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#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                if (!pfn_valid(pfn))
 426                        continue;
 427
 428                /*
 429                 * Check for overlapping nodes/zones. It's possible on some
 430                 * configurations to have a setup like
 431                 * node0 node1 node0
 432                 * i.e. it's possible that all pages within a zones range of
 433                 * pages do not belong to a single zone.
 434                 */
 435                page = pfn_to_page(pfn);
 436                if (page_zone(page) != zone)
 437                        continue;
 438
 439                /* Check the block is suitable for migration */
 440                if (!suitable_migration_target(page))
 441                        continue;
 442
 443                /*
 444                 * Found a block suitable for isolating free pages from. Now
 445                 * we disabled interrupts, double check things are ok and
 446                 * isolate the pages. This is to minimise the time IRQs
 447                 * are disabled
 448                 */
 449                isolated = 0;
 450                spin_lock_irqsave(&zone->lock, flags);
 451                if (suitable_migration_target(page)) {
 452                        end_pfn = min(pfn + pageblock_nr_pages, zone_end_pfn);
 453                        isolated = isolate_freepages_block(pfn, end_pfn,
 454                                                           freelist, false);
 455                        nr_freepages += isolated;
 456                }
 457                spin_unlock_irqrestore(&zone->lock, flags);
 458
 459                /*
 460                 * Record the highest PFN we isolated pages from. When next
 461                 * looking for free pages, the search will restart here as
 462                 * page migration may have returned some pages to the allocator
 463                 */
 464                if (isolated)
 465                        high_pfn = max(high_pfn, pfn);
 466        }
 467
 468        /* split_free_page does not map the pages */
 469        map_pages(freelist);
 470
 471        cc->free_pfn = high_pfn;
 472        cc->nr_freepages = nr_freepages;
 473}
 474
 475/*
 476 * This is a migrate-callback that "allocates" freepages by taking pages
 477 * from the isolated freelists in the block we are migrating to.
 478 */
 479static struct page *compaction_alloc(struct page *migratepage,
 480                                        unsigned long data,
 481                                        int **result)
 482{
 483        struct compact_control *cc = (struct compact_control *)data;
 484        struct page *freepage;
 485
 486        /* Isolate free pages if necessary */
 487        if (list_empty(&cc->freepages)) {
 488                isolate_freepages(cc->zone, cc);
 489
 490                if (list_empty(&cc->freepages))
 491                        return NULL;
 492        }
 493
 494        freepage = list_entry(cc->freepages.next, struct page, lru);
 495        list_del(&freepage->lru);
 496        cc->nr_freepages--;
 497
 498        return freepage;
 499}
 500
 501/*
 502 * We cannot control nr_migratepages and nr_freepages fully when migration is
 503 * running as migrate_pages() has no knowledge of compact_control. When
 504 * migration is complete, we count the number of pages on the lists by hand.
 505 */
 506static void update_nr_listpages(struct compact_control *cc)
 507{
 508        int nr_migratepages = 0;
 509        int nr_freepages = 0;
 510        struct page *page;
 511
 512        list_for_each_entry(page, &cc->migratepages, lru)
 513                nr_migratepages++;
 514        list_for_each_entry(page, &cc->freepages, lru)
 515                nr_freepages++;
 516
 517        cc->nr_migratepages = nr_migratepages;
 518        cc->nr_freepages = nr_freepages;
 519}
 520
 521/* possible outcome of isolate_migratepages */
 522typedef enum {
 523        ISOLATE_ABORT,          /* Abort compaction now */
 524        ISOLATE_NONE,           /* No pages isolated, continue scanning */
 525        ISOLATE_SUCCESS,        /* Pages isolated, migrate */
 526} isolate_migrate_t;
 527
 528/*
 529 * Isolate all pages that can be migrated from the block pointed to by
 530 * the migrate scanner within compact_control.
