linux/mm/compaction.c
<<
>>
Prefs
   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
  53/*
  54 * Fragmentation score check interval for proactive compaction purposes.
  55 */
  56static const unsigned int HPAGE_FRAG_CHECK_INTERVAL_MSEC = 500;
  57
  58/*
  59 * Page order with-respect-to which proactive compaction
  60 * calculates external fragmentation, which is used as
  61 * the "fragmentation score" of a node/zone.
  62 */
  63#if defined CONFIG_TRANSPARENT_HUGEPAGE
  64#define COMPACTION_HPAGE_ORDER  HPAGE_PMD_ORDER
  65#elif defined CONFIG_HUGETLBFS
  66#define COMPACTION_HPAGE_ORDER  HUGETLB_PAGE_ORDER
  67#else
  68#define COMPACTION_HPAGE_ORDER  (PMD_SHIFT - PAGE_SHIFT)
  69#endif
  70
  71static unsigned long release_freepages(struct list_head *freelist)
  72{
  73        struct page *page, *next;
  74        unsigned long high_pfn = 0;
  75
  76        list_for_each_entry_safe(page, next, freelist, lru) {
  77                unsigned long pfn = page_to_pfn(page);
  78                list_del(&page->lru);
  79                __free_page(page);
  80                if (pfn > high_pfn)
  81                        high_pfn = pfn;
  82        }
  83
  84        return high_pfn;
  85}
  86
  87static void split_map_pages(struct list_head *list)
  88{
  89        unsigned int i, order, nr_pages;
  90        struct page *page, *next;
  91        LIST_HEAD(tmp_list);
  92
  93        list_for_each_entry_safe(page, next, list, lru) {
  94                list_del(&page->lru);
  95
  96                order = page_private(page);
  97                nr_pages = 1 << order;
  98
  99                post_alloc_hook(page, order, __GFP_MOVABLE);
 100                if (order)
 101                        split_page(page, order);
 102
 103                for (i = 0; i < nr_pages; i++) {
 104                        list_add(&page->lru, &tmp_list);
 105                        page++;
 106                }
 107        }
 108
 109        list_splice(&tmp_list, list);
 110}
 111
 112#ifdef CONFIG_COMPACTION
 113
 114int PageMovable(struct page *page)
 115{
 116        struct address_space *mapping;
 117
 118        VM_BUG_ON_PAGE(!PageLocked(page), page);
 119        if (!__PageMovable(page))
 120                return 0;
 121
 122        mapping = page_mapping(page);
 123        if (mapping && mapping->a_ops && mapping->a_ops->isolate_page)
 124                return 1;
 125
 126        return 0;
 127}
 128EXPORT_SYMBOL(PageMovable);
 129
 130void __SetPageMovable(struct page *page, struct address_space *mapping)
 131{
 132        VM_BUG_ON_PAGE(!PageLocked(page), page);
 133        VM_BUG_ON_PAGE((unsigned long)mapping & PAGE_MAPPING_MOVABLE, page);
 134        page->mapping = (void *)((unsigned long)mapping | PAGE_MAPPING_MOVABLE);
 135}
 136EXPORT_SYMBOL(__SetPageMovable);
 137
 138void __ClearPageMovable(struct page *page)
 139{
 140        VM_BUG_ON_PAGE(!PageMovable(page), page);
 141        /*
 142         * Clear registered address_space val with keeping PAGE_MAPPING_MOVABLE
 143         * flag so that VM can catch up released page by driver after isolation.
 144         * With it, VM migration doesn't try to put it back.
 145         */
 146        page->mapping = (void *)((unsigned long)page->mapping &
 147                                PAGE_MAPPING_MOVABLE);
 148}
 149EXPORT_SYMBOL(__ClearPageMovable);
 150
 151/* Do not skip compaction more than 64 times */
 152#define COMPACT_MAX_DEFER_SHIFT 6
 153
 154/*
 155 * Compaction is deferred when compaction fails to result in a page
 156 * allocation success. 1 << compact_defer_shift, compactions are skipped up
 157 * to a limit of 1 << COMPACT_MAX_DEFER_SHIFT
 158 */
 159static void defer_compaction(struct zone *zone, int order)
 160{
 161        zone->compact_considered = 0;
 162        zone->compact_defer_shift++;
 163
 164        if (order < zone->compact_order_failed)
 165                zone->compact_order_failed = order;
 166
 167        if (zone->compact_defer_shift > COMPACT_MAX_DEFER_SHIFT)
 168                zone->compact_defer_shift = COMPACT_MAX_DEFER_SHIFT;
 169
 170        trace_mm_compaction_defer_compaction(zone, order);
 171}
 172
 173/* Returns true if compaction should be skipped this time */
 174static bool compaction_deferred(struct zone *zone, int order)
 175{
 176        unsigned long defer_limit = 1UL << zone->compact_defer_shift;
 177
 178        if (order < zone->compact_order_failed)
 179                return false;
 180
 181        /* Avoid possible overflow */
 182        if (++zone->compact_considered >= defer_limit) {
 183                zone->compact_considered = defer_limit;
 184                return false;
 185        }
 186
 187        trace_mm_compaction_deferred(zone, order);
 188
 189        return true;
 190}
 191
 192/*
 193 * Update defer tracking counters after successful compaction of given order,
 194 * which means an allocation either succeeded (alloc_success == true) or is
 195 * expected to succeed.
 196 */
 197void compaction_defer_reset(struct zone *zone, int order,
 198                bool alloc_success)
 199{
 200        if (alloc_success) {
 201                zone->compact_considered = 0;
 202                zone->compact_defer_shift = 0;
 203        }
 204        if (order >= zone->compact_order_failed)
 205                zone->compact_order_failed = order + 1;
 206
 207        trace_mm_compaction_defer_reset(zone, order);
 208}
 209
 210/* Returns true if restarting compaction after many failures */
 211static bool compaction_restarting(struct zone *zone, int order)
 212{
 213        if (order < zone->compact_order_failed)
 214                return false;
 215
 216        return zone->compact_defer_shift == COMPACT_MAX_DEFER_SHIFT &&
 217                zone->compact_considered >= 1UL << zone->compact_defer_shift;
 218}
 219
 220/* Returns true if the pageblock should be scanned for pages to isolate. */
 221static inline bool isolation_suitable(struct compact_control *cc,
 222                                        struct page *page)
 223{
 224        if (cc->ignore_skip_hint)
 225                return true;
 226
 227        return !get_pageblock_skip(page);
 228}
 229
 230static void reset_cached_positions(struct zone *zone)
 231{
 232        zone->compact_cached_migrate_pfn[0] = zone->zone_start_pfn;
 233        zone->compact_cached_migrate_pfn[1] = zone->zone_start_pfn;
 234        zone->compact_cached_free_pfn =
 235                                pageblock_start_pfn(zone_end_pfn(zone) - 1);
 236}
 237
 238/*
 239 * Compound pages of >= pageblock_order should consistently be skipped until
 240 * released. It is always pointless to compact pages of such order (if they are
 241 * migratable), and the pageblocks they occupy cannot contain any free pages.
 242 */
 243static bool pageblock_skip_persistent(struct page *page)
 244{
 245        if (!PageCompound(page))
 246                return false;
 247
 248        page = compound_head(page);
 249
 250        if (compound_order(page) >= pageblock_order)
 251                return true;
 252
 253        return false;
 254}
 255
 256static bool
 257__reset_isolation_pfn(struct zone *zone, unsigned long pfn, bool check_source,
 258                                                        bool check_target)
 259{
 260        struct page *page = pfn_to_online_page(pfn);
 261        struct page *block_page;
 262        struct page *end_page;
 263        unsigned long block_pfn;
 264
 265        if (!page)
 266                return false;
 267        if (zone != page_zone(page))
 268                return false;
 269        if (pageblock_skip_persistent(page))
 270                return false;
 271
 272        /*
 273         * If skip is already cleared do no further checking once the
 274         * restart points have been set.
 275         */
 276        if (check_source && check_target && !get_pageblock_skip(page))
 277                return true;
 278
 279        /*
 280         * If clearing skip for the target scanner, do not select a
 281         * non-movable pageblock as the starting point.
 282         */
 283        if (!check_source && check_target &&
 284            get_pageblock_migratetype(page) != MIGRATE_MOVABLE)
 285                return false;
 286
 287        /* Ensure the start of the pageblock or zone is online and valid */
 288        block_pfn = pageblock_start_pfn(pfn);
 289        block_pfn = max(block_pfn, zone->zone_start_pfn);
 290        block_page = pfn_to_online_page(block_pfn);
 291        if (block_page) {
 292                page = block_page;
 293                pfn = block_pfn;
 294        }
 295
 296        /* Ensure the end of the pageblock or zone is online and valid */
 297        block_pfn = pageblock_end_pfn(pfn) - 1;
 298        block_pfn = min(block_pfn, zone_end_pfn(zone) - 1);
 299        end_page = pfn_to_online_page(block_pfn);
 300        if (!end_page)
 301                return false;
 302
 303        /*
 304         * Only clear the hint if a sample indicates there is either a
 305         * free page or an LRU page in the block. One or other condition
 306         * is necessary for the block to be a migration source/target.
 307         */
 308        do {
 309                if (pfn_valid_within(pfn)) {
 310                        if (check_source && PageLRU(page)) {
 311                                clear_pageblock_skip(page);
 312                                return true;
 313                        }
 314
 315                        if (check_target && PageBuddy(page)) {
 316                                clear_pageblock_skip(page);
 317                                return true;
 318                        }
 319                }
 320
 321                page += (1 << PAGE_ALLOC_COSTLY_ORDER);
 322                pfn += (1 << PAGE_ALLOC_COSTLY_ORDER);
 323        } while (page <= end_page);
 324
 325        return false;
 326}
 327
 328/*
 329 * This function is called to clear all cached information on pageblocks that
 330 * should be skipped for page isolation when the migrate and free page scanner
 331 * meet.
 332 */
 333static void __reset_isolation_suitable(struct zone *zone)
 334{
 335        unsigned long migrate_pfn = zone->zone_start_pfn;
 336        unsigned long free_pfn = zone_end_pfn(zone) - 1;
 337        unsigned long reset_migrate = free_pfn;
 338        unsigned long reset_free = migrate_pfn;
 339        bool source_set = false;
 340        bool free_set = false;
 341
 342        if (!zone->compact_blockskip_flush)
 343                return;
 344
 345        zone->compact_blockskip_flush = false;
 346
 347        /*
 348         * Walk the zone and update pageblock skip information. Source looks
 349         * for PageLRU while target looks for PageBuddy. When the scanner
 350         * is found, both PageBuddy and PageLRU are checked as the pageblock
 351         * is suitable as both source and target.
 352         */
 353        for (; migrate_pfn < free_pfn; migrate_pfn += pageblock_nr_pages,
 354                                        free_pfn -= pageblock_nr_pages) {
 355                cond_resched();
 356
 357                /* Update the migrate PFN */
 358                if (__reset_isolation_pfn(zone, migrate_pfn, true, source_set) &&
 359                    migrate_pfn < reset_migrate) {
 360                        source_set = true;
 361                        reset_migrate = migrate_pfn;
 362                        zone->compact_init_migrate_pfn = reset_migrate;
 363                        zone->compact_cached_migrate_pfn[0] = reset_migrate;
 364                        zone->compact_cached_migrate_pfn[1] = reset_migrate;
 365                }
 366
 367                /* Update the free PFN */
 368                if (__reset_isolation_pfn(zone, free_pfn, free_set, true) &&
 369                    free_pfn > reset_free) {
 370                        free_set = true;
 371                        reset_free = free_pfn;
 372                        zone->compact_init_free_pfn = reset_free;
 373                        zone->compact_cached_free_pfn = reset_free;
 374                }
 375        }
 376
 377        /* Leave no distance if no suitable block was reset */
 378        if (reset_migrate >= reset_free) {
 379                zone->compact_cached_migrate_pfn[0] = migrate_pfn;
 380                zone->compact_cached_migrate_pfn[1] = migrate_pfn;
 381                zone->compact_cached_free_pfn = free_pfn;
 382        }
 383}
 384
 385void reset_isolation_suitable(pg_data_t *pgdat)
 386{
 387        int zoneid;
 388
 389        for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
 390                struct zone *zone = &pgdat->node_zones[zoneid];
 391                if (!populated_zone(zone))
 392                        continue;
 393
 394                /* Only flush if a full compaction finished recently */
 395                if (zone->compact_blockskip_flush)
 396                        __reset_isolation_suitable(zone);
 397        }
 398}
 399
 400/*
 401 * Sets the pageblock skip bit if it was clear. Note that this is a hint as
 402 * locks are not required for read/writers. Returns true if it was already set.
 403 */
 404static bool test_and_set_skip(struct compact_control *cc, struct page *page,
 405                                                        unsigned long pfn)
 406{
 407        bool skip;
 408
 409        /* Do no update if skip hint is being ignored */
 410        if (cc->ignore_skip_hint)
 411                return false;
 412
 413        if (!IS_ALIGNED(pfn, pageblock_nr_pages))
 414                return false;
 415
 416        skip = get_pageblock_skip(page);
 417        if (!skip && !cc->no_set_skip_hint)
 418                set_pageblock_skip(page);
 419
 420        return skip;
 421}
 422
 423static void update_cached_migrate(struct compact_control *cc, unsigned long pfn)
 424{
 425        struct zone *zone = cc->zone;
 426
 427        pfn = pageblock_end_pfn(pfn);
 428
 429        /* Set for isolation rather than compaction */
 430        if (cc->no_set_skip_hint)
 431                return;
 432
 433        if (pfn > zone->compact_cached_migrate_pfn[0])
 434                zone->compact_cached_migrate_pfn[0] = pfn;
 435        if (cc->mode != MIGRATE_ASYNC &&
 436            pfn > zone->compact_cached_migrate_pfn[1])
 437                zone->compact_cached_migrate_pfn[1] = pfn;
 438}
 439
 440/*
 441 * If no pages were isolated then mark this pageblock to be skipped in the
 442 * future. The information is later cleared by __reset_isolation_suitable().
