linux/mm/compaction.c
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   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * linux/mm/compaction.c
   4 *
   5 * Memory compaction for the reduction of external fragmentation. Note that
   6 * this heavily depends upon page migration to do all the real heavy
   7 * lifting
   8 *
   9 * Copyright IBM Corp. 2007-2010 Mel Gorman <mel@csn.ul.ie>
  10 */
  11#include <linux/cpu.h>
  12#include <linux/swap.h>
  13#include <linux/migrate.h>
  14#include <linux/compaction.h>
  15#include <linux/mm_inline.h>
  16#include <linux/sched/signal.h>
  17#include <linux/backing-dev.h>
  18#include <linux/sysctl.h>
  19#include <linux/sysfs.h>
  20#include <linux/page-isolation.h>
  21#include <linux/kasan.h>
  22#include <linux/kthread.h>
  23#include <linux/freezer.h>
  24#include <linux/page_owner.h>
  25#include <linux/psi.h>
  26#include "internal.h"
  27
  28#ifdef CONFIG_COMPACTION
  29static inline void count_compact_event(enum vm_event_item item)
  30{
  31        count_vm_event(item);
  32}
  33
  34static inline void count_compact_events(enum vm_event_item item, long delta)
  35{
  36        count_vm_events(item, delta);
  37}
  38#else
  39#define count_compact_event(item) do { } while (0)
  40#define count_compact_events(item, delta) do { } while (0)
  41#endif
  42
  43#if defined CONFIG_COMPACTION || defined CONFIG_CMA
  44
  45#define CREATE_TRACE_POINTS
  46#include <trace/events/compaction.h>
  47
  48#define block_start_pfn(pfn, order)     round_down(pfn, 1UL << (order))
  49#define block_end_pfn(pfn, order)       ALIGN((pfn) + 1, 1UL << (order))
  50#define pageblock_start_pfn(pfn)        block_start_pfn(pfn, pageblock_order)
  51#define pageblock_end_pfn(pfn)          block_end_pfn(pfn, pageblock_order)
  52
  53static unsigned long release_freepages(struct list_head *freelist)
  54{
  55        struct page *page, *next;
  56        unsigned long high_pfn = 0;
  57
  58        list_for_each_entry_safe(page, next, freelist, lru) {
  59                unsigned long pfn = page_to_pfn(page);
  60                list_del(&page->lru);
  61                __free_page(page);
  62                if (pfn > high_pfn)
  63                        high_pfn = pfn;
  64        }
  65
  66        return high_pfn;
  67}
  68
  69static void split_map_pages(struct list_head *list)
  70{
  71        unsigned int i, order, nr_pages;
  72        struct page *page, *next;
  73        LIST_HEAD(tmp_list);
  74
  75        list_for_each_entry_safe(page, next, list, lru) {
  76                list_del(&page->lru);
  77
  78                order = page_private(page);
  79                nr_pages = 1 << order;
  80
  81                post_alloc_hook(page, order, __GFP_MOVABLE);
  82                if (order)
  83                        split_page(page, order);
  84
  85                for (i = 0; i < nr_pages; i++) {
  86                        list_add(&page->lru, &tmp_list);
  87                        page++;
  88                }
  89        }
  90
  91        list_splice(&tmp_list, list);
  92}
  93
  94#ifdef CONFIG_COMPACTION
  95
  96int PageMovable(struct page *page)
  97{
  98        struct address_space *mapping;
  99
 100        VM_BUG_ON_PAGE(!PageLocked(page), page);
 101        if (!__PageMovable(page))
 102                return 0;
 103
 104        mapping = page_mapping(page);
 105        if (mapping && mapping->a_ops && mapping->a_ops->isolate_page)
 106                return 1;
 107
 108        return 0;
 109}
 110EXPORT_SYMBOL(PageMovable);
 111
 112void __SetPageMovable(struct page *page, struct address_space *mapping)
 113{
 114        VM_BUG_ON_PAGE(!PageLocked(page), page);
 115        VM_BUG_ON_PAGE((unsigned long)mapping & PAGE_MAPPING_MOVABLE, page);
 116        page->mapping = (void *)((unsigned long)mapping | PAGE_MAPPING_MOVABLE);
 117}
 118EXPORT_SYMBOL(__SetPageMovable);
 119
 120void __ClearPageMovable(struct page *page)
 121{
 122        VM_BUG_ON_PAGE(!PageLocked(page), page);
 123        VM_BUG_ON_PAGE(!PageMovable(page), page);
 124        /*
 125         * Clear registered address_space val with keeping PAGE_MAPPING_MOVABLE
 126         * flag so that VM can catch up released page by driver after isolation.
 127         * With it, VM migration doesn't try to put it back.
 128         */
 129        page->mapping = (void *)((unsigned long)page->mapping &
 130                                PAGE_MAPPING_MOVABLE);
 131}
 132EXPORT_SYMBOL(__ClearPageMovable);
 133
 134/* Do not skip compaction more than 64 times */
 135#define COMPACT_MAX_DEFER_SHIFT 6
 136
 137/*
 138 * Compaction is deferred when compaction fails to result in a page
 139 * allocation success. 1 << compact_defer_limit compactions are skipped up
 140 * to a limit of 1 << COMPACT_MAX_DEFER_SHIFT
 141 */
 142void defer_compaction(struct zone *zone, int order)
 143{
 144        zone->compact_considered = 0;
 145        zone->compact_defer_shift++;
 146
 147        if (order < zone->compact_order_failed)
 148                zone->compact_order_failed = order;
 149
 150        if (zone->compact_defer_shift > COMPACT_MAX_DEFER_SHIFT)
 151                zone->compact_defer_shift = COMPACT_MAX_DEFER_SHIFT;
 152
 153        trace_mm_compaction_defer_compaction(zone, order);
 154}
 155
 156/* Returns true if compaction should be skipped this time */
 157bool compaction_deferred(struct zone *zone, int order)
 158{
 159        unsigned long defer_limit = 1UL << zone->compact_defer_shift;
 160
 161        if (order < zone->compact_order_failed)
 162                return false;
 163
 164        /* Avoid possible overflow */
 165        if (++zone->compact_considered > defer_limit)
 166                zone->compact_considered = defer_limit;
 167
 168        if (zone->compact_considered >= defer_limit)
 169                return false;
 170
 171        trace_mm_compaction_deferred(zone, order);
 172
 173        return true;
 174}
 175
 176/*
 177 * Update defer tracking counters after successful compaction of given order,
 178 * which means an allocation either succeeded (alloc_success == true) or is
 179 * expected to succeed.
 180 */
 181void compaction_defer_reset(struct zone *zone, int order,
 182                bool alloc_success)
 183{
 184        if (alloc_success) {
 185                zone->compact_considered = 0;
 186                zone->compact_defer_shift = 0;
 187        }
 188        if (order >= zone->compact_order_failed)
 189                zone->compact_order_failed = order + 1;
 190
 191        trace_mm_compaction_defer_reset(zone, order);
 192}
 193
 194/* Returns true if restarting compaction after many failures */
 195bool compaction_restarting(struct zone *zone, int order)
 196{
 197        if (order < zone->compact_order_failed)
 198                return false;
 199
 200        return zone->compact_defer_shift == COMPACT_MAX_DEFER_SHIFT &&
 201                zone->compact_considered >= 1UL << zone->compact_defer_shift;
 202}
 203
 204/* Returns true if the pageblock should be scanned for pages to isolate. */
 205static inline bool isolation_suitable(struct compact_control *cc,
 206                                        struct page *page)
 207{
 208        if (cc->ignore_skip_hint)
 209                return true;
 210
 211        return !get_pageblock_skip(page);
 212}
 213
 214static void reset_cached_positions(struct zone *zone)
 215{
 216        zone->compact_cached_migrate_pfn[0] = zone->zone_start_pfn;
 217        zone->compact_cached_migrate_pfn[1] = zone->zone_start_pfn;
 218        zone->compact_cached_free_pfn =
 219                                pageblock_start_pfn(zone_end_pfn(zone) - 1);
 220}
 221
 222/*
 223 * Compound pages of >= pageblock_order should consistenly be skipped until
 224 * released. It is always pointless to compact pages of such order (if they are
 225 * migratable), and the pageblocks they occupy cannot contain any free pages.
 226 */
 227static bool pageblock_skip_persistent(struct page *page)
 228{
 229        if (!PageCompound(page))
 230                return false;
 231
 232        page = compound_head(page);
 233
 234        if (compound_order(page) >= pageblock_order)
 235                return true;
 236
 237        return false;
 238}
 239
 240static bool
 241__reset_isolation_pfn(struct zone *zone, unsigned long pfn, bool check_source,
 242                                                        bool check_target)
 243{
 244        struct page *page = pfn_to_online_page(pfn);
 245        struct page *block_page;
 246        struct page *end_page;
 247        unsigned long block_pfn;
 248
 249        if (!page)
 250                return false;
 251        if (zone != page_zone(page))
 252                return false;
 253        if (pageblock_skip_persistent(page))
 254                return false;
 255
 256        /*
 257         * If skip is already cleared do no further checking once the
 258         * restart points have been set.
 259         */
 260        if (check_source && check_target && !get_pageblock_skip(page))
 261                return true;
 262
 263        /*
 264         * If clearing skip for the target scanner, do not select a
 265         * non-movable pageblock as the starting point.
 266         */
 267        if (!check_source && check_target &&
 268            get_pageblock_migratetype(page) != MIGRATE_MOVABLE)
 269                return false;
 270
 271        /* Ensure the start of the pageblock or zone is online and valid */
 272        block_pfn = pageblock_start_pfn(pfn);
 273        block_pfn = max(block_pfn, zone->zone_start_pfn);
 274        block_page = pfn_to_online_page(block_pfn);
 275        if (block_page) {
 276                page = block_page;
 277                pfn = block_pfn;
 278        }
 279
 280        /* Ensure the end of the pageblock or zone is online and valid */
 281        block_pfn = pageblock_end_pfn(pfn) - 1;
 282        block_pfn = min(block_pfn, zone_end_pfn(zone) - 1);
 283        end_page = pfn_to_online_page(block_pfn);
 284        if (!end_page)
 285                return false;
 286
 287        /*
 288         * Only clear the hint if a sample indicates there is either a
 289         * free page or an LRU page in the block. One or other condition
 290         * is necessary for the block to be a migration source/target.
 291         */
 292        do {
 293                if (pfn_valid_within(pfn)) {
 294                        if (check_source && PageLRU(page)) {
 295                                clear_pageblock_skip(page);
 296                                return true;
 297                        }
 298
 299                        if (check_target && PageBuddy(page)) {
 300                                clear_pageblock_skip(page);
 301                                return true;
 302                        }
 303                }
 304
 305                page += (1 << PAGE_ALLOC_COSTLY_ORDER);
 306                pfn += (1 << PAGE_ALLOC_COSTLY_ORDER);
 307        } while (page <= end_page);
 308
 309        return false;
 310}
 311
 312/*
 313 * This function is called to clear all cached information on pageblocks that
 314 * should be skipped for page isolation when the migrate and free page scanner
 315 * meet.
 316 */
 317static void __reset_isolation_suitable(struct zone *zone)
 318{
 319        unsigned long migrate_pfn = zone->zone_start_pfn;
 320        unsigned long free_pfn = zone_end_pfn(zone) - 1;
 321        unsigned long reset_migrate = free_pfn;
 322        unsigned long reset_free = migrate_pfn;
 323        bool source_set = false;
 324        bool free_set = false;
 325
 326        if (!zone->compact_blockskip_flush)
 327                return;
 328
 329        zone->compact_blockskip_flush = false;
 330
 331        /*
 332         * Walk the zone and update pageblock skip information. Source looks
 333         * for PageLRU while target looks for PageBuddy. When the scanner
 334         * is found, both PageBuddy and PageLRU are checked as the pageblock
 335         * is suitable as both source and target.
