linux/mm/compaction.c
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   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        pfn = cc->free_pfn;
 148        low_pfn = cc->migrate_pfn + pageblock_nr_pages;
 149        high_pfn = low_pfn;
 150
 151        /*
 152         * Isolate free pages until enough are available to migrate the
 153         * pages on cc->migratepages. We stop searching if the migrate
 154         * and free page scanners meet or enough free pages are isolated.
 155         */
 156        spin_lock_irqsave(&zone->lock, flags);
 157        for (; pfn > low_pfn && cc->nr_migratepages > nr_freepages;
 158                                        pfn -= pageblock_nr_pages) {
 159                unsigned long isolated;
 160
 161                if (!pfn_valid(pfn))
 162                        continue;
 163
 164                /*
 165                 * Check for overlapping nodes/zones. It's possible on some
 166                 * configurations to have a setup like
 167                 * node0 node1 node0
 168                 * i.e. it's possible that all pages within a zones range of
 169                 * pages do not belong to a single zone.
 170                 */
 171                page = pfn_to_page(pfn);
 172                if (page_zone(page) != zone)
 173                        continue;
 174
 175                /* Check the block is suitable for migration */
 176                if (!suitable_migration_target(page))
 177                        continue;
 178
 179                /* Found a block suitable for isolating free pages from */
 180                isolated = isolate_freepages_block(zone, pfn, freelist);
 181                nr_freepages += isolated;
 182
 183                /*
 184                 * Record the highest PFN we isolated pages from. When next
 185                 * looking for free pages, the search will restart here as
 186                 * page migration may have returned some pages to the allocator
 187                 */
 188                if (isolated)
 189                        high_pfn = max(high_pfn, pfn);
 190        }
 191        spin_unlock_irqrestore(&zone->lock, flags);
 192
 193        /* split_free_page does not map the pages */
 194        list_for_each_entry(page, freelist, lru) {
 195                arch_alloc_page(page, 0);
 196                kernel_map_pages(page, 1, 1);
 197        }
 198
 199        cc->free_pfn = high_pfn;
 200        cc->nr_freepages = nr_freepages;
 201}
 202
 203/* Update the number of anon and file isolated pages in the zone */
 204static void acct_isolated(struct zone *zone, struct compact_control *cc)
 205{
 206        struct page *page;
 207        unsigned int count[NR_LRU_LISTS] = { 0, };
 208
 209        list_for_each_entry(page, &cc->migratepages, lru) {
 210                int lru = page_lru_base_type(page);
 211                count[lru]++;
 212        }
 213
 214        cc->nr_anon = count[LRU_ACTIVE_ANON] + count[LRU_INACTIVE_ANON];
 215        cc->nr_file = count[LRU_ACTIVE_FILE] + count[LRU_INACTIVE_FILE];
 216        __mod_zone_page_state(zone, NR_ISOLATED_ANON, cc->nr_anon);
 217        __mod_zone_page_state(zone, NR_ISOLATED_FILE, cc->nr_file);
 218}
 219
 220/* Similar to reclaim, but different enough that they don't share logic */
 221static bool too_many_isolated(struct zone *zone)
 222{
 223        unsigned long active, inactive, isolated;
 224
 225        inactive = zone_page_state(zone, NR_INACTIVE_FILE) +
 226                                        zone_page_state(zone, NR_INACTIVE_ANON);
 227        active = zone_page_state(zone, NR_ACTIVE_FILE) +
 228                                        zone_page_state(zone, NR_ACTIVE_ANON);
 229        isolated = zone_page_state(zone, NR_ISOLATED_FILE) +
 230                                        zone_page_state(zone, NR_ISOLATED_ANON);
 231
 232        return isolated > (inactive + active) / 2;
 233}
 234
 235/*
 236 * Isolate all pages that can be migrated from the block pointed to by
 237 * the migrate scanner within compact_control.
