linux/mm/compaction.c
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   1/*
   2 * linux/mm/compaction.c
   3 *
   4 * Memory compaction for the reduction of external fragmentation. Note that
   5 * this heavily depends upon page migration to do all the real heavy
   6 * lifting
   7 *
   8 * Copyright IBM Corp. 2007-2010 Mel Gorman <mel@csn.ul.ie>
   9 */
  10#include <linux/swap.h>
  11#include <linux/migrate.h>
  12#include <linux/compaction.h>
  13#include <linux/mm_inline.h>
  14#include <linux/backing-dev.h>
  15#include <linux/sysctl.h>
  16#include <linux/sysfs.h>
  17#include <linux/balloon_compaction.h>
  18#include <linux/page-isolation.h>
  19#include "internal.h"
  20
  21#ifdef CONFIG_COMPACTION
  22static inline void count_compact_event(enum vm_event_item item)
  23{
  24        count_vm_event(item);
  25}
  26
  27static inline void count_compact_events(enum vm_event_item item, long delta)
  28{
  29        count_vm_events(item, delta);
  30}
  31#else
  32#define count_compact_event(item) do { } while (0)
  33#define count_compact_events(item, delta) do { } while (0)
  34#endif
  35
  36#if defined CONFIG_COMPACTION || defined CONFIG_CMA
  37
  38#define CREATE_TRACE_POINTS
  39#include <trace/events/compaction.h>
  40
  41static unsigned long release_freepages(struct list_head *freelist)
  42{
  43        struct page *page, *next;
  44        unsigned long count = 0;
  45
  46        list_for_each_entry_safe(page, next, freelist, lru) {
  47                list_del(&page->lru);
  48                __free_page(page);
  49                count++;
  50        }
  51
  52        return count;
  53}
  54
  55static void map_pages(struct list_head *list)
  56{
  57        struct page *page;
  58
  59        list_for_each_entry(page, list, lru) {
  60                arch_alloc_page(page, 0);
  61                kernel_map_pages(page, 1, 1);
  62        }
  63}
  64
  65static inline bool migrate_async_suitable(int migratetype)
  66{
  67        return is_migrate_cma(migratetype) || migratetype == MIGRATE_MOVABLE;
  68}
  69
  70#ifdef CONFIG_COMPACTION
  71/* Returns true if the pageblock should be scanned for pages to isolate. */
  72static inline bool isolation_suitable(struct compact_control *cc,
  73                                        struct page *page)
  74{
  75        if (cc->ignore_skip_hint)
  76                return true;
  77
  78        return !get_pageblock_skip(page);
  79}
  80
  81/*
  82 * This function is called to clear all cached information on pageblocks that
  83 * should be skipped for page isolation when the migrate and free page scanner
  84 * meet.
  85 */
  86static void __reset_isolation_suitable(struct zone *zone)
  87{
  88        unsigned long start_pfn = zone->zone_start_pfn;
  89        unsigned long end_pfn = zone_end_pfn(zone);
  90        unsigned long pfn;
  91
  92        zone->compact_cached_migrate_pfn = start_pfn;
  93        zone->compact_cached_free_pfn = end_pfn;
  94        zone->compact_blockskip_flush = false;
  95
  96        /* Walk the zone and mark every pageblock as suitable for isolation */
  97        for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages) {
  98                struct page *page;
  99
 100                cond_resched();
 101
 102                if (!pfn_valid(pfn))
 103                        continue;
 104
 105                page = pfn_to_page(pfn);
 106                if (zone != page_zone(page))
 107                        continue;
 108
 109                clear_pageblock_skip(page);
 110        }
 111}
 112
 113void reset_isolation_suitable(pg_data_t *pgdat)
 114{
 115        int zoneid;
 116
 117        for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
 118                struct zone *zone = &pgdat->node_zones[zoneid];
 119                if (!populated_zone(zone))
 120                        continue;
 121
 122                /* Only flush if a full compaction finished recently */
 123                if (zone->compact_blockskip_flush)
 124                        __reset_isolation_suitable(zone);
 125        }
 126}
 127
 128/*
 129 * If no pages were isolated then mark this pageblock to be skipped in the
 130 * future. The information is later cleared by __reset_isolation_suitable().
 131 */
 132static void update_pageblock_skip(struct compact_control *cc,
 133                        struct page *page, unsigned long nr_isolated,
 134                        bool migrate_scanner)
 135{
 136        struct zone *zone = cc->zone;
 137        if (!page)
 138                return;
 139
 140        if (!nr_isolated) {
 141                unsigned long pfn = page_to_pfn(page);
 142                set_pageblock_skip(page);
 143
 144                /* Update where compaction should restart */
 145                if (migrate_scanner) {
 146                        if (!cc->finished_update_migrate &&
 147                            pfn > zone->compact_cached_migrate_pfn)
 148                                zone->compact_cached_migrate_pfn = pfn;
 149                } else {
 150                        if (!cc->finished_update_free &&
 151                            pfn < zone->compact_cached_free_pfn)
 152                                zone->compact_cached_free_pfn = pfn;
 153                }
 154        }
 155}
 156#else
 157static inline bool isolation_suitable(struct compact_control *cc,
 158                                        struct page *page)
 159{
 160        return true;
 161}
 162
 163static void update_pageblock_skip(struct compact_control *cc,
 164                        struct page *page, unsigned long nr_isolated,
 165                        bool migrate_scanner)
 166{
 167}
 168#endif /* CONFIG_COMPACTION */
 169
 170static inline bool should_release_lock(spinlock_t *lock)
 171{
 172        return need_resched() || spin_is_contended(lock);
 173}
 174
 175/*
 176 * Compaction requires the taking of some coarse locks that are potentially
 177 * very heavily contended. Check if the process needs to be scheduled or
 178 * if the lock is contended. For async compaction, back out in the event
 179 * if contention is severe. For sync compaction, schedule.
