mm/compaction.c

   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/cpu.h>
  11 #include <linux/swap.h>
  12 #include <linux/migrate.h>
  13 #include <linux/compaction.h>
  14 #include <linux/mm_inline.h>
  15 #include <linux/backing-dev.h>
  16 #include <linux/sysctl.h>
  17 #include <linux/sysfs.h>
  18 #include <linux/page-isolation.h>
  19 #include <linux/kasan.h>
  20 #include <linux/kthread.h>
  21 #include <linux/freezer.h>
  22 #include <linux/page_owner.h>
  23 #include "internal.h"
  24
  25 #ifdef CONFIG_COMPACTION
  26 static inline void count_compact_event(enum vm_event_item item)
  27 {
  28         count_vm_event(item);
  29 }
  30
  31 static inline void count_compact_events(enum vm_event_item item, long delta)
  32 {
  33         count_vm_events(item, delta);
  34 }
  35 #else
  36 #define count_compact_event(item) do { } while (0)
  37 #define count_compact_events(item, delta) do { } while (0)
  38 #endif
  39
  40 #if defined CONFIG_COMPACTION || defined CONFIG_CMA
  41
  42 #define CREATE_TRACE_POINTS
  43 #include <trace/events/compaction.h>
  44
  45 #define block_start_pfn(pfn, order)     round_down(pfn, 1UL << (order))
  46 #define block_end_pfn(pfn, order)       ALIGN((pfn) + 1, 1UL << (order))
  47 #define pageblock_start_pfn(pfn)        block_start_pfn(pfn, pageblock_order)
  48 #define pageblock_end_pfn(pfn)          block_end_pfn(pfn, pageblock_order)
  49
  50 static unsigned long release_freepages(struct list_head *freelist)
  51 {
  52         struct page *page, *next;
  53         unsigned long high_pfn = 0;
  54
  55         list_for_each_entry_safe(page, next, freelist, lru) {
  56                 unsigned long pfn = page_to_pfn(page);
  57                 list_del(&page->lru);
  58                 __free_page(page);
  59                 if (pfn > high_pfn)
  60                         high_pfn = pfn;
  61         }
  62
  63         return high_pfn;
  64 }
  65
  66 static void map_pages(struct list_head *list)
  67 {
  68         unsigned int i, order, nr_pages;
  69         struct page *page, *next;
  70         LIST_HEAD(tmp_list);
  71
  72         list_for_each_entry_safe(page, next, list, lru) {
  73                 list_del(&page->lru);
  74
  75                 order = page_private(page);
  76                 nr_pages = 1 << order;
  77
  78                 post_alloc_hook(page, order, __GFP_MOVABLE);
  79                 if (order)
  80                         split_page(page, order);
  81
  82                 for (i = 0; i < nr_pages; i++) {
  83                         list_add(&page->lru, &tmp_list);
  84                         page++;
  85                 }
  86         }
  87
  88         list_splice(&tmp_list, list);
  89 }
  90
  91 static inline bool migrate_async_suitable(int migratetype)
  92 {
  93         return is_migrate_cma(migratetype) || migratetype == MIGRATE_MOVABLE;
  94 }
  95
  96 #ifdef CONFIG_COMPACTION
  97
  98 int PageMovable(struct page *page)
  99 {
 100         struct address_space *mapping;
 101
 102         VM_BUG_ON_PAGE(!PageLocked(page), page);
 103         if (!__PageMovable(page))
 104                 return 0;
 105
 106         mapping = page_mapping(page);
 107         if (mapping && mapping->a_ops && mapping->a_ops->isolate_page)
 108                 return 1;
 109
 110         return 0;
 111 }
 112 EXPORT_SYMBOL(PageMovable);
 113
 114 void __SetPageMovable(struct page *page, struct address_space *mapping)
 115 {
 116         VM_BUG_ON_PAGE(!PageLocked(page), page);
 117         VM_BUG_ON_PAGE((unsigned long)mapping & PAGE_MAPPING_MOVABLE, page);
 118         page->mapping = (void *)((unsigned long)mapping | PAGE_MAPPING_MOVABLE);
 119 }
 120 EXPORT_SYMBOL(__SetPageMovable);
 121
 122 void __ClearPageMovable(struct page *page)
 123 {
 124         VM_BUG_ON_PAGE(!PageLocked(page), page);
 125         VM_BUG_ON_PAGE(!PageMovable(page), page);
 126         /*
 127          * Clear registered address_space val with keeping PAGE_MAPPING_MOVABLE
 128          * flag so that VM can catch up released page by driver after isolation.