 443 */
 444static void update_pageblock_skip(struct compact_control *cc,
 445                        struct page *page, unsigned long pfn)
 446{
 447        struct zone *zone = cc->zone;
 448
 449        if (cc->no_set_skip_hint)
 450                return;
 451
 452        if (!page)
 453                return;
 454
 455        set_pageblock_skip(page);
 456
 457        /* Update where async and sync compaction should restart */
 458        if (pfn < zone->compact_cached_free_pfn)
 459                zone->compact_cached_free_pfn = pfn;
 460}
 461#else
 462static inline bool isolation_suitable(struct compact_control *cc,
 463                                        struct page *page)
 464{
 465        return true;
 466}
 467
 468static inline bool pageblock_skip_persistent(struct page *page)
 469{
 470        return false;
 471}
 472
 473static inline void update_pageblock_skip(struct compact_control *cc,
 474                        struct page *page, unsigned long pfn)
 475{
 476}
 477
 478static void update_cached_migrate(struct compact_control *cc, unsigned long pfn)
 479{
 480}
 481
 482static bool test_and_set_skip(struct compact_control *cc, struct page *page,
 483                                                        unsigned long pfn)
 484{
 485        return false;
 486}
 487#endif /* CONFIG_COMPACTION */
 488
 489/*
 490 * Compaction requires the taking of some coarse locks that are potentially
 491 * very heavily contended. For async compaction, trylock and record if the
 492 * lock is contended. The lock will still be acquired but compaction will
 493 * abort when the current block is finished regardless of success rate.
 494 * Sync compaction acquires the lock.
 495 *
 496 * Always returns true which makes it easier to track lock state in callers.
 497 */
 498static bool compact_lock_irqsave(spinlock_t *lock, unsigned long *flags,
 499                                                struct compact_control *cc)
 500        __acquires(lock)
 501{
 502        /* Track if the lock is contended in async mode */
 503        if (cc->mode == MIGRATE_ASYNC && !cc->contended) {
 504                if (spin_trylock_irqsave(lock, *flags))
 505                        return true;
 506
 507                cc->contended = true;
 508        }
 509
 510        spin_lock_irqsave(lock, *flags);
 511        return true;
 512}
 513
 514/*
 515 * Compaction requires the taking of some coarse locks that are potentially
 516 * very heavily contended. The lock should be periodically unlocked to avoid
 517 * having disabled IRQs for a long time, even when there is nobody waiting on
 518 * the lock. It might also be that allowing the IRQs will result in
 519 * need_resched() becoming true. If scheduling is needed, async compaction
 520 * aborts. Sync compaction schedules.
 521 * Either compaction type will also abort if a fatal signal is pending.
 522 * In either case if the lock was locked, it is dropped and not regained.
 523 *
 524 * Returns true if compaction should abort due to fatal signal pending, or
 525 *              async compaction due to need_resched()
 526 * Returns false when compaction can continue (sync compaction might have
 527 *              scheduled)
 528 */
 529static bool compact_unlock_should_abort(spinlock_t *lock,
 530                unsigned long flags, bool *locked, struct compact_control *cc)
 531{
 532        if (*locked) {
 533                spin_unlock_irqrestore(lock, flags);
 534                *locked = false;
 535        }
 536
 537        if (fatal_signal_pending(current)) {
 538                cc->contended = true;
 539                return true;
 540        }
 541
 542        cond_resched();
 543
 544        return false;
 545}
 546
 547/*
 548 * Isolate free pages onto a private freelist. If @strict is true, will abort
 549 * returning 0 on any invalid PFNs or non-free pages inside of the pageblock
 550 * (even though it may still end up isolating some pages).
 551 */
 552static unsigned long isolate_freepages_block(struct compact_control *cc,
 553                                unsigned long *start_pfn,
 554                                unsigned long end_pfn,
 555                                struct list_head *freelist,
 556                                unsigned int stride,
 557                                bool strict)
 558{
 559        int nr_scanned = 0, total_isolated = 0;
 560        struct page *cursor;
 561        unsigned long flags = 0;
 562        bool locked = false;
 563        unsigned long blockpfn = *start_pfn;
 564        unsigned int order;
 565
 566        /* Strict mode is for isolation, speed is secondary */
 567        if (strict)
 568                stride = 1;
 569
 570        cursor = pfn_to_page(blockpfn);
 571
 572        /* Isolate free pages. */
 573        for (; blockpfn < end_pfn; blockpfn += stride, cursor += stride) {
 574                int isolated;
 575                struct page *page = cursor;
 576
 577                /*
 578                 * Periodically drop the lock (if held) regardless of its
 579                 * contention, to give chance to IRQs. Abort if fatal signal
 580                 * pending or async compaction detects need_resched()
 581                 */
 582                if (!(blockpfn % SWAP_CLUSTER_MAX)
 583                    && compact_unlock_should_abort(&cc->zone->lock, flags,
 584                                                                &locked, cc))
 585                        break;
 586
 587                nr_scanned++;
 588                if (!pfn_valid_within(blockpfn))
 589                        goto isolate_fail;
 590
 591                /*
 592                 * For compound pages such as THP and hugetlbfs, we can save
 593                 * potentially a lot of iterations if we skip them at once.
 594                 * The check is racy, but we can consider only valid values
 595                 * and the only danger is skipping too much.
 596                 */
 597                if (PageCompound(page)) {
 598                        const unsigned int order = compound_order(page);
 599
 600                        if (likely(order < MAX_ORDER)) {
 601                                blockpfn += (1UL << order) - 1;
 602                                cursor += (1UL << order) - 1;
 603                        }
 604                        goto isolate_fail;
 605                }
 606
 607                if (!PageBuddy(page))
 608                        goto isolate_fail;
 609
 610                /*
 611                 * If we already hold the lock, we can skip some rechecking.
 612                 * Note that if we hold the lock now, checked_pageblock was
 613                 * already set in some previous iteration (or strict is true),
 614                 * so it is correct to skip the suitable migration target
 615                 * recheck as well.
 616                 */
 617                if (!locked) {
 618                        locked = compact_lock_irqsave(&cc->zone->lock,
 619                                                                &flags, cc);
 620
 621                        /* Recheck this is a buddy page under lock */
 622                        if (!PageBuddy(page))
 623                                goto isolate_fail;
 624                }
 625
 626                /* Found a free page, will break it into order-0 pages */
 627                order = buddy_order(page);
 628                isolated = __isolate_free_page(page, order);
 629                if (!isolated)
 630                        break;
 631                set_page_private(page, order);
 632
 633                total_isolated += isolated;
 634                cc->nr_freepages += isolated;
 635                list_add_tail(&page->lru, freelist);
 636
 637                if (!strict && cc->nr_migratepages <= cc->nr_freepages) {
 638                        blockpfn += isolated;
 639                        break;
 640                }
 641                /* Advance to the end of split page */
 642                blockpfn += isolated - 1;
 643                cursor += isolated - 1;
 644                continue;
 645
 646isolate_fail:
 647                if (strict)
 648                        break;
 649                else
 650                        continue;
 651
 652        }
 653
 654        if (locked)
 655                spin_unlock_irqrestore(&cc->zone->lock, flags);
 656
 657        /*
 658         * There is a tiny chance that we have read bogus compound_order(),
 659         * so be careful to not go outside of the pageblock.
 660         */
 661        if (unlikely(blockpfn > end_pfn))
 662                blockpfn = end_pfn;
 663
 664        trace_mm_compaction_isolate_freepages(*start_pfn, blockpfn,
 665                                        nr_scanned, total_isolated);
 666
 667        /* Record how far we have got within the block */
 668        *start_pfn = blockpfn;
 669
 670        /*
 671         * If strict isolation is requested by CMA then check that all the
 672         * pages requested were isolated. If there were any failures, 0 is
 673         * returned and CMA will fail.
 674         */
 675        if (strict && blockpfn < end_pfn)
 676                total_isolated = 0;
 677
 678        cc->total_free_scanned += nr_scanned;
 679        if (total_isolated)
 680                count_compact_events(COMPACTISOLATED, total_isolated);
 681        return total_isolated;
 682}
 683
 684/**
 685 * isolate_freepages_range() - isolate free pages.
 686 * @cc:        Compaction control structure.
 687 * @start_pfn: The first PFN to start isolating.
 688 * @end_pfn:   The one-past-last PFN.
 689 *
 690 * Non-free pages, invalid PFNs, or zone boundaries within the
 691 * [start_pfn, end_pfn) range are considered errors, cause function to
 692 * undo its actions and return zero.
 693 *
 694 * Otherwise, function returns one-past-the-last PFN of isolated page
 695 * (which may be greater then end_pfn if end fell in a middle of
 696 * a free page).
 697 */
 698unsigned long
 699isolate_freepages_range(struct compact_control *cc,
 700                        unsigned long start_pfn, unsigned long end_pfn)
 701{
 702        unsigned long isolated, pfn, block_start_pfn, block_end_pfn;
 703        LIST_HEAD(freelist);
 704
 705        pfn = start_pfn;
 706        block_start_pfn = pageblock_start_pfn(pfn);
 707        if (block_start_pfn < cc->zone->zone_start_pfn)
 708                block_start_pfn = cc->zone->zone_start_pfn;
 709        block_end_pfn = pageblock_end_pfn(pfn);
 710
 711        for (; pfn < end_pfn; pfn += isolated,
 712                                block_start_pfn = block_end_pfn,
 713                                block_end_pfn += pageblock_nr_pages) {
 714                /* Protect pfn from changing by isolate_freepages_block */
 715                unsigned long isolate_start_pfn = pfn;
 716
 717                block_end_pfn = min(block_end_pfn, end_pfn);
 718
 719                /*
 720                 * pfn could pass the block_end_pfn if isolated freepage
 721                 * is more than pageblock order. In this case, we adjust
 722                 * scanning range to right one.
 723                 */
 724                if (pfn >= block_end_pfn) {
 725                        block_start_pfn = pageblock_start_pfn(pfn);
 726                        block_end_pfn = pageblock_end_pfn(pfn);
 727                        block_end_pfn = min(block_end_pfn, end_pfn);
 728                }
 729
 730                if (!pageblock_pfn_to_page(block_start_pfn,
 731                                        block_end_pfn, cc->zone))
 732                        break;
 733
 734                isolated = isolate_freepages_block(cc, &isolate_start_pfn,
 735                                        block_end_pfn, &freelist, 0, true);
 736
 737                /*
 738                 * In strict mode, isolate_freepages_block() returns 0 if
 739                 * there are any holes in the block (ie. invalid PFNs or
 740                 * non-free pages).
 741                 */
 742                if (!isolated)
 743                        break;
 744
 745                /*
 746                 * If we managed to isolate pages, it is always (1 << n) *
 747                 * pageblock_nr_pages for some non-negative n.  (Max order
 748                 * page may span two pageblocks).
 749                 */
 750        }
 751
 752        /* __isolate_free_page() does not map the pages */
 753        split_map_pages(&freelist);
 754
 755        if (pfn < end_pfn) {
 756                /* Loop terminated early, cleanup. */
 757                release_freepages(&freelist);
 758                return 0;
 759        }
 760
 761        /* We don't use freelists for anything. */
 762        return pfn;
 763}
 764
 765/* Similar to reclaim, but different enough that they don't share logic */
 766static bool too_many_isolated(pg_data_t *pgdat)
 767{
 768        unsigned long active, inactive, isolated;
 769
 770        inactive = node_page_state(pgdat, NR_INACTIVE_FILE) +
 771                        node_page_state(pgdat, NR_INACTIVE_ANON);
 772        active = node_page_state(pgdat, NR_ACTIVE_FILE) +
 773                        node_page_state(pgdat, NR_ACTIVE_ANON);
 774        isolated = node_page_state(pgdat, NR_ISOLATED_FILE) +
 775                        node_page_state(pgdat, NR_ISOLATED_ANON);
 776
 777        return isolated > (inactive + active) / 2;
 778}
 779
 780/**
 781 * isolate_migratepages_block() - isolate all migrate-able pages within
 782 *                                a single pageblock
 783 * @cc:         Compaction control structure.
 784 * @low_pfn:    The first PFN to isolate
 785 * @end_pfn:    The one-past-the-last PFN to isolate, within same pageblock
 786 * @isolate_mode: Isolation mode to be used.
 787 *
 788 * Isolate all pages that can be migrated from the range specified by
 789 * [low_pfn, end_pfn). The range is expected to be within same pageblock.
 790 * Returns errno, like -EAGAIN or -EINTR in case e.g signal pending or congestion,
 791 * -ENOMEM in case we could not allocate a page, or 0.
 792 * cc->migrate_pfn will contain the next pfn to scan.
 793 *
 794 * The pages are isolated on cc->migratepages list (not required to be empty),
 795 * and cc->nr_migratepages is updated accordingly.