 531 */
 532static isolate_migrate_t isolate_migratepages(struct zone *zone,
 533                                        struct compact_control *cc)
 534{
 535        unsigned long low_pfn, end_pfn;
 536
 537        /* Do not scan outside zone boundaries */
 538        low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);
 539
 540        /* Only scan within a pageblock boundary */
 541        end_pfn = ALIGN(low_pfn + pageblock_nr_pages, pageblock_nr_pages);
 542
 543        /* Do not cross the free scanner or scan within a memory hole */
 544        if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
 545                cc->migrate_pfn = end_pfn;
 546                return ISOLATE_NONE;
 547        }
 548
 549        /* Perform the isolation */
 550        low_pfn = isolate_migratepages_range(zone, cc, low_pfn, end_pfn);
 551        if (!low_pfn)
 552                return ISOLATE_ABORT;
 553
 554        cc->migrate_pfn = low_pfn;
 555
 556        return ISOLATE_SUCCESS;
 557}
 558
 559static int compact_finished(struct zone *zone,
 560                            struct compact_control *cc)
 561{
 562        unsigned int order;
 563        unsigned long watermark;
 564
 565        if (fatal_signal_pending(current))
 566                return COMPACT_PARTIAL;
 567
 568        /* Compaction run completes if the migrate and free scanner meet */
 569        if (cc->free_pfn <= cc->migrate_pfn)
 570                return COMPACT_COMPLETE;
 571
 572        /*
 573         * order == -1 is expected when compacting via
 574         * /proc/sys/vm/compact_memory
 575         */
 576        if (cc->order == -1)
 577                return COMPACT_CONTINUE;
 578
 579        /* Compaction run is not finished if the watermark is not met */
 580        watermark = low_wmark_pages(zone);
 581        watermark += (1 << cc->order);
 582
 583        if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0))
 584                return COMPACT_CONTINUE;
 585
 586        /* Direct compactor: Is a suitable page free? */
 587        for (order = cc->order; order < MAX_ORDER; order++) {
 588                /* Job done if page is free of the right migratetype */
 589                if (!list_empty(&zone->free_area[order].free_list[cc->migratetype]))
 590                        return COMPACT_PARTIAL;
 591
 592                /* Job done if allocation would set block type */
 593                if (order >= pageblock_order && zone->free_area[order].nr_free)
 594                        return COMPACT_PARTIAL;
 595        }
 596
 597        return COMPACT_CONTINUE;
 598}
 599
 600/*
 601 * compaction_suitable: Is this suitable to run compaction on this zone now?
 602 * Returns
 603 *   COMPACT_SKIPPED  - If there are too few free pages for compaction
 604 *   COMPACT_PARTIAL  - If the allocation would succeed without compaction
 605 *   COMPACT_CONTINUE - If compaction should run now
 606 */
 607unsigned long compaction_suitable(struct zone *zone, int order)
 608{
 609        int fragindex;
 610        unsigned long watermark;
 611
 612        /*
 613         * order == -1 is expected when compacting via
 614         * /proc/sys/vm/compact_memory
 615         */
 616        if (order == -1)
 617                return COMPACT_CONTINUE;
 618
 619        /*
 620         * Watermarks for order-0 must be met for compaction. Note the 2UL.
 621         * This is because during migration, copies of pages need to be
 622         * allocated and for a short time, the footprint is higher
 623         */
 624        watermark = low_wmark_pages(zone) + (2UL << order);
 625        if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
 626                return COMPACT_SKIPPED;
 627
 628        /*
 629         * fragmentation index determines if allocation failures are due to
 630         * low memory or external fragmentation
 631         *
 632         * index of -1000 implies allocations might succeed depending on
 633         * watermarks
 634         * index towards 0 implies failure is due to lack of memory
 635         * index towards 1000 implies failure is due to fragmentation
 636         *
 637         * Only compact if a failure would be due to fragmentation.