 129          * With it, VM migration doesn't try to put it back.
 130          */
 131         page->mapping = (void *)((unsigned long)page->mapping &
 132                                 PAGE_MAPPING_MOVABLE);
 133 }
 134 EXPORT_SYMBOL(__ClearPageMovable);
 135
 136 /* Do not skip compaction more than 64 times */
 137 #define COMPACT_MAX_DEFER_SHIFT 6
 138
 139 /*
 140  * Compaction is deferred when compaction fails to result in a page
 141  * allocation success. 1 << compact_defer_limit compactions are skipped up
 142  * to a limit of 1 << COMPACT_MAX_DEFER_SHIFT
 143  */
 144 void defer_compaction(struct zone *zone, int order)
 145 {
 146         zone->compact_considered = 0;
 147         zone->compact_defer_shift++;
 148
 149         if (order < zone->compact_order_failed)
 150                 zone->compact_order_failed = order;
 151
 152         if (zone->compact_defer_shift > COMPACT_MAX_DEFER_SHIFT)
 153                 zone->compact_defer_shift = COMPACT_MAX_DEFER_SHIFT;
 154
 155         trace_mm_compaction_defer_compaction(zone, order);
 156 }
 157
 158 /* Returns true if compaction should be skipped this time */
 159 bool compaction_deferred(struct zone *zone, int order)
 160 {
 161         unsigned long defer_limit = 1UL << zone->compact_defer_shift;
 162
 163         if (order < zone->compact_order_failed)
 164                 return false;
 165
 166         /* Avoid possible overflow */
 167         if (++zone->compact_considered > defer_limit)
 168                 zone->compact_considered = defer_limit;
 169
 170         if (zone->compact_considered >= defer_limit)
 171                 return false;
 172
 173         trace_mm_compaction_deferred(zone, order);
 174
 175         return true;
 176 }
 177
 178 /*
 179  * Update defer tracking counters after successful compaction of given order,
 180  * which means an allocation either succeeded (alloc_success == true) or is
 181  * expected to succeed.
 182  */
 183 void compaction_defer_reset(struct zone *zone, int order,
 184                 bool alloc_success)
 185 {
 186         if (alloc_success) {
 187                 zone->compact_considered = 0;
 188                 zone->compact_defer_shift = 0;
 189         }
 190         if (order >= zone->compact_order_failed)
 191                 zone->compact_order_failed = order + 1;
 192
 193         trace_mm_compaction_defer_reset(zone, order);
 194 }
 195
 196 /* Returns true if restarting compaction after many failures */
 197 bool compaction_restarting(struct zone *zone, int order)
 198 {
 199         if (order < zone->compact_order_failed)
 200                 return false;
 201
 202         return zone->compact_defer_shift == COMPACT_MAX_DEFER_SHIFT &&
 203                 zone->compact_considered >= 1UL << zone->compact_defer_shift;
 204 }
 205
 206 /* Returns true if the pageblock should be scanned for pages to isolate. */
 207 static inline bool isolation_suitable(struct compact_control *cc,
 208                                         struct page *page)
 209 {
 210         if (cc->ignore_skip_hint)
 211                 return true;
 212
 213         return !get_pageblock_skip(page);
 214 }
 215
 216 static void reset_cached_positions(struct zone *zone)
 217 {
 218         zone->compact_cached_migrate_pfn[0] = zone->zone_start_pfn;
 219         zone->compact_cached_migrate_pfn[1] = zone->zone_start_pfn;
 220         zone->compact_cached_free_pfn =
 221                                 pageblock_start_pfn(zone_end_pfn(zone) - 1);
 222 }
 223
 224 /*
 225  * This function is called to clear all cached information on pageblocks that
 226  * should be skipped for page isolation when the migrate and free page scanner
 227  * meet.