 796 */
 797static int
 798isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 799                        unsigned long end_pfn, isolate_mode_t isolate_mode)
 800{
 801        pg_data_t *pgdat = cc->zone->zone_pgdat;
 802        unsigned long nr_scanned = 0, nr_isolated = 0;
 803        struct lruvec *lruvec;
 804        unsigned long flags = 0;
 805        struct lruvec *locked = NULL;
 806        struct page *page = NULL, *valid_page = NULL;
 807        unsigned long start_pfn = low_pfn;
 808        bool skip_on_failure = false;
 809        unsigned long next_skip_pfn = 0;
 810        bool skip_updated = false;
 811        int ret = 0;
 812
 813        cc->migrate_pfn = low_pfn;
 814
 815        /*
 816         * Ensure that there are not too many pages isolated from the LRU
 817         * list by either parallel reclaimers or compaction. If there are,
 818         * delay for some time until fewer pages are isolated
 819         */
 820        while (unlikely(too_many_isolated(pgdat))) {
 821                /* stop isolation if there are still pages not migrated */
 822                if (cc->nr_migratepages)
 823                        return -EAGAIN;
 824
 825                /* async migration should just abort */
 826                if (cc->mode == MIGRATE_ASYNC)
 827                        return -EAGAIN;
 828
 829                congestion_wait(BLK_RW_ASYNC, HZ/10);
 830
 831                if (fatal_signal_pending(current))
 832                        return -EINTR;
 833        }
 834
 835        cond_resched();
 836
 837        if (cc->direct_compaction && (cc->mode == MIGRATE_ASYNC)) {
 838                skip_on_failure = true;
 839                next_skip_pfn = block_end_pfn(low_pfn, cc->order);
 840        }
 841
 842        /* Time to isolate some pages for migration */
 843        for (; low_pfn < end_pfn; low_pfn++) {
 844
 845                if (skip_on_failure && low_pfn >= next_skip_pfn) {
 846                        /*
 847                         * We have isolated all migration candidates in the
 848                         * previous order-aligned block, and did not skip it due
 849                         * to failure. We should migrate the pages now and
 850                         * hopefully succeed compaction.
 851                         */
 852                        if (nr_isolated)
 853                                break;
 854
 855                        /*
 856                         * We failed to isolate in the previous order-aligned
 857                         * block. Set the new boundary to the end of the
 858                         * current block. Note we can't simply increase
 859                         * next_skip_pfn by 1 << order, as low_pfn might have
 860                         * been incremented by a higher number due to skipping
 861                         * a compound or a high-order buddy page in the
 862                         * previous loop iteration.
 863                         */
 864                        next_skip_pfn = block_end_pfn(low_pfn, cc->order);
 865                }
 866
 867                /*
 868                 * Periodically drop the lock (if held) regardless of its
 869                 * contention, to give chance to IRQs. Abort completely if
 870                 * a fatal signal is pending.
 871                 */
 872                if (!(low_pfn % SWAP_CLUSTER_MAX)) {
 873                        if (locked) {
 874                                unlock_page_lruvec_irqrestore(locked, flags);
 875                                locked = NULL;
 876                        }
 877
 878                        if (fatal_signal_pending(current)) {
 879                                cc->contended = true;
 880                                ret = -EINTR;
 881
 882                                goto fatal_pending;
 883                        }
 884
 885                        cond_resched();
 886                }
 887
 888                if (!pfn_valid_within(low_pfn))
 889                        goto isolate_fail;
 890                nr_scanned++;
 891
 892                page = pfn_to_page(low_pfn);
 893
 894                /*
 895                 * Check if the pageblock has already been marked skipped.
 896                 * Only the aligned PFN is checked as the caller isolates
 897                 * COMPACT_CLUSTER_MAX at a time so the second call must
 898                 * not falsely conclude that the block should be skipped.
 899                 */
 900                if (!valid_page && IS_ALIGNED(low_pfn, pageblock_nr_pages)) {
 901                        if (!cc->ignore_skip_hint && get_pageblock_skip(page)) {
 902                                low_pfn = end_pfn;
 903                                page = NULL;
 904                                goto isolate_abort;
 905                        }
 906                        valid_page = page;
 907                }
 908
 909                if (PageHuge(page) && cc->alloc_contig) {
 910                        ret = isolate_or_dissolve_huge_page(page, &cc->migratepages);
 911
 912                        /*
 913                         * Fail isolation in case isolate_or_dissolve_huge_page()
 914                         * reports an error. In case of -ENOMEM, abort right away.
 915                         */
 916                        if (ret < 0) {
 917                                 /* Do not report -EBUSY down the chain */
 918                                if (ret == -EBUSY)
 919                                        ret = 0;
 920                                low_pfn += (1UL << compound_order(page)) - 1;
 921                                goto isolate_fail;
 922                        }
 923
 924                        if (PageHuge(page)) {
 925                                /*
 926                                 * Hugepage was successfully isolated and placed
 927                                 * on the cc->migratepages list.
 928                                 */
 929                                low_pfn += compound_nr(page) - 1;
 930                                goto isolate_success_no_list;
 931                        }
 932
 933                        /*
 934                         * Ok, the hugepage was dissolved. Now these pages are
 935                         * Buddy and cannot be re-allocated because they are
 936                         * isolated. Fall-through as the check below handles
 937                         * Buddy pages.
 938                         */
 939                }
 940
 941                /*
 942                 * Skip if free. We read page order here without zone lock
 943                 * which is generally unsafe, but the race window is small and
 944                 * the worst thing that can happen is that we skip some
 945                 * potential isolation targets.
 946                 */
 947                if (PageBuddy(page)) {
 948                        unsigned long freepage_order = buddy_order_unsafe(page);
 949
 950                        /*
 951                         * Without lock, we cannot be sure that what we got is
 952                         * a valid page order. Consider only values in the
 953                         * valid order range to prevent low_pfn overflow.
 954                         */
 955                        if (freepage_order > 0 && freepage_order < MAX_ORDER)
 956                                low_pfn += (1UL << freepage_order) - 1;
 957                        continue;
 958                }
 959
 960                /*
 961                 * Regardless of being on LRU, compound pages such as THP and
 962                 * hugetlbfs are not to be compacted unless we are attempting
 963                 * an allocation much larger than the huge page size (eg CMA).
 964                 * We can potentially save a lot of iterations if we skip them
 965                 * at once. The check is racy, but we can consider only valid
 966                 * values and the only danger is skipping too much.
 967                 */
 968                if (PageCompound(page) && !cc->alloc_contig) {
 969                        const unsigned int order = compound_order(page);
 970
 971                        if (likely(order < MAX_ORDER))
 972                                low_pfn += (1UL << order) - 1;
 973                        goto isolate_fail;
 974                }
 975
 976                /*
 977                 * Check may be lockless but that's ok as we recheck later.
 978                 * It's possible to migrate LRU and non-lru movable pages.
 979                 * Skip any other type of page
 980                 */
 981                if (!PageLRU(page)) {
 982                        /*
 983                         * __PageMovable can return false positive so we need
 984                         * to verify it under page_lock.
 985                         */
 986                        if (unlikely(__PageMovable(page)) &&
 987                                        !PageIsolated(page)) {
 988                                if (locked) {
 989                                        unlock_page_lruvec_irqrestore(locked, flags);
 990                                        locked = NULL;
 991                                }
 992
 993                                if (!isolate_movable_page(page, isolate_mode))
 994                                        goto isolate_success;
 995                        }
 996
 997                        goto isolate_fail;
 998                }
 999
1000                /*
1001                 * Migration will fail if an anonymous page is pinned in memory,
1002                 * so avoid taking lru_lock and isolating it unnecessarily in an
1003                 * admittedly racy check.
1004                 */
1005                if (!page_mapping(page) &&
1006                    page_count(page) > page_mapcount(page))
1007                        goto isolate_fail;
1008
1009                /*
1010                 * Only allow to migrate anonymous pages in GFP_NOFS context
1011                 * because those do not depend on fs locks.
1012                 */
1013                if (!(cc->gfp_mask & __GFP_FS) && page_mapping(page))
1014                        goto isolate_fail;
1015
1016                /*
1017                 * Be careful not to clear PageLRU until after we're
1018                 * sure the page is not being freed elsewhere -- the
1019                 * page release code relies on it.
1020                 */
1021                if (unlikely(!get_page_unless_zero(page)))
1022                        goto isolate_fail;
1023
1024                if (!__isolate_lru_page_prepare(page, isolate_mode))
1025                        goto isolate_fail_put;
1026
1027                /* Try isolate the page */
1028                if (!TestClearPageLRU(page))
1029                        goto isolate_fail_put;
1030
1031                lruvec = mem_cgroup_page_lruvec(page);
1032
1033                /* If we already hold the lock, we can skip some rechecking */
1034                if (lruvec != locked) {
1035                        if (locked)
1036                                unlock_page_lruvec_irqrestore(locked, flags);
1037
1038                        compact_lock_irqsave(&lruvec->lru_lock, &flags, cc);
1039                        locked = lruvec;
1040
1041                        lruvec_memcg_debug(lruvec, page);
1042
1043                        /* Try get exclusive access under lock */
1044                        if (!skip_updated) {
1045                                skip_updated = true;
1046                                if (test_and_set_skip(cc, page, low_pfn))
1047                                        goto isolate_abort;
1048                        }
1049
1050                        /*
1051                         * Page become compound since the non-locked check,
1052                         * and it's on LRU. It can only be a THP so the order
1053                         * is safe to read and it's 0 for tail pages.
1054                         */
1055                        if (unlikely(PageCompound(page) && !cc->alloc_contig)) {
1056                                low_pfn += compound_nr(page) - 1;
1057                                SetPageLRU(page);
1058                                goto isolate_fail_put;
1059                        }
1060                }
1061
1062                /* The whole page is taken off the LRU; skip the tail pages. */
1063                if (PageCompound(page))
1064                        low_pfn += compound_nr(page) - 1;
1065
1066                /* Successfully isolated */
1067                del_page_from_lru_list(page, lruvec);
1068                mod_node_page_state(page_pgdat(page),
1069                                NR_ISOLATED_ANON + page_is_file_lru(page),
1070                                thp_nr_pages(page));
1071
1072isolate_success:
1073                list_add(&page->lru, &cc->migratepages);
1074isolate_success_no_list:
1075                cc->nr_migratepages += compound_nr(page);
1076                nr_isolated += compound_nr(page);
1077
1078                /*
1079                 * Avoid isolating too much unless this block is being
1080                 * rescanned (e.g. dirty/writeback pages, parallel allocation)
1081                 * or a lock is contended. For contention, isolate quickly to
1082                 * potentially remove one source of contention.
1083                 */
1084                if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX &&
1085                    !cc->rescan && !cc->contended) {
1086                        ++low_pfn;
1087                        break;
1088                }
1089
1090                continue;
1091
1092isolate_fail_put:
1093                /* Avoid potential deadlock in freeing page under lru_lock */
1094                if (locked) {
1095                        unlock_page_lruvec_irqrestore(locked, flags);
1096                        locked = NULL;
1097                }
1098                put_page(page);
1099
1100isolate_fail:
1101                if (!skip_on_failure && ret != -ENOMEM)
1102                        continue;
1103
1104                /*
1105                 * We have isolated some pages, but then failed. Release them
1106                 * instead of migrating, as we cannot form the cc->order buddy
1107                 * page anyway.
1108                 */
1109                if (nr_isolated) {
1110                        if (locked) {
1111                                unlock_page_lruvec_irqrestore(locked, flags);
1112                                locked = NULL;
1113                        }
1114                        putback_movable_pages(&cc->migratepages);
1115                        cc->nr_migratepages = 0;
1116                        nr_isolated = 0;
1117                }
1118
1119                if (low_pfn < next_skip_pfn) {
1120                        low_pfn = next_skip_pfn - 1;
1121                        /*
1122                         * The check near the loop beginning would have updated
1123                         * next_skip_pfn too, but this is a bit simpler.
1124                         */
1125                        next_skip_pfn += 1UL << cc->order;
1126                }
1127
1128                if (ret == -ENOMEM)
1129                        break;
1130        }
1131
1132        /*
1133         * The PageBuddy() check could have potentially brought us outside
1134         * the range to be scanned.
1135         */
1136        if (unlikely(low_pfn > end_pfn))
1137                low_pfn = end_pfn;
1138
1139        page = NULL;
1140
1141isolate_abort:
1142        if (locked)
1143                unlock_page_lruvec_irqrestore(locked, flags);
1144        if (page) {
1145                SetPageLRU(page);
1146                put_page(page);
1147        }
1148
1149        /*
1150         * Updated the cached scanner pfn once the pageblock has been scanned
1151         * Pages will either be migrated in which case there is no point
1152         * scanning in the near future or migration failed in which case the
1153         * failure reason may persist. The block is marked for skipping if
1154         * there were no pages isolated in the block or if the block is
1155         * rescanned twice in a row.
1156         */
1157        if (low_pfn == end_pfn && (!nr_isolated || cc->rescan)) {
1158                if (valid_page && !skip_updated)
1159                        set_pageblock_skip(valid_page);
1160                update_cached_migrate(cc, low_pfn);
1161        }
1162
1163        trace_mm_compaction_isolate_migratepages(start_pfn, low_pfn,
1164                                                nr_scanned, nr_isolated);
1165
1166fatal_pending:
1167        cc->total_migrate_scanned += nr_scanned;
1168        if (nr_isolated)
1169                count_compact_events(COMPACTISOLATED, nr_isolated);
1170
1171        cc->migrate_pfn = low_pfn;
1172
1173        return ret;
1174}
1175
1176/**
1177 * isolate_migratepages_range() - isolate migrate-able pages in a PFN range
1178 * @cc:        Compaction control structure.
1179 * @start_pfn: The first PFN to start isolating.
