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