 228  */
 229 static void __reset_isolation_suitable(struct zone *zone)
 230 {
 231         unsigned long start_pfn = zone->zone_start_pfn;
 232         unsigned long end_pfn = zone_end_pfn(zone);
 233         unsigned long pfn;
 234
 235         zone->compact_blockskip_flush = false;
 236
 237         /* Walk the zone and mark every pageblock as suitable for isolation */
 238         for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages) {
 239                 struct page *page;
 240
 241                 cond_resched();
 242
 243                 if (!pfn_valid(pfn))
 244                         continue;
 245
 246                 page = pfn_to_page(pfn);
 247                 if (zone != page_zone(page))
 248                         continue;
 249
 250                 clear_pageblock_skip(page);
 251         }
 252
 253         reset_cached_positions(zone);
 254 }
 255
 256 void reset_isolation_suitable(pg_data_t *pgdat)
 257 {
 258         int zoneid;
 259
 260         for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
 261                 struct zone *zone = &pgdat->node_zones[zoneid];
 262                 if (!populated_zone(zone))
 263                         continue;
 264
 265                 /* Only flush if a full compaction finished recently */
 266                 if (zone->compact_blockskip_flush)
 267                         __reset_isolation_suitable(zone);
 268         }
 269 }
 270
 271 /*
 272  * If no pages were isolated then mark this pageblock to be skipped in the
 273  * future. The information is later cleared by __reset_isolation_suitable().
 274  */
 275 static void update_pageblock_skip(struct compact_control *cc,
 276                         struct page *page, unsigned long nr_isolated,
 277                         bool migrate_scanner)
 278 {
 279         struct zone *zone = cc->zone;
 280         unsigned long pfn;
 281
 282         if (cc->ignore_skip_hint)
 283                 return;
 284
 285         if (!page)
 286                 return;
 287
 288         if (nr_isolated)
 289                 return;
 290
 291         set_pageblock_skip(page);
 292
 293         pfn = page_to_pfn(page);
 294
 295         /* Update where async and sync compaction should restart */
 296         if (migrate_scanner) {
 297                 if (pfn > zone->compact_cached_migrate_pfn[0])
 298                         zone->compact_cached_migrate_pfn[0] = pfn;
 299                 if (cc->mode != MIGRATE_ASYNC &&
 300                     pfn > zone->compact_cached_migrate_pfn[1])
 301                         zone->compact_cached_migrate_pfn[1] = pfn;
 302         } else {
 303                 if (pfn < zone->compact_cached_free_pfn)
 304                         zone->compact_cached_free_pfn = pfn;
 305         }
 306 }
 307 #else
 308 static inline bool isolation_suitable(struct compact_control *cc,
 309                                         struct page *page)
 310 {
 311         return true;
 312 }
 313
 314 static void update_pageblock_skip(struct compact_control *cc,
 315                         struct page *page, unsigned long nr_isolated,
 316                         bool migrate_scanner)
 317 {
 318 }
 319 #endif /* CONFIG_COMPACTION */
 320
 321 /*
 322  * Compaction requires the taking of some coarse locks that are potentially
 323  * very heavily contended. For async compaction, back out if the lock cannot
 324  * be taken immediately. For sync compaction, spin on the lock if needed.
 325  *
 326  * Returns true if the lock is held
 327  * Returns false if the lock is not held and compaction should abort
 328  */
 329 static bool compact_trylock_irqsave(spinlock_t *lock, unsigned long *flags,
 330                                                 struct compact_control *cc)
 331 {
 332         if (cc->mode == MIGRATE_ASYNC) {
 333                 if (!spin_trylock_irqsave(lock, *flags)) {
 334                         cc->contended = true;
 335                         return false;
 336                 }
 337         } else {
 338                 spin_lock_irqsave(lock, *flags);
 339         }
 340
 341         return true;
 342 }
 343
 344 /*
 345  * Compaction requires the taking of some coarse locks that are potentially
 346  * very heavily contended. The lock should be periodically unlocked to avoid
 347  * having disabled IRQs for a long time, even when there is nobody waiting on
 348  * the lock. It might also be that allowing the IRQs will result in
 349  * need_resched() becoming true. If scheduling is needed, async compaction
 350  * aborts. Sync compaction schedules.