 180 *
 181 * Returns true if the lock is held.
 182 * Returns false if the lock is released and compaction should abort
 183 */
 184static bool compact_checklock_irqsave(spinlock_t *lock, unsigned long *flags,
 185                                      bool locked, struct compact_control *cc)
 186{
 187        if (should_release_lock(lock)) {
 188                if (locked) {
 189                        spin_unlock_irqrestore(lock, *flags);
 190                        locked = false;
 191                }
 192
 193                /* async aborts if taking too long or contended */
 194                if (!cc->sync) {
 195                        cc->contended = true;
 196                        return false;
 197                }
 198
 199                cond_resched();
 200        }
 201
 202        if (!locked)
 203                spin_lock_irqsave(lock, *flags);
 204        return true;
 205}
 206
 207static inline bool compact_trylock_irqsave(spinlock_t *lock,
 208                        unsigned long *flags, struct compact_control *cc)
 209{
 210        return compact_checklock_irqsave(lock, flags, false, cc);
 211}
 212
 213/* Returns true if the page is within a block suitable for migration to */
 214static bool suitable_migration_target(struct page *page)
 215{
 216        int migratetype = get_pageblock_migratetype(page);
 217
 218        /* Don't interfere with memory hot-remove or the min_free_kbytes blocks */
 219        if (migratetype == MIGRATE_RESERVE)
 220                return false;
 221
 222        if (is_migrate_isolate(migratetype))
 223                return false;
 224
 225        /* If the page is a large free page, then allow migration */
 226        if (PageBuddy(page) && page_order(page) >= pageblock_order)
 227                return true;
 228
 229        /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
 230        if (migrate_async_suitable(migratetype))
 231                return true;
 232
 233        /* Otherwise skip the block */
 234        return false;
 235}
 236
 237/*
 238 * Isolate free pages onto a private freelist. Caller must hold zone->lock.
 239 * If @strict is true, will abort returning 0 on any invalid PFNs or non-free
 240 * pages inside of the pageblock (even though it may still end up isolating
 241 * some pages).
 242 */
 243static unsigned long isolate_freepages_block(struct compact_control *cc,
 244                                unsigned long blockpfn,
 245                                unsigned long end_pfn,
 246                                struct list_head *freelist,
 247                                bool strict)
 248{
 249        int nr_scanned = 0, total_isolated = 0;
 250        struct page *cursor, *valid_page = NULL;
 251        unsigned long nr_strict_required = end_pfn - blockpfn;
 252        unsigned long flags;
 253        bool locked = false;
 254
 255        cursor = pfn_to_page(blockpfn);
 256
 257        /* Isolate free pages. */
 258        for (; blockpfn < end_pfn; blockpfn++, cursor++) {
 259                int isolated, i;
 260                struct page *page = cursor;
 261
 262                nr_scanned++;
 263                if (!pfn_valid_within(blockpfn))
 264                        continue;
 265                if (!valid_page)
 266                        valid_page = page;
 267                if (!PageBuddy(page))
 268                        continue;
 269
 270                /*
 271                 * The zone lock must be held to isolate freepages.
 272                 * Unfortunately this is a very coarse lock and can be
 273                 * heavily contended if there are parallel allocations
 274                 * or parallel compactions. For async compaction do not
 275                 * spin on the lock and we acquire the lock as late as
 276                 * possible.
 277                 */
 278                locked = compact_checklock_irqsave(&cc->zone->lock, &flags,
 279                                                                locked, cc);
 280                if (!locked)
 281                        break;
 282
 283                /* Recheck this is a suitable migration target under lock */
 284                if (!strict && !suitable_migration_target(page))
 285                        break;
 286
 287                /* Recheck this is a buddy page under lock */
 288                if (!PageBuddy(page))
 289                        continue;
 290
 291                /* Found a free page, break it into order-0 pages */
 292                isolated = split_free_page(page);
 293                if (!isolated && strict)
 294                        break;
 295                total_isolated += isolated;
 296                for (i = 0; i < isolated; i++) {
 297                        list_add(&page->lru, freelist);
 298                        page++;
 299                }
 300
 301                /* If a page was split, advance to the end of it */
 302                if (isolated) {
 303                        blockpfn += isolated - 1;
 304                        cursor += isolated - 1;
 305                }
 306        }
 307
 308        trace_mm_compaction_isolate_freepages(nr_scanned, total_isolated);
 309
 310        /*
 311         * If strict isolation is requested by CMA then check that all the
 312         * pages requested were isolated. If there were any failures, 0 is
 313         * returned and CMA will fail.
 314         */
 315        if (strict && nr_strict_required > total_isolated)
 316                total_isolated = 0;
 317
 318        if (locked)
 319                spin_unlock_irqrestore(&cc->zone->lock, flags);
 320
 321        /* Update the pageblock-skip if the whole pageblock was scanned */
 322        if (blockpfn == end_pfn)
 323                update_pageblock_skip(cc, valid_page, total_isolated, false);
 324
 325        count_compact_events(COMPACTFREE_SCANNED, nr_scanned);
 326        if (total_isolated)
 327                count_compact_events(COMPACTISOLATED, total_isolated);
 328        return total_isolated;
 329}
 330
 331/**
 332 * isolate_freepages_range() - isolate free pages.