 336         */
 337        for (; migrate_pfn < free_pfn; migrate_pfn += pageblock_nr_pages,
 338                                        free_pfn -= pageblock_nr_pages) {
 339                cond_resched();
 340
 341                /* Update the migrate PFN */
 342                if (__reset_isolation_pfn(zone, migrate_pfn, true, source_set) &&
 343                    migrate_pfn < reset_migrate) {
 344                        source_set = true;
 345                        reset_migrate = migrate_pfn;
 346                        zone->compact_init_migrate_pfn = reset_migrate;
 347                        zone->compact_cached_migrate_pfn[0] = reset_migrate;
 348                        zone->compact_cached_migrate_pfn[1] = reset_migrate;
 349                }
 350
 351                /* Update the free PFN */
 352                if (__reset_isolation_pfn(zone, free_pfn, free_set, true) &&
 353                    free_pfn > reset_free) {
 354                        free_set = true;
 355                        reset_free = free_pfn;
 356                        zone->compact_init_free_pfn = reset_free;
 357                        zone->compact_cached_free_pfn = reset_free;
 358                }
 359        }
 360
 361        /* Leave no distance if no suitable block was reset */
 362        if (reset_migrate >= reset_free) {
 363                zone->compact_cached_migrate_pfn[0] = migrate_pfn;
 364                zone->compact_cached_migrate_pfn[1] = migrate_pfn;
 365                zone->compact_cached_free_pfn = free_pfn;
 366        }
 367}
 368
 369void reset_isolation_suitable(pg_data_t *pgdat)
 370{
 371        int zoneid;
 372
 373        for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
 374                struct zone *zone = &pgdat->node_zones[zoneid];
 375                if (!populated_zone(zone))
 376                        continue;
 377
 378                /* Only flush if a full compaction finished recently */
 379                if (zone->compact_blockskip_flush)
 380                        __reset_isolation_suitable(zone);
 381        }
 382}
 383
 384/*
 385 * Sets the pageblock skip bit if it was clear. Note that this is a hint as
 386 * locks are not required for read/writers. Returns true if it was already set.
 387 */
 388static bool test_and_set_skip(struct compact_control *cc, struct page *page,
 389                                                        unsigned long pfn)
 390{
 391        bool skip;
 392
 393        /* Do no update if skip hint is being ignored */
 394        if (cc->ignore_skip_hint)
 395                return false;
 396
 397        if (!IS_ALIGNED(pfn, pageblock_nr_pages))
 398                return false;
 399
 400        skip = get_pageblock_skip(page);
 401        if (!skip && !cc->no_set_skip_hint)
 402                set_pageblock_skip(page);
 403
 404        return skip;
 405}
 406
 407static void update_cached_migrate(struct compact_control *cc, unsigned long pfn)
 408{
 409        struct zone *zone = cc->zone;
 410
 411        pfn = pageblock_end_pfn(pfn);
 412
 413        /* Set for isolation rather than compaction */
 414        if (cc->no_set_skip_hint)
 415                return;
 416
 417        if (pfn > zone->compact_cached_migrate_pfn[0])
 418                zone->compact_cached_migrate_pfn[0] = pfn;
 419        if (cc->mode != MIGRATE_ASYNC &&
 420            pfn > zone->compact_cached_migrate_pfn[1])
 421                zone->compact_cached_migrate_pfn[1] = pfn;
 422}
 423
 424/*
 425 * If no pages were isolated then mark this pageblock to be skipped in the
 426 * future. The information is later cleared by __reset_isolation_suitable().
 427 */
 428static void update_pageblock_skip(struct compact_control *cc,
 429                        struct page *page, unsigned long pfn)
 430{
 431        struct zone *zone = cc->zone;
 432
 433        if (cc->no_set_skip_hint)
 434                return;
 435
 436        if (!page)
 437                return;
 438
 439        set_pageblock_skip(page);
 440
 441        /* Update where async and sync compaction should restart */
 442        if (pfn < zone->compact_cached_free_pfn)
 443                zone->compact_cached_free_pfn = pfn;
 444}
 445#else
 446static inline bool isolation_suitable(struct compact_control *cc,
 447                                        struct page *page)
 448{
 449        return true;
 450}
 451
 452static inline bool pageblock_skip_persistent(struct page *page)
 453{
 454        return false;
 455}
 456
 457static inline void update_pageblock_skip(struct compact_control *cc,
 458                        struct page *page, unsigned long pfn)
 459{
 460}
 461
 462static void update_cached_migrate(struct compact_control *cc, unsigned long pfn)
 463{
 464}
 465
 466static bool test_and_set_skip(struct compact_control *cc, struct page *page,
 467                                                        unsigned long pfn)
 468{
 469        return false;
 470}
 471#endif /* CONFIG_COMPACTION */
 472
 473/*
 474 * Compaction requires the taking of some coarse locks that are potentially
 475 * very heavily contended. For async compaction, trylock and record if the
 476 * lock is contended. The lock will still be acquired but compaction will
 477 * abort when the current block is finished regardless of success rate.
 478 * Sync compaction acquires the lock.
 479 *
 480 * Always returns true which makes it easier to track lock state in callers.
 481 */
 482static bool compact_lock_irqsave(spinlock_t *lock, unsigned long *flags,
 483                                                struct compact_control *cc)
 484{
 485        /* Track if the lock is contended in async mode */
 486        if (cc->mode == MIGRATE_ASYNC && !cc->contended) {
 487                if (spin_trylock_irqsave(lock, *flags))
 488                        return true;
 489
 490                cc->contended = true;
 491        }
 492
 493        spin_lock_irqsave(lock, *flags);
 494        return true;
 495}
 496
 497/*
 498 * Compaction requires the taking of some coarse locks that are potentially
 499 * very heavily contended. The lock should be periodically unlocked to avoid
 500 * having disabled IRQs for a long time, even when there is nobody waiting on
 501 * the lock. It might also be that allowing the IRQs will result in
 502 * need_resched() becoming true. If scheduling is needed, async compaction
 503 * aborts. Sync compaction schedules.
 504 * Either compaction type will also abort if a fatal signal is pending.
 505 * In either case if the lock was locked, it is dropped and not regained.
 506 *
 507 * Returns true if compaction should abort due to fatal signal pending, or
 508 *              async compaction due to need_resched()
 509 * Returns false when compaction can continue (sync compaction might have
 510 *              scheduled)
 511 */
 512static bool compact_unlock_should_abort(spinlock_t *lock,
 513                unsigned long flags, bool *locked, struct compact_control *cc)
 514{
 515        if (*locked) {
 516                spin_unlock_irqrestore(lock, flags);
 517                *locked = false;
 518        }
 519
 520        if (fatal_signal_pending(current)) {
 521                cc->contended = true;
 522                return true;
 523        }
 524
 525        cond_resched();
 526
 527        return false;
 528}
 529
 530/*
 531 * Isolate free pages onto a private freelist. If @strict is true, will abort
 532 * returning 0 on any invalid PFNs or non-free pages inside of the pageblock
 533 * (even though it may still end up isolating some pages).
 534 */
 535static unsigned long isolate_freepages_block(struct compact_control *cc,
 536                                unsigned long *start_pfn,
 537                                unsigned long end_pfn,
 538                                struct list_head *freelist,
 539                                unsigned int stride,
 540                                bool strict)
 541{
 542        int nr_scanned = 0, total_isolated = 0;
 543        struct page *cursor;
 544        unsigned long flags = 0;
 545        bool locked = false;
 546        unsigned long blockpfn = *start_pfn;
 547        unsigned int order;
 548
 549        /* Strict mode is for isolation, speed is secondary */
 550        if (strict)
 551                stride = 1;
 552
 553        cursor = pfn_to_page(blockpfn);
 554
 555        /* Isolate free pages. */
 556        for (; blockpfn < end_pfn; blockpfn += stride, cursor += stride) {
 557                int isolated;
 558                struct page *page = cursor;
 559
 560                /*
 561                 * Periodically drop the lock (if held) regardless of its
 562                 * contention, to give chance to IRQs. Abort if fatal signal
 563                 * pending or async compaction detects need_resched()
 564                 */
 565                if (!(blockpfn % SWAP_CLUSTER_MAX)
 566                    && compact_unlock_should_abort(&cc->zone->lock, flags,
 567                                                                &locked, cc))
 568                        break;
 569
 570                nr_scanned++;
 571                if (!pfn_valid_within(blockpfn))
 572                        goto isolate_fail;
 573
 574                /*
 575                 * For compound pages such as THP and hugetlbfs, we can save
 576                 * potentially a lot of iterations if we skip them at once.
 577                 * The check is racy, but we can consider only valid values
 578                 * and the only danger is skipping too much.
 579                 */
 580                if (PageCompound(page)) {
 581                        const unsigned int order = compound_order(page);
 582
 583                        if (likely(order < MAX_ORDER)) {
 584                                blockpfn += (1UL << order) - 1;
 585                                cursor += (1UL << order) - 1;
 586                        }
 587                        goto isolate_fail;
 588                }
 589
 590                if (!PageBuddy(page))
 591                        goto isolate_fail;
 592
 593                /*
 594                 * If we already hold the lock, we can skip some rechecking.
 595                 * Note that if we hold the lock now, checked_pageblock was
 596                 * already set in some previous iteration (or strict is true),
 597                 * so it is correct to skip the suitable migration target
 598                 * recheck as well.
 599                 */
 600                if (!locked) {
 601                        locked = compact_lock_irqsave(&cc->zone->lock,
 602                                                                &flags, cc);
 603
 604                        /* Recheck this is a buddy page under lock */
 605                        if (!PageBuddy(page))
 606                                goto isolate_fail;
 607                }
 608
 609                /* Found a free page, will break it into order-0 pages */
 610                order = page_order(page);
 611                isolated = __isolate_free_page(page, order);
 612                if (!isolated)
 613                        break;
 614                set_page_private(page, order);
 615
 616                total_isolated += isolated;
 617                cc->nr_freepages += isolated;
 618                list_add_tail(&page->lru, freelist);
 619
 620                if (!strict && cc->nr_migratepages <= cc->nr_freepages) {
 621                        blockpfn += isolated;
 622                        break;
 623                }
 624                /* Advance to the end of split page */
 625                blockpfn += isolated - 1;
 626                cursor += isolated - 1;
 627                continue;
 628
 629isolate_fail:
 630                if (strict)
 631                        break;
 632                else
 633                        continue;
 634
 635        }
 636
 637        if (locked)
 638                spin_unlock_irqrestore(&cc->zone->lock, flags);
 639
 640        /*
 641         * There is a tiny chance that we have read bogus compound_order(),
 642         * so be careful to not go outside of the pageblock.
 643         */
 644        if (unlikely(blockpfn > end_pfn))
 645                blockpfn = end_pfn;
 646
 647        trace_mm_compaction_isolate_freepages(*start_pfn, blockpfn,
 648                                        nr_scanned, total_isolated);
 649
 650        /* Record how far we have got within the block */
 651        *start_pfn = blockpfn;
 652
 653        /*
 654         * If strict isolation is requested by CMA then check that all the
 655         * pages requested were isolated. If there were any failures, 0 is
 656         * returned and CMA will fail.
 657         */
 658        if (strict && blockpfn < end_pfn)
 659                total_isolated = 0;
 660
 661        cc->total_free_scanned += nr_scanned;
 662        if (total_isolated)
 663                count_compact_events(COMPACTISOLATED, total_isolated);
 664        return total_isolated;
 665}
 666
 667/**
 668 * isolate_freepages_range() - isolate free pages.
 669 * @cc:        Compaction control structure.
 670 * @start_pfn: The first PFN to start isolating.
 671 * @end_pfn:   The one-past-last PFN.
 672 *
 673 * Non-free pages, invalid PFNs, or zone boundaries within the
 674 * [start_pfn, end_pfn) range are considered errors, cause function to
 675 * undo its actions and return zero.
 676 *
 677 * Otherwise, function returns one-past-the-last PFN of isolated page
 678 * (which may be greater then end_pfn if end fell in a middle of
 679 * a free page).
 680 */
 681unsigned long
 682isolate_freepages_range(struct compact_control *cc,
 683                        unsigned long start_pfn, unsigned long end_pfn)
 684{
 685        unsigned long isolated, pfn, block_start_pfn, block_end_pfn;
 686        LIST_HEAD(freelist);
 687
 688        pfn = start_pfn;
 689        block_start_pfn = pageblock_start_pfn(pfn);
 690        if (block_start_pfn < cc->zone->zone_start_pfn)
 691                block_start_pfn = cc->zone->zone_start_pfn;
 692        block_end_pfn = pageblock_end_pfn(pfn);
 693
 694        for (; pfn < end_pfn; pfn += isolated,
 695                                block_start_pfn = block_end_pfn,
 696                                block_end_pfn += pageblock_nr_pages) {
 697                /* Protect pfn from changing by isolate_freepages_block */
 698                unsigned long isolate_start_pfn = pfn;
 699
 700                block_end_pfn = min(block_end_pfn, end_pfn);
 701
 702                /*
 703                 * pfn could pass the block_end_pfn if isolated freepage
 704                 * is more than pageblock order. In this case, we adjust
 705                 * scanning range to right one.