 351  * Either compaction type will also abort if a fatal signal is pending.
 352  * In either case if the lock was locked, it is dropped and not regained.
 353  *
 354  * Returns true if compaction should abort due to fatal signal pending, or
 355  *              async compaction due to need_resched()
 356  * Returns false when compaction can continue (sync compaction might have
 357  *              scheduled)
 358  */
 359 static bool compact_unlock_should_abort(spinlock_t *lock,
 360                 unsigned long flags, bool *locked, struct compact_control *cc)
 361 {
 362         if (*locked) {
 363                 spin_unlock_irqrestore(lock, flags);
 364                 *locked = false;
 365         }
 366
 367         if (fatal_signal_pending(current)) {
 368                 cc->contended = true;
 369                 return true;
 370         }
 371
 372         if (need_resched()) {
 373                 if (cc->mode == MIGRATE_ASYNC) {
 374                         cc->contended = true;
 375                         return true;
 376                 }
 377                 cond_resched();
 378         }
 379
 380         return false;
 381 }
 382
 383 /*
 384  * Aside from avoiding lock contention, compaction also periodically checks
 385  * need_resched() and either schedules in sync compaction or aborts async
 386  * compaction. This is similar to what compact_unlock_should_abort() does, but
 387  * is used where no lock is concerned.
 388  *
 389  * Returns false when no scheduling was needed, or sync compaction scheduled.
 390  * Returns true when async compaction should abort.
 391  */
 392 static inline bool compact_should_abort(struct compact_control *cc)
 393 {
 394         /* async compaction aborts if contended */
 395         if (need_resched()) {
 396                 if (cc->mode == MIGRATE_ASYNC) {
 397                         cc->contended = true;
 398                         return true;
 399                 }
 400
 401                 cond_resched();
 402         }
 403
 404         return false;
 405 }
 406
 407 /*
 408  * Isolate free pages onto a private freelist. If @strict is true, will abort
 409  * returning 0 on any invalid PFNs or non-free pages inside of the pageblock
 410  * (even though it may still end up isolating some pages).
 411  */
 412 static unsigned long isolate_freepages_block(struct compact_control *cc,
 413                                 unsigned long *start_pfn,
 414                                 unsigned long end_pfn,
 415                                 struct list_head *freelist,
 416                                 bool strict)
 417 {
 418         int nr_scanned = 0, total_isolated = 0;
 419         struct page *cursor, *valid_page = NULL;
 420         unsigned long flags = 0;
 421         bool locked = false;
 422         unsigned long blockpfn = *start_pfn;
 423         unsigned int order;
 424
 425         cursor = pfn_to_page(blockpfn);
 426
 427         /* Isolate free pages. */
 428         for (; blockpfn < end_pfn; blockpfn++, cursor++) {
 429                 int isolated;
 430                 struct page *page = cursor;
 431
 432                 /*
 433                  * Periodically drop the lock (if held) regardless of its
 434                  * contention, to give chance to IRQs. Abort if fatal signal
 435                  * pending or async compaction detects need_resched()
 436                  */
 437                 if (!(blockpfn % SWAP_CLUSTER_MAX)
 438                     && compact_unlock_should_abort(&cc->zone->lock, flags,
 439                                                                 &locked, cc))
 440                         break;
 441
 442                 nr_scanned++;
 443                 if (!pfn_valid_within(blockpfn))
 444                         goto isolate_fail;
 445
 446                 if (!valid_page)
 447                         valid_page = page;
 448
 449                 /*
 450                  * For compound pages such as THP and hugetlbfs, we can save
 451                  * potentially a lot of iterations if we skip them at once.