 638         */
 639        fragindex = fragmentation_index(zone, order);
 640        if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
 641                return COMPACT_SKIPPED;
 642
 643        if (fragindex == -1000 && zone_watermark_ok(zone, order, watermark,
 644            0, 0))
 645                return COMPACT_PARTIAL;
 646
 647        return COMPACT_CONTINUE;
 648}
 649
 650static int compact_zone(struct zone *zone, struct compact_control *cc)
 651{
 652        int ret;
 653
 654        ret = compaction_suitable(zone, cc->order);
 655        switch (ret) {
 656        case COMPACT_PARTIAL:
 657        case COMPACT_SKIPPED:
 658                /* Compaction is likely to fail */
 659                return ret;
 660        case COMPACT_CONTINUE:
 661                /* Fall through to compaction */
 662                ;
 663        }
 664
 665        /* Setup to move all movable pages to the end of the zone */
 666        cc->migrate_pfn = zone->zone_start_pfn;
 667        cc->free_pfn = cc->migrate_pfn + zone->spanned_pages;
 668        cc->free_pfn &= ~(pageblock_nr_pages-1);
 669
 670        migrate_prep_local();
 671
 672        while ((ret = compact_finished(zone, cc)) == COMPACT_CONTINUE) {
 673                unsigned long nr_migrate, nr_remaining;
 674                int err;
 675
 676                switch (isolate_migratepages(zone, cc)) {
 677                case ISOLATE_ABORT:
 678                        ret = COMPACT_PARTIAL;
 679                        goto out;
 680                case ISOLATE_NONE:
 681                        continue;
 682                case ISOLATE_SUCCESS:
 683                        ;
 684                }
 685
 686                nr_migrate = cc->nr_migratepages;
 687                err = migrate_pages(&cc->migratepages, compaction_alloc,
 688                                (unsigned long)cc, false,
 689                                cc->sync ? MIGRATE_SYNC_LIGHT : MIGRATE_ASYNC);
 690                update_nr_listpages(cc);
 691                nr_remaining = cc->nr_migratepages;
 692
 693                count_vm_event(COMPACTBLOCKS);
 694                count_vm_events(COMPACTPAGES, nr_migrate - nr_remaining);
 695                if (nr_remaining)
 696                        count_vm_events(COMPACTPAGEFAILED, nr_remaining);
 697                trace_mm_compaction_migratepages(nr_migrate - nr_remaining,
 698                                                nr_remaining);
 699
 700                /* Release LRU pages not migrated */
 701                if (err) {
 702                        putback_lru_pages(&cc->migratepages);
 703                        cc->nr_migratepages = 0;
 704                        if (err == -ENOMEM) {
 705                                ret = COMPACT_PARTIAL;
 706                                goto out;
 707                        }
 708                }
 709        }
 710
 711out:
 712        /* Release free pages and check accounting */
 713        cc->nr_freepages -= release_freepages(&cc->freepages);
 714        VM_BUG_ON(cc->nr_freepages != 0);
 715
 716        return ret;
 717}
 718
 719static unsigned long compact_zone_order(struct zone *zone,
 720                                 int order, gfp_t gfp_mask,
 721                                 bool sync)
 722{
 723        struct compact_control cc = {
 724                .nr_freepages = 0,
 725                .nr_migratepages = 0,
 726                .order = order,
 727                .migratetype = allocflags_to_migratetype(gfp_mask),
 728                .zone = zone,
 729                .sync = sync,
 730        };
 731        INIT_LIST_HEAD(&cc.freepages);
 732        INIT_LIST_HEAD(&cc.migratepages);
 733
 734        return compact_zone(zone, &cc);
 735}
 736
 737int sysctl_extfrag_threshold = 500;
 738
 739/**
 740 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
 741 * @zonelist: The zonelist used for the current allocation
 742 * @order: The order of the current allocation
 743 * @gfp_mask: The GFP mask of the current allocation
 744 * @nodemask: The allowed nodes to allocate from
 745 * @sync: Whether migration is synchronous or not
 746 *
 747 * This is the main entry point for direct page compaction.