 706                 */
 707                if (pfn >= block_end_pfn) {
 708                        block_start_pfn = pageblock_start_pfn(pfn);
 709                        block_end_pfn = pageblock_end_pfn(pfn);
 710                        block_end_pfn = min(block_end_pfn, end_pfn);
 711                }
 712
 713                if (!pageblock_pfn_to_page(block_start_pfn,
 714                                        block_end_pfn, cc->zone))
 715                        break;
 716
 717                isolated = isolate_freepages_block(cc, &isolate_start_pfn,
 718                                        block_end_pfn, &freelist, 0, true);
 719
 720                /*
 721                 * In strict mode, isolate_freepages_block() returns 0 if
 722                 * there are any holes in the block (ie. invalid PFNs or
 723                 * non-free pages).
 724                 */
 725                if (!isolated)
 726                        break;
 727
 728                /*
 729                 * If we managed to isolate pages, it is always (1 << n) *
 730                 * pageblock_nr_pages for some non-negative n.  (Max order
 731                 * page may span two pageblocks).
 732                 */
 733        }
 734
 735        /* __isolate_free_page() does not map the pages */
 736        split_map_pages(&freelist);
 737
 738        if (pfn < end_pfn) {
 739                /* Loop terminated early, cleanup. */
 740                release_freepages(&freelist);
 741                return 0;
 742        }
 743
 744        /* We don't use freelists for anything. */
 745        return pfn;
 746}
 747
 748/* Similar to reclaim, but different enough that they don't share logic */
 749static bool too_many_isolated(pg_data_t *pgdat)
 750{
 751        unsigned long active, inactive, isolated;
 752
 753        inactive = node_page_state(pgdat, NR_INACTIVE_FILE) +
 754                        node_page_state(pgdat, NR_INACTIVE_ANON);
 755        active = node_page_state(pgdat, NR_ACTIVE_FILE) +
 756                        node_page_state(pgdat, NR_ACTIVE_ANON);
 757        isolated = node_page_state(pgdat, NR_ISOLATED_FILE) +
 758                        node_page_state(pgdat, NR_ISOLATED_ANON);
 759
 760        return isolated > (inactive + active) / 2;
 761}
 762
 763/**
 764 * isolate_migratepages_block() - isolate all migrate-able pages within
 765 *                                a single pageblock
 766 * @cc:         Compaction control structure.
 767 * @low_pfn:    The first PFN to isolate
 768 * @end_pfn:    The one-past-the-last PFN to isolate, within same pageblock
 769 * @isolate_mode: Isolation mode to be used.
 770 *
 771 * Isolate all pages that can be migrated from the range specified by
 772 * [low_pfn, end_pfn). The range is expected to be within same pageblock.
 773 * Returns zero if there is a fatal signal pending, otherwise PFN of the
 774 * first page that was not scanned (which may be both less, equal to or more
 775 * than end_pfn).
 776 *
 777 * The pages are isolated on cc->migratepages list (not required to be empty),
 778 * and cc->nr_migratepages is updated accordingly. The cc->migrate_pfn field
 779 * is neither read nor updated.
 780 */
 781static unsigned long
 782isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 783                        unsigned long end_pfn, isolate_mode_t isolate_mode)
 784{
 785        pg_data_t *pgdat = cc->zone->zone_pgdat;
 786        unsigned long nr_scanned = 0, nr_isolated = 0;
 787        struct lruvec *lruvec;
 788        unsigned long flags = 0;
 789        bool locked = false;
 790        struct page *page = NULL, *valid_page = NULL;
 791        unsigned long start_pfn = low_pfn;
 792        bool skip_on_failure = false;
 793        unsigned long next_skip_pfn = 0;
 794        bool skip_updated = false;
 795
 796        /*
 797         * Ensure that there are not too many pages isolated from the LRU
 798         * list by either parallel reclaimers or compaction. If there are,
 799         * delay for some time until fewer pages are isolated
 800         */
 801        while (unlikely(too_many_isolated(pgdat))) {
 802                /* async migration should just abort */
 803                if (cc->mode == MIGRATE_ASYNC)
 804                        return 0;
 805
 806                congestion_wait(BLK_RW_ASYNC, HZ/10);
 807
 808                if (fatal_signal_pending(current))
 809                        return 0;
 810        }
 811
 812        cond_resched();
 813
 814        if (cc->direct_compaction && (cc->mode == MIGRATE_ASYNC)) {
 815                skip_on_failure = true;
 816                next_skip_pfn = block_end_pfn(low_pfn, cc->order);
 817        }
 818
 819        /* Time to isolate some pages for migration */
 820        for (; low_pfn < end_pfn; low_pfn++) {
 821
 822                if (skip_on_failure && low_pfn >= next_skip_pfn) {
 823                        /*
 824                         * We have isolated all migration candidates in the
 825                         * previous order-aligned block, and did not skip it due
 826                         * to failure. We should migrate the pages now and
 827                         * hopefully succeed compaction.
 828                         */
 829                        if (nr_isolated)
 830                                break;
 831
 832                        /*
 833                         * We failed to isolate in the previous order-aligned
 834                         * block. Set the new boundary to the end of the
 835                         * current block. Note we can't simply increase
 836                         * next_skip_pfn by 1 << order, as low_pfn might have
 837                         * been incremented by a higher number due to skipping
 838                         * a compound or a high-order buddy page in the
 839                         * previous loop iteration.
 840                         */
 841                        next_skip_pfn = block_end_pfn(low_pfn, cc->order);
 842                }
 843
 844                /*
 845                 * Periodically drop the lock (if held) regardless of its
 846                 * contention, to give chance to IRQs. Abort completely if
 847                 * a fatal signal is pending.
 848                 */
 849                if (!(low_pfn % SWAP_CLUSTER_MAX)
 850                    && compact_unlock_should_abort(&pgdat->lru_lock,
 851                                            flags, &locked, cc)) {
 852                        low_pfn = 0;
 853                        goto fatal_pending;
 854                }
 855
 856                if (!pfn_valid_within(low_pfn))
 857                        goto isolate_fail;
 858                nr_scanned++;
 859
 860                page = pfn_to_page(low_pfn);
 861
 862                /*
 863                 * Check if the pageblock has already been marked skipped.
 864                 * Only the aligned PFN is checked as the caller isolates
 865                 * COMPACT_CLUSTER_MAX at a time so the second call must
 866                 * not falsely conclude that the block should be skipped.
 867                 */
 868                if (!valid_page && IS_ALIGNED(low_pfn, pageblock_nr_pages)) {
 869                        if (!cc->ignore_skip_hint && get_pageblock_skip(page)) {
 870                                low_pfn = end_pfn;
 871                                goto isolate_abort;
 872                        }
 873                        valid_page = page;
 874                }
 875
 876                /*
 877                 * Skip if free. We read page order here without zone lock
 878                 * which is generally unsafe, but the race window is small and
 879                 * the worst thing that can happen is that we skip some
 880                 * potential isolation targets.
 881                 */
 882                if (PageBuddy(page)) {
 883                        unsigned long freepage_order = page_order_unsafe(page);
 884
 885                        /*
 886                         * Without lock, we cannot be sure that what we got is
 887                         * a valid page order. Consider only values in the
 888                         * valid order range to prevent low_pfn overflow.
 889                         */
 890                        if (freepage_order > 0 && freepage_order < MAX_ORDER)
 891                                low_pfn += (1UL << freepage_order) - 1;
 892                        continue;
 893                }
 894
 895                /*
 896                 * Regardless of being on LRU, compound pages such as THP and
 897                 * hugetlbfs are not to be compacted. We can potentially save
 898                 * a lot of iterations if we skip them at once. The check is
 899                 * racy, but we can consider only valid values and the only
 900                 * danger is skipping too much.
 901                 */
 902                if (PageCompound(page)) {
 903                        const unsigned int order = compound_order(page);
 904
 905                        if (likely(order < MAX_ORDER))
 906                                low_pfn += (1UL << order) - 1;
 907                        goto isolate_fail;
 908                }
 909
 910                /*
 911                 * Check may be lockless but that's ok as we recheck later.
 912                 * It's possible to migrate LRU and non-lru movable pages.
 913                 * Skip any other type of page
 914                 */
 915                if (!PageLRU(page)) {
 916                        /*
 917                         * __PageMovable can return false positive so we need
 918                         * to verify it under page_lock.
 919                         */
 920                        if (unlikely(__PageMovable(page)) &&
 921                                        !PageIsolated(page)) {
 922                                if (locked) {
 923                                        spin_unlock_irqrestore(&pgdat->lru_lock,
 924                                                                        flags);
 925                                        locked = false;
 926                                }
 927
 928                                if (!isolate_movable_page(page, isolate_mode))
 929                                        goto isolate_success;
 930                        }
 931
 932                        goto isolate_fail;
 933                }
 934
 935                /*
 936                 * Migration will fail if an anonymous page is pinned in memory,
 937                 * so avoid taking lru_lock and isolating it unnecessarily in an
 938                 * admittedly racy check.
 939                 */
 940                if (!page_mapping(page) &&
 941                    page_count(page) > page_mapcount(page))
 942                        goto isolate_fail;
 943
 944                /*
 945                 * Only allow to migrate anonymous pages in GFP_NOFS context
 946                 * because those do not depend on fs locks.
 947                 */
 948                if (!(cc->gfp_mask & __GFP_FS) && page_mapping(page))
 949                        goto isolate_fail;
 950
 951                /* If we already hold the lock, we can skip some rechecking */
 952                if (!locked) {
 953                        locked = compact_lock_irqsave(&pgdat->lru_lock,
 954                                                                &flags, cc);
 955
 956                        /* Try get exclusive access under lock */
 957                        if (!skip_updated) {
 958                                skip_updated = true;
 959                                if (test_and_set_skip(cc, page, low_pfn))
 960                                        goto isolate_abort;
 961                        }
 962
 963                        /* Recheck PageLRU and PageCompound under lock */
 964                        if (!PageLRU(page))
 965                                goto isolate_fail;
 966
 967                        /*
 968                         * Page become compound since the non-locked check,
 969                         * and it's on LRU. It can only be a THP so the order
 970                         * is safe to read and it's 0 for tail pages.
 971                         */
 972                        if (unlikely(PageCompound(page))) {
 973                                low_pfn += compound_nr(page) - 1;
 974                                goto isolate_fail;
 975                        }
 976                }
 977
 978                lruvec = mem_cgroup_page_lruvec(page, pgdat);
 979
 980                /* Try isolate the page */
 981                if (__isolate_lru_page(page, isolate_mode) != 0)
 982                        goto isolate_fail;
 983
 984                VM_BUG_ON_PAGE(PageCompound(page), page);
 985
 986                /* Successfully isolated */
 987                del_page_from_lru_list(page, lruvec, page_lru(page));
 988                inc_node_page_state(page,
 989                                NR_ISOLATED_ANON + page_is_file_cache(page));
 990
 991isolate_success:
 992                list_add(&page->lru, &cc->migratepages);
 993                cc->nr_migratepages++;
 994                nr_isolated++;
 995
 996                /*
 997                 * Avoid isolating too much unless this block is being
 998                 * rescanned (e.g. dirty/writeback pages, parallel allocation)
 999                 * or a lock is contended. For contention, isolate quickly to
1000                 * potentially remove one source of contention.
1001                 */
1002                if (cc->nr_migratepages == COMPACT_CLUSTER_MAX &&
1003                    !cc->rescan && !cc->contended) {
1004                        ++low_pfn;
1005                        break;
1006                }
1007
1008                continue;
1009isolate_fail:
1010                if (!skip_on_failure)
1011                        continue;
1012
1013                /*
1014                 * We have isolated some pages, but then failed. Release them
1015                 * instead of migrating, as we cannot form the cc->order buddy
1016                 * page anyway.
1017                 */
1018                if (nr_isolated) {
1019                        if (locked) {
1020                                spin_unlock_irqrestore(&pgdat->lru_lock, flags);
1021                                locked = false;
1022                        }
1023                        putback_movable_pages(&cc->migratepages);
1024                        cc->nr_migratepages = 0;
1025                        nr_isolated = 0;
1026                }
1027
1028                if (low_pfn < next_skip_pfn) {
1029                        low_pfn = next_skip_pfn - 1;
1030                        /*
1031                         * The check near the loop beginning would have updated
1032                         * next_skip_pfn too, but this is a bit simpler.
1033                         */
1034                        next_skip_pfn += 1UL << cc->order;
1035                }
1036        }
1037
1038        /*
1039         * The PageBuddy() check could have potentially brought us outside
1040         * the range to be scanned.