 452                  * The check is racy, but we can consider only valid values
 453                  * and the only danger is skipping too much.
 454                  */
 455                 if (PageCompound(page)) {
 456                         unsigned int comp_order = compound_order(page);
 457
 458                         if (likely(comp_order < MAX_ORDER)) {
 459                                 blockpfn += (1UL << comp_order) - 1;
 460                                 cursor += (1UL << comp_order) - 1;
 461                         }
 462
 463                         goto isolate_fail;
 464                 }
 465
 466                 if (!PageBuddy(page))
 467                         goto isolate_fail;
 468
 469                 /*
 470                  * If we already hold the lock, we can skip some rechecking.
 471                  * Note that if we hold the lock now, checked_pageblock was
 472                  * already set in some previous iteration (or strict is true),
 473                  * so it is correct to skip the suitable migration target
 474                  * recheck as well.
 475                  */
 476                 if (!locked) {
 477                         /*
 478                          * The zone lock must be held to isolate freepages.
 479                          * Unfortunately this is a very coarse lock and can be
 480                          * heavily contended if there are parallel allocations
 481                          * or parallel compactions. For async compaction do not
 482                          * spin on the lock and we acquire the lock as late as
 483                          * possible.
 484                          */
 485                         locked = compact_trylock_irqsave(&cc->zone->lock,
 486                                                                 &flags, cc);
 487                         if (!locked)
 488                                 break;
 489
 490                         /* Recheck this is a buddy page under lock */
 491                         if (!PageBuddy(page))
 492                                 goto isolate_fail;
 493                 }
 494
 495                 /* Found a free page, will break it into order-0 pages */
 496                 order = page_order(page);
 497                 isolated = __isolate_free_page(page, order);
 498                 if (!isolated)
 499                         break;
 500                 set_page_private(page, order);
 501
 502                 total_isolated += isolated;
 503                 cc->nr_freepages += isolated;
 504                 list_add_tail(&page->lru, freelist);
 505
 506                 if (!strict && cc->nr_migratepages <= cc->nr_freepages) {
 507                         blockpfn += isolated;
 508                         break;
 509                 }
 510                 /* Advance to the end of split page */
 511                 blockpfn += isolated - 1;
 512                 cursor += isolated - 1;
 513                 continue;
 514
 515 isolate_fail:
 516                 if (strict)
 517                         break;
 518                 else
 519                         continue;
 520
 521         }
 522
 523         if (locked)
 524                 spin_unlock_irqrestore(&cc->zone->lock, flags);
 525
 526         /*
 527          * There is a tiny chance that we have read bogus compound_order(),
 528          * so be careful to not go outside of the pageblock.
 529          */
 530         if (unlikely(blockpfn > end_pfn))
 531                 blockpfn = end_pfn;
 532
 533         trace_mm_compaction_isolate_freepages(*start_pfn, blockpfn,
 534                                         nr_scanned, total_isolated);
 535
 536         /* Record how far we have got within the block */
 537         *start_pfn = blockpfn;
 538
 539         /*
 540          * If strict isolation is requested by CMA then check that all the
 541          * pages requested were isolated. If there were any failures, 0 is
 542          * returned and CMA will fail.
 543          */
 544         if (strict && blockpfn < end_pfn)
 545                 total_isolated = 0;
 546
 547         /* Update the pageblock-skip if the whole pageblock was scanned */
 548         if (blockpfn == end_pfn)
 549                 update_pageblock_skip(cc, valid_page, total_isolated, false);
 550
 551         count_compact_events(COMPACTFREE_SCANNED, nr_scanned);
 552         if (total_isolated)
 553                 count_compact_events(COMPACTISOLATED, total_isolated);
 554         return total_isolated;
 555 }
 556
 557 /**
 558  * isolate_freepages_range() - isolate free pages.
 559  * @start_pfn: The first PFN to start isolating.
 560  * @end_pfn:   The one-past-last PFN.
 561  *
 562  * Non-free pages, invalid PFNs, or zone boundaries within the
 563  * [start_pfn, end_pfn) range are considered errors, cause function to
 564  * undo its actions and return zero.