 333 * @start_pfn: The first PFN to start isolating.
 334 * @end_pfn:   The one-past-last PFN.
 335 *
 336 * Non-free pages, invalid PFNs, or zone boundaries within the
 337 * [start_pfn, end_pfn) range are considered errors, cause function to
 338 * undo its actions and return zero.
 339 *
 340 * Otherwise, function returns one-past-the-last PFN of isolated page
 341 * (which may be greater then end_pfn if end fell in a middle of
 342 * a free page).
 343 */
 344unsigned long
 345isolate_freepages_range(struct compact_control *cc,
 346                        unsigned long start_pfn, unsigned long end_pfn)
 347{
 348        unsigned long isolated, pfn, block_end_pfn;
 349        LIST_HEAD(freelist);
 350
 351        for (pfn = start_pfn; pfn < end_pfn; pfn += isolated) {
 352                if (!pfn_valid(pfn) || cc->zone != page_zone(pfn_to_page(pfn)))
 353                        break;
 354
 355                /*
 356                 * On subsequent iterations ALIGN() is actually not needed,
 357                 * but we keep it that we not to complicate the code.
 358                 */
 359                block_end_pfn = ALIGN(pfn + 1, pageblock_nr_pages);
 360                block_end_pfn = min(block_end_pfn, end_pfn);
 361
 362                isolated = isolate_freepages_block(cc, pfn, block_end_pfn,
 363                                                   &freelist, true);
 364
 365                /*
 366                 * In strict mode, isolate_freepages_block() returns 0 if
 367                 * there are any holes in the block (ie. invalid PFNs or
 368                 * non-free pages).
 369                 */
 370                if (!isolated)
 371                        break;
 372
 373                /*
 374                 * If we managed to isolate pages, it is always (1 << n) *
 375                 * pageblock_nr_pages for some non-negative n.  (Max order
 376                 * page may span two pageblocks).
 377                 */
 378        }
 379
 380        /* split_free_page does not map the pages */
 381        map_pages(&freelist);
 382
 383        if (pfn < end_pfn) {
 384                /* Loop terminated early, cleanup. */
 385                release_freepages(&freelist);
 386                return 0;
 387        }
 388
 389        /* We don't use freelists for anything. */
 390        return pfn;
 391}
 392
 393/* Update the number of anon and file isolated pages in the zone */
 394static void acct_isolated(struct zone *zone, bool locked, struct compact_control *cc)
 395{
 396        struct page *page;
 397        unsigned int count[2] = { 0, };
 398
 399        list_for_each_entry(page, &cc->migratepages, lru)
 400                count[!!page_is_file_cache(page)]++;
 401
 402        /* If locked we can use the interrupt unsafe versions */
 403        if (locked) {
 404                __mod_zone_page_state(zone, NR_ISOLATED_ANON, count[0]);
 405                __mod_zone_page_state(zone, NR_ISOLATED_FILE, count[1]);
 406        } else {
 407                mod_zone_page_state(zone, NR_ISOLATED_ANON, count[0]);
 408                mod_zone_page_state(zone, NR_ISOLATED_FILE, count[1]);
 409        }
 410}
 411
 412/* Similar to reclaim, but different enough that they don't share logic */
 413static bool too_many_isolated(struct zone *zone)
 414{
 415        unsigned long active, inactive, isolated;
 416
 417        inactive = zone_page_state(zone, NR_INACTIVE_FILE) +
 418                                        zone_page_state(zone, NR_INACTIVE_ANON);
 419        active = zone_page_state(zone, NR_ACTIVE_FILE) +
 420                                        zone_page_state(zone, NR_ACTIVE_ANON);
 421        isolated = zone_page_state(zone, NR_ISOLATED_FILE) +
 422                                        zone_page_state(zone, NR_ISOLATED_ANON);
 423
 424        return isolated > (inactive + active) / 2;
 425}
 426
 427/**
 428 * isolate_migratepages_range() - isolate all migrate-able pages in range.
 429 * @zone:       Zone pages are in.
 430 * @cc:         Compaction control structure.
 431 * @low_pfn:    The first PFN of the range.
 432 * @end_pfn:    The one-past-the-last PFN of the range.
 433 * @unevictable: true if it allows to isolate unevictable pages
 434 *
 435 * Isolate all pages that can be migrated from the range specified by
 436 * [low_pfn, end_pfn).  Returns zero if there is a fatal signal
 437 * pending), otherwise PFN of the first page that was not scanned
 438 * (which may be both less, equal to or more then end_pfn).
 439 *
 440 * Assumes that cc->migratepages is empty and cc->nr_migratepages is
 441 * zero.
 442 *
 443 * Apart from cc->migratepages and cc->nr_migratetypes this function
 444 * does not modify any cc's fields, in particular it does not modify
 445 * (or read for that matter) cc->migrate_pfn.