1180 * @end_pfn:   The one-past-last PFN.
1181 *
1182 * Returns -EAGAIN when contented, -EINTR in case of a signal pending, -ENOMEM
1183 * in case we could not allocate a page, or 0.
1184 */
1185int
1186isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn,
1187                                                        unsigned long end_pfn)
1188{
1189        unsigned long pfn, block_start_pfn, block_end_pfn;
1190        int ret = 0;
1191
1192        /* Scan block by block. First and last block may be incomplete */
1193        pfn = start_pfn;
1194        block_start_pfn = pageblock_start_pfn(pfn);
1195        if (block_start_pfn < cc->zone->zone_start_pfn)
1196                block_start_pfn = cc->zone->zone_start_pfn;
1197        block_end_pfn = pageblock_end_pfn(pfn);
1198
1199        for (; pfn < end_pfn; pfn = block_end_pfn,
1200                                block_start_pfn = block_end_pfn,
1201                                block_end_pfn += pageblock_nr_pages) {
1202
1203                block_end_pfn = min(block_end_pfn, end_pfn);
1204
1205                if (!pageblock_pfn_to_page(block_start_pfn,
1206                                        block_end_pfn, cc->zone))
1207                        continue;
1208
1209                ret = isolate_migratepages_block(cc, pfn, block_end_pfn,
1210                                                 ISOLATE_UNEVICTABLE);
1211
1212                if (ret)
1213                        break;
1214
1215                if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX)
1216                        break;
1217        }
1218
1219        return ret;
1220}
1221
1222#endif /* CONFIG_COMPACTION || CONFIG_CMA */
1223#ifdef CONFIG_COMPACTION
1224
1225static bool suitable_migration_source(struct compact_control *cc,
1226                                                        struct page *page)
1227{
1228        int block_mt;
1229
1230        if (pageblock_skip_persistent(page))
1231                return false;
1232
1233        if ((cc->mode != MIGRATE_ASYNC) || !cc->direct_compaction)
1234                return true;
1235
1236        block_mt = get_pageblock_migratetype(page);
1237
1238        if (cc->migratetype == MIGRATE_MOVABLE)
1239                return is_migrate_movable(block_mt);
1240        else
1241                return block_mt == cc->migratetype;
1242}
1243
1244/* Returns true if the page is within a block suitable for migration to */
1245static bool suitable_migration_target(struct compact_control *cc,
1246                                                        struct page *page)
1247{
1248        /* If the page is a large free page, then disallow migration */
1249        if (PageBuddy(page)) {
1250                /*
1251                 * We are checking page_order without zone->lock taken. But
1252                 * the only small danger is that we skip a potentially suitable
1253                 * pageblock, so it's not worth to check order for valid range.
1254                 */
1255                if (buddy_order_unsafe(page) >= pageblock_order)
1256                        return false;
1257        }
1258
1259        if (cc->ignore_block_suitable)
1260                return true;
1261
1262        /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
1263        if (is_migrate_movable(get_pageblock_migratetype(page)))
1264                return true;
1265
1266        /* Otherwise skip the block */
1267        return false;
1268}
1269
1270static inline unsigned int
1271freelist_scan_limit(struct compact_control *cc)
1272{
1273        unsigned short shift = BITS_PER_LONG - 1;
1274
1275        return (COMPACT_CLUSTER_MAX >> min(shift, cc->fast_search_fail)) + 1;
1276}
1277
1278/*
1279 * Test whether the free scanner has reached the same or lower pageblock than
1280 * the migration scanner, and compaction should thus terminate.
1281 */
1282static inline bool compact_scanners_met(struct compact_control *cc)
1283{
1284        return (cc->free_pfn >> pageblock_order)
1285                <= (cc->migrate_pfn >> pageblock_order);
1286}
1287
1288/*
1289 * Used when scanning for a suitable migration target which scans freelists
1290 * in reverse. Reorders the list such as the unscanned pages are scanned
1291 * first on the next iteration of the free scanner
1292 */
1293static void
1294move_freelist_head(struct list_head *freelist, struct page *freepage)
1295{
1296        LIST_HEAD(sublist);
1297
1298        if (!list_is_last(freelist, &freepage->lru)) {
1299                list_cut_before(&sublist, freelist, &freepage->lru);
1300                list_splice_tail(&sublist, freelist);
1301        }
1302}
1303
1304/*
1305 * Similar to move_freelist_head except used by the migration scanner
1306 * when scanning forward. It's possible for these list operations to
1307 * move against each other if they search the free list exactly in
1308 * lockstep.
1309 */
1310static void
1311move_freelist_tail(struct list_head *freelist, struct page *freepage)
1312{
1313        LIST_HEAD(sublist);
1314
1315        if (!list_is_first(freelist, &freepage->lru)) {
1316                list_cut_position(&sublist, freelist, &freepage->lru);
1317                list_splice_tail(&sublist, freelist);
1318        }
1319}
1320
1321static void
1322fast_isolate_around(struct compact_control *cc, unsigned long pfn, unsigned long nr_isolated)
1323{
1324        unsigned long start_pfn, end_pfn;
1325        struct page *page;
1326
1327        /* Do not search around if there are enough pages already */
1328        if (cc->nr_freepages >= cc->nr_migratepages)
1329                return;
1330
1331        /* Minimise scanning during async compaction */
1332        if (cc->direct_compaction && cc->mode == MIGRATE_ASYNC)
1333                return;
1334
1335        /* Pageblock boundaries */
1336        start_pfn = max(pageblock_start_pfn(pfn), cc->zone->zone_start_pfn);
1337        end_pfn = min(pageblock_end_pfn(pfn), zone_end_pfn(cc->zone));
1338
1339        page = pageblock_pfn_to_page(start_pfn, end_pfn, cc->zone);
1340        if (!page)
1341                return;
1342
1343        /* Scan before */
1344        if (start_pfn != pfn) {
1345                isolate_freepages_block(cc, &start_pfn, pfn, &cc->freepages, 1, false);
1346                if (cc->nr_freepages >= cc->nr_migratepages)
1347                        return;
1348        }
1349
1350        /* Scan after */
1351        start_pfn = pfn + nr_isolated;
1352        if (start_pfn < end_pfn)
1353                isolate_freepages_block(cc, &start_pfn, end_pfn, &cc->freepages, 1, false);
1354
1355        /* Skip this pageblock in the future as it's full or nearly full */
1356        if (cc->nr_freepages < cc->nr_migratepages)
1357                set_pageblock_skip(page);
1358}
1359
1360/* Search orders in round-robin fashion */
1361static int next_search_order(struct compact_control *cc, int order)
1362{
1363        order--;
1364        if (order < 0)
1365                order = cc->order - 1;
1366
1367        /* Search wrapped around? */
1368        if (order == cc->search_order) {
1369                cc->search_order--;
1370                if (cc->search_order < 0)
1371                        cc->search_order = cc->order - 1;
1372                return -1;
1373        }
1374
1375        return order;
1376}
1377
1378static unsigned long
1379fast_isolate_freepages(struct compact_control *cc)
1380{
1381        unsigned int limit = max(1U, freelist_scan_limit(cc) >> 1);
1382        unsigned int nr_scanned = 0;
1383        unsigned long low_pfn, min_pfn, highest = 0;
1384        unsigned long nr_isolated = 0;
1385        unsigned long distance;
1386        struct page *page = NULL;
1387        bool scan_start = false;
1388        int order;
1389
1390        /* Full compaction passes in a negative order */
1391        if (cc->order <= 0)
1392                return cc->free_pfn;
1393
1394        /*
1395         * If starting the scan, use a deeper search and use the highest
1396         * PFN found if a suitable one is not found.
1397         */
1398        if (cc->free_pfn >= cc->zone->compact_init_free_pfn) {
1399                limit = pageblock_nr_pages >> 1;
1400                scan_start = true;
1401        }
1402
1403        /*
1404         * Preferred point is in the top quarter of the scan space but take
1405         * a pfn from the top half if the search is problematic.
1406         */
1407        distance = (cc->free_pfn - cc->migrate_pfn);
1408        low_pfn = pageblock_start_pfn(cc->free_pfn - (distance >> 2));
1409        min_pfn = pageblock_start_pfn(cc->free_pfn - (distance >> 1));
1410
1411        if (WARN_ON_ONCE(min_pfn > low_pfn))
1412                low_pfn = min_pfn;
1413
1414        /*
1415         * Search starts from the last successful isolation order or the next
1416         * order to search after a previous failure
1417         */
1418        cc->search_order = min_t(unsigned int, cc->order - 1, cc->search_order);
1419
1420        for (order = cc->search_order;
1421             !page && order >= 0;
1422             order = next_search_order(cc, order)) {
1423                struct free_area *area = &cc->zone->free_area[order];
1424                struct list_head *freelist;
1425                struct page *freepage;
1426                unsigned long flags;
1427                unsigned int order_scanned = 0;
1428                unsigned long high_pfn = 0;
1429
1430                if (!area->nr_free)
1431                        continue;
1432
1433                spin_lock_irqsave(&cc->zone->lock, flags);
1434                freelist = &area->free_list[MIGRATE_MOVABLE];
1435                list_for_each_entry_reverse(freepage, freelist, lru) {
1436                        unsigned long pfn;
1437
1438                        order_scanned++;
1439                        nr_scanned++;
1440                        pfn = page_to_pfn(freepage);
1441
1442                        if (pfn >= highest)
1443                                highest = max(pageblock_start_pfn(pfn),
1444                                              cc->zone->zone_start_pfn);
1445
1446                        if (pfn >= low_pfn) {
1447                                cc->fast_search_fail = 0;
1448                                cc->search_order = order;
1449                                page = freepage;
1450                                break;
1451                        }
1452
1453                        if (pfn >= min_pfn && pfn > high_pfn) {
1454                                high_pfn = pfn;
1455
1456                                /* Shorten the scan if a candidate is found */
1457                                limit >>= 1;
1458                        }
1459
1460                        if (order_scanned >= limit)
1461                                break;
1462                }
1463
1464                /* Use a minimum pfn if a preferred one was not found */
1465                if (!page && high_pfn) {
1466                        page = pfn_to_page(high_pfn);
1467
1468                        /* Update freepage for the list reorder below */
1469                        freepage = page;
1470                }
1471
1472                /* Reorder to so a future search skips recent pages */
1473                move_freelist_head(freelist, freepage);
1474
1475                /* Isolate the page if available */
1476                if (page) {
1477                        if (__isolate_free_page(page, order)) {
1478                                set_page_private(page, order);
1479                                nr_isolated = 1 << order;
1480                                cc->nr_freepages += nr_isolated;
1481                                list_add_tail(&page->lru, &cc->freepages);
1482                                count_compact_events(COMPACTISOLATED, nr_isolated);
1483                        } else {
1484                                /* If isolation fails, abort the search */
1485                                order = cc->search_order + 1;
1486                                page = NULL;
1487                        }
1488                }
1489
1490                spin_unlock_irqrestore(&cc->zone->lock, flags);
1491
1492                /*
1493                 * Smaller scan on next order so the total scan is related
1494                 * to freelist_scan_limit.
1495                 */
1496                if (order_scanned >= limit)
1497                        limit = max(1U, limit >> 1);
1498        }
1499
1500        if (!page) {
1501                cc->fast_search_fail++;
1502                if (scan_start) {
1503                        /*
1504                         * Use the highest PFN found above min. If one was
1505                         * not found, be pessimistic for direct compaction
1506                         * and use the min mark.
1507                         */
1508                        if (highest) {
1509                                page = pfn_to_page(highest);
1510                                cc->free_pfn = highest;
1511                        } else {
1512                                if (cc->direct_compaction && pfn_valid(min_pfn)) {
1513                                        page = pageblock_pfn_to_page(min_pfn,
1514                                                min(pageblock_end_pfn(min_pfn),
1515                                                    zone_end_pfn(cc->zone)),
1516                                                cc->zone);
1517                                        cc->free_pfn = min_pfn;
1518                                }
1519                        }
1520                }
1521        }
1522
1523        if (highest && highest >= cc->zone->compact_cached_free_pfn) {
1524                highest -= pageblock_nr_pages;
1525                cc->zone->compact_cached_free_pfn = highest;
1526        }
1527
1528        cc->total_free_scanned += nr_scanned;
1529        if (!page)
1530                return cc->free_pfn;
1531
1532        low_pfn = page_to_pfn(page);
1533        fast_isolate_around(cc, low_pfn, nr_isolated);
1534        return low_pfn;
1535}
1536
1537/*
1538 * Based on information in the current compact_control, find blocks
1539 * suitable for isolating free pages from and then isolate them.
1540 */
1541static void isolate_freepages(struct compact_control *cc)
1542{
1543        struct zone *zone = cc->zone;
1544        struct page *page;
1545        unsigned long block_start_pfn;  /* start of current pageblock */
1546        unsigned long isolate_start_pfn; /* exact pfn we start at */
1547        unsigned long block_end_pfn;    /* end of current pageblock */
1548        unsigned long low_pfn;       /* lowest pfn scanner is able to scan */
1549        struct list_head *freelist = &cc->freepages;
1550        unsigned int stride;
1551
1552        /* Try a small search of the free lists for a candidate */
1553        isolate_start_pfn = fast_isolate_freepages(cc);
1554        if (cc->nr_freepages)
1555                goto splitmap;
1556
1557        /*
1558         * Initialise the free scanner. The starting point is where we last
1559         * successfully isolated from, zone-cached value, or the end of the
1560         * zone when isolating for the first time. For looping we also need
1561         * this pfn aligned down to the pageblock boundary, because we do
1562         * block_start_pfn -= pageblock_nr_pages in the for loop.