 748 */
 749unsigned long try_to_compact_pages(struct zonelist *zonelist,
 750                        int order, gfp_t gfp_mask, nodemask_t *nodemask,
 751                        bool sync)
 752{
 753        enum zone_type high_zoneidx = gfp_zone(gfp_mask);
 754        int may_enter_fs = gfp_mask & __GFP_FS;
 755        int may_perform_io = gfp_mask & __GFP_IO;
 756        struct zoneref *z;
 757        struct zone *zone;
 758        int rc = COMPACT_SKIPPED;
 759
 760        /*
 761         * Check whether it is worth even starting compaction. The order check is
 762         * made because an assumption is made that the page allocator can satisfy
 763         * the "cheaper" orders without taking special steps
 764         */
 765        if (!order || !may_enter_fs || !may_perform_io)
 766                return rc;
 767
 768        count_vm_event(COMPACTSTALL);
 769
 770        /* Compact each zone in the list */
 771        for_each_zone_zonelist_nodemask(zone, z, zonelist, high_zoneidx,
 772                                                                nodemask) {
 773                int status;
 774
 775                status = compact_zone_order(zone, order, gfp_mask, sync);
 776                rc = max(status, rc);
 777
 778                /* If a normal allocation would succeed, stop compacting */
 779                if (zone_watermark_ok(zone, order, low_wmark_pages(zone), 0, 0))
 780                        break;
 781        }
 782
 783        return rc;
 784}
 785
 786
 787/* Compact all zones within a node */
 788static int __compact_pgdat(pg_data_t *pgdat, struct compact_control *cc)
 789{
 790        int zoneid;
 791        struct zone *zone;
 792
 793        for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
 794
 795                zone = &pgdat->node_zones[zoneid];
 796                if (!populated_zone(zone))
 797                        continue;
 798
 799                cc->nr_freepages = 0;
 800                cc->nr_migratepages = 0;
 801                cc->zone = zone;
 802                INIT_LIST_HEAD(&cc->freepages);
 803                INIT_LIST_HEAD(&cc->migratepages);
 804
 805                if (cc->order == -1 || !compaction_deferred(zone, cc->order))
 806                        compact_zone(zone, cc);
 807
 808                if (cc->order > 0) {
 809                        int ok = zone_watermark_ok(zone, cc->order,
 810                                                low_wmark_pages(zone), 0, 0);
 811                        if (ok && cc->order > zone->compact_order_failed)
 812                                zone->compact_order_failed = cc->order + 1;
 813                        /* Currently async compaction is never deferred. */
 814                        else if (!ok && cc->sync)
 815                                defer_compaction(zone, cc->order);
 816                }
 817
 818                VM_BUG_ON(!list_empty(&cc->freepages));
 819                VM_BUG_ON(!list_empty(&cc->migratepages));
 820        }
 821
 822        return 0;
 823}
 824
 825int compact_pgdat(pg_data_t *pgdat, int order)
 826{
 827        struct compact_control cc = {
 828                .order = order,
 829                .sync = false,
 830        };
 831
 832        return __compact_pgdat(pgdat, &cc);
 833}
 834
 835static int compact_node(int nid)
 836{
 837        struct compact_control cc = {
 838                .order = -1,
 839                .sync = true,
 840        };
 841
 842        return __compact_pgdat(NODE_DATA(nid), &cc);
 843}
 844
 845/* Compact all nodes in the system */
 846static int compact_nodes(void)
 847{
 848        int nid;
 849
 850        /* Flush pending updates to the LRU lists */
 851        lru_add_drain_all();
 852
 853        for_each_online_node(nid)
 854                compact_node(nid);
 855
 856        return COMPACT_COMPLETE;
 857}
 858
 859/* The written value is actually unused, all memory is compacted */
 860int sysctl_compact_memory;
 861
 862/* This is the entry point for compacting all nodes via /proc/sys/vm */
 863int sysctl_compaction_handler(struct ctl_table *table, int write,
 864                        void __user *buffer, size_t *length, loff_t *ppos)
 865{
 866        if (write)
 867                return compact_nodes();
 868
 869        return 0;
 870}
 871
 872int sysctl_extfrag_handler(struct ctl_table *table, int write,
 873                        void __user *buffer, size_t *length, loff_t *ppos)
 874{
 875        proc_dointvec_minmax(table, write, buffer, length, ppos);
 876
 877        return 0;
 878}
 879
 880#if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
 881ssize_t sysfs_compact_node(struct device *dev,
 882                        struct device_attribute *attr,
 883                        const char *buf, size_t count)
 884{
 885        int nid = dev->id;
 886
 887        if (nid >= 0 && nid < nr_node_ids && node_online(nid)) {
 888                /* Flush pending updates to the LRU lists */
 889                lru_add_drain_all();
 890
 891                compact_node(nid);
 892        }
 893
 894        return count;
 895}
 896static DEVICE_ATTR(compact, S_IWUSR, NULL, sysfs_compact_node);
 897
 898int compaction_register_node(struct node *node)
 899{
 900        return device_create_file(&node->dev, &dev_attr_compact);
 901}
 902
 903void compaction_unregister_node(struct node *node)
 904{
 905        return device_remove_file(&node->dev, &dev_attr_compact);
 906}
 907#endif /* CONFIG_SYSFS && CONFIG_NUMA */
 908
 909#endif /* CONFIG_COMPACTION */
 910
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