 238 */
 239static unsigned long isolate_migratepages(struct zone *zone,
 240                                        struct compact_control *cc)
 241{
 242        unsigned long low_pfn, end_pfn;
 243        unsigned long last_pageblock_nr = 0, pageblock_nr;
 244        unsigned long nr_scanned = 0, nr_isolated = 0;
 245        struct list_head *migratelist = &cc->migratepages;
 246
 247        /* Do not scan outside zone boundaries */
 248        low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);
 249
 250        /* Only scan within a pageblock boundary */
 251        end_pfn = ALIGN(low_pfn + pageblock_nr_pages, pageblock_nr_pages);
 252
 253        /* Do not cross the free scanner or scan within a memory hole */
 254        if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
 255                cc->migrate_pfn = end_pfn;
 256                return 0;
 257        }
 258
 259        /*
 260         * Ensure that there are not too many pages isolated from the LRU
 261         * list by either parallel reclaimers or compaction. If there are,
 262         * delay for some time until fewer pages are isolated
 263         */
 264        while (unlikely(too_many_isolated(zone))) {
 265                congestion_wait(BLK_RW_ASYNC, HZ/10);
 266
 267                if (fatal_signal_pending(current))
 268                        return 0;
 269        }
 270
 271        /* Time to isolate some pages for migration */
 272        spin_lock_irq(&zone->lru_lock);
 273        for (; low_pfn < end_pfn; low_pfn++) {
 274                struct page *page;
 275                if (!pfn_valid_within(low_pfn))
 276                        continue;
 277                nr_scanned++;
 278
 279                /* Get the page and skip if free */
 280                page = pfn_to_page(low_pfn);
 281                if (PageBuddy(page))
 282                        continue;
 283
 284                /*
 285                 * For async migration, also only scan in MOVABLE blocks. Async
 286                 * migration is optimistic to see if the minimum amount of work
 287                 * satisfies the allocation
 288                 */
 289                pageblock_nr = low_pfn >> pageblock_order;
 290                if (!cc->sync && last_pageblock_nr != pageblock_nr &&
 291                                get_pageblock_migratetype(page) != MIGRATE_MOVABLE) {
 292                        low_pfn += pageblock_nr_pages;
 293                        low_pfn = ALIGN(low_pfn, pageblock_nr_pages) - 1;
 294                        last_pageblock_nr = pageblock_nr;
 295                        continue;
 296                }
 297
 298                if (!PageLRU(page))
 299                        continue;
 300
 301                /*
 302                 * PageLRU is set, and lru_lock excludes isolation,
 303                 * splitting and collapsing (collapsing has already
 304                 * happened if PageLRU is set).
 305                 */
 306                if (PageTransHuge(page)) {
 307                        low_pfn += (1 << compound_order(page)) - 1;
 308                        continue;
 309                }
 310
 311                /* Try isolate the page */
 312                if (__isolate_lru_page(page, ISOLATE_BOTH, 0) != 0)
 313                        continue;
 314
 315                VM_BUG_ON(PageTransCompound(page));
 316
 317                /* Successfully isolated */
 318                del_page_from_lru_list(zone, page, page_lru(page));
 319                list_add(&page->lru, migratelist);
 320                cc->nr_migratepages++;
 321                nr_isolated++;
 322
 323                /* Avoid isolating too much */
 324                if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
 325                        break;
 326        }
 327
 328        acct_isolated(zone, cc);
 329
 330        spin_unlock_irq(&zone->lru_lock);
 331        cc->migrate_pfn = low_pfn;
 332
 333        trace_mm_compaction_isolate_migratepages(nr_scanned, nr_isolated);
 334
 335        return cc->nr_migratepages;
 336}
 337
 338/*
 339 * This is a migrate-callback that "allocates" freepages by taking pages
 340 * from the isolated freelists in the block we are migrating to.