 565  *
 566  * Otherwise, function returns one-past-the-last PFN of isolated page
 567  * (which may be greater then end_pfn if end fell in a middle of
 568  * a free page).
 569  */
 570 unsigned long
 571 isolate_freepages_range(struct compact_control *cc,
 572                         unsigned long start_pfn, unsigned long end_pfn)
 573 {
 574         unsigned long isolated, pfn, block_start_pfn, block_end_pfn;
 575         LIST_HEAD(freelist);
 576
 577         pfn = start_pfn;
 578         block_start_pfn = pageblock_start_pfn(pfn);
 579         if (block_start_pfn < cc->zone->zone_start_pfn)
 580                 block_start_pfn = cc->zone->zone_start_pfn;
 581         block_end_pfn = pageblock_end_pfn(pfn);
 582
 583         for (; pfn < end_pfn; pfn += isolated,
 584                                 block_start_pfn = block_end_pfn,
 585                                 block_end_pfn += pageblock_nr_pages) {
 586                 /* Protect pfn from changing by isolate_freepages_block */
 587                 unsigned long isolate_start_pfn = pfn;
 588
 589                 block_end_pfn = min(block_end_pfn, end_pfn);
 590
 591                 /*
 592                  * pfn could pass the block_end_pfn if isolated freepage
 593                  * is more than pageblock order. In this case, we adjust
 594                  * scanning range to right one.
 595                  */
 596                 if (pfn >= block_end_pfn) {
 597                         block_start_pfn = pageblock_start_pfn(pfn);
 598                         block_end_pfn = pageblock_end_pfn(pfn);
 599                         block_end_pfn = min(block_end_pfn, end_pfn);
 600                 }
 601
 602                 if (!pageblock_pfn_to_page(block_start_pfn,
 603                                         block_end_pfn, cc->zone))
 604                         break;
 605
 606                 isolated = isolate_freepages_block(cc, &isolate_start_pfn,
 607                                                 block_end_pfn, &freelist, true);
 608
 609                 /*
 610                  * In strict mode, isolate_freepages_block() returns 0 if
 611                  * there are any holes in the block (ie. invalid PFNs or
 612                  * non-free pages).
 613                  */
 614                 if (!isolated)
 615                         break;
 616
 617                 /*
 618                  * If we managed to isolate pages, it is always (1 << n) *
 619                  * pageblock_nr_pages for some non-negative n.  (Max order
 620                  * page may span two pageblocks).
 621                  */
 622         }
 623
 624         /* __isolate_free_page() does not map the pages */
 625         map_pages(&freelist);
 626
 627         if (pfn < end_pfn) {
 628                 /* Loop terminated early, cleanup. */
 629                 release_freepages(&freelist);
 630                 return 0;
 631         }
 632
 633         /* We don't use freelists for anything. */
 634         return pfn;
 635 }
 636
 637 /* Similar to reclaim, but different enough that they don't share logic */
 638 static bool too_many_isolated(struct zone *zone)
 639 {
 640         unsigned long active, inactive, isolated;
 641
 642         inactive = node_page_state(zone->zone_pgdat, NR_INACTIVE_FILE) +
 643                         node_page_state(zone->zone_pgdat, NR_INACTIVE_ANON);
 644         active = node_page_state(zone->zone_pgdat, NR_ACTIVE_FILE) +
 645                         node_page_state(zone->zone_pgdat, NR_ACTIVE_ANON);
 646         isolated = node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE) +
 647                         node_page_state(zone->zone_pgdat, NR_ISOLATED_ANON);
 648
 649         return isolated > (inactive + active) / 2;
 650 }
 651
 652 /**
 653  * isolate_migratepages_block() - isolate all migrate-able pages within
 654  *                                a single pageblock
 655  * @cc:         Compaction control structure.
 656  * @low_pfn:    The first PFN to isolate
 657  * @end_pfn:    The one-past-the-last PFN to isolate, within same pageblock
 658  * @isolate_mode: Isolation mode to be used.