 446 */
 447unsigned long
 448isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
 449                unsigned long low_pfn, unsigned long end_pfn, bool unevictable)
 450{
 451        unsigned long last_pageblock_nr = 0, pageblock_nr;
 452        unsigned long nr_scanned = 0, nr_isolated = 0;
 453        struct list_head *migratelist = &cc->migratepages;
 454        isolate_mode_t mode = 0;
 455        struct lruvec *lruvec;
 456        unsigned long flags;
 457        bool locked = false;
 458        struct page *page = NULL, *valid_page = NULL;
 459
 460        /*
 461         * Ensure that there are not too many pages isolated from the LRU
 462         * list by either parallel reclaimers or compaction. If there are,
 463         * delay for some time until fewer pages are isolated
 464         */
 465        while (unlikely(too_many_isolated(zone))) {
 466                /* async migration should just abort */
 467                if (!cc->sync)
 468                        return 0;
 469
 470                congestion_wait(BLK_RW_ASYNC, HZ/10);
 471
 472                if (fatal_signal_pending(current))
 473                        return 0;
 474        }
 475
 476        /* Time to isolate some pages for migration */
 477        cond_resched();
 478        for (; low_pfn < end_pfn; low_pfn++) {
 479                /* give a chance to irqs before checking need_resched() */
 480                if (locked && !((low_pfn+1) % SWAP_CLUSTER_MAX)) {
 481                        if (should_release_lock(&zone->lru_lock)) {
 482                                spin_unlock_irqrestore(&zone->lru_lock, flags);
 483                                locked = false;
 484                        }
 485                }
 486
 487                /*
 488                 * migrate_pfn does not necessarily start aligned to a
 489                 * pageblock. Ensure that pfn_valid is called when moving
 490                 * into a new MAX_ORDER_NR_PAGES range in case of large
 491                 * memory holes within the zone
 492                 */
 493                if ((low_pfn & (MAX_ORDER_NR_PAGES - 1)) == 0) {
 494                        if (!pfn_valid(low_pfn)) {
 495                                low_pfn += MAX_ORDER_NR_PAGES - 1;
 496                                continue;
 497                        }
 498                }
 499
 500                if (!pfn_valid_within(low_pfn))
 501                        continue;
 502                nr_scanned++;
 503
 504                /*
 505                 * Get the page and ensure the page is within the same zone.
 506                 * See the comment in isolate_freepages about overlapping
 507                 * nodes. It is deliberate that the new zone lock is not taken
 508                 * as memory compaction should not move pages between nodes.
 509                 */
 510                page = pfn_to_page(low_pfn);
 511                if (page_zone(page) != zone)
 512                        continue;
 513
 514                if (!valid_page)
 515                        valid_page = page;
 516
 517                /* If isolation recently failed, do not retry */
 518                pageblock_nr = low_pfn >> pageblock_order;
 519                if (!isolation_suitable(cc, page))
 520                        goto next_pageblock;
 521
 522                /* Skip if free */
 523                if (PageBuddy(page))
 524                        continue;
 525
 526                /*
 527                 * For async migration, also only scan in MOVABLE blocks. Async
 528                 * migration is optimistic to see if the minimum amount of work
 529                 * satisfies the allocation
 530                 */
 531                if (!cc->sync && last_pageblock_nr != pageblock_nr &&
 532                    !migrate_async_suitable(get_pageblock_migratetype(page))) {
 533                        cc->finished_update_migrate = true;
 534                        goto next_pageblock;
 535                }
 536
 537                /*
 538                 * Check may be lockless but that's ok as we recheck later.
 539                 * It's possible to migrate LRU pages and balloon pages
 540                 * Skip any other type of page
 541                 */
 542                if (!PageLRU(page)) {
 543                        if (unlikely(balloon_page_movable(page))) {
 544                                if (locked && balloon_page_isolate(page)) {
 545                                        /* Successfully isolated */
 546                                        cc->finished_update_migrate = true;
 547                                        list_add(&page->lru, migratelist);
 548                                        cc->nr_migratepages++;
 549                                        nr_isolated++;
 550                                        goto check_compact_cluster;
 551                                }
 552                        }
 553                        continue;
 554                }
 555
 556                /*
 557                 * PageLRU is set. lru_lock normally excludes isolation
 558                 * splitting and collapsing (collapsing has already happened
 559                 * if PageLRU is set) but the lock is not necessarily taken
 560                 * here and it is wasteful to take it just to check transhuge.
 561                 * Check TransHuge without lock and skip the whole pageblock if
 562                 * it's either a transhuge or hugetlbfs page, as calling
 563                 * compound_order() without preventing THP from splitting the
 564                 * page underneath us may return surprising results.
 565                 */
 566                if (PageTransHuge(page)) {
 567                        if (!locked)
 568                                goto next_pageblock;
 569                        low_pfn += (1 << compound_order(page)) - 1;
 570                        continue;
 571                }
 572
 573                /* Check if it is ok to still hold the lock */
 574                locked = compact_checklock_irqsave(&zone->lru_lock, &flags,
 575                                                                locked, cc);
 576                if (!locked || fatal_signal_pending(current))
 577                        break;
 578
 579                /* Recheck PageLRU and PageTransHuge under lock */
 580                if (!PageLRU(page))
 581                        continue;
 582                if (PageTransHuge(page)) {
 583                        low_pfn += (1 << compound_order(page)) - 1;
 584                        continue;
 585                }
 586
 587                if (!cc->sync)
 588                        mode |= ISOLATE_ASYNC_MIGRATE;
 589
 590                if (unevictable)
 591                        mode |= ISOLATE_UNEVICTABLE;
 592
 593                lruvec = mem_cgroup_page_lruvec(page, zone);
 594
 595                /* Try isolate the page */
 596                if (__isolate_lru_page(page, mode) != 0)
 597                        continue;
 598
 599                VM_BUG_ON(PageTransCompound(page));
 600
 601                /* Successfully isolated */
 602                cc->finished_update_migrate = true;
 603                del_page_from_lru_list(page, lruvec, page_lru(page));
 604                list_add(&page->lru, migratelist);
 605                cc->nr_migratepages++;
 606                nr_isolated++;
 607
 608check_compact_cluster:
 609                /* Avoid isolating too much */
 610                if (cc->nr_migratepages == COMPACT_CLUSTER_MAX) {
 611                        ++low_pfn;
 612                        break;
 613                }
 614
 615                continue;
 616
 617next_pageblock:
 618                low_pfn = ALIGN(low_pfn + 1, pageblock_nr_pages) - 1;
 619                last_pageblock_nr = pageblock_nr;
 620        }
 621
 622        acct_isolated(zone, locked, cc);
 623
 624        if (locked)
 625                spin_unlock_irqrestore(&zone->lru_lock, flags);
 626
 627        /* Update the pageblock-skip if the whole pageblock was scanned */
 628        if (low_pfn == end_pfn)
 629                update_pageblock_skip(cc, valid_page, nr_isolated, true);
 630
 631        trace_mm_compaction_isolate_migratepages(nr_scanned, nr_isolated);
 632
 633        count_compact_events(COMPACTMIGRATE_SCANNED, nr_scanned);
 634        if (nr_isolated)
 635                count_compact_events(COMPACTISOLATED, nr_isolated);
 636
 637        return low_pfn;
 638}
 639
 640#endif /* CONFIG_COMPACTION || CONFIG_CMA */
 641#ifdef CONFIG_COMPACTION
 642/*
 643 * Based on information in the current compact_control, find blocks
 644 * suitable for isolating free pages from and then isolate them.