 341 */
 342static struct page *compaction_alloc(struct page *migratepage,
 343                                        unsigned long data,
 344                                        int **result)
 345{
 346        struct compact_control *cc = (struct compact_control *)data;
 347        struct page *freepage;
 348
 349        /* Isolate free pages if necessary */
 350        if (list_empty(&cc->freepages)) {
 351                isolate_freepages(cc->zone, cc);
 352
 353                if (list_empty(&cc->freepages))
 354                        return NULL;
 355        }
 356
 357        freepage = list_entry(cc->freepages.next, struct page, lru);
 358        list_del(&freepage->lru);
 359        cc->nr_freepages--;
 360
 361        return freepage;
 362}
 363
 364/*
 365 * We cannot control nr_migratepages and nr_freepages fully when migration is
 366 * running as migrate_pages() has no knowledge of compact_control. When
 367 * migration is complete, we count the number of pages on the lists by hand.
 368 */
 369static void update_nr_listpages(struct compact_control *cc)
 370{
 371        int nr_migratepages = 0;
 372        int nr_freepages = 0;
 373        struct page *page;
 374
 375        list_for_each_entry(page, &cc->migratepages, lru)
 376                nr_migratepages++;
 377        list_for_each_entry(page, &cc->freepages, lru)
 378                nr_freepages++;
 379
 380        cc->nr_migratepages = nr_migratepages;
 381        cc->nr_freepages = nr_freepages;
 382}
 383
 384static int compact_finished(struct zone *zone,
 385                            struct compact_control *cc)
 386{
 387        unsigned int order;
 388        unsigned long watermark;
 389
 390        if (fatal_signal_pending(current))
 391                return COMPACT_PARTIAL;
 392
 393        /* Compaction run completes if the migrate and free scanner meet */
 394        if (cc->free_pfn <= cc->migrate_pfn)
 395                return COMPACT_COMPLETE;
 396
 397        /* Compaction run is not finished if the watermark is not met */
 398        watermark = low_wmark_pages(zone);
 399        watermark += (1 << cc->order);
 400
 401        if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0))
 402                return COMPACT_CONTINUE;
 403
 404        /*
 405         * order == -1 is expected when compacting via
 406         * /proc/sys/vm/compact_memory
 407         */
 408        if (cc->order == -1)
 409                return COMPACT_CONTINUE;
 410
 411        /* Direct compactor: Is a suitable page free? */
 412        for (order = cc->order; order < MAX_ORDER; order++) {
 413                /* Job done if page is free of the right migratetype */
 414                if (!list_empty(&zone->free_area[order].free_list[cc->migratetype]))
 415                        return COMPACT_PARTIAL;
 416
 417                /* Job done if allocation would set block type */
 418                if (order >= pageblock_order && zone->free_area[order].nr_free)
 419                        return COMPACT_PARTIAL;
 420        }
 421
 422        return COMPACT_CONTINUE;
 423}
 424
 425/*
 426 * compaction_suitable: Is this suitable to run compaction on this zone now?
 427 * Returns
 428 *   COMPACT_SKIPPED  - If there are too few free pages for compaction
 429 *   COMPACT_PARTIAL  - If the allocation would succeed without compaction
 430 *   COMPACT_CONTINUE - If compaction should run now
 431 */
 432unsigned long compaction_suitable(struct zone *zone, int order)
 433{
 434        int fragindex;
 435        unsigned long watermark;
 436
 437        /*
 438         * Watermarks for order-0 must be met for compaction. Note the 2UL.
 439         * This is because during migration, copies of pages need to be
 440         * allocated and for a short time, the footprint is higher
 441         */
 442        watermark = low_wmark_pages(zone) + (2UL << order);
 443        if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
 444                return COMPACT_SKIPPED;
 445
 446        /*
 447         * order == -1 is expected when compacting via
 448         * /proc/sys/vm/compact_memory
 449         */
 450        if (order == -1)
 451                return COMPACT_CONTINUE;
 452
 453        /*
 454         * fragmentation index determines if allocation failures are due to
 455         * low memory or external fragmentation
 456         *
 457         * index of -1 implies allocations might succeed dependingon watermarks
 458         * index towards 0 implies failure is due to lack of memory
 459         * index towards 1000 implies failure is due to fragmentation
 460         *
 461         * Only compact if a failure would be due to fragmentation.