1563         * For ending point, take care when isolating in last pageblock of a
1564         * zone which ends in the middle of a pageblock.
1565         * The low boundary is the end of the pageblock the migration scanner
1566         * is using.
1567         */
1568        isolate_start_pfn = cc->free_pfn;
1569        block_start_pfn = pageblock_start_pfn(isolate_start_pfn);
1570        block_end_pfn = min(block_start_pfn + pageblock_nr_pages,
1571                                                zone_end_pfn(zone));
1572        low_pfn = pageblock_end_pfn(cc->migrate_pfn);
1573        stride = cc->mode == MIGRATE_ASYNC ? COMPACT_CLUSTER_MAX : 1;
1574
1575        /*
1576         * Isolate free pages until enough are available to migrate the
1577         * pages on cc->migratepages. We stop searching if the migrate
1578         * and free page scanners meet or enough free pages are isolated.
1579         */
1580        for (; block_start_pfn >= low_pfn;
1581                                block_end_pfn = block_start_pfn,
1582                                block_start_pfn -= pageblock_nr_pages,
1583                                isolate_start_pfn = block_start_pfn) {
1584                unsigned long nr_isolated;
1585
1586                /*
1587                 * This can iterate a massively long zone without finding any
1588                 * suitable migration targets, so periodically check resched.
1589                 */
1590                if (!(block_start_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages)))
1591                        cond_resched();
1592
1593                page = pageblock_pfn_to_page(block_start_pfn, block_end_pfn,
1594                                                                        zone);
1595                if (!page)
1596                        continue;
1597
1598                /* Check the block is suitable for migration */
1599                if (!suitable_migration_target(cc, page))
1600                        continue;
1601
1602                /* If isolation recently failed, do not retry */
1603                if (!isolation_suitable(cc, page))
1604                        continue;
1605
1606                /* Found a block suitable for isolating free pages from. */
1607                nr_isolated = isolate_freepages_block(cc, &isolate_start_pfn,
1608                                        block_end_pfn, freelist, stride, false);
1609
1610                /* Update the skip hint if the full pageblock was scanned */
1611                if (isolate_start_pfn == block_end_pfn)
1612                        update_pageblock_skip(cc, page, block_start_pfn);
1613
1614                /* Are enough freepages isolated? */
1615                if (cc->nr_freepages >= cc->nr_migratepages) {
1616                        if (isolate_start_pfn >= block_end_pfn) {
1617                                /*
1618                                 * Restart at previous pageblock if more
1619                                 * freepages can be isolated next time.
1620                                 */
1621                                isolate_start_pfn =
1622                                        block_start_pfn - pageblock_nr_pages;
1623                        }
1624                        break;
1625                } else if (isolate_start_pfn < block_end_pfn) {
1626                        /*
1627                         * If isolation failed early, do not continue
1628                         * needlessly.
1629                         */
1630                        break;
1631                }
1632
1633                /* Adjust stride depending on isolation */
1634                if (nr_isolated) {
1635                        stride = 1;
1636                        continue;
1637                }
1638                stride = min_t(unsigned int, COMPACT_CLUSTER_MAX, stride << 1);
1639        }
1640
1641        /*
1642         * Record where the free scanner will restart next time. Either we
1643         * broke from the loop and set isolate_start_pfn based on the last
1644         * call to isolate_freepages_block(), or we met the migration scanner
1645         * and the loop terminated due to isolate_start_pfn < low_pfn
1646         */
1647        cc->free_pfn = isolate_start_pfn;
1648
1649splitmap:
1650        /* __isolate_free_page() does not map the pages */
1651        split_map_pages(freelist);
1652}
1653
1654/*
1655 * This is a migrate-callback that "allocates" freepages by taking pages
1656 * from the isolated freelists in the block we are migrating to.
1657 */
1658static struct page *compaction_alloc(struct page *migratepage,
1659                                        unsigned long data)
1660{
1661        struct compact_control *cc = (struct compact_control *)data;
1662        struct page *freepage;
1663
1664        if (list_empty(&cc->freepages)) {
1665                isolate_freepages(cc);
1666
1667                if (list_empty(&cc->freepages))
1668                        return NULL;
1669        }
1670
1671        freepage = list_entry(cc->freepages.next, struct page, lru);
1672        list_del(&freepage->lru);
1673        cc->nr_freepages--;
1674
1675        return freepage;
1676}
1677
1678/*
1679 * This is a migrate-callback that "frees" freepages back to the isolated
1680 * freelist.  All pages on the freelist are from the same zone, so there is no
1681 * special handling needed for NUMA.
1682 */
1683static void compaction_free(struct page *page, unsigned long data)
1684{
1685        struct compact_control *cc = (struct compact_control *)data;
1686
1687        list_add(&page->lru, &cc->freepages);
1688        cc->nr_freepages++;
1689}
1690
1691/* possible outcome of isolate_migratepages */
1692typedef enum {
1693        ISOLATE_ABORT,          /* Abort compaction now */
1694        ISOLATE_NONE,           /* No pages isolated, continue scanning */
1695        ISOLATE_SUCCESS,        /* Pages isolated, migrate */
1696} isolate_migrate_t;
1697
1698/*
1699 * Allow userspace to control policy on scanning the unevictable LRU for
1700 * compactable pages.
1701 */
1702#ifdef CONFIG_PREEMPT_RT
1703int sysctl_compact_unevictable_allowed __read_mostly = 0;
1704#else
1705int sysctl_compact_unevictable_allowed __read_mostly = 1;
1706#endif
1707
1708static inline void
1709update_fast_start_pfn(struct compact_control *cc, unsigned long pfn)
1710{
1711        if (cc->fast_start_pfn == ULONG_MAX)
1712                return;
1713
1714        if (!cc->fast_start_pfn)
1715                cc->fast_start_pfn = pfn;
1716
1717        cc->fast_start_pfn = min(cc->fast_start_pfn, pfn);
1718}
1719
1720static inline unsigned long
1721reinit_migrate_pfn(struct compact_control *cc)
1722{
1723        if (!cc->fast_start_pfn || cc->fast_start_pfn == ULONG_MAX)
1724                return cc->migrate_pfn;
1725
1726        cc->migrate_pfn = cc->fast_start_pfn;
1727        cc->fast_start_pfn = ULONG_MAX;
1728
1729        return cc->migrate_pfn;
1730}
1731
1732/*
1733 * Briefly search the free lists for a migration source that already has
1734 * some free pages to reduce the number of pages that need migration
1735 * before a pageblock is free.
1736 */
1737static unsigned long fast_find_migrateblock(struct compact_control *cc)
1738{
1739        unsigned int limit = freelist_scan_limit(cc);
1740        unsigned int nr_scanned = 0;
1741        unsigned long distance;
1742        unsigned long pfn = cc->migrate_pfn;
1743        unsigned long high_pfn;
1744        int order;
1745        bool found_block = false;
1746
1747        /* Skip hints are relied on to avoid repeats on the fast search */
1748        if (cc->ignore_skip_hint)
1749                return pfn;
1750
1751        /*
1752         * If the migrate_pfn is not at the start of a zone or the start
1753         * of a pageblock then assume this is a continuation of a previous
1754         * scan restarted due to COMPACT_CLUSTER_MAX.
1755         */
1756        if (pfn != cc->zone->zone_start_pfn && pfn != pageblock_start_pfn(pfn))
1757                return pfn;
1758
1759        /*
1760         * For smaller orders, just linearly scan as the number of pages
1761         * to migrate should be relatively small and does not necessarily
1762         * justify freeing up a large block for a small allocation.
1763         */
1764        if (cc->order <= PAGE_ALLOC_COSTLY_ORDER)
1765                return pfn;
1766
1767        /*
1768         * Only allow kcompactd and direct requests for movable pages to
1769         * quickly clear out a MOVABLE pageblock for allocation. This
1770         * reduces the risk that a large movable pageblock is freed for
1771         * an unmovable/reclaimable small allocation.
1772         */
1773        if (cc->direct_compaction && cc->migratetype != MIGRATE_MOVABLE)
1774                return pfn;
1775
1776        /*
1777         * When starting the migration scanner, pick any pageblock within the
1778         * first half of the search space. Otherwise try and pick a pageblock
1779         * within the first eighth to reduce the chances that a migration
1780         * target later becomes a source.
1781         */
1782        distance = (cc->free_pfn - cc->migrate_pfn) >> 1;
1783        if (cc->migrate_pfn != cc->zone->zone_start_pfn)
1784                distance >>= 2;
1785        high_pfn = pageblock_start_pfn(cc->migrate_pfn + distance);
1786
1787        for (order = cc->order - 1;
1788             order >= PAGE_ALLOC_COSTLY_ORDER && !found_block && nr_scanned < limit;
1789             order--) {
1790                struct free_area *area = &cc->zone->free_area[order];
1791                struct list_head *freelist;
1792                unsigned long flags;
1793                struct page *freepage;
1794
1795                if (!area->nr_free)
1796                        continue;
1797
1798                spin_lock_irqsave(&cc->zone->lock, flags);
1799                freelist = &area->free_list[MIGRATE_MOVABLE];
1800                list_for_each_entry(freepage, freelist, lru) {
1801                        unsigned long free_pfn;
1802
1803                        if (nr_scanned++ >= limit) {
1804                                move_freelist_tail(freelist, freepage);
1805                                break;
1806                        }
1807
1808                        free_pfn = page_to_pfn(freepage);
1809                        if (free_pfn < high_pfn) {
1810                                /*
1811                                 * Avoid if skipped recently. Ideally it would
1812                                 * move to the tail but even safe iteration of
1813                                 * the list assumes an entry is deleted, not
1814                                 * reordered.
1815                                 */
1816                                if (get_pageblock_skip(freepage))
1817                                        continue;
1818
1819                                /* Reorder to so a future search skips recent pages */
1820                                move_freelist_tail(freelist, freepage);
1821
1822                                update_fast_start_pfn(cc, free_pfn);
1823                                pfn = pageblock_start_pfn(free_pfn);
1824                                cc->fast_search_fail = 0;
1825                                found_block = true;
1826                                set_pageblock_skip(freepage);
1827                                break;
1828                        }
1829                }
1830                spin_unlock_irqrestore(&cc->zone->lock, flags);
1831        }
1832
1833        cc->total_migrate_scanned += nr_scanned;
1834
1835        /*
1836         * If fast scanning failed then use a cached entry for a page block
1837         * that had free pages as the basis for starting a linear scan.
1838         */
1839        if (!found_block) {
1840                cc->fast_search_fail++;
1841                pfn = reinit_migrate_pfn(cc);
1842        }
1843        return pfn;
1844}
1845
1846/*
1847 * Isolate all pages that can be migrated from the first suitable block,
1848 * starting at the block pointed to by the migrate scanner pfn within
1849 * compact_control.
1850 */
1851static isolate_migrate_t isolate_migratepages(struct compact_control *cc)
1852{
1853        unsigned long block_start_pfn;
1854        unsigned long block_end_pfn;
1855        unsigned long low_pfn;
1856        struct page *page;
1857        const isolate_mode_t isolate_mode =
1858                (sysctl_compact_unevictable_allowed ? ISOLATE_UNEVICTABLE : 0) |
1859                (cc->mode != MIGRATE_SYNC ? ISOLATE_ASYNC_MIGRATE : 0);
1860        bool fast_find_block;
1861
1862        /*
1863         * Start at where we last stopped, or beginning of the zone as
1864         * initialized by compact_zone(). The first failure will use
1865         * the lowest PFN as the starting point for linear scanning.
1866         */
1867        low_pfn = fast_find_migrateblock(cc);
1868        block_start_pfn = pageblock_start_pfn(low_pfn);
1869        if (block_start_pfn < cc->zone->zone_start_pfn)
1870                block_start_pfn = cc->zone->zone_start_pfn;
1871
1872        /*
1873         * fast_find_migrateblock marks a pageblock skipped so to avoid
1874         * the isolation_suitable check below, check whether the fast
1875         * search was successful.
1876         */
1877        fast_find_block = low_pfn != cc->migrate_pfn && !cc->fast_search_fail;
1878
1879        /* Only scan within a pageblock boundary */
1880        block_end_pfn = pageblock_end_pfn(low_pfn);
1881
1882        /*
1883         * Iterate over whole pageblocks until we find the first suitable.
1884         * Do not cross the free scanner.
1885         */
1886        for (; block_end_pfn <= cc->free_pfn;
1887                        fast_find_block = false,
1888                        cc->migrate_pfn = low_pfn = block_end_pfn,
1889                        block_start_pfn = block_end_pfn,
1890                        block_end_pfn += pageblock_nr_pages) {
1891
1892                /*
1893                 * This can potentially iterate a massively long zone with
1894                 * many pageblocks unsuitable, so periodically check if we
1895                 * need to schedule.
1896                 */
1897                if (!(low_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages)))
1898                        cond_resched();
1899
1900                page = pageblock_pfn_to_page(block_start_pfn,
1901                                                block_end_pfn, cc->zone);
1902                if (!page)
1903                        continue;
1904
1905                /*
1906                 * If isolation recently failed, do not retry. Only check the
1907                 * pageblock once. COMPACT_CLUSTER_MAX causes a pageblock
1908                 * to be visited multiple times. Assume skip was checked
1909                 * before making it "skip" so other compaction instances do
1910                 * not scan the same block.