 645 */
 646static void isolate_freepages(struct zone *zone,
 647                                struct compact_control *cc)
 648{
 649        struct page *page;
 650        unsigned long high_pfn, low_pfn, pfn, z_end_pfn, end_pfn;
 651        int nr_freepages = cc->nr_freepages;
 652        struct list_head *freelist = &cc->freepages;
 653
 654        /*
 655         * Initialise the free scanner. The starting point is where we last
 656         * scanned from (or the end of the zone if starting). The low point
 657         * is the end of the pageblock the migration scanner is using.
 658         */
 659        pfn = cc->free_pfn;
 660        low_pfn = cc->migrate_pfn + pageblock_nr_pages;
 661
 662        /*
 663         * Take care that if the migration scanner is at the end of the zone
 664         * that the free scanner does not accidentally move to the next zone
 665         * in the next isolation cycle.
 666         */
 667        high_pfn = min(low_pfn, pfn);
 668
 669        z_end_pfn = zone_end_pfn(zone);
 670
 671        /*
 672         * Isolate free pages until enough are available to migrate the
 673         * pages on cc->migratepages. We stop searching if the migrate
 674         * and free page scanners meet or enough free pages are isolated.
 675         */
 676        for (; pfn > low_pfn && cc->nr_migratepages > nr_freepages;
 677                                        pfn -= pageblock_nr_pages) {
 678                unsigned long isolated;
 679
 680                /*
 681                 * This can iterate a massively long zone without finding any
 682                 * suitable migration targets, so periodically check if we need
 683                 * to schedule.
 684                 */
 685                cond_resched();
 686
 687                if (!pfn_valid(pfn))
 688                        continue;
 689
 690                /*
 691                 * Check for overlapping nodes/zones. It's possible on some
 692                 * configurations to have a setup like
 693                 * node0 node1 node0
 694                 * i.e. it's possible that all pages within a zones range of
 695                 * pages do not belong to a single zone.
 696                 */
 697                page = pfn_to_page(pfn);
 698                if (page_zone(page) != zone)
 699                        continue;
 700
 701                /* Check the block is suitable for migration */
 702                if (!suitable_migration_target(page))
 703                        continue;
 704
 705                /* If isolation recently failed, do not retry */
 706                if (!isolation_suitable(cc, page))
 707                        continue;
 708
 709                /* Found a block suitable for isolating free pages from */
 710                isolated = 0;
 711
 712                /*
 713                 * As pfn may not start aligned, pfn+pageblock_nr_page
 714                 * may cross a MAX_ORDER_NR_PAGES boundary and miss
 715                 * a pfn_valid check. Ensure isolate_freepages_block()
 716                 * only scans within a pageblock
 717                 */
 718                end_pfn = ALIGN(pfn + 1, pageblock_nr_pages);
 719                end_pfn = min(end_pfn, z_end_pfn);
 720                isolated = isolate_freepages_block(cc, pfn, end_pfn,
 721                                                   freelist, false);
 722                nr_freepages += isolated;
 723
 724                /*
 725                 * Record the highest PFN we isolated pages from. When next
 726                 * looking for free pages, the search will restart here as
 727                 * page migration may have returned some pages to the allocator
 728                 */
 729                if (isolated) {
 730                        cc->finished_update_free = true;
 731                        high_pfn = max(high_pfn, pfn);
 732                }
 733        }
 734
 735        /* split_free_page does not map the pages */
 736        map_pages(freelist);
 737
 738        cc->free_pfn = high_pfn;
 739        cc->nr_freepages = nr_freepages;
 740}
 741
 742/*
 743 * This is a migrate-callback that "allocates" freepages by taking pages
 744 * from the isolated freelists in the block we are migrating to.