 462         */
 463        fragindex = fragmentation_index(zone, order);
 464        if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
 465                return COMPACT_SKIPPED;
 466
 467        if (fragindex == -1 && zone_watermark_ok(zone, order, watermark, 0, 0))
 468                return COMPACT_PARTIAL;
 469
 470        return COMPACT_CONTINUE;
 471}
 472
 473static int compact_zone(struct zone *zone, struct compact_control *cc)
 474{
 475        int ret;
 476
 477        ret = compaction_suitable(zone, cc->order);
 478        switch (ret) {
 479        case COMPACT_PARTIAL:
 480        case COMPACT_SKIPPED:
 481                /* Compaction is likely to fail */
 482                return ret;
 483        case COMPACT_CONTINUE:
 484                /* Fall through to compaction */
 485                ;
 486        }
 487
 488        /* Setup to move all movable pages to the end of the zone */
 489        cc->migrate_pfn = zone->zone_start_pfn;
 490        cc->free_pfn = cc->migrate_pfn + zone->spanned_pages;
 491        cc->free_pfn &= ~(pageblock_nr_pages-1);
 492
 493        migrate_prep_local();
 494
 495        while ((ret = compact_finished(zone, cc)) == COMPACT_CONTINUE) {
 496                unsigned long nr_migrate, nr_remaining;
 497
 498                if (!isolate_migratepages(zone, cc))
 499                        continue;
 500
 501                nr_migrate = cc->nr_migratepages;
 502                migrate_pages(&cc->migratepages, compaction_alloc,
 503                                (unsigned long)cc, false,
 504                                cc->sync);
 505                update_nr_listpages(cc);
 506                nr_remaining = cc->nr_migratepages;
 507
 508                count_vm_event(COMPACTBLOCKS);
 509                count_vm_events(COMPACTPAGES, nr_migrate - nr_remaining);
 510                if (nr_remaining)
 511                        count_vm_events(COMPACTPAGEFAILED, nr_remaining);
 512                trace_mm_compaction_migratepages(nr_migrate - nr_remaining,
 513                                                nr_remaining);
 514
 515                /* Release LRU pages not migrated */
 516                if (!list_empty(&cc->migratepages)) {
 517                        putback_lru_pages(&cc->migratepages);
 518                        cc->nr_migratepages = 0;
 519                }
 520
 521        }
 522
 523        /* Release free pages and check accounting */
 524        cc->nr_freepages -= release_freepages(&cc->freepages);
 525        VM_BUG_ON(cc->nr_freepages != 0);
 526
 527        return ret;
 528}
 529
 530unsigned long compact_zone_order(struct zone *zone,
 531                                 int order, gfp_t gfp_mask,
 532                                 bool sync)
 533{
 534        struct compact_control cc = {
 535                .nr_freepages = 0,
 536                .nr_migratepages = 0,
 537                .order = order,
 538                .migratetype = allocflags_to_migratetype(gfp_mask),
 539                .zone = zone,
 540                .sync = sync,
 541        };
 542        INIT_LIST_HEAD(&cc.freepages);
 543        INIT_LIST_HEAD(&cc.migratepages);
 544
 545        return compact_zone(zone, &cc);
 546}
 547
 548int sysctl_extfrag_threshold = 500;
 549
 550/**
 551 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
 552 * @zonelist: The zonelist used for the current allocation
 553 * @order: The order of the current allocation
 554 * @gfp_mask: The GFP mask of the current allocation
 555 * @nodemask: The allowed nodes to allocate from
 556 * @sync: Whether migration is synchronous or not
 557 *
 558 * This is the main entry point for direct page compaction.
