_listpages(cc);
564        nr_remaining = cc->nr_migratepages;
565
566        count_vm_event(COMPACTBLOCKS);
567        count_vm_events(COMPACTPAGES, nr_migrate - nr_remaining);
568        if (nr_remaining)
569            count_vm_events(COMPACTPAGEFAILED, nr_remaining);
570        trace_mm_compaction_migratepages(nr_migrate - nr_remaining,
571                        nr_remaining);
572
573        /* Release LRU pages not migrated */
574        if (err) {
575            putback_lru_pages(&cc->migratepages);
576            cc->nr_migratepages = 0;
577        }
578
579    }
580
581out:
582    /* Release free pages and check accounting */
583    cc->nr_freepages -= release_freepages(&cc->freepages);
584    VM_BUG_ON(cc->nr_freepages != 0);
585
586    return ret;
587}
588
589unsigned long compact_zone_order(struct zone *zone,
590                 int order, gfp_t gfp_mask,
591                 bool sync)
592{
593    struct compact_control cc = {
594        .nr_freepages = 0,
595        .nr_migratepages = 0,
596        .order = order,
597        .migratetype = allocflags_to_migratetype(gfp_mask),
598        .zone = zone,
599        .sync = sync,
600    };
601    INIT_LIST_HEAD(&cc.freepages);
602    INIT_LIST_HEAD(&cc.migratepages);
603
604    return compact_zone(zone, &cc);
605}
606
607int sysctl_extfrag_threshold = 500;
608
609/**
610 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
611 * @zonelist: The zonelist used for the current allocation
612 * @order: The order of the current allocation
613 * @gfp_mask: The GFP mask of the current allocation
614 * @nodemask: The allowed nodes to allocate from
615 * @sync: Whether migration is synchronous or not
616 *
617 * This is the main entry point for direct page compaction.
618 */
619unsigned long try_to_compact_pages(struct zonelist *zonelist,
620            int order, gfp_t gfp_mask, nodemask_t *nodemask,
621            bool sync)
622{
623    enum zone_type high_zoneidx = gfp_zone(gfp_mask);
624    int may_enter_fs = gfp_mask & __GFP_FS;
625    int may_perform_io = gfp_mask & __GFP_IO;
626    struct zoneref *z;
627    struct zone *zone;
628    int rc = COMPACT_SKIPPED;
629
630    /*
631     * Check whether it is worth even starting compaction. The order check is
632     * made because an assumption is made that the page allocator can satisfy
633     * the "cheaper" orders without taking special steps
634     */
635    if (!order || !may_enter_fs || !may_perform_io)
636        return rc;
637
638    count_vm_event(COMPACTSTALL);
639
640    /* Compact each zone in the list */
641    for_each_zone_zonelist_nodemask(zone, z, zonelist, high_zoneidx,
642                                nodemask) {
643        int status;
644
645        status = compact_zone_order(zone, order, gfp_mask, sync);
646        rc = max(status, rc);
647
648        /* If a normal allocation would succeed, stop compacting */
649        if (zone_watermark_ok(zone, order, low_wmark_pages(zone), 0, 0))
650            break;
651    }
652
653    return rc;
654}
655
656
657/* Compact all zones within a node */
658static int compact_node(int nid)
659{
660    int zoneid;
661    pg_data_t *pgdat;
662    struct zone *zone;
663
664    if (nid < 0 || nid >= nr_node_ids || !node_online(nid))
665        return -EINVAL;
666    pgdat = NODE_DATA(nid);
667
668    /* Flush pending updates to the LRU lists */
669    lru_add_drain_all();
670
671    for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
672        struct compact_control cc = {
673            .nr_freepages = 0,
674            .nr_migratepages = 0,
675            .order = -1,
676        };
677
678        zone = &pgdat->node_zones[zoneid];
679        if (!populated_zone(zone))
680            continue;
681
682        cc.zone = zone;
683        INIT_LIST_HEAD(&cc.freepages);
684        INIT_LIST_HEAD(&cc.migratepages);
685
686        compact_zone(zone, &cc);
687
688        VM_BUG_ON(!list_empty(&cc.freepages));
689        VM_BUG_ON(!list_empty(&cc.migratepages));
690    }
691
692    return 0;
693}
694
695/* Compact all nodes in the system */
696static int compact_nodes(void)
697{
698    int nid;
699
700    for_each_online_node(nid)
701        compact_node(nid);
702
703    return COMPACT_COMPLETE;
704}
705
706/* The written value is actually unused, all memory is compacted */
707int sysctl_compact_memory;
708
709/* This is the entry point for compacting all nodes via /proc/sys/vm */
710int sysctl_compaction_handler(struct ctl_table *table, int write,
711            void __user *buffer, size_t *length, loff_t *ppos)
712{
713    if (write)
714        return compact_nodes();
715
716    return 0;
717}
718
719int sysctl_extfrag_handler(struct ctl_table *table, int write,
720            void __user *buffer, size_t *length, loff_t *ppos)
721{
722    proc_dointvec_minmax(table, write, buffer, length, ppos);
723
724    return 0;
725}
726
727#if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
728ssize_t sysfs_compact_node(struct sys_device *dev,
729            struct sysdev_attribute *attr,
730            const char *buf, size_t count)
731{
732    compact_node(dev->id);
733
734    return count;
735}
736static SYSDEV_ATTR(compact, S_IWUSR, NULL, sysfs_compact_node);
737
738int compaction_register_node(struct node *node)
739{
740    return sysdev_create_file(&node->sysdev, &attr_compact);
741}
742
743void compaction_unregister_node(struct node *node)
744{
745    return sysdev_remove_file(&node->sysdev, &attr_compact);
746}
747#endif /* CONFIG_SYSFS && CONFIG_NUMA */
748

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