 745 */
 746static struct page *compaction_alloc(struct page *migratepage,
 747                                        unsigned long data,
 748                                        int **result)
 749{
 750        struct compact_control *cc = (struct compact_control *)data;
 751        struct page *freepage;
 752
 753        /* Isolate free pages if necessary */
 754        if (list_empty(&cc->freepages)) {
 755                isolate_freepages(cc->zone, cc);
 756
 757                if (list_empty(&cc->freepages))
 758                        return NULL;
 759        }
 760
 761        freepage = list_entry(cc->freepages.next, struct page, lru);
 762        list_del(&freepage->lru);
 763        cc->nr_freepages--;
 764
 765        return freepage;
 766}
 767
 768/*
 769 * We cannot control nr_migratepages and nr_freepages fully when migration is
 770 * running as migrate_pages() has no knowledge of compact_control. When
 771 * migration is complete, we count the number of pages on the lists by hand.
 772 */
 773static void update_nr_listpages(struct compact_control *cc)
 774{
 775        int nr_migratepages = 0;
 776        int nr_freepages = 0;
 777        struct page *page;
 778
 779        list_for_each_entry(page, &cc->migratepages, lru)
 780                nr_migratepages++;
 781        list_for_each_entry(page, &cc->freepages, lru)
 782                nr_freepages++;
 783
 784        cc->nr_migratepages = nr_migratepages;
 785        cc->nr_freepages = nr_freepages;
 786}
 787
 788/* possible outcome of isolate_migratepages */
 789typedef enum {
 790        ISOLATE_ABORT,          /* Abort compaction now */
 791        ISOLATE_NONE,           /* No pages isolated, continue scanning */
 792        ISOLATE_SUCCESS,        /* Pages isolated, migrate */
 793} isolate_migrate_t;
 794
 795/*
 796 * Isolate all pages that can be migrated from the block pointed to by
 797 * the migrate scanner within compact_control.
 798 */
 799static isolate_migrate_t isolate_migratepages(struct zone *zone,
 800                                        struct compact_control *cc)
 801{
 802        unsigned long low_pfn, end_pfn;
 803
 804        /* Do not scan outside zone boundaries */
 805        low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);
 806
 807        /* Only scan within a pageblock boundary */
 808        end_pfn = ALIGN(low_pfn + 1, pageblock_nr_pages);
 809
 810        /* Do not cross the free scanner or scan within a memory hole */
 811        if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
 812                cc->migrate_pfn = end_pfn;
 813                return ISOLATE_NONE;
 814        }
 815
 816        /* Perform the isolation */
 817        low_pfn = isolate_migratepages_range(zone, cc, low_pfn, end_pfn, false);
 818        if (!low_pfn || cc->contended)
 819                return ISOLATE_ABORT;
 820
 821        cc->migrate_pfn = low_pfn;
 822
 823        return ISOLATE_SUCCESS;
 824}
 825
 826static int compact_finished(struct zone *zone,
 827                            struct compact_control *cc)
 828{
 829        unsigned int order;
 830        unsigned long watermark;
 831
 832        if (fatal_signal_pending(current))
 833                return COMPACT_PARTIAL;
 834
 835        /* Compaction run completes if the migrate and free scanner meet */
 836        if (cc->free_pfn <= cc->migrate_pfn) {
 837                /*
 838                 * Mark that the PG_migrate_skip information should be cleared
 839                 * by kswapd when it goes to sleep. kswapd does not set the
 840                 * flag itself as the decision to be clear should be directly
 841                 * based on an allocation request.
 842                 */
 843                if (!current_is_kswapd())
 844                        zone->compact_blockskip_flush = true;
 845
 846                return COMPACT_COMPLETE;
 847        }
 848
 849        /*
 850         * order == -1 is expected when compacting via
 851         * /proc/sys/vm/compact_memory
 852         */
 853        if (cc->order == -1)
 854                return COMPACT_CONTINUE;
 855
 856        /* Compaction run is not finished if the watermark is not met */
 857        watermark = low_wmark_pages(zone);
 858        watermark += (1 << cc->order);
 859
 860        if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0))
 861                return COMPACT_CONTINUE;
 862
 863        /* Direct compactor: Is a suitable page free? */
 864        for (order = cc->order; order < MAX_ORDER; order++) {
 865                struct free_area *area = &zone->free_area[order];
 866
 867                /* Job done if page is free of the right migratetype */
 868                if (!list_empty(&area->free_list[cc->migratetype]))
 869                        return COMPACT_PARTIAL;
 870
 871                /* Job done if allocation would set block type */
 872                if (cc->order >= pageblock_order && area->nr_free)
 873                        return COMPACT_PARTIAL;
 874        }
 875
 876        return COMPACT_CONTINUE;
 877}
 878
 879/*
 880 * compaction_suitable: Is this suitable to run compaction on this zone now?
 881 * Returns
 882 *   COMPACT_SKIPPED  - If there are too few free pages for compaction
 883 *   COMPACT_PARTIAL  - If the allocation would succeed without compaction
 884 *   COMPACT_CONTINUE - If compaction should run now
 885 */
 886unsigned long compaction_suitable(struct zone *zone, int order)
 887{
 888        int fragindex;
 889        unsigned long watermark;
 890
 891        /*
 892         * order == -1 is expected when compacting via
 893         * /proc/sys/vm/compact_memory
 894         */
 895        if (order == -1)
 896                return COMPACT_CONTINUE;
 897
 898        /*
 899         * Watermarks for order-0 must be met for compaction. Note the 2UL.
 900         * This is because during migration, copies of pages need to be
 901         * allocated and for a short time, the footprint is higher
 902         */
 903        watermark = low_wmark_pages(zone) + (2UL << order);
 904        if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
 905                return COMPACT_SKIPPED;
 906
 907        /*
 908         * fragmentation index determines if allocation failures are due to
 909         * low memory or external fragmentation
 910         *
 911         * index of -1000 implies allocations might succeed depending on
 912         * watermarks
 913         * index towards 0 implies failure is due to lack of memory
 914         * index towards 1000 implies failure is due to fragmentation
 915         *
 916         * Only compact if a failure would be due to fragmentation.