1911                 */
1912                if (IS_ALIGNED(low_pfn, pageblock_nr_pages) &&
1913                    !fast_find_block && !isolation_suitable(cc, page))
1914                        continue;
1915
1916                /*
1917                 * For async compaction, also only scan in MOVABLE blocks
1918                 * without huge pages. Async compaction is optimistic to see
1919                 * if the minimum amount of work satisfies the allocation.
1920                 * The cached PFN is updated as it's possible that all
1921                 * remaining blocks between source and target are unsuitable
1922                 * and the compaction scanners fail to meet.
1923                 */
1924                if (!suitable_migration_source(cc, page)) {
1925                        update_cached_migrate(cc, block_end_pfn);
1926                        continue;
1927                }
1928
1929                /* Perform the isolation */
1930                if (isolate_migratepages_block(cc, low_pfn, block_end_pfn,
1931                                                isolate_mode))
1932                        return ISOLATE_ABORT;
1933
1934                /*
1935                 * Either we isolated something and proceed with migration. Or
1936                 * we failed and compact_zone should decide if we should
1937                 * continue or not.
1938                 */
1939                break;
1940        }
1941
1942        return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE;
1943}
1944
1945/*
1946 * order == -1 is expected when compacting via
1947 * /proc/sys/vm/compact_memory
1948 */
1949static inline bool is_via_compact_memory(int order)
1950{
1951        return order == -1;
1952}
1953
1954static bool kswapd_is_running(pg_data_t *pgdat)
1955{
1956        return pgdat->kswapd && task_is_running(pgdat->kswapd);
1957}
1958
1959/*
1960 * A zone's fragmentation score is the external fragmentation wrt to the
1961 * COMPACTION_HPAGE_ORDER. It returns a value in the range [0, 100].
1962 */
1963static unsigned int fragmentation_score_zone(struct zone *zone)
1964{
1965        return extfrag_for_order(zone, COMPACTION_HPAGE_ORDER);
1966}
1967
1968/*
1969 * A weighted zone's fragmentation score is the external fragmentation
1970 * wrt to the COMPACTION_HPAGE_ORDER scaled by the zone's size. It
1971 * returns a value in the range [0, 100].
1972 *
1973 * The scaling factor ensures that proactive compaction focuses on larger
1974 * zones like ZONE_NORMAL, rather than smaller, specialized zones like
1975 * ZONE_DMA32. For smaller zones, the score value remains close to zero,
1976 * and thus never exceeds the high threshold for proactive compaction.
1977 */
1978static unsigned int fragmentation_score_zone_weighted(struct zone *zone)
1979{
1980        unsigned long score;
1981
1982        score = zone->present_pages * fragmentation_score_zone(zone);
1983        return div64_ul(score, zone->zone_pgdat->node_present_pages + 1);
1984}
1985
1986/*
1987 * The per-node proactive (background) compaction process is started by its
1988 * corresponding kcompactd thread when the node's fragmentation score
1989 * exceeds the high threshold. The compaction process remains active till
1990 * the node's score falls below the low threshold, or one of the back-off
1991 * conditions is met.
1992 */
1993static unsigned int fragmentation_score_node(pg_data_t *pgdat)
1994{
1995        unsigned int score = 0;
1996        int zoneid;
1997
1998        for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
1999                struct zone *zone;
2000
2001                zone = &pgdat->node_zones[zoneid];
2002                score += fragmentation_score_zone_weighted(zone);
2003        }
2004
2005        return score;
2006}
2007
2008static unsigned int fragmentation_score_wmark(pg_data_t *pgdat, bool low)
2009{
2010        unsigned int wmark_low;
2011
2012        /*
2013         * Cap the low watermark to avoid excessive compaction
2014         * activity in case a user sets the proactiveness tunable
2015         * close to 100 (maximum).
2016         */
2017        wmark_low = max(100U - sysctl_compaction_proactiveness, 5U);
2018        return low ? wmark_low : min(wmark_low + 10, 100U);
2019}
2020
2021static bool should_proactive_compact_node(pg_data_t *pgdat)
2022{
2023        int wmark_high;
2024
2025        if (!sysctl_compaction_proactiveness || kswapd_is_running(pgdat))
2026                return false;
2027
2028        wmark_high = fragmentation_score_wmark(pgdat, false);
2029        return fragmentation_score_node(pgdat) > wmark_high;
2030}
2031
2032static enum compact_result __compact_finished(struct compact_control *cc)
2033{
2034        unsigned int order;
2035        const int migratetype = cc->migratetype;
2036        int ret;
2037
2038        /* Compaction run completes if the migrate and free scanner meet */
2039        if (compact_scanners_met(cc)) {
2040                /* Let the next compaction start anew. */
2041                reset_cached_positions(cc->zone);
2042
2043                /*
2044                 * Mark that the PG_migrate_skip information should be cleared
2045                 * by kswapd when it goes to sleep. kcompactd does not set the
2046                 * flag itself as the decision to be clear should be directly
2047                 * based on an allocation request.
2048                 */
2049                if (cc->direct_compaction)
2050                        cc->zone->compact_blockskip_flush = true;
2051
2052                if (cc->whole_zone)
2053                        return COMPACT_COMPLETE;
2054                else
2055                        return COMPACT_PARTIAL_SKIPPED;
2056        }
2057
2058        if (cc->proactive_compaction) {
2059                int score, wmark_low;
2060                pg_data_t *pgdat;
2061
2062                pgdat = cc->zone->zone_pgdat;
2063                if (kswapd_is_running(pgdat))
2064                        return COMPACT_PARTIAL_SKIPPED;
2065
2066                score = fragmentation_score_zone(cc->zone);
2067                wmark_low = fragmentation_score_wmark(pgdat, true);
2068
2069                if (score > wmark_low)
2070                        ret = COMPACT_CONTINUE;
2071                else
2072                        ret = COMPACT_SUCCESS;
2073
2074                goto out;
2075        }
2076
2077        if (is_via_compact_memory(cc->order))
2078                return COMPACT_CONTINUE;
2079
2080        /*
2081         * Always finish scanning a pageblock to reduce the possibility of
2082         * fallbacks in the future. This is particularly important when
2083         * migration source is unmovable/reclaimable but it's not worth
2084         * special casing.
2085         */
2086        if (!IS_ALIGNED(cc->migrate_pfn, pageblock_nr_pages))
2087                return COMPACT_CONTINUE;
2088
2089        /* Direct compactor: Is a suitable page free? */
2090        ret = COMPACT_NO_SUITABLE_PAGE;
2091        for (order = cc->order; order < MAX_ORDER; order++) {
2092                struct free_area *area = &cc->zone->free_area[order];
2093                bool can_steal;
2094
2095                /* Job done if page is free of the right migratetype */
2096                if (!free_area_empty(area, migratetype))
2097                        return COMPACT_SUCCESS;
2098
2099#ifdef CONFIG_CMA
2100                /* MIGRATE_MOVABLE can fallback on MIGRATE_CMA */
2101                if (migratetype == MIGRATE_MOVABLE &&
2102                        !free_area_empty(area, MIGRATE_CMA))
2103                        return COMPACT_SUCCESS;
2104#endif
2105                /*
2106                 * Job done if allocation would steal freepages from
2107                 * other migratetype buddy lists.
2108                 */
2109                if (find_suitable_fallback(area, order, migratetype,
2110                                                true, &can_steal) != -1) {
2111
2112                        /* movable pages are OK in any pageblock */
2113                        if (migratetype == MIGRATE_MOVABLE)
2114                                return COMPACT_SUCCESS;
2115
2116                        /*
2117                         * We are stealing for a non-movable allocation. Make
2118                         * sure we finish compacting the current pageblock
2119                         * first so it is as free as possible and we won't
2120                         * have to steal another one soon. This only applies
2121                         * to sync compaction, as async compaction operates
2122                         * on pageblocks of the same migratetype.
2123                         */
2124                        if (cc->mode == MIGRATE_ASYNC ||
2125                                        IS_ALIGNED(cc->migrate_pfn,
2126                                                        pageblock_nr_pages)) {
2127                                return COMPACT_SUCCESS;
2128                        }
2129
2130                        ret = COMPACT_CONTINUE;
2131                        break;
2132                }
2133        }
2134
2135out:
2136        if (cc->contended || fatal_signal_pending(current))
2137                ret = COMPACT_CONTENDED;
2138
2139        return ret;
2140}
2141
2142static enum compact_result compact_finished(struct compact_control *cc)
2143{
2144        int ret;
2145
2146        ret = __compact_finished(cc);
2147        trace_mm_compaction_finished(cc->zone, cc->order, ret);
2148        if (ret == COMPACT_NO_SUITABLE_PAGE)
2149                ret = COMPACT_CONTINUE;
2150
2151        return ret;
2152}
2153
2154static enum compact_result __compaction_suitable(struct zone *zone, int order,
2155                                        unsigned int alloc_flags,
2156                                        int highest_zoneidx,
2157                                        unsigned long wmark_target)
2158{
2159        unsigned long watermark;
2160
2161        if (is_via_compact_memory(order))
2162                return COMPACT_CONTINUE;
2163
2164        watermark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK);
2165        /*
2166         * If watermarks for high-order allocation are already met, there
2167         * should be no need for compaction at all.
2168         */
2169        if (zone_watermark_ok(zone, order, watermark, highest_zoneidx,
2170                                                                alloc_flags))
2171                return COMPACT_SUCCESS;
2172
2173        /*
2174         * Watermarks for order-0 must be met for compaction to be able to
2175         * isolate free pages for migration targets. This means that the
2176         * watermark and alloc_flags have to match, or be more pessimistic than
2177         * the check in __isolate_free_page(). We don't use the direct
2178         * compactor's alloc_flags, as they are not relevant for freepage
2179         * isolation. We however do use the direct compactor's highest_zoneidx
2180         * to skip over zones where lowmem reserves would prevent allocation
2181         * even if compaction succeeds.
2182         * For costly orders, we require low watermark instead of min for
2183         * compaction to proceed to increase its chances.
2184         * ALLOC_CMA is used, as pages in CMA pageblocks are considered
2185         * suitable migration targets
2186         */
2187        watermark = (order > PAGE_ALLOC_COSTLY_ORDER) ?
2188                                low_wmark_pages(zone) : min_wmark_pages(zone);
2189        watermark += compact_gap(order);
2190        if (!__zone_watermark_ok(zone, 0, watermark, highest_zoneidx,
2191                                                ALLOC_CMA, wmark_target))
2192                return COMPACT_SKIPPED;
2193
2194        return COMPACT_CONTINUE;
2195}
2196
2197/*
2198 * compaction_suitable: Is this suitable to run compaction on this zone now?
2199 * Returns
2200 *   COMPACT_SKIPPED  - If there are too few free pages for compaction
2201 *   COMPACT_SUCCESS  - If the allocation would succeed without compaction
2202 *   COMPACT_CONTINUE - If compaction should run now
2203 */
2204enum compact_result compaction_suitable(struct zone *zone, int order,
2205                                        unsigned int alloc_flags,
2206                                        int highest_zoneidx)
2207{
2208        enum compact_result ret;
2209        int fragindex;
2210
2211        ret = __compaction_suitable(zone, order, alloc_flags, highest_zoneidx,
2212                                    zone_page_state(zone, NR_FREE_PAGES));
2213        /*
2214         * fragmentation index determines if allocation failures are due to
2215         * low memory or external fragmentation
2216         *
2217         * index of -1000 would imply allocations might succeed depending on
2218         * watermarks, but we already failed the high-order watermark check
2219         * index towards 0 implies failure is due to lack of memory
2220         * index towards 1000 implies failure is due to fragmentation
2221         *
2222         * Only compact if a failure would be due to fragmentation. Also
2223         * ignore fragindex for non-costly orders where the alternative to
2224         * a successful reclaim/compaction is OOM. Fragindex and the
2225         * vm.extfrag_threshold sysctl is meant as a heuristic to prevent
2226         * excessive compaction for costly orders, but it should not be at the
2227         * expense of system stability.
2228         */
2229        if (ret == COMPACT_CONTINUE && (order > PAGE_ALLOC_COSTLY_ORDER)) {
2230                fragindex = fragmentation_index(zone, order);
2231                if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
2232                        ret = COMPACT_NOT_SUITABLE_ZONE;
2233        }
2234
2235        trace_mm_compaction_suitable(zone, order, ret);
2236        if (ret == COMPACT_NOT_SUITABLE_ZONE)
2237                ret = COMPACT_SKIPPED;
2238
2239        return ret;
2240}
2241
2242bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
2243                int alloc_flags)
2244{
2245        struct zone *zone;
2246        struct zoneref *z;
2247
2248        /*
2249         * Make sure at least one zone would pass __compaction_suitable if we continue
2250         * retrying the reclaim.
2251         */
2252        for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
2253                                ac->highest_zoneidx, ac->nodemask) {
2254                unsigned long available;
2255                enum compact_result compact_result;
2256
2257                /*
2258                 * Do not consider all the reclaimable memory because we do not
2259                 * want to trash just for a single high order allocation which
2260                 * is even not guaranteed to appear even if __compaction_suitable
2261                 * is happy about the watermark check.
2262                 */
2263                available = zone_reclaimable_pages(zone) / order;
2264                available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
2265                compact_result = __compaction_suitable(zone, order, alloc_flags,
2266                                ac->highest_zoneidx, available);
2267                if (compact_result != COMPACT_SKIPPED)
2268                        return true;
2269        }
2270
2271        return false;
2272}
2273
2274static enum compact_result
2275compact_zone(struct compact_control *cc, struct capture_control *capc)
2276{
2277        enum compact_result ret;
2278        unsigned long start_pfn = cc->zone->zone_start_pfn;
2279        unsigned long end_pfn = zone_end_pfn(cc->zone);
2280        unsigned long last_migrated_pfn;
2281        const bool sync = cc->mode != MIGRATE_ASYNC;
2282        bool update_cached;
2283
2284        /*
2285         * These counters track activities during zone compaction.  Initialize
2286         * them before compacting a new zone.