1041         */
1042        if (unlikely(low_pfn > end_pfn))
1043                low_pfn = end_pfn;
1044
1045isolate_abort:
1046        if (locked)
1047                spin_unlock_irqrestore(&pgdat->lru_lock, flags);
1048
1049        /*
1050         * Updated the cached scanner pfn once the pageblock has been scanned
1051         * Pages will either be migrated in which case there is no point
1052         * scanning in the near future or migration failed in which case the
1053         * failure reason may persist. The block is marked for skipping if
1054         * there were no pages isolated in the block or if the block is
1055         * rescanned twice in a row.
1056         */
1057        if (low_pfn == end_pfn && (!nr_isolated || cc->rescan)) {
1058                if (valid_page && !skip_updated)
1059                        set_pageblock_skip(valid_page);
1060                update_cached_migrate(cc, low_pfn);
1061        }
1062
1063        trace_mm_compaction_isolate_migratepages(start_pfn, low_pfn,
1064                                                nr_scanned, nr_isolated);
1065
1066fatal_pending:
1067        cc->total_migrate_scanned += nr_scanned;
1068        if (nr_isolated)
1069                count_compact_events(COMPACTISOLATED, nr_isolated);
1070
1071        return low_pfn;
1072}
1073
1074/**
1075 * isolate_migratepages_range() - isolate migrate-able pages in a PFN range
1076 * @cc:        Compaction control structure.
1077 * @start_pfn: The first PFN to start isolating.
1078 * @end_pfn:   The one-past-last PFN.
1079 *
1080 * Returns zero if isolation fails fatally due to e.g. pending signal.
1081 * Otherwise, function returns one-past-the-last PFN of isolated page
1082 * (which may be greater than end_pfn if end fell in a middle of a THP page).
1083 */
1084unsigned long
1085isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn,
1086                                                        unsigned long end_pfn)
1087{
1088        unsigned long pfn, block_start_pfn, block_end_pfn;
1089
1090        /* Scan block by block. First and last block may be incomplete */
1091        pfn = start_pfn;
1092        block_start_pfn = pageblock_start_pfn(pfn);
1093        if (block_start_pfn < cc->zone->zone_start_pfn)
1094                block_start_pfn = cc->zone->zone_start_pfn;
1095        block_end_pfn = pageblock_end_pfn(pfn);
1096
1097        for (; pfn < end_pfn; pfn = block_end_pfn,
1098                                block_start_pfn = block_end_pfn,
1099                                block_end_pfn += pageblock_nr_pages) {
1100
1101                block_end_pfn = min(block_end_pfn, end_pfn);
1102
1103                if (!pageblock_pfn_to_page(block_start_pfn,
1104                                        block_end_pfn, cc->zone))
1105                        continue;
1106
1107                pfn = isolate_migratepages_block(cc, pfn, block_end_pfn,
1108                                                        ISOLATE_UNEVICTABLE);
1109
1110                if (!pfn)
1111                        break;
1112
1113                if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
1114                        break;
1115        }
1116
1117        return pfn;
1118}
1119
1120#endif /* CONFIG_COMPACTION || CONFIG_CMA */
1121#ifdef CONFIG_COMPACTION
1122
1123static bool suitable_migration_source(struct compact_control *cc,
1124                                                        struct page *page)
1125{
1126        int block_mt;
1127
1128        if (pageblock_skip_persistent(page))
1129                return false;
1130
1131        if ((cc->mode != MIGRATE_ASYNC) || !cc->direct_compaction)
1132                return true;
1133
1134        block_mt = get_pageblock_migratetype(page);
1135
1136        if (cc->migratetype == MIGRATE_MOVABLE)
1137                return is_migrate_movable(block_mt);
1138        else
1139                return block_mt == cc->migratetype;
1140}
1141
1142/* Returns true if the page is within a block suitable for migration to */
1143static bool suitable_migration_target(struct compact_control *cc,
1144                                                        struct page *page)
1145{
1146        /* If the page is a large free page, then disallow migration */
1147        if (PageBuddy(page)) {
1148                /*
1149                 * We are checking page_order without zone->lock taken. But
1150                 * the only small danger is that we skip a potentially suitable
1151                 * pageblock, so it's not worth to check order for valid range.
1152                 */
1153                if (page_order_unsafe(page) >= pageblock_order)
1154                        return false;
1155        }
1156
1157        if (cc->ignore_block_suitable)
1158                return true;
1159
1160        /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
1161        if (is_migrate_movable(get_pageblock_migratetype(page)))
1162                return true;
1163
1164        /* Otherwise skip the block */
1165        return false;
1166}
1167
1168static inline unsigned int
1169freelist_scan_limit(struct compact_control *cc)
1170{
1171        unsigned short shift = BITS_PER_LONG - 1;
1172
1173        return (COMPACT_CLUSTER_MAX >> min(shift, cc->fast_search_fail)) + 1;
1174}
1175
1176/*
1177 * Test whether the free scanner has reached the same or lower pageblock than
1178 * the migration scanner, and compaction should thus terminate.
1179 */
1180static inline bool compact_scanners_met(struct compact_control *cc)
1181{
1182        return (cc->free_pfn >> pageblock_order)
1183                <= (cc->migrate_pfn >> pageblock_order);
1184}
1185
1186/*
1187 * Used when scanning for a suitable migration target which scans freelists
1188 * in reverse. Reorders the list such as the unscanned pages are scanned
1189 * first on the next iteration of the free scanner
1190 */
1191static void
1192move_freelist_head(struct list_head *freelist, struct page *freepage)
1193{
1194        LIST_HEAD(sublist);
1195
1196        if (!list_is_last(freelist, &freepage->lru)) {
1197                list_cut_before(&sublist, freelist, &freepage->lru);
1198                if (!list_empty(&sublist))
1199                        list_splice_tail(&sublist, freelist);
1200        }
1201}
1202
1203/*
1204 * Similar to move_freelist_head except used by the migration scanner
1205 * when scanning forward. It's possible for these list operations to
1206 * move against each other if they search the free list exactly in
1207 * lockstep.
1208 */
1209static void
1210move_freelist_tail(struct list_head *freelist, struct page *freepage)
1211{
1212        LIST_HEAD(sublist);
1213
1214        if (!list_is_first(freelist, &freepage->lru)) {
1215                list_cut_position(&sublist, freelist, &freepage->lru);
1216                if (!list_empty(&sublist))
1217                        list_splice_tail(&sublist, freelist);
1218        }
1219}
1220
1221static void
1222fast_isolate_around(struct compact_control *cc, unsigned long pfn, unsigned long nr_isolated)
1223{
1224        unsigned long start_pfn, end_pfn;
1225        struct page *page = pfn_to_page(pfn);
1226
1227        /* Do not search around if there are enough pages already */
1228        if (cc->nr_freepages >= cc->nr_migratepages)
1229                return;
1230
1231        /* Minimise scanning during async compaction */
1232        if (cc->direct_compaction && cc->mode == MIGRATE_ASYNC)
1233                return;
1234
1235        /* Pageblock boundaries */
1236        start_pfn = pageblock_start_pfn(pfn);
1237        end_pfn = min(pageblock_end_pfn(pfn), zone_end_pfn(cc->zone)) - 1;
1238
1239        /* Scan before */
1240        if (start_pfn != pfn) {
1241                isolate_freepages_block(cc, &start_pfn, pfn, &cc->freepages, 1, false);
1242                if (cc->nr_freepages >= cc->nr_migratepages)
1243                        return;
1244        }
1245
1246        /* Scan after */
1247        start_pfn = pfn + nr_isolated;
1248        if (start_pfn < end_pfn)
1249                isolate_freepages_block(cc, &start_pfn, end_pfn, &cc->freepages, 1, false);
1250
1251        /* Skip this pageblock in the future as it's full or nearly full */
1252        if (cc->nr_freepages < cc->nr_migratepages)
1253                set_pageblock_skip(page);
1254}
1255
1256/* Search orders in round-robin fashion */
1257static int next_search_order(struct compact_control *cc, int order)
1258{
1259        order--;
1260        if (order < 0)
1261                order = cc->order - 1;
1262
1263        /* Search wrapped around? */
1264        if (order == cc->search_order) {
1265                cc->search_order--;
1266                if (cc->search_order < 0)
1267                        cc->search_order = cc->order - 1;
1268                return -1;
1269        }
1270
1271        return order;
1272}
1273
1274static unsigned long
1275fast_isolate_freepages(struct compact_control *cc)
1276{
1277        unsigned int limit = min(1U, freelist_scan_limit(cc) >> 1);
1278        unsigned int nr_scanned = 0;
1279        unsigned long low_pfn, min_pfn, high_pfn = 0, highest = 0;
1280        unsigned long nr_isolated = 0;
1281        unsigned long distance;
1282        struct page *page = NULL;
1283        bool scan_start = false;
1284        int order;
1285
1286        /* Full compaction passes in a negative order */
1287        if (cc->order <= 0)
1288                return cc->free_pfn;
1289
1290        /*
1291         * If starting the scan, use a deeper search and use the highest
1292         * PFN found if a suitable one is not found.
1293         */
1294        if (cc->free_pfn >= cc->zone->compact_init_free_pfn) {
1295                limit = pageblock_nr_pages >> 1;
1296                scan_start = true;
1297        }
1298
1299        /*
1300         * Preferred point is in the top quarter of the scan space but take
1301         * a pfn from the top half if the search is problematic.
1302         */
1303        distance = (cc->free_pfn - cc->migrate_pfn);
1304        low_pfn = pageblock_start_pfn(cc->free_pfn - (distance >> 2));
1305        min_pfn = pageblock_start_pfn(cc->free_pfn - (distance >> 1));
1306
1307        if (WARN_ON_ONCE(min_pfn > low_pfn))
1308                low_pfn = min_pfn;
1309
1310        /*
1311         * Search starts from the last successful isolation order or the next
1312         * order to search after a previous failure
1313         */
1314        cc->search_order = min_t(unsigned int, cc->order - 1, cc->search_order);
1315
1316        for (order = cc->search_order;
1317             !page && order >= 0;
1318             order = next_search_order(cc, order)) {
1319                struct free_area *area = &cc->zone->free_area[order];
1320                struct list_head *freelist;
1321                struct page *freepage;
1322                unsigned long flags;
1323                unsigned int order_scanned = 0;
1324
1325                if (!area->nr_free)
1326                        continue;
1327
1328                spin_lock_irqsave(&cc->zone->lock, flags);
1329                freelist = &area->free_list[MIGRATE_MOVABLE];
1330                list_for_each_entry_reverse(freepage, freelist, lru) {
1331                        unsigned long pfn;
1332
1333                        order_scanned++;
1334                        nr_scanned++;
1335                        pfn = page_to_pfn(freepage);
1336
1337                        if (pfn >= highest)
1338                                highest = pageblock_start_pfn(pfn);
1339
1340                        if (pfn >= low_pfn) {
1341                                cc->fast_search_fail = 0;
1342                                cc->search_order = order;
1343                                page = freepage;
1344                                break;
1345                        }
1346
1347                        if (pfn >= min_pfn && pfn > high_pfn) {
1348                                high_pfn = pfn;
1349
1350                                /* Shorten the scan if a candidate is found */
1351                                limit >>= 1;
1352                        }
1353
1354                        if (order_scanned >= limit)
1355                                break;
1356                }
1357
1358                /* Use a minimum pfn if a preferred one was not found */
1359                if (!page && high_pfn) {
1360                        page = pfn_to_page(high_pfn);
1361
1362                        /* Update freepage for the list reorder below */
1363                        freepage = page;
1364                }
1365
1366                /* Reorder to so a future search skips recent pages */
1367                move_freelist_head(freelist, freepage);
1368
1369                /* Isolate the page if available */
1370                if (page) {
1371                        if (__isolate_free_page(page, order)) {
1372                                set_page_private(page, order);
1373                                nr_isolated = 1 << order;
1374                                cc->nr_freepages += nr_isolated;
1375                                list_add_tail(&page->lru, &cc->freepages);
1376                                count_compact_events(COMPACTISOLATED, nr_isolated);
1377                        } else {
1378                                /* If isolation fails, abort the search */
1379                                order = cc->search_order + 1;
1380                                page = NULL;
1381                        }
1382                }
1383
1384                spin_unlock_irqrestore(&cc->zone->lock, flags);
1385
1386                /*
1387                 * Smaller scan on next order so the total scan ig related
1388                 * to freelist_scan_limit.