 917         */
 918        fragindex = fragmentation_index(zone, order);
 919        if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
 920                return COMPACT_SKIPPED;
 921
 922        if (fragindex == -1000 && zone_watermark_ok(zone, order, watermark,
 923            0, 0))
 924                return COMPACT_PARTIAL;
 925
 926        return COMPACT_CONTINUE;
 927}
 928
 929static int compact_zone(struct zone *zone, struct compact_control *cc)
 930{
 931        int ret;
 932        unsigned long start_pfn = zone->zone_start_pfn;
 933        unsigned long end_pfn = zone_end_pfn(zone);
 934
 935        ret = compaction_suitable(zone, cc->order);
 936        switch (ret) {
 937        case COMPACT_PARTIAL:
 938        case COMPACT_SKIPPED:
 939                /* Compaction is likely to fail */
 940                return ret;
 941        case COMPACT_CONTINUE:
 942                /* Fall through to compaction */
 943                ;
 944        }
 945
 946        /*
 947         * Setup to move all movable pages to the end of the zone. Used cached
 948         * information on where the scanners should start but check that it
 949         * is initialised by ensuring the values are within zone boundaries.
 950         */
 951        cc->migrate_pfn = zone->compact_cached_migrate_pfn;
 952        cc->free_pfn = zone->compact_cached_free_pfn;
 953        if (cc->free_pfn < start_pfn || cc->free_pfn > end_pfn) {
 954                cc->free_pfn = end_pfn & ~(pageblock_nr_pages-1);
 955                zone->compact_cached_free_pfn = cc->free_pfn;
 956        }
 957        if (cc->migrate_pfn < start_pfn || cc->migrate_pfn > end_pfn) {
 958                cc->migrate_pfn = start_pfn;
 959                zone->compact_cached_migrate_pfn = cc->migrate_pfn;
 960        }
 961
 962        /*
 963         * Clear pageblock skip if there were failures recently and compaction
 964         * is about to be retried after being deferred. kswapd does not do
 965         * this reset as it'll reset the cached information when going to sleep.
 966         */
 967        if (compaction_restarting(zone, cc->order) && !current_is_kswapd())
 968                __reset_isolation_suitable(zone);
 969
 970        migrate_prep_local();
 971
 972        while ((ret = compact_finished(zone, cc)) == COMPACT_CONTINUE) {
 973                unsigned long nr_migrate, nr_remaining;
 974                int err;
 975
 976                switch (isolate_migratepages(zone, cc)) {
 977                case ISOLATE_ABORT:
 978                        ret = COMPACT_PARTIAL;
 979                        putback_movable_pages(&cc->migratepages);
 980                        cc->nr_migratepages = 0;
 981                        goto out;
 982                case ISOLATE_NONE:
 983                        continue;
 984                case ISOLATE_SUCCESS:
 985                        ;
 986                }
 987
 988                nr_migrate = cc->nr_migratepages;
 989                err = migrate_pages(&cc->migratepages, compaction_alloc,
 990                                (unsigned long)cc,
 991                                cc->sync ? MIGRATE_SYNC_LIGHT : MIGRATE_ASYNC,
 992                                MR_COMPACTION);
 993                update_nr_listpages(cc);
 994                nr_remaining = cc->nr_migratepages;
 995
 996                trace_mm_compaction_migratepages(nr_migrate - nr_remaining,
 997                                                nr_remaining);
 998
 999                /* Release isolated pages not migrated */
1000                if (err) {
1001                        putback_movable_pages(&cc->migratepages);
1002                        cc->nr_migratepages = 0;
1003                        if (err == -ENOMEM) {
1004                                ret = COMPACT_PARTIAL;
1005                                goto out;
1006                        }
1007                }
1008        }
1009
1010out:
1011        /* Release free pages and check accounting */
1012        cc->nr_freepages -= release_freepages(&cc->freepages);
1013        VM_BUG_ON(cc->nr_freepages != 0);
1014
1015        return ret;
1016}
1017
1018static unsigned long compact_zone_order(struct zone *zone,
1019                                 int order, gfp_t gfp_mask,
1020                                 bool sync, bool *contended)
1021{
1022        unsigned long ret;
1023        struct compact_control cc = {
1024                .nr_freepages = 0,
1025                .nr_migratepages = 0,
1026                .order = order,
1027                .migratetype = allocflags_to_migratetype(gfp_mask),
1028                .zone = zone,
1029                .sync = sync,
1030        };
1031        INIT_LIST_HEAD(&cc.freepages);
1032        INIT_LIST_HEAD(&cc.migratepages);
1033
1034        ret = compact_zone(zone, &cc);
1035
1036        VM_BUG_ON(!list_empty(&cc.freepages));
1037        VM_BUG_ON(!list_empty(&cc.migratepages));
1038
1039        *contended = cc.contended;
1040        return ret;
1041}
1042
1043int sysctl_extfrag_threshold = 500;
1044
1045/**
1046 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
1047 * @zonelist: The zonelist used for the current allocation
1048 * @order: The order of the current allocation
1049 * @gfp_mask: The GFP mask of the current allocation
1050 * @nodemask: The allowed nodes to allocate from
1051 * @sync: Whether migration is synchronous or not
1052 * @contended: Return value that is true if compaction was aborted due to lock contention
1053 * @page: Optionally capture a free page of the requested order during compaction
1054 *
1055 * This is the main entry point for direct page compaction.