2287         */
2288        cc->total_migrate_scanned = 0;
2289        cc->total_free_scanned = 0;
2290        cc->nr_migratepages = 0;
2291        cc->nr_freepages = 0;
2292        INIT_LIST_HEAD(&cc->freepages);
2293        INIT_LIST_HEAD(&cc->migratepages);
2294
2295        cc->migratetype = gfp_migratetype(cc->gfp_mask);
2296        ret = compaction_suitable(cc->zone, cc->order, cc->alloc_flags,
2297                                                        cc->highest_zoneidx);
2298        /* Compaction is likely to fail */
2299        if (ret == COMPACT_SUCCESS || ret == COMPACT_SKIPPED)
2300                return ret;
2301
2302        /* huh, compaction_suitable is returning something unexpected */
2303        VM_BUG_ON(ret != COMPACT_CONTINUE);
2304
2305        /*
2306         * Clear pageblock skip if there were failures recently and compaction
2307         * is about to be retried after being deferred.
2308         */
2309        if (compaction_restarting(cc->zone, cc->order))
2310                __reset_isolation_suitable(cc->zone);
2311
2312        /*
2313         * Setup to move all movable pages to the end of the zone. Used cached
2314         * information on where the scanners should start (unless we explicitly
2315         * want to compact the whole zone), but check that it is initialised
2316         * by ensuring the values are within zone boundaries.
2317         */
2318        cc->fast_start_pfn = 0;
2319        if (cc->whole_zone) {
2320                cc->migrate_pfn = start_pfn;
2321                cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
2322        } else {
2323                cc->migrate_pfn = cc->zone->compact_cached_migrate_pfn[sync];
2324                cc->free_pfn = cc->zone->compact_cached_free_pfn;
2325                if (cc->free_pfn < start_pfn || cc->free_pfn >= end_pfn) {
2326                        cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
2327                        cc->zone->compact_cached_free_pfn = cc->free_pfn;
2328                }
2329                if (cc->migrate_pfn < start_pfn || cc->migrate_pfn >= end_pfn) {
2330                        cc->migrate_pfn = start_pfn;
2331                        cc->zone->compact_cached_migrate_pfn[0] = cc->migrate_pfn;
2332                        cc->zone->compact_cached_migrate_pfn[1] = cc->migrate_pfn;
2333                }
2334
2335                if (cc->migrate_pfn <= cc->zone->compact_init_migrate_pfn)
2336                        cc->whole_zone = true;
2337        }
2338
2339        last_migrated_pfn = 0;
2340
2341        /*
2342         * Migrate has separate cached PFNs for ASYNC and SYNC* migration on
2343         * the basis that some migrations will fail in ASYNC mode. However,
2344         * if the cached PFNs match and pageblocks are skipped due to having
2345         * no isolation candidates, then the sync state does not matter.
2346         * Until a pageblock with isolation candidates is found, keep the
2347         * cached PFNs in sync to avoid revisiting the same blocks.
2348         */
2349        update_cached = !sync &&
2350                cc->zone->compact_cached_migrate_pfn[0] == cc->zone->compact_cached_migrate_pfn[1];
2351
2352        trace_mm_compaction_begin(start_pfn, cc->migrate_pfn,
2353                                cc->free_pfn, end_pfn, sync);
2354
2355        /* lru_add_drain_all could be expensive with involving other CPUs */
2356        lru_add_drain();
2357
2358        while ((ret = compact_finished(cc)) == COMPACT_CONTINUE) {
2359                int err;
2360                unsigned long iteration_start_pfn = cc->migrate_pfn;
2361
2362                /*
2363                 * Avoid multiple rescans which can happen if a page cannot be
2364                 * isolated (dirty/writeback in async mode) or if the migrated
2365                 * pages are being allocated before the pageblock is cleared.
2366                 * The first rescan will capture the entire pageblock for
2367                 * migration. If it fails, it'll be marked skip and scanning
2368                 * will proceed as normal.
2369                 */
2370                cc->rescan = false;
2371                if (pageblock_start_pfn(last_migrated_pfn) ==
2372                    pageblock_start_pfn(iteration_start_pfn)) {
2373                        cc->rescan = true;
2374                }
2375
2376                switch (isolate_migratepages(cc)) {
2377                case ISOLATE_ABORT:
2378                        ret = COMPACT_CONTENDED;
2379                        putback_movable_pages(&cc->migratepages);
2380                        cc->nr_migratepages = 0;
2381                        goto out;
2382                case ISOLATE_NONE:
2383                        if (update_cached) {
2384                                cc->zone->compact_cached_migrate_pfn[1] =
2385                                        cc->zone->compact_cached_migrate_pfn[0];
2386                        }
2387
2388                        /*
2389                         * We haven't isolated and migrated anything, but
2390                         * there might still be unflushed migrations from
2391                         * previous cc->order aligned block.
2392                         */
2393                        goto check_drain;
2394                case ISOLATE_SUCCESS:
2395                        update_cached = false;
2396                        last_migrated_pfn = iteration_start_pfn;
2397                }
2398
2399                err = migrate_pages(&cc->migratepages, compaction_alloc,
2400                                compaction_free, (unsigned long)cc, cc->mode,
2401                                MR_COMPACTION);
2402
2403                trace_mm_compaction_migratepages(cc->nr_migratepages, err,
2404                                                        &cc->migratepages);
2405
2406                /* All pages were either migrated or will be released */
2407                cc->nr_migratepages = 0;
2408                if (err) {
2409                        putback_movable_pages(&cc->migratepages);
2410                        /*
2411                         * migrate_pages() may return -ENOMEM when scanners meet
2412                         * and we want compact_finished() to detect it
2413                         */
2414                        if (err == -ENOMEM && !compact_scanners_met(cc)) {
2415                                ret = COMPACT_CONTENDED;
2416                                goto out;
2417                        }
2418                        /*
2419                         * We failed to migrate at least one page in the current
2420                         * order-aligned block, so skip the rest of it.
2421                         */
2422                        if (cc->direct_compaction &&
2423                                                (cc->mode == MIGRATE_ASYNC)) {
2424                                cc->migrate_pfn = block_end_pfn(
2425                                                cc->migrate_pfn - 1, cc->order);
2426                                /* Draining pcplists is useless in this case */
2427                                last_migrated_pfn = 0;
2428                        }
2429                }
2430
2431check_drain:
2432                /*
2433                 * Has the migration scanner moved away from the previous
2434                 * cc->order aligned block where we migrated from? If yes,
2435                 * flush the pages that were freed, so that they can merge and
2436                 * compact_finished() can detect immediately if allocation
2437                 * would succeed.
2438                 */
2439                if (cc->order > 0 && last_migrated_pfn) {
2440                        unsigned long current_block_start =
2441                                block_start_pfn(cc->migrate_pfn, cc->order);
2442
2443                        if (last_migrated_pfn < current_block_start) {
2444                                lru_add_drain_cpu_zone(cc->zone);
2445                                /* No more flushing until we migrate again */
2446                                last_migrated_pfn = 0;
2447                        }
2448                }
2449
2450                /* Stop if a page has been captured */
2451                if (capc && capc->page) {
2452                        ret = COMPACT_SUCCESS;
2453                        break;
2454                }
2455        }
2456
2457out:
2458        /*
2459         * Release free pages and update where the free scanner should restart,
2460         * so we don't leave any returned pages behind in the next attempt.
2461         */
2462        if (cc->nr_freepages > 0) {
2463                unsigned long free_pfn = release_freepages(&cc->freepages);
2464
2465                cc->nr_freepages = 0;
2466                VM_BUG_ON(free_pfn == 0);
2467                /* The cached pfn is always the first in a pageblock */
2468                free_pfn = pageblock_start_pfn(free_pfn);
2469                /*
2470                 * Only go back, not forward. The cached pfn might have been
2471                 * already reset to zone end in compact_finished()
2472                 */
2473                if (free_pfn > cc->zone->compact_cached_free_pfn)
2474                        cc->zone->compact_cached_free_pfn = free_pfn;
2475        }
2476
2477        count_compact_events(COMPACTMIGRATE_SCANNED, cc->total_migrate_scanned);
2478        count_compact_events(COMPACTFREE_SCANNED, cc->total_free_scanned);
2479
2480        trace_mm_compaction_end(start_pfn, cc->migrate_pfn,
2481                                cc->free_pfn, end_pfn, sync, ret);
2482
2483        return ret;
2484}
2485
2486static enum compact_result compact_zone_order(struct zone *zone, int order,
2487                gfp_t gfp_mask, enum compact_priority prio,
2488                unsigned int alloc_flags, int highest_zoneidx,
2489                struct page **capture)
2490{
2491        enum compact_result ret;
2492        struct compact_control cc = {
2493                .order = order,
2494                .search_order = order,
2495                .gfp_mask = gfp_mask,
2496                .zone = zone,
2497                .mode = (prio == COMPACT_PRIO_ASYNC) ?
2498                                        MIGRATE_ASYNC : MIGRATE_SYNC_LIGHT,
2499                .alloc_flags = alloc_flags,
2500                .highest_zoneidx = highest_zoneidx,
2501                .direct_compaction = true,
2502                .whole_zone = (prio == MIN_COMPACT_PRIORITY),
2503                .ignore_skip_hint = (prio == MIN_COMPACT_PRIORITY),
2504                .ignore_block_suitable = (prio == MIN_COMPACT_PRIORITY)
2505        };
2506        struct capture_control capc = {
2507                .cc = &cc,
2508                .page = NULL,
2509        };
2510
2511        /*
2512         * Make sure the structs are really initialized before we expose the
2513         * capture control, in case we are interrupted and the interrupt handler
2514         * frees a page.
2515         */
2516        barrier();
2517        WRITE_ONCE(current->capture_control, &capc);
2518
2519        ret = compact_zone(&cc, &capc);
2520
2521        VM_BUG_ON(!list_empty(&cc.freepages));
2522        VM_BUG_ON(!list_empty(&cc.migratepages));
2523
2524        /*
2525         * Make sure we hide capture control first before we read the captured
2526         * page pointer, otherwise an interrupt could free and capture a page
2527         * and we would leak it.
2528         */
2529        WRITE_ONCE(current->capture_control, NULL);
2530        *capture = READ_ONCE(capc.page);
2531        /*
2532         * Technically, it is also possible that compaction is skipped but
2533         * the page is still captured out of luck(IRQ came and freed the page).
2534         * Returning COMPACT_SUCCESS in such cases helps in properly accounting
2535         * the COMPACT[STALL|FAIL] when compaction is skipped.
2536         */
2537        if (*capture)
2538                ret = COMPACT_SUCCESS;
2539
2540        return ret;
2541}
2542
2543int sysctl_extfrag_threshold = 500;
2544
2545/**
2546 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
2547 * @gfp_mask: The GFP mask of the current allocation
2548 * @order: The order of the current allocation
2549 * @alloc_flags: The allocation flags of the current allocation
2550 * @ac: The context of current allocation
2551 * @prio: Determines how hard direct compaction should try to succeed
2552 * @capture: Pointer to free page created by compaction will be stored here
2553 *
2554 * This is the main entry point for direct page compaction.
2555 */
2556enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
2557                unsigned int alloc_flags, const struct alloc_context *ac,
2558                enum compact_priority prio, struct page **capture)
2559{
2560        int may_perform_io = gfp_mask & __GFP_IO;
2561        struct zoneref *z;
2562        struct zone *zone;
2563        enum compact_result rc = COMPACT_SKIPPED;
2564
2565        /*
2566         * Check if the GFP flags allow compaction - GFP_NOIO is really
2567         * tricky context because the migration might require IO
2568         */
2569        if (!may_perform_io)
2570                return COMPACT_SKIPPED;
2571
2572        trace_mm_compaction_try_to_compact_pages(order, gfp_mask, prio);
2573
2574        /* Compact each zone in the list */
2575        for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
2576                                        ac->highest_zoneidx, ac->nodemask) {
2577                enum compact_result status;
2578
2579                if (prio > MIN_COMPACT_PRIORITY
2580                                        && compaction_deferred(zone, order)) {
2581                        rc = max_t(enum compact_result, COMPACT_DEFERRED, rc);
2582                        continue;
2583                }
2584
2585                status = compact_zone_order(zone, order, gfp_mask, prio,
2586                                alloc_flags, ac->highest_zoneidx, capture);
2587                rc = max(status, rc);
2588
2589                /* The allocation should succeed, stop compacting */
2590                if (status == COMPACT_SUCCESS) {
2591                        /*
2592                         * We think the allocation will succeed in this zone,
2593                         * but it is not certain, hence the false. The caller
2594                         * will repeat this with true if allocation indeed
2595                         * succeeds in this zone.
2596                         */
2597                        compaction_defer_reset(zone, order, false);
2598
2599                        break;
2600                }
2601
2602                if (prio != COMPACT_PRIO_ASYNC && (status == COMPACT_COMPLETE ||
2603                                        status == COMPACT_PARTIAL_SKIPPED))
2604                        /*
2605                         * We think that allocation won't succeed in this zone
2606                         * so we defer compaction there. If it ends up
2607                         * succeeding after all, it will be reset.