1389                 */
1390                if (order_scanned >= limit)
1391                        limit = min(1U, limit >> 1);
1392        }
1393
1394        if (!page) {
1395                cc->fast_search_fail++;
1396                if (scan_start) {
1397                        /*
1398                         * Use the highest PFN found above min. If one was
1399                         * not found, be pessemistic for direct compaction
1400                         * and use the min mark.
1401                         */
1402                        if (highest) {
1403                                page = pfn_to_page(highest);
1404                                cc->free_pfn = highest;
1405                        } else {
1406                                if (cc->direct_compaction && pfn_valid(min_pfn)) {
1407                                        page = pfn_to_page(min_pfn);
1408                                        cc->free_pfn = min_pfn;
1409                                }
1410                        }
1411                }
1412        }
1413
1414        if (highest && highest >= cc->zone->compact_cached_free_pfn) {
1415                highest -= pageblock_nr_pages;
1416                cc->zone->compact_cached_free_pfn = highest;
1417        }
1418
1419        cc->total_free_scanned += nr_scanned;
1420        if (!page)
1421                return cc->free_pfn;
1422
1423        low_pfn = page_to_pfn(page);
1424        fast_isolate_around(cc, low_pfn, nr_isolated);
1425        return low_pfn;
1426}
1427
1428/*
1429 * Based on information in the current compact_control, find blocks
1430 * suitable for isolating free pages from and then isolate them.
1431 */
1432static void isolate_freepages(struct compact_control *cc)
1433{
1434        struct zone *zone = cc->zone;
1435        struct page *page;
1436        unsigned long block_start_pfn;  /* start of current pageblock */
1437        unsigned long isolate_start_pfn; /* exact pfn we start at */
1438        unsigned long block_end_pfn;    /* end of current pageblock */
1439        unsigned long low_pfn;       /* lowest pfn scanner is able to scan */
1440        struct list_head *freelist = &cc->freepages;
1441        unsigned int stride;
1442
1443        /* Try a small search of the free lists for a candidate */
1444        isolate_start_pfn = fast_isolate_freepages(cc);
1445        if (cc->nr_freepages)
1446                goto splitmap;
1447
1448        /*
1449         * Initialise the free scanner. The starting point is where we last
1450         * successfully isolated from, zone-cached value, or the end of the
1451         * zone when isolating for the first time. For looping we also need
1452         * this pfn aligned down to the pageblock boundary, because we do
1453         * block_start_pfn -= pageblock_nr_pages in the for loop.
1454         * For ending point, take care when isolating in last pageblock of a
1455         * a zone which ends in the middle of a pageblock.
1456         * The low boundary is the end of the pageblock the migration scanner
1457         * is using.
1458         */
1459        isolate_start_pfn = cc->free_pfn;
1460        block_start_pfn = pageblock_start_pfn(isolate_start_pfn);
1461        block_end_pfn = min(block_start_pfn + pageblock_nr_pages,
1462                                                zone_end_pfn(zone));
1463        low_pfn = pageblock_end_pfn(cc->migrate_pfn);
1464        stride = cc->mode == MIGRATE_ASYNC ? COMPACT_CLUSTER_MAX : 1;
1465
1466        /*
1467         * Isolate free pages until enough are available to migrate the
1468         * pages on cc->migratepages. We stop searching if the migrate
1469         * and free page scanners meet or enough free pages are isolated.
1470         */
1471        for (; block_start_pfn >= low_pfn;
1472                                block_end_pfn = block_start_pfn,
1473                                block_start_pfn -= pageblock_nr_pages,
1474                                isolate_start_pfn = block_start_pfn) {
1475                unsigned long nr_isolated;
1476
1477                /*
1478                 * This can iterate a massively long zone without finding any
1479                 * suitable migration targets, so periodically check resched.
1480                 */
1481                if (!(block_start_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages)))
1482                        cond_resched();
1483
1484                page = pageblock_pfn_to_page(block_start_pfn, block_end_pfn,
1485                                                                        zone);
1486                if (!page)
1487                        continue;
1488
1489                /* Check the block is suitable for migration */
1490                if (!suitable_migration_target(cc, page))
1491                        continue;
1492
1493                /* If isolation recently failed, do not retry */
1494                if (!isolation_suitable(cc, page))
1495                        continue;
1496
1497                /* Found a block suitable for isolating free pages from. */
1498                nr_isolated = isolate_freepages_block(cc, &isolate_start_pfn,
1499                                        block_end_pfn, freelist, stride, false);
1500
1501                /* Update the skip hint if the full pageblock was scanned */
1502                if (isolate_start_pfn == block_end_pfn)
1503                        update_pageblock_skip(cc, page, block_start_pfn);
1504
1505                /* Are enough freepages isolated? */
1506                if (cc->nr_freepages >= cc->nr_migratepages) {
1507                        if (isolate_start_pfn >= block_end_pfn) {
1508                                /*
1509                                 * Restart at previous pageblock if more
1510                                 * freepages can be isolated next time.
1511                                 */
1512                                isolate_start_pfn =
1513                                        block_start_pfn - pageblock_nr_pages;
1514                        }
1515                        break;
1516                } else if (isolate_start_pfn < block_end_pfn) {
1517                        /*
1518                         * If isolation failed early, do not continue
1519                         * needlessly.
1520                         */
1521                        break;
1522                }
1523
1524                /* Adjust stride depending on isolation */
1525                if (nr_isolated) {
1526                        stride = 1;
1527                        continue;
1528                }
1529                stride = min_t(unsigned int, COMPACT_CLUSTER_MAX, stride << 1);
1530        }
1531
1532        /*
1533         * Record where the free scanner will restart next time. Either we
1534         * broke from the loop and set isolate_start_pfn based on the last
1535         * call to isolate_freepages_block(), or we met the migration scanner
1536         * and the loop terminated due to isolate_start_pfn < low_pfn
1537         */
1538        cc->free_pfn = isolate_start_pfn;
1539
1540splitmap:
1541        /* __isolate_free_page() does not map the pages */
1542        split_map_pages(freelist);
1543}
1544
1545/*
1546 * This is a migrate-callback that "allocates" freepages by taking pages
1547 * from the isolated freelists in the block we are migrating to.
1548 */
1549static struct page *compaction_alloc(struct page *migratepage,
1550                                        unsigned long data)
1551{
1552        struct compact_control *cc = (struct compact_control *)data;
1553        struct page *freepage;
1554
1555        if (list_empty(&cc->freepages)) {
1556                isolate_freepages(cc);
1557
1558                if (list_empty(&cc->freepages))
1559                        return NULL;
1560        }
1561
1562        freepage = list_entry(cc->freepages.next, struct page, lru);
1563        list_del(&freepage->lru);
1564        cc->nr_freepages--;
1565
1566        return freepage;
1567}
1568
1569/*
1570 * This is a migrate-callback that "frees" freepages back to the isolated
1571 * freelist.  All pages on the freelist are from the same zone, so there is no
1572 * special handling needed for NUMA.
1573 */
1574static void compaction_free(struct page *page, unsigned long data)
1575{
1576        struct compact_control *cc = (struct compact_control *)data;
1577
1578        list_add(&page->lru, &cc->freepages);
1579        cc->nr_freepages++;
1580}
1581
1582/* possible outcome of isolate_migratepages */
1583typedef enum {
1584        ISOLATE_ABORT,          /* Abort compaction now */
1585        ISOLATE_NONE,           /* No pages isolated, continue scanning */
1586        ISOLATE_SUCCESS,        /* Pages isolated, migrate */
1587} isolate_migrate_t;
1588
1589/*
1590 * Allow userspace to control policy on scanning the unevictable LRU for
1591 * compactable pages.
1592 */
1593int sysctl_compact_unevictable_allowed __read_mostly = 1;
1594
1595static inline void
1596update_fast_start_pfn(struct compact_control *cc, unsigned long pfn)
1597{
1598        if (cc->fast_start_pfn == ULONG_MAX)
1599                return;
1600
1601        if (!cc->fast_start_pfn)
1602                cc->fast_start_pfn = pfn;
1603
1604        cc->fast_start_pfn = min(cc->fast_start_pfn, pfn);
1605}
1606
1607static inline unsigned long
1608reinit_migrate_pfn(struct compact_control *cc)
1609{
1610        if (!cc->fast_start_pfn || cc->fast_start_pfn == ULONG_MAX)
1611                return cc->migrate_pfn;
1612
1613        cc->migrate_pfn = cc->fast_start_pfn;
1614        cc->fast_start_pfn = ULONG_MAX;
1615
1616        return cc->migrate_pfn;
1617}
1618
1619/*
1620 * Briefly search the free lists for a migration source that already has
1621 * some free pages to reduce the number of pages that need migration
1622 * before a pageblock is free.
1623 */
1624static unsigned long fast_find_migrateblock(struct compact_control *cc)
1625{
1626        unsigned int limit = freelist_scan_limit(cc);
1627        unsigned int nr_scanned = 0;
1628        unsigned long distance;
1629        unsigned long pfn = cc->migrate_pfn;
1630        unsigned long high_pfn;
1631        int order;
1632
1633        /* Skip hints are relied on to avoid repeats on the fast search */
1634        if (cc->ignore_skip_hint)
1635                return pfn;
1636
1637        /*
1638         * If the migrate_pfn is not at the start of a zone or the start
1639         * of a pageblock then assume this is a continuation of a previous
1640         * scan restarted due to COMPACT_CLUSTER_MAX.
1641         */
1642        if (pfn != cc->zone->zone_start_pfn && pfn != pageblock_start_pfn(pfn))
1643                return pfn;
1644
1645        /*
1646         * For smaller orders, just linearly scan as the number of pages
1647         * to migrate should be relatively small and does not necessarily
1648         * justify freeing up a large block for a small allocation.
1649         */
1650        if (cc->order <= PAGE_ALLOC_COSTLY_ORDER)
1651                return pfn;
1652
1653        /*
1654         * Only allow kcompactd and direct requests for movable pages to
1655         * quickly clear out a MOVABLE pageblock for allocation. This
1656         * reduces the risk that a large movable pageblock is freed for
1657         * an unmovable/reclaimable small allocation.
1658         */
1659        if (cc->direct_compaction && cc->migratetype != MIGRATE_MOVABLE)
1660                return pfn;
1661
1662        /*
1663         * When starting the migration scanner, pick any pageblock within the
1664         * first half of the search space. Otherwise try and pick a pageblock
1665         * within the first eighth to reduce the chances that a migration
1666         * target later becomes a source.
1667         */
1668        distance = (cc->free_pfn - cc->migrate_pfn) >> 1;
1669        if (cc->migrate_pfn != cc->zone->zone_start_pfn)
1670                distance >>= 2;
1671        high_pfn = pageblock_start_pfn(cc->migrate_pfn + distance);
1672
1673        for (order = cc->order - 1;
1674             order >= PAGE_ALLOC_COSTLY_ORDER && pfn == cc->migrate_pfn && nr_scanned < limit;
1675             order--) {
1676                struct free_area *area = &cc->zone->free_area[order];
1677                struct list_head *freelist;
1678                unsigned long flags;
1679                struct page *freepage;
1680
1681                if (!area->nr_free)
1682                        continue;
1683
1684                spin_lock_irqsave(&cc->zone->lock, flags);
1685                freelist = &area->free_list[MIGRATE_MOVABLE];
1686                list_for_each_entry(freepage, freelist, lru) {
1687                        unsigned long free_pfn;
1688
1689                        nr_scanned++;
1690                        free_pfn = page_to_pfn(freepage);
1691                        if (free_pfn < high_pfn) {
1692                                /*
1693                                 * Avoid if skipped recently. Ideally it would
1694                                 * move to the tail but even safe iteration of
1695                                 * the list assumes an entry is deleted, not
1696                                 * reordered.
1697                                 */
1698                                if (get_pageblock_skip(freepage)) {
1699                                        if (list_is_last(freelist, &freepage->lru))
1700                                                break;
1701
1702                                        continue;
1703                                }
1704
1705                                /* Reorder to so a future search skips recent pages */
1706                                move_freelist_tail(freelist, freepage);
1707
1708                                update_fast_start_pfn(cc, free_pfn);
1709                                pfn = pageblock_start_pfn(free_pfn);
1710                                cc->fast_search_fail = 0;
1711                                set_pageblock_skip(freepage);
1712                                break;
1713                        }
1714
1715                        if (nr_scanned >= limit) {
1716                                cc->fast_search_fail++;
1717                                move_freelist_tail(freelist, freepage);
1718                                break;
1719                        }
1720                }
1721                spin_unlock_irqrestore(&cc->zone->lock, flags);
1722        }
1723
1724        cc->total_migrate_scanned += nr_scanned;
1725
1726        /*
1727         * If fast scanning failed then use a cached entry for a page block
1728         * that had free pages as the basis for starting a linear scan.