1056 */
1057unsigned long try_to_compact_pages(struct zonelist *zonelist,
1058                        int order, gfp_t gfp_mask, nodemask_t *nodemask,
1059                        bool sync, bool *contended)
1060{
1061        enum zone_type high_zoneidx = gfp_zone(gfp_mask);
1062        int may_enter_fs = gfp_mask & __GFP_FS;
1063        int may_perform_io = gfp_mask & __GFP_IO;
1064        struct zoneref *z;
1065        struct zone *zone;
1066        int rc = COMPACT_SKIPPED;
1067        int alloc_flags = 0;
1068
1069        /* Check if the GFP flags allow compaction */
1070        if (!order || !may_enter_fs || !may_perform_io)
1071                return rc;
1072
1073        count_compact_event(COMPACTSTALL);
1074
1075#ifdef CONFIG_CMA
1076        if (allocflags_to_migratetype(gfp_mask) == MIGRATE_MOVABLE)
1077                alloc_flags |= ALLOC_CMA;
1078#endif
1079        /* Compact each zone in the list */
1080        for_each_zone_zonelist_nodemask(zone, z, zonelist, high_zoneidx,
1081                                                                nodemask) {
1082                int status;
1083
1084                status = compact_zone_order(zone, order, gfp_mask, sync,
1085                                                contended);
1086                rc = max(status, rc);
1087
1088                /* If a normal allocation would succeed, stop compacting */
1089                if (zone_watermark_ok(zone, order, low_wmark_pages(zone), 0,
1090                                      alloc_flags))
1091                        break;
1092        }
1093
1094        return rc;
1095}
1096
1097
1098/* Compact all zones within a node */
1099static void __compact_pgdat(pg_data_t *pgdat, struct compact_control *cc)
1100{
1101        int zoneid;
1102        struct zone *zone;
1103
1104        for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
1105
1106                zone = &pgdat->node_zones[zoneid];
1107                if (!populated_zone(zone))
1108                        continue;
1109
1110                cc->nr_freepages = 0;
1111                cc->nr_migratepages = 0;
1112                cc->zone = zone;
1113                INIT_LIST_HEAD(&cc->freepages);
1114                INIT_LIST_HEAD(&cc->migratepages);
1115
1116                if (cc->order == -1 || !compaction_deferred(zone, cc->order))
1117                        compact_zone(zone, cc);
1118
1119                if (cc->order > 0) {
1120                        int ok = zone_watermark_ok(zone, cc->order,
1121                                                low_wmark_pages(zone), 0, 0);
1122                        if (ok && cc->order >= zone->compact_order_failed)
1123                                zone->compact_order_failed = cc->order + 1;
1124                        /* Currently async compaction is never deferred. */
1125                        else if (!ok && cc->sync)
1126                                defer_compaction(zone, cc->order);
1127                }
1128
1129                VM_BUG_ON(!list_empty(&cc->freepages));
1130                VM_BUG_ON(!list_empty(&cc->migratepages));
1131        }
1132}
1133
1134void compact_pgdat(pg_data_t *pgdat, int order)
1135{
1136        struct compact_control cc = {
1137                .order = order,
1138                .sync = false,
1139        };
1140
1141        if (!order)
1142                return;
1143
1144        __compact_pgdat(pgdat, &cc);
1145}
1146
1147static void compact_node(int nid)
1148{
1149        struct compact_control cc = {
1150                .order = -1,
1151                .sync = true,
1152        };
1153
1154        __compact_pgdat(NODE_DATA(nid), &cc);
1155}
1156
1157/* Compact all nodes in the system */
1158static void compact_nodes(void)
1159{
1160        int nid;
1161
1162        /* Flush pending updates to the LRU lists */
1163        lru_add_drain_all();
1164
1165        for_each_online_node(nid)
1166                compact_node(nid);
1167}
1168
1169/* The written value is actually unused, all memory is compacted */
1170int sysctl_compact_memory;
1171
1172/* This is the entry point for compacting all nodes via /proc/sys/vm */
1173int sysctl_compaction_handler(struct ctl_table *table, int write,
1174                        void __user *buffer, size_t *length, loff_t *ppos)
1175{
1176        if (write)
1177                compact_nodes();
1178
1179        return 0;
1180}
1181
1182int sysctl_extfrag_handler(struct ctl_table *table, int write,
1183                        void __user *buffer, size_t *length, loff_t *ppos)
1184{
1185        proc_dointvec_minmax(table, write, buffer, length, ppos);
1186
1187        return 0;
1188}
1189
1190#if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
1191ssize_t sysfs_compact_node(struct device *dev,
1192                        struct device_attribute *attr,
1193                        const char *buf, size_t count)
1194{
1195        int nid = dev->id;
1196
1197        if (nid >= 0 && nid < nr_node_ids && node_online(nid)) {
1198                /* Flush pending updates to the LRU lists */
1199                lru_add_drain_all();
1200
1201                compact_node(nid);
1202        }
1203
1204        return count;
1205}
1206static DEVICE_ATTR(compact, S_IWUSR, NULL, sysfs_compact_node);
1207
1208int compaction_register_node(struct node *node)
1209{
1210        return device_create_file(&node->dev, &dev_attr_compact);
1211}
1212
1213void compaction_unregister_node(struct node *node)
1214{
1215        return device_remove_file(&node->dev, &dev_attr_compact);
1216}
1217#endif /* CONFIG_SYSFS && CONFIG_NUMA */
1218
1219#endif /* CONFIG_COMPACTION */
1220
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