 559 */
 560unsigned long try_to_compact_pages(struct zonelist *zonelist,
 561                        int order, gfp_t gfp_mask, nodemask_t *nodemask,
 562                        bool sync)
 563{
 564        enum zone_type high_zoneidx = gfp_zone(gfp_mask);
 565        int may_enter_fs = gfp_mask & __GFP_FS;
 566        int may_perform_io = gfp_mask & __GFP_IO;
 567        struct zoneref *z;
 568        struct zone *zone;
 569        int rc = COMPACT_SKIPPED;
 570
 571        /*
 572         * Check whether it is worth even starting compaction. The order check is
 573         * made because an assumption is made that the page allocator can satisfy
 574         * the "cheaper" orders without taking special steps
 575         */
 576        if (!order || !may_enter_fs || !may_perform_io)
 577                return rc;
 578
 579        count_vm_event(COMPACTSTALL);
 580
 581        /* Compact each zone in the list */
 582        for_each_zone_zonelist_nodemask(zone, z, zonelist, high_zoneidx,
 583                                                                nodemask) {
 584                int status;
 585
 586                status = compact_zone_order(zone, order, gfp_mask, sync);
 587                rc = max(status, rc);
 588
 589                /* If a normal allocation would succeed, stop compacting */
 590                if (zone_watermark_ok(zone, order, low_wmark_pages(zone), 0, 0))
 591                        break;
 592        }
 593
 594        return rc;
 595}
 596
 597
 598/* Compact all zones within a node */
 599static int compact_node(int nid)
 600{
 601        int zoneid;
 602        pg_data_t *pgdat;
 603        struct zone *zone;
 604
 605        if (nid < 0 || nid >= nr_node_ids || !node_online(nid))
 606                return -EINVAL;
 607        pgdat = NODE_DATA(nid);
 608
 609        /* Flush pending updates to the LRU lists */
 610        lru_add_drain_all();
 611
 612        for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
 613                struct compact_control cc = {
 614                        .nr_freepages = 0,
 615                        .nr_migratepages = 0,
 616                        .order = -1,
 617                };
 618
 619                zone = &pgdat->node_zones[zoneid];
 620                if (!populated_zone(zone))
 621                        continue;
 622
 623                cc.zone = zone;
 624                INIT_LIST_HEAD(&cc.freepages);
 625                INIT_LIST_HEAD(&cc.migratepages);
 626
 627                compact_zone(zone, &cc);
 628
 629                VM_BUG_ON(!list_empty(&cc.freepages));
 630                VM_BUG_ON(!list_empty(&cc.migratepages));
 631        }
 632
 633        return 0;
 634}
 635
 636/* Compact all nodes in the system */
 637static int compact_nodes(void)
 638{
 639        int nid;
 640
 641        for_each_online_node(nid)
 642                compact_node(nid);
 643
 644        return COMPACT_COMPLETE;
 645}
 646
 647/* The written value is actually unused, all memory is compacted */
 648int sysctl_compact_memory;
 649
 650/* This is the entry point for compacting all nodes via /proc/sys/vm */
 651int sysctl_compaction_handler(struct ctl_table *table, int write,
 652                        void __user *buffer, size_t *length, loff_t *ppos)
 653{
 654        if (write)
 655                return compact_nodes();
 656
 657        return 0;
 658}
 659
 660int sysctl_extfrag_handler(struct ctl_table *table, int write,
 661                        void __user *buffer, size_t *length, loff_t *ppos)
 662{
 663        proc_dointvec_minmax(table, write, buffer, length, ppos);
 664
 665        return 0;
 666}
 667
 668#if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
 669ssize_t sysfs_compact_node(struct sys_device *dev,
 670                        struct sysdev_attribute *attr,
 671                        const char *buf, size_t count)
 672{
 673        compact_node(dev->id);
 674
 675        return count;
 676}
 677static SYSDEV_ATTR(compact, S_IWUSR, NULL, sysfs_compact_node);
 678
 679int compaction_register_node(struct node *node)
 680{
 681        return sysdev_create_file(&node->sysdev, &attr_compact);
 682}
 683
 684void compaction_unregister_node(struct node *node)
 685{
 686        return sysdev_remove_file(&node->sysdev, &attr_compact);
 687}
 688#endif /* CONFIG_SYSFS && CONFIG_NUMA */
 689