1729         */
1730        if (pfn == cc->migrate_pfn)
1731                pfn = reinit_migrate_pfn(cc);
1732
1733        return pfn;
1734}
1735
1736/*
1737 * Isolate all pages that can be migrated from the first suitable block,
1738 * starting at the block pointed to by the migrate scanner pfn within
1739 * compact_control.
1740 */
1741static isolate_migrate_t isolate_migratepages(struct compact_control *cc)
1742{
1743        unsigned long block_start_pfn;
1744        unsigned long block_end_pfn;
1745        unsigned long low_pfn;
1746        struct page *page;
1747        const isolate_mode_t isolate_mode =
1748                (sysctl_compact_unevictable_allowed ? ISOLATE_UNEVICTABLE : 0) |
1749                (cc->mode != MIGRATE_SYNC ? ISOLATE_ASYNC_MIGRATE : 0);
1750        bool fast_find_block;
1751
1752        /*
1753         * Start at where we last stopped, or beginning of the zone as
1754         * initialized by compact_zone(). The first failure will use
1755         * the lowest PFN as the starting point for linear scanning.
1756         */
1757        low_pfn = fast_find_migrateblock(cc);
1758        block_start_pfn = pageblock_start_pfn(low_pfn);
1759        if (block_start_pfn < cc->zone->zone_start_pfn)
1760                block_start_pfn = cc->zone->zone_start_pfn;
1761
1762        /*
1763         * fast_find_migrateblock marks a pageblock skipped so to avoid
1764         * the isolation_suitable check below, check whether the fast
1765         * search was successful.
1766         */
1767        fast_find_block = low_pfn != cc->migrate_pfn && !cc->fast_search_fail;
1768
1769        /* Only scan within a pageblock boundary */
1770        block_end_pfn = pageblock_end_pfn(low_pfn);
1771
1772        /*
1773         * Iterate over whole pageblocks until we find the first suitable.
1774         * Do not cross the free scanner.
1775         */
1776        for (; block_end_pfn <= cc->free_pfn;
1777                        fast_find_block = false,
1778                        low_pfn = block_end_pfn,
1779                        block_start_pfn = block_end_pfn,
1780                        block_end_pfn += pageblock_nr_pages) {
1781
1782                /*
1783                 * This can potentially iterate a massively long zone with
1784                 * many pageblocks unsuitable, so periodically check if we
1785                 * need to schedule.
1786                 */
1787                if (!(low_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages)))
1788                        cond_resched();
1789
1790                page = pageblock_pfn_to_page(block_start_pfn,
1791                                                block_end_pfn, cc->zone);
1792                if (!page)
1793                        continue;
1794
1795                /*
1796                 * If isolation recently failed, do not retry. Only check the
1797                 * pageblock once. COMPACT_CLUSTER_MAX causes a pageblock
1798                 * to be visited multiple times. Assume skip was checked
1799                 * before making it "skip" so other compaction instances do
1800                 * not scan the same block.
1801                 */
1802                if (IS_ALIGNED(low_pfn, pageblock_nr_pages) &&
1803                    !fast_find_block && !isolation_suitable(cc, page))
1804                        continue;
1805
1806                /*
1807                 * For async compaction, also only scan in MOVABLE blocks
1808                 * without huge pages. Async compaction is optimistic to see
1809                 * if the minimum amount of work satisfies the allocation.
1810                 * The cached PFN is updated as it's possible that all
1811                 * remaining blocks between source and target are unsuitable
1812                 * and the compaction scanners fail to meet.
1813                 */
1814                if (!suitable_migration_source(cc, page)) {
1815                        update_cached_migrate(cc, block_end_pfn);
1816                        continue;
1817                }
1818
1819                /* Perform the isolation */
1820                low_pfn = isolate_migratepages_block(cc, low_pfn,
1821                                                block_end_pfn, isolate_mode);
1822
1823                if (!low_pfn)
1824                        return ISOLATE_ABORT;
1825
1826                /*
1827                 * Either we isolated something and proceed with migration. Or
1828                 * we failed and compact_zone should decide if we should
1829                 * continue or not.
1830                 */
1831                break;
1832        }
1833
1834        /* Record where migration scanner will be restarted. */
1835        cc->migrate_pfn = low_pfn;
1836
1837        return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE;
1838}
1839
1840/*
1841 * order == -1 is expected when compacting via
1842 * /proc/sys/vm/compact_memory
1843 */
1844static inline bool is_via_compact_memory(int order)
1845{
1846        return order == -1;
1847}
1848
1849static enum compact_result __compact_finished(struct compact_control *cc)
1850{
1851        unsigned int order;
1852        const int migratetype = cc->migratetype;
1853        int ret;
1854
1855        /* Compaction run completes if the migrate and free scanner meet */
1856        if (compact_scanners_met(cc)) {
1857                /* Let the next compaction start anew. */
1858                reset_cached_positions(cc->zone);
1859
1860                /*
1861                 * Mark that the PG_migrate_skip information should be cleared
1862                 * by kswapd when it goes to sleep. kcompactd does not set the
1863                 * flag itself as the decision to be clear should be directly
1864                 * based on an allocation request.
1865                 */
1866                if (cc->direct_compaction)
1867                        cc->zone->compact_blockskip_flush = true;
1868
1869                if (cc->whole_zone)
1870                        return COMPACT_COMPLETE;
1871                else
1872                        return COMPACT_PARTIAL_SKIPPED;
1873        }
1874
1875        if (is_via_compact_memory(cc->order))
1876                return COMPACT_CONTINUE;
1877
1878        /*
1879         * Always finish scanning a pageblock to reduce the possibility of
1880         * fallbacks in the future. This is particularly important when
1881         * migration source is unmovable/reclaimable but it's not worth
1882         * special casing.
1883         */
1884        if (!IS_ALIGNED(cc->migrate_pfn, pageblock_nr_pages))
1885                return COMPACT_CONTINUE;
1886
1887        /* Direct compactor: Is a suitable page free? */
1888        ret = COMPACT_NO_SUITABLE_PAGE;
1889        for (order = cc->order; order < MAX_ORDER; order++) {
1890                struct free_area *area = &cc->zone->free_area[order];
1891                bool can_steal;
1892
1893                /* Job done if page is free of the right migratetype */
1894                if (!free_area_empty(area, migratetype))
1895                        return COMPACT_SUCCESS;
1896
1897#ifdef CONFIG_CMA
1898                /* MIGRATE_MOVABLE can fallback on MIGRATE_CMA */
1899                if (migratetype == MIGRATE_MOVABLE &&
1900                        !free_area_empty(area, MIGRATE_CMA))
1901                        return COMPACT_SUCCESS;
1902#endif
1903                /*
1904                 * Job done if allocation would steal freepages from
1905                 * other migratetype buddy lists.
1906                 */
1907                if (find_suitable_fallback(area, order, migratetype,
1908                                                true, &can_steal) != -1) {
1909
1910                        /* movable pages are OK in any pageblock */
1911                        if (migratetype == MIGRATE_MOVABLE)
1912                                return COMPACT_SUCCESS;
1913
1914                        /*
1915                         * We are stealing for a non-movable allocation. Make
1916                         * sure we finish compacting the current pageblock
1917                         * first so it is as free as possible and we won't
1918                         * have to steal another one soon. This only applies
1919                         * to sync compaction, as async compaction operates
1920                         * on pageblocks of the same migratetype.
1921                         */
1922                        if (cc->mode == MIGRATE_ASYNC ||
1923                                        IS_ALIGNED(cc->migrate_pfn,
1924                                                        pageblock_nr_pages)) {
1925                                return COMPACT_SUCCESS;
1926                        }
1927
1928                        ret = COMPACT_CONTINUE;
1929                        break;
1930                }
1931        }
1932
1933        if (cc->contended || fatal_signal_pending(current))
1934                ret = COMPACT_CONTENDED;
1935
1936        return ret;
1937}
1938
1939static enum compact_result compact_finished(struct compact_control *cc)
1940{
1941        int ret;
1942
1943        ret = __compact_finished(cc);
1944        trace_mm_compaction_finished(cc->zone, cc->order, ret);
1945        if (ret == COMPACT_NO_SUITABLE_PAGE)
1946                ret = COMPACT_CONTINUE;
1947
1948        return ret;
1949}
1950
1951/*
1952 * compaction_suitable: Is this suitable to run compaction on this zone now?
1953 * Returns
1954 *   COMPACT_SKIPPED  - If there are too few free pages for compaction
1955 *   COMPACT_SUCCESS  - If the allocation would succeed without compaction
1956 *   COMPACT_CONTINUE - If compaction should run now
1957 */
1958static enum compact_result __compaction_suitable(struct zone *zone, int order,
1959                                        unsigned int alloc_flags,
1960                                        int classzone_idx,
1961                                        unsigned long wmark_target)
1962{
1963        unsigned long watermark;
1964
1965        if (is_via_compact_memory(order))
1966                return COMPACT_CONTINUE;
1967
1968        watermark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK);
1969        /*
1970         * If watermarks for high-order allocation are already met, there
1971         * should be no need for compaction at all.
1972         */
1973        if (zone_watermark_ok(zone, order, watermark, classzone_idx,
1974                                                                alloc_flags))
1975                return COMPACT_SUCCESS;
1976
1977        /*
1978         * Watermarks for order-0 must be met for compaction to be able to
1979         * isolate free pages for migration targets. This means that the
1980         * watermark and alloc_flags have to match, or be more pessimistic than
1981         * the check in __isolate_free_page(). We don't use the direct
1982         * compactor's alloc_flags, as they are not relevant for freepage
1983         * isolation. We however do use the direct compactor's classzone_idx to
1984         * skip over zones where lowmem reserves would prevent allocation even
1985         * if compaction succeeds.
1986         * For costly orders, we require low watermark instead of min for
1987         * compaction to proceed to increase its chances.
1988         * ALLOC_CMA is used, as pages in CMA pageblocks are considered
1989         * suitable migration targets
1990         */
1991        watermark = (order > PAGE_ALLOC_COSTLY_ORDER) ?
1992                                low_wmark_pages(zone) : min_wmark_pages(zone);
1993        watermark += compact_gap(order);
1994        if (!__zone_watermark_ok(zone, 0, watermark, classzone_idx,
1995                                                ALLOC_CMA, wmark_target))
1996                return COMPACT_SKIPPED;
1997
1998        return COMPACT_CONTINUE;
1999}
2000
2001enum compact_result compaction_suitable(struct zone *zone, int order,
2002                                        unsigned int alloc_flags,
2003                                        int classzone_idx)
2004{
2005        enum compact_result ret;
2006        int fragindex;
2007
2008        ret = __compaction_suitable(zone, order, alloc_flags, classzone_idx,
2009                                    zone_page_state(zone, NR_FREE_PAGES));
2010        /*
2011         * fragmentation index determines if allocation failures are due to
2012         * low memory or external fragmentation
2013         *
2014         * index of -1000 would imply allocations might succeed depending on
2015         * watermarks, but we already failed the high-order watermark check
2016         * index towards 0 implies failure is due to lack of memory
2017         * index towards 1000 implies failure is due to fragmentation
2018         *
2019         * Only compact if a failure would be due to fragmentation. Also
2020         * ignore fragindex for non-costly orders where the alternative to
2021         * a successful reclaim/compaction is OOM. Fragindex and the
2022         * vm.extfrag_threshold sysctl is meant as a heuristic to prevent
2023         * excessive compaction for costly orders, but it should not be at the
2024         * expense of system stability.
2025         */
2026        if (ret == COMPACT_CONTINUE && (order > PAGE_ALLOC_COSTLY_ORDER)) {
2027                fragindex = fragmentation_index(zone, order);
2028                if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
2029                        ret = COMPACT_NOT_SUITABLE_ZONE;
2030        }
2031
2032        trace_mm_compaction_suitable(zone, order, ret);
2033        if (ret == COMPACT_NOT_SUITABLE_ZONE)
2034                ret = COMPACT_SKIPPED;
2035
2036        return ret;
2037}
2038
2039bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
2040                int alloc_flags)
2041{
2042        struct zone *zone;
2043        struct zoneref *z;
2044
2045        /*
2046         * Make sure at least one zone would pass __compaction_suitable if we continue
2047         * retrying the reclaim.