2608                         */
2609                        defer_compaction(zone, order);
2610
2611                /*
2612                 * We might have stopped compacting due to need_resched() in
2613                 * async compaction, or due to a fatal signal detected. In that
2614                 * case do not try further zones
2615                 */
2616                if ((prio == COMPACT_PRIO_ASYNC && need_resched())
2617                                        || fatal_signal_pending(current))
2618                        break;
2619        }
2620
2621        return rc;
2622}
2623
2624/*
2625 * Compact all zones within a node till each zone's fragmentation score
2626 * reaches within proactive compaction thresholds (as determined by the
2627 * proactiveness tunable).
2628 *
2629 * It is possible that the function returns before reaching score targets
2630 * due to various back-off conditions, such as, contention on per-node or
2631 * per-zone locks.
2632 */
2633static void proactive_compact_node(pg_data_t *pgdat)
2634{
2635        int zoneid;
2636        struct zone *zone;
2637        struct compact_control cc = {
2638                .order = -1,
2639                .mode = MIGRATE_SYNC_LIGHT,
2640                .ignore_skip_hint = true,
2641                .whole_zone = true,
2642                .gfp_mask = GFP_KERNEL,
2643                .proactive_compaction = true,
2644        };
2645
2646        for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
2647                zone = &pgdat->node_zones[zoneid];
2648                if (!populated_zone(zone))
2649                        continue;
2650
2651                cc.zone = zone;
2652
2653                compact_zone(&cc, NULL);
2654
2655                VM_BUG_ON(!list_empty(&cc.freepages));
2656                VM_BUG_ON(!list_empty(&cc.migratepages));
2657        }
2658}
2659
2660/* Compact all zones within a node */
2661static void compact_node(int nid)
2662{
2663        pg_data_t *pgdat = NODE_DATA(nid);
2664        int zoneid;
2665        struct zone *zone;
2666        struct compact_control cc = {
2667                .order = -1,
2668                .mode = MIGRATE_SYNC,
2669                .ignore_skip_hint = true,
2670                .whole_zone = true,
2671                .gfp_mask = GFP_KERNEL,
2672        };
2673
2674
2675        for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
2676
2677                zone = &pgdat->node_zones[zoneid];
2678                if (!populated_zone(zone))
2679                        continue;
2680
2681                cc.zone = zone;
2682
2683                compact_zone(&cc, NULL);
2684
2685                VM_BUG_ON(!list_empty(&cc.freepages));
2686                VM_BUG_ON(!list_empty(&cc.migratepages));
2687        }
2688}
2689
2690/* Compact all nodes in the system */
2691static void compact_nodes(void)
2692{
2693        int nid;
2694
2695        /* Flush pending updates to the LRU lists */
2696        lru_add_drain_all();
2697
2698        for_each_online_node(nid)
2699                compact_node(nid);
2700}
2701
2702/*
2703 * Tunable for proactive compaction. It determines how
2704 * aggressively the kernel should compact memory in the
2705 * background. It takes values in the range [0, 100].
2706 */
2707unsigned int __read_mostly sysctl_compaction_proactiveness = 20;
2708
2709/*
2710 * This is the entry point for compacting all nodes via
2711 * /proc/sys/vm/compact_memory
2712 */
2713int sysctl_compaction_handler(struct ctl_table *table, int write,
2714                        void *buffer, size_t *length, loff_t *ppos)
2715{
2716        if (write)
2717                compact_nodes();
2718
2719        return 0;
2720}
2721
2722#if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
2723static ssize_t compact_store(struct device *dev,
2724                             struct device_attribute *attr,
2725                             const char *buf, size_t count)
2726{
2727        int nid = dev->id;
2728
2729        if (nid >= 0 && nid < nr_node_ids && node_online(nid)) {
2730                /* Flush pending updates to the LRU lists */
2731                lru_add_drain_all();
2732
2733                compact_node(nid);
2734        }
2735
2736        return count;
2737}
2738static DEVICE_ATTR_WO(compact);
2739
2740int compaction_register_node(struct node *node)
2741{
2742        return device_create_file(&node->dev, &dev_attr_compact);
2743}
2744
2745void compaction_unregister_node(struct node *node)
2746{
2747        return device_remove_file(&node->dev, &dev_attr_compact);
2748}
2749#endif /* CONFIG_SYSFS && CONFIG_NUMA */
2750
2751static inline bool kcompactd_work_requested(pg_data_t *pgdat)
2752{
2753        return pgdat->kcompactd_max_order > 0 || kthread_should_stop();
2754}
2755
2756static bool kcompactd_node_suitable(pg_data_t *pgdat)
2757{
2758        int zoneid;
2759        struct zone *zone;
2760        enum zone_type highest_zoneidx = pgdat->kcompactd_highest_zoneidx;
2761
2762        for (zoneid = 0; zoneid <= highest_zoneidx; zoneid++) {
2763                zone = &pgdat->node_zones[zoneid];
2764
2765                if (!populated_zone(zone))
2766                        continue;
2767
2768                if (compaction_suitable(zone, pgdat->kcompactd_max_order, 0,
2769                                        highest_zoneidx) == COMPACT_CONTINUE)
2770                        return true;
2771        }
2772
2773        return false;
2774}
2775
2776static void kcompactd_do_work(pg_data_t *pgdat)
2777{
2778        /*
2779         * With no special task, compact all zones so that a page of requested
2780         * order is allocatable.
2781         */
2782        int zoneid;
2783        struct zone *zone;
2784        struct compact_control cc = {
2785                .order = pgdat->kcompactd_max_order,
2786                .search_order = pgdat->kcompactd_max_order,
2787                .highest_zoneidx = pgdat->kcompactd_highest_zoneidx,
2788                .mode = MIGRATE_SYNC_LIGHT,
2789                .ignore_skip_hint = false,
2790                .gfp_mask = GFP_KERNEL,
2791        };
2792        trace_mm_compaction_kcompactd_wake(pgdat->node_id, cc.order,
2793                                                        cc.highest_zoneidx);
2794        count_compact_event(KCOMPACTD_WAKE);
2795
2796        for (zoneid = 0; zoneid <= cc.highest_zoneidx; zoneid++) {
2797                int status;
2798
2799                zone = &pgdat->node_zones[zoneid];
2800                if (!populated_zone(zone))
2801                        continue;
2802
2803                if (compaction_deferred(zone, cc.order))
2804                        continue;
2805
2806                if (compaction_suitable(zone, cc.order, 0, zoneid) !=
2807                                                        COMPACT_CONTINUE)
2808                        continue;
2809
2810                if (kthread_should_stop())
2811                        return;
2812
2813                cc.zone = zone;
2814                status = compact_zone(&cc, NULL);
2815
2816                if (status == COMPACT_SUCCESS) {
2817                        compaction_defer_reset(zone, cc.order, false);
2818                } else if (status == COMPACT_PARTIAL_SKIPPED || status == COMPACT_COMPLETE) {
2819                        /*
2820                         * Buddy pages may become stranded on pcps that could
2821                         * otherwise coalesce on the zone's free area for
2822                         * order >= cc.order.  This is ratelimited by the
2823                         * upcoming deferral.
2824                         */
2825                        drain_all_pages(zone);
2826
2827                        /*
2828                         * We use sync migration mode here, so we defer like
2829                         * sync direct compaction does.
2830                         */
2831                        defer_compaction(zone, cc.order);
2832                }
2833
2834                count_compact_events(KCOMPACTD_MIGRATE_SCANNED,
2835                                     cc.total_migrate_scanned);
2836                count_compact_events(KCOMPACTD_FREE_SCANNED,
2837                                     cc.total_free_scanned);
2838
2839                VM_BUG_ON(!list_empty(&cc.freepages));
2840                VM_BUG_ON(!list_empty(&cc.migratepages));
2841        }
2842
2843        /*
2844         * Regardless of success, we are done until woken up next. But remember
2845         * the requested order/highest_zoneidx in case it was higher/tighter
2846         * than our current ones
2847         */
2848        if (pgdat->kcompactd_max_order <= cc.order)
2849                pgdat->kcompactd_max_order = 0;
2850        if (pgdat->kcompactd_highest_zoneidx >= cc.highest_zoneidx)
2851                pgdat->kcompactd_highest_zoneidx = pgdat->nr_zones - 1;
2852}
2853
2854void wakeup_kcompactd(pg_data_t *pgdat, int order, int highest_zoneidx)
2855{
2856        if (!order)
2857                return;
2858
2859        if (pgdat->kcompactd_max_order < order)
2860                pgdat->kcompactd_max_order = order;
2861
2862        if (pgdat->kcompactd_highest_zoneidx > highest_zoneidx)
2863                pgdat->kcompactd_highest_zoneidx = highest_zoneidx;
2864
2865        /*
2866         * Pairs with implicit barrier in wait_event_freezable()
2867         * such that wakeups are not missed.
2868         */
2869        if (!wq_has_sleeper(&pgdat->kcompactd_wait))
2870                return;
2871
2872        if (!kcompactd_node_suitable(pgdat))
2873                return;
2874
2875        trace_mm_compaction_wakeup_kcompactd(pgdat->node_id, order,
2876                                                        highest_zoneidx);
2877        wake_up_interruptible(&pgdat->kcompactd_wait);
2878}
2879
2880/*
2881 * The background compaction daemon, started as a kernel thread
2882 * from the init process.
2883 */
2884static int kcompactd(void *p)
2885{
2886        pg_data_t *pgdat = (pg_data_t *)p;
2887        struct task_struct *tsk = current;
2888        unsigned int proactive_defer = 0;
2889
2890        const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
2891
2892        if (!cpumask_empty(cpumask))
2893                set_cpus_allowed_ptr(tsk, cpumask);
2894
2895        set_freezable();
2896
2897        pgdat->kcompactd_max_order = 0;
2898        pgdat->kcompactd_highest_zoneidx = pgdat->nr_zones - 1;
2899
2900        while (!kthread_should_stop()) {
2901                unsigned long pflags;
2902
2903                trace_mm_compaction_kcompactd_sleep(pgdat->node_id);
2904                if (wait_event_freezable_timeout(pgdat->kcompactd_wait,
2905                        kcompactd_work_requested(pgdat),
2906                        msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC))) {
2907
2908                        psi_memstall_enter(&pflags);
2909                        kcompactd_do_work(pgdat);
2910                        psi_memstall_leave(&pflags);
2911                        continue;
2912                }
2913
2914                /* kcompactd wait timeout */
2915                if (should_proactive_compact_node(pgdat)) {
2916                        unsigned int prev_score, score;
2917
2918                        if (proactive_defer) {
2919                                proactive_defer--;
2920                                continue;
2921                        }
2922                        prev_score = fragmentation_score_node(pgdat);
2923                        proactive_compact_node(pgdat);
2924                        score = fragmentation_score_node(pgdat);
2925                        /*
2926                         * Defer proactive compaction if the fragmentation
2927                         * score did not go down i.e. no progress made.
2928                         */
2929                        proactive_defer = score < prev_score ?
2930                                        0 : 1 << COMPACT_MAX_DEFER_SHIFT;
2931                }
2932        }
2933
2934        return 0;
2935}
2936
2937/*
2938 * This kcompactd start function will be called by init and node-hot-add.
2939 * On node-hot-add, kcompactd will moved to proper cpus if cpus are hot-added.
2940 */
2941int kcompactd_run(int nid)
2942{
2943        pg_data_t *pgdat = NODE_DATA(nid);
2944        int ret = 0;
2945
2946        if (pgdat->kcompactd)
2947                return 0;
2948
2949        pgdat->kcompactd = kthread_run(kcompactd, pgdat, "kcompactd%d", nid);
2950        if (IS_ERR(pgdat->kcompactd)) {
2951                pr_err("Failed to start kcompactd on node %d\n", nid);
2952                ret = PTR_ERR(pgdat->kcompactd);
2953                pgdat->kcompactd = NULL;
2954        }
2955        return ret;
2956}
2957
2958/*
2959 * Called by memory hotplug when all memory in a node is offlined. Caller must
2960 * hold mem_hotplug_begin/end().
2961 */
2962void kcompactd_stop(int nid)
2963{
2964        struct task_struct *kcompactd = NODE_DATA(nid)->kcompactd;
2965
2966        if (kcompactd) {
2967                kthread_stop(kcompactd);
2968                NODE_DATA(nid)->kcompactd = NULL;
2969        }
2970}
2971
2972/*
2973 * It's optimal to keep kcompactd on the same CPUs as their memory, but
2974 * not required for correctness. So if the last cpu in a node goes
2975 * away, we get changed to run anywhere: as the first one comes back,
2976 * restore their cpu bindings.
2977 */
2978static int kcompactd_cpu_online(unsigned int cpu)
2979{
2980        int nid;
2981
2982        for_each_node_state(nid, N_MEMORY) {
2983                pg_data_t *pgdat = NODE_DATA(nid);
2984                const struct cpumask *mask;
2985
2986                mask = cpumask_of_node(pgdat->node_id);
2987
2988                if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
2989                        /* One of our CPUs online: restore mask */
2990                        set_cpus_allowed_ptr(pgdat->kcompactd, mask);
2991        }
2992        return 0;
2993}
2994
2995static int __init kcompactd_init(void)
2996{
2997        int nid;
2998        int ret;
2999
3000        ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
3001                                        "mm/compaction:online",
3002                                        kcompactd_cpu_online, NULL);
3003        if (ret < 0) {
3004                pr_err("kcompactd: failed to register hotplug callbacks.\n");
3005                return ret;
3006        }
3007
3008        for_each_node_state(nid, N_MEMORY)
3009                kcompactd_run(nid);
3010        return 0;
3011}
3012subsys_initcall(kcompactd_init)
3013
3014#endif /* CONFIG_COMPACTION */
3015
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.