2048         */
2049        for_each_zone_zonelist_nodemask(zone, z, ac->zonelist, ac->high_zoneidx,
2050                                        ac->nodemask) {
2051                unsigned long available;
2052                enum compact_result compact_result;
2053
2054                /*
2055                 * Do not consider all the reclaimable memory because we do not
2056                 * want to trash just for a single high order allocation which
2057                 * is even not guaranteed to appear even if __compaction_suitable
2058                 * is happy about the watermark check.
2059                 */
2060                available = zone_reclaimable_pages(zone) / order;
2061                available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
2062                compact_result = __compaction_suitable(zone, order, alloc_flags,
2063                                ac_classzone_idx(ac), available);
2064                if (compact_result != COMPACT_SKIPPED)
2065                        return true;
2066        }
2067
2068        return false;
2069}
2070
2071static enum compact_result
2072compact_zone(struct compact_control *cc, struct capture_control *capc)
2073{
2074        enum compact_result ret;
2075        unsigned long start_pfn = cc->zone->zone_start_pfn;
2076        unsigned long end_pfn = zone_end_pfn(cc->zone);
2077        unsigned long last_migrated_pfn;
2078        const bool sync = cc->mode != MIGRATE_ASYNC;
2079        bool update_cached;
2080
2081        /*
2082         * These counters track activities during zone compaction.  Initialize
2083         * them before compacting a new zone.
2084         */
2085        cc->total_migrate_scanned = 0;
2086        cc->total_free_scanned = 0;
2087        cc->nr_migratepages = 0;
2088        cc->nr_freepages = 0;
2089        INIT_LIST_HEAD(&cc->freepages);
2090        INIT_LIST_HEAD(&cc->migratepages);
2091
2092        cc->migratetype = gfpflags_to_migratetype(cc->gfp_mask);
2093        ret = compaction_suitable(cc->zone, cc->order, cc->alloc_flags,
2094                                                        cc->classzone_idx);
2095        /* Compaction is likely to fail */
2096        if (ret == COMPACT_SUCCESS || ret == COMPACT_SKIPPED)
2097                return ret;
2098
2099        /* huh, compaction_suitable is returning something unexpected */
2100        VM_BUG_ON(ret != COMPACT_CONTINUE);
2101
2102        /*
2103         * Clear pageblock skip if there were failures recently and compaction
2104         * is about to be retried after being deferred.
2105         */
2106        if (compaction_restarting(cc->zone, cc->order))
2107                __reset_isolation_suitable(cc->zone);
2108
2109        /*
2110         * Setup to move all movable pages to the end of the zone. Used cached
2111         * information on where the scanners should start (unless we explicitly
2112         * want to compact the whole zone), but check that it is initialised
2113         * by ensuring the values are within zone boundaries.
2114         */
2115        cc->fast_start_pfn = 0;
2116        if (cc->whole_zone) {
2117                cc->migrate_pfn = start_pfn;
2118                cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
2119        } else {
2120                cc->migrate_pfn = cc->zone->compact_cached_migrate_pfn[sync];
2121                cc->free_pfn = cc->zone->compact_cached_free_pfn;
2122                if (cc->free_pfn < start_pfn || cc->free_pfn >= end_pfn) {
2123                        cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
2124                        cc->zone->compact_cached_free_pfn = cc->free_pfn;
2125                }
2126                if (cc->migrate_pfn < start_pfn || cc->migrate_pfn >= end_pfn) {
2127                        cc->migrate_pfn = start_pfn;
2128                        cc->zone->compact_cached_migrate_pfn[0] = cc->migrate_pfn;
2129                        cc->zone->compact_cached_migrate_pfn[1] = cc->migrate_pfn;
2130                }
2131
2132                if (cc->migrate_pfn <= cc->zone->compact_init_migrate_pfn)
2133                        cc->whole_zone = true;
2134        }
2135
2136        last_migrated_pfn = 0;
2137
2138        /*
2139         * Migrate has separate cached PFNs for ASYNC and SYNC* migration on
2140         * the basis that some migrations will fail in ASYNC mode. However,
2141         * if the cached PFNs match and pageblocks are skipped due to having
2142         * no isolation candidates, then the sync state does not matter.
2143         * Until a pageblock with isolation candidates is found, keep the
2144         * cached PFNs in sync to avoid revisiting the same blocks.
2145         */
2146        update_cached = !sync &&
2147                cc->zone->compact_cached_migrate_pfn[0] == cc->zone->compact_cached_migrate_pfn[1];
2148
2149        trace_mm_compaction_begin(start_pfn, cc->migrate_pfn,
2150                                cc->free_pfn, end_pfn, sync);
2151
2152        migrate_prep_local();
2153
2154        while ((ret = compact_finished(cc)) == COMPACT_CONTINUE) {
2155                int err;
2156                unsigned long start_pfn = cc->migrate_pfn;
2157
2158                /*
2159                 * Avoid multiple rescans which can happen if a page cannot be
2160                 * isolated (dirty/writeback in async mode) or if the migrated
2161                 * pages are being allocated before the pageblock is cleared.
2162                 * The first rescan will capture the entire pageblock for
2163                 * migration. If it fails, it'll be marked skip and scanning
2164                 * will proceed as normal.
2165                 */
2166                cc->rescan = false;
2167                if (pageblock_start_pfn(last_migrated_pfn) ==
2168                    pageblock_start_pfn(start_pfn)) {
2169                        cc->rescan = true;
2170                }
2171
2172                switch (isolate_migratepages(cc)) {
2173                case ISOLATE_ABORT:
2174                        ret = COMPACT_CONTENDED;
2175                        putback_movable_pages(&cc->migratepages);
2176                        cc->nr_migratepages = 0;
2177                        last_migrated_pfn = 0;
2178                        goto out;
2179                case ISOLATE_NONE:
2180                        if (update_cached) {
2181                                cc->zone->compact_cached_migrate_pfn[1] =
2182                                        cc->zone->compact_cached_migrate_pfn[0];
2183                        }
2184
2185                        /*
2186                         * We haven't isolated and migrated anything, but
2187                         * there might still be unflushed migrations from
2188                         * previous cc->order aligned block.
2189                         */
2190                        goto check_drain;
2191                case ISOLATE_SUCCESS:
2192                        update_cached = false;
2193                        last_migrated_pfn = start_pfn;
2194                        ;
2195                }
2196
2197                err = migrate_pages(&cc->migratepages, compaction_alloc,
2198                                compaction_free, (unsigned long)cc, cc->mode,
2199                                MR_COMPACTION);
2200
2201                trace_mm_compaction_migratepages(cc->nr_migratepages, err,
2202                                                        &cc->migratepages);
2203
2204                /* All pages were either migrated or will be released */
2205                cc->nr_migratepages = 0;
2206                if (err) {
2207                        putback_movable_pages(&cc->migratepages);
2208                        /*
2209                         * migrate_pages() may return -ENOMEM when scanners meet
2210                         * and we want compact_finished() to detect it
2211                         */
2212                        if (err == -ENOMEM && !compact_scanners_met(cc)) {
2213                                ret = COMPACT_CONTENDED;
2214                                goto out;
2215                        }
2216                        /*
2217                         * We failed to migrate at least one page in the current
2218                         * order-aligned block, so skip the rest of it.
2219                         */
2220                        if (cc->direct_compaction &&
2221                                                (cc->mode == MIGRATE_ASYNC)) {
2222                                cc->migrate_pfn = block_end_pfn(
2223                                                cc->migrate_pfn - 1, cc->order);
2224                                /* Draining pcplists is useless in this case */
2225                                last_migrated_pfn = 0;
2226                        }
2227                }
2228
2229check_drain:
2230                /*
2231                 * Has the migration scanner moved away from the previous
2232                 * cc->order aligned block where we migrated from? If yes,
2233                 * flush the pages that were freed, so that they can merge and
2234                 * compact_finished() can detect immediately if allocation
2235                 * would succeed.
2236                 */
2237                if (cc->order > 0 && last_migrated_pfn) {
2238                        int cpu;
2239                        unsigned long current_block_start =
2240                                block_start_pfn(cc->migrate_pfn, cc->order);
2241
2242                        if (last_migrated_pfn < current_block_start) {
2243                                cpu = get_cpu();
2244                                lru_add_drain_cpu(cpu);
2245                                drain_local_pages(cc->zone);
2246                                put_cpu();
2247                                /* No more flushing until we migrate again */
2248                                last_migrated_pfn = 0;
2249                        }
2250                }
2251
2252                /* Stop if a page has been captured */
2253                if (capc && capc->page) {
2254                        ret = COMPACT_SUCCESS;
2255                        break;
2256                }
2257        }
2258
2259out:
2260        /*
2261         * Release free pages and update where the free scanner should restart,
2262         * so we don't leave any returned pages behind in the next attempt.
2263         */
2264        if (cc->nr_freepages > 0) {
2265                unsigned long free_pfn = release_freepages(&cc->freepages);
2266
2267                cc->nr_freepages = 0;
2268                VM_BUG_ON(free_pfn == 0);
2269                /* The cached pfn is always the first in a pageblock */
2270                free_pfn = pageblock_start_pfn(free_pfn);
2271                /*
2272                 * Only go back, not forward. The cached pfn might have been
2273                 * already reset to zone end in compact_finished()
2274                 */
2275                if (free_pfn > cc->zone->compact_cached_free_pfn)
2276                        cc->zone->compact_cached_free_pfn = free_pfn;
2277        }
2278
2279        count_compact_events(COMPACTMIGRATE_SCANNED, cc->total_migrate_scanned);
2280        count_compact_events(COMPACTFREE_SCANNED, cc->total_free_scanned);
2281
2282        trace_mm_compaction_end(start_pfn, cc->migrate_pfn,
2283                                cc->free_pfn, end_pfn, sync, ret);
2284
2285        return ret;
2286}
2287
2288static enum compact_result compact_zone_order(struct zone *zone, int order,
2289                gfp_t gfp_mask, enum compact_priority prio,
2290                unsigned int alloc_flags, int classzone_idx,
2291                struct page **capture)
2292{
2293        enum compact_result ret;
2294        struct compact_control cc = {
2295                .order = order,
2296                .search_order = order,
2297                .gfp_mask = gfp_mask,
2298                .zone = zone,
2299                .mode = (prio == COMPACT_PRIO_ASYNC) ?
2300                                        MIGRATE_ASYNC : MIGRATE_SYNC_LIGHT,
2301                .alloc_flags = alloc_flags,
2302                .classzone_idx = classzone_idx,
2303                .direct_compaction = true,
2304                .whole_zone = (prio == MIN_COMPACT_PRIORITY),
2305                .ignore_skip_hint = (prio == MIN_COMPACT_PRIORITY),
2306                .ignore_block_suitable = (prio == MIN_COMPACT_PRIORITY)
2307        };
2308        struct capture_control capc = {
2309                .cc = &cc,
2310                .page = NULL,
2311        };
2312
2313        if (capture)
2314                current->capture_control = &capc;
2315
2316        ret = compact_zone(&cc, &capc);
2317
2318        VM_BUG_ON(!list_empty(&cc.freepages));
2319        VM_BUG_ON(!list_empty(&cc.migratepages));
2320
2321        *capture = capc.page;
2322        current->capture_control = NULL;
2323
2324        return ret;
2325}
2326
2327int sysctl_extfrag_threshold = 500;
2328
2329/**
2330 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
2331 * @gfp_mask: The GFP mask of the current allocation
2332 * @order: The order of the current allocation
2333 * @alloc_flags: The allocation flags of the current allocation
2334 * @ac: The context of current allocation
2335 * @prio: Determines how hard direct compaction should try to succeed
2336 *
2337 * This is the main entry point for direct page compaction.
2338 */
2339enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
2340                unsigned int alloc_flags, const struct alloc_context *ac,
2341                enum compact_priority prio, struct page **capture)
2342{
2343        int may_perform_io = gfp_mask & __GFP_IO;
2344        struct zoneref *z;
2345        struct zone *zone;
2346        enum compact_result rc = COMPACT_SKIPPED;
2347
2348        /*
2349         * Check if the GFP flags allow compaction - GFP_NOIO is really
2350         * tricky context because the migration might require IO
2351         */
2352        if (!may_perform_io)
2353                return COMPACT_SKIPPED;
2354
2355        trace_mm_compaction_try_to_compact_pages(order, gfp_mask, prio);
2356
2357        /* Compact each zone in the list */
2358        for_each_zone_zonelist_nodemask(zone, z, ac->zonelist, ac->high_zoneidx,
2359                                                                ac->nodemask) {
2360                enum compact_result status;
2361
2362                if (prio > MIN_COMPACT_PRIORITY
2363                                        && compaction_deferred(zone, order)) {
2364                        rc = max_t(enum compact_result, COMPACT_DEFERRED, rc);
2365                        continue;
2366                }
2367
2368                status = compact_zone_order(zone, order, gfp_mask, prio,
2369                                alloc_flags, ac_classzone_idx(ac), capture);
2370                rc = max(status, rc);
2371
2372                /* The allocation should succeed, stop compacting */
2373                if (status == COMPACT_SUCCESS) {
2374                        /*
2375                         * We think the allocation will succeed in this zone,
2376                         * but it is not certain, hence the false. The caller
2377                         * will repeat this with true if allocation indeed
2378                         * succeeds in this zone.
2379                         */
2380                        compaction_defer_reset(zone, order, false);
2381
2382                        break;
2383                }
2384
2385                if (prio != COMPACT_PRIO_ASYNC && (status == COMPACT_COMPLETE ||
2386                                        status == COMPACT_PARTIAL_SKIPPED))
2387                        /*
2388                         * We think that allocation won't succeed in this zone
2389                         * so we defer compaction there. If it ends up
2390                         * succeeding after all, it will be reset.
2391                         */
2392                        defer_compaction(zone, order);
2393
2394                /*
2395                 * We might have stopped compacting due to need_resched() in
2396                 * async compaction, or due to a fatal signal detected. In that
2397                 * case do not try further zones
2398                 */
2399                if ((prio == COMPACT_PRIO_ASYNC && need_resched())
2400                                        || fatal_signal_pending(current))
2401                        break;
2402        }
2403
2404        return rc;
2405}
2406
2407
2408/* Compact all zones within a node */
2409static void compact_node(int nid)
2410{
2411        pg_data_t *pgdat = NODE_DATA(nid);
2412        int zoneid;
2413        struct zone *zone;
2414        struct compact_control cc = {
2415                .order = -1,
2416                .mode = MIGRATE_SYNC,
2417                .ignore_skip_hint = true,
2418                .whole_zone = true,
2419                .gfp_mask = GFP_KERNEL,
2420        };
2421
2422
2423        for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
2424
2425                zone = &pgdat->node_zones[zoneid];
2426                if (!populated_zone(zone))
2427                        continue;
2428
2429                cc.zone = zone;
2430
2431                compact_zone(&cc, NULL);
2432
2433                VM_BUG_ON(!list_empty(&cc.freepages));
2434                VM_BUG_ON(!list_empty(&cc.migratepages));
2435        }
2436}
2437
2438/* Compact all nodes in the system */
2439static void compact_nodes(void)
2440{
2441        int nid;
2442
2443        /* Flush pending updates to the LRU lists */
2444        lru_add_drain_all();
2445
2446        for_each_online_node(nid)
2447                compact_node(nid);
2448}
2449
2450/* The written value is actually unused, all memory is compacted */
2451int sysctl_compact_memory;
2452
2453/*
2454 * This is the entry point for compacting all nodes via
2455 * /proc/sys/vm/compact_memory
2456 */
2457int sysctl_compaction_handler(struct ctl_table *table, int write,
2458                        void __user *buffer, size_t *length, loff_t *ppos)
2459{
2460        if (write)
2461                compact_nodes();
2462
2463        return 0;
2464}
2465
2466#if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
2467static ssize_t sysfs_compact_node(struct device *dev,
2468                        struct device_attribute *attr,
2469                        const char *buf, size_t count)
2470{
2471        int nid = dev->id;
2472
2473        if (nid >= 0 && nid < nr_node_ids && node_online(nid)) {
2474                /* Flush pending updates to the LRU lists */
2475                lru_add_drain_all();
2476
2477                compact_node(nid);
2478        }
2479
2480        return count;
2481}
2482static DEVICE_ATTR(compact, 0200, NULL, sysfs_compact_node);
2483
2484int compaction_register_node(struct node *node)
2485{
2486        return device_create_file(&node->dev, &dev_attr_compact);
2487}
2488
2489void compaction_unregister_node(struct node *node)
2490{
2491        return device_remove_file(&node->dev, &dev_attr_compact);
2492}
2493#endif /* CONFIG_SYSFS && CONFIG_NUMA */
2494
2495static inline bool kcompactd_work_requested(pg_data_t *pgdat)
2496{
2497        return pgdat->kcompactd_max_order > 0 || kthread_should_stop();
2498}
2499
2500static bool kcompactd_node_suitable(pg_data_t *pgdat)
2501{
2502        int zoneid;
2503        struct zone *zone;
2504        enum zone_type classzone_idx = pgdat->kcompactd_classzone_idx;
2505
2506        for (zoneid = 0; zoneid <= classzone_idx; zoneid++) {
2507                zone = &pgdat->node_zones[zoneid];
2508
2509                if (!populated_zone(zone))
2510                        continue;
2511
2512                if (compaction_suitable(zone, pgdat->kcompactd_max_order, 0,
2513                                        classzone_idx) == COMPACT_CONTINUE)
2514                        return true;
2515        }
2516
2517        return false;
2518}
2519
2520static void kcompactd_do_work(pg_data_t *pgdat)
2521{
2522        /*
2523         * With no special task, compact all zones so that a page of requested
2524         * order is allocatable.
2525         */
2526        int zoneid;
2527        struct zone *zone;
2528        struct compact_control cc = {
2529                .order = pgdat->kcompactd_max_order,
2530                .search_order = pgdat->kcompactd_max_order,
2531                .classzone_idx = pgdat->kcompactd_classzone_idx,
2532                .mode = MIGRATE_SYNC_LIGHT,
2533                .ignore_skip_hint = false,
2534                .gfp_mask = GFP_KERNEL,
2535        };
2536        trace_mm_compaction_kcompactd_wake(pgdat->node_id, cc.order,
2537                                                        cc.classzone_idx);
2538        count_compact_event(KCOMPACTD_WAKE);
2539
2540        for (zoneid = 0; zoneid <= cc.classzone_idx; zoneid++) {
2541                int status;
2542
2543                zone = &pgdat->node_zones[zoneid];
2544                if (!populated_zone(zone))
2545                        continue;
2546
2547                if (compaction_deferred(zone, cc.order))
2548                        continue;
2549
2550                if (compaction_suitable(zone, cc.order, 0, zoneid) !=
2551                                                        COMPACT_CONTINUE)
2552                        continue;
2553
2554                if (kthread_should_stop())
2555                        return;
2556
2557                cc.zone = zone;
2558                status = compact_zone(&cc, NULL);
2559
2560                if (status == COMPACT_SUCCESS) {
2561                        compaction_defer_reset(zone, cc.order, false);
2562                } else if (status == COMPACT_PARTIAL_SKIPPED || status == COMPACT_COMPLETE) {
2563                        /*
2564                         * Buddy pages may become stranded on pcps that could
2565                         * otherwise coalesce on the zone's free area for
2566                         * order >= cc.order.  This is ratelimited by the
2567                         * upcoming deferral.
2568                         */
2569                        drain_all_pages(zone);
2570
2571                        /*
2572                         * We use sync migration mode here, so we defer like
2573                         * sync direct compaction does.
2574                         */
2575                        defer_compaction(zone, cc.order);
2576                }
2577
2578                count_compact_events(KCOMPACTD_MIGRATE_SCANNED,
2579                                     cc.total_migrate_scanned);
2580                count_compact_events(KCOMPACTD_FREE_SCANNED,
2581                                     cc.total_free_scanned);
2582
2583                VM_BUG_ON(!list_empty(&cc.freepages));
2584                VM_BUG_ON(!list_empty(&cc.migratepages));
2585        }
2586
2587        /*
2588         * Regardless of success, we are done until woken up next. But remember
2589         * the requested order/classzone_idx in case it was higher/tighter than
2590         * our current ones
2591         */
2592        if (pgdat->kcompactd_max_order <= cc.order)
2593                pgdat->kcompactd_max_order = 0;
2594        if (pgdat->kcompactd_classzone_idx >= cc.classzone_idx)
2595                pgdat->kcompactd_classzone_idx = pgdat->nr_zones - 1;
2596}
2597
2598void wakeup_kcompactd(pg_data_t *pgdat, int order, int classzone_idx)
2599{
2600        if (!order)
2601                return;
2602
2603        if (pgdat->kcompactd_max_order < order)
2604                pgdat->kcompactd_max_order = order;
2605
2606        if (pgdat->kcompactd_classzone_idx > classzone_idx)
2607                pgdat->kcompactd_classzone_idx = classzone_idx;
2608
2609        /*
2610         * Pairs with implicit barrier in wait_event_freezable()
2611         * such that wakeups are not missed.
2612         */
2613        if (!wq_has_sleeper(&pgdat->kcompactd_wait))
2614                return;
2615
2616        if (!kcompactd_node_suitable(pgdat))
2617                return;
2618
2619        trace_mm_compaction_wakeup_kcompactd(pgdat->node_id, order,
2620                                                        classzone_idx);
2621        wake_up_interruptible(&pgdat->kcompactd_wait);
2622}
2623
2624/*
2625 * The background compaction daemon, started as a kernel thread
2626 * from the init process.
2627 */
2628static int kcompactd(void *p)
2629{
2630        pg_data_t *pgdat = (pg_data_t*)p;
2631        struct task_struct *tsk = current;
2632
2633        const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
2634
2635        if (!cpumask_empty(cpumask))
2636                set_cpus_allowed_ptr(tsk, cpumask);
2637
2638        set_freezable();
2639
2640        pgdat->kcompactd_max_order = 0;
2641        pgdat->kcompactd_classzone_idx = pgdat->nr_zones - 1;
2642
2643        while (!kthread_should_stop()) {
2644                unsigned long pflags;
2645
2646                trace_mm_compaction_kcompactd_sleep(pgdat->node_id);
2647                wait_event_freezable(pgdat->kcompactd_wait,
2648                                kcompactd_work_requested(pgdat));
2649
2650                psi_memstall_enter(&pflags);
2651                kcompactd_do_work(pgdat);
2652                psi_memstall_leave(&pflags);
2653        }
2654
2655        return 0;
2656}
2657
2658/*
2659 * This kcompactd start function will be called by init and node-hot-add.
2660 * On node-hot-add, kcompactd will moved to proper cpus if cpus are hot-added.
2661 */
2662int kcompactd_run(int nid)
2663{
2664        pg_data_t *pgdat = NODE_DATA(nid);
2665        int ret = 0;
2666
2667        if (pgdat->kcompactd)
2668                return 0;
2669
2670        pgdat->kcompactd = kthread_run(kcompactd, pgdat, "kcompactd%d", nid);
2671        if (IS_ERR(pgdat->kcompactd)) {
2672                pr_err("Failed to start kcompactd on node %d\n", nid);
2673                ret = PTR_ERR(pgdat->kcompactd);
2674                pgdat->kcompactd = NULL;
2675        }
2676        return ret;
2677}
2678
2679/*
2680 * Called by memory hotplug when all memory in a node is offlined. Caller must
2681 * hold mem_hotplug_begin/end().
2682 */
2683void kcompactd_stop(int nid)
2684{
2685        struct task_struct *kcompactd = NODE_DATA(nid)->kcompactd;
2686
2687        if (kcompactd) {
2688                kthread_stop(kcompactd);
2689                NODE_DATA(nid)->kcompactd = NULL;
2690        }
2691}
2692
2693/*
2694 * It's optimal to keep kcompactd on the same CPUs as their memory, but
2695 * not required for correctness. So if the last cpu in a node goes
2696 * away, we get changed to run anywhere: as the first one comes back,
2697 * restore their cpu bindings.
2698 */
2699static int kcompactd_cpu_online(unsigned int cpu)
2700{
2701        int nid;
2702
2703        for_each_node_state(nid, N_MEMORY) {
2704                pg_data_t *pgdat = NODE_DATA(nid);
2705                const struct cpumask *mask;
2706
2707                mask = cpumask_of_node(pgdat->node_id);
2708
2709                if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
2710                        /* One of our CPUs online: restore mask */
2711                        set_cpus_allowed_ptr(pgdat->kcompactd, mask);
2712        }
2713        return 0;
2714}
2715
2716static int __init kcompactd_init(void)
2717{
2718        int nid;
2719        int ret;
2720
2721        ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
2722                                        "mm/compaction:online",
2723                                        kcompactd_cpu_online, NULL);
2724        if (ret < 0) {
2725                pr_err("kcompactd: failed to register hotplug callbacks.\n");
2726                return ret;
2727        }
2728
2729        for_each_node_state(nid, N_MEMORY)
2730                kcompactd_run(nid);
2731        return 0;
2732}
2733subsys_initcall(kcompactd_init)
2734
2735#endif /* CONFIG_COMPACTION */
2736