 659  *
 660  * Isolate all pages that can be migrated from the range specified by
 661  * [low_pfn, end_pfn). The range is expected to be within same pageblock.
 662  * Returns zero if there is a fatal signal pending, otherwise PFN of the
 663  * first page that was not scanned (which may be both less, equal to or more
 664  * than end_pfn).
 665  *
 666  * The pages are isolated on cc->migratepages list (not required to be empty),
 667  * and cc->nr_migratepages is updated accordingly. The cc->migrate_pfn field
 668  * is neither read nor updated.
 669  */
 670 static unsigned long
 671 isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 672                         unsigned long end_pfn, isolate_mode_t isolate_mode)
 673 {
 674         struct zone *zone = cc->zone;
 675         unsigned long nr_scanned = 0, nr_isolated = 0;
 676         struct lruvec *lruvec;
 677         unsigned long flags = 0;
 678         bool locked = false;
 679         struct page *page = NULL, *valid_page = NULL;
 680         unsigned long start_pfn = low_pfn;
 681         bool skip_on_failure = false;
 682         unsigned long next_skip_pfn = 0;
 683
 684         /*
 685          * Ensure that there are not too many pages isolated from the LRU
 686          * list by either parallel reclaimers or compaction. If there are,
 687          * delay for some time until fewer pages are isolated
 688          */
 689         while (unlikely(too_many_isolated(zone))) {
 690                 /* async migration should just abort */
 691                 if (cc->mode == MIGRATE_ASYNC)
 692                         return 0;
 693
 694                 congestion_wait(BLK_RW_ASYNC, HZ/10);
 695
 696                 if (fatal_signal_pending(current))
 697                         return 0;
 698         }
 699
 700         if (compact_should_abort(cc))
 701                 return 0;
 702
 703         if (cc->direct_compaction && (cc->mode == MIGRATE_ASYNC)) {
 704                 skip_on_failure = true;
 705                 next_skip_pfn = block_end_pfn(low_pfn, cc->order);
 706         }
 707
 708         /* Time to isolate some pages for migration */
 709         for (; low_pfn < end_pfn; low_pfn++) {
 710
 711                 if (skip_on_failure && low_pfn >= next_skip_pfn) {
 712                         /*
 713                          * We have isolated all migration candidates in the
 714                          * previous order-aligned block, and did not skip it due
 715                          * to failure. We should migrate the pages now and
 716                          * hopefully succeed compaction.
 717                          */
 718                         if (nr_isolated)
 719                                 break;
 720
 721                         /*
 722                          * We failed to isolate in the previous order-aligned
 723                          * block. Set the new boundary to the end of the
 724                          * current block. Note we can't simply increase
 725                          * next_skip_pfn by 1 << order, as low_pfn might have
 726                          * been incremented by a higher number due to skipping
 727                          * a compound or a high-order buddy page in the
 728                          * previous loop iteration.
 729                          */
 730                         next_skip_pfn = block_end_pfn(low_pfn, cc->order);
 731                 }
 732
 733                 /*
 734                  * Periodically drop the lock (if held) regardless of its
 735                  * contention, to give chance to IRQs. Abort async compaction
 736                  * if contended.
 737                  */
 738                 if (!(low_pfn % SWAP_CLUSTER_MAX)
 739                     && compact_unlock_should_abort(zone_lru_lock(zone), flags,
 740                                                                 &locked, cc))
 741                         break;
 742
 743                 if (!pfn_valid_within(low_pfn))
 744                         goto isolate_fail;
 745                 nr_scanned++;
 746
 747                 page = pfn_to_page(low_pfn);
 748
 749                 if (!valid_page)
 750                         valid_page = page;
 751
 752                 /*
 753                  * Skip if free. We read page order here without zone lock
 754                  * which is generally unsafe, but the race window is small and
 755                  * the worst thing that can happen is that we skip some
 756                  * potential isolation targets.
 757                  */
 758                 if (PageBuddy(page)) {
 759                         unsigned long freepage_order = page_order_unsafe(page);
 760
 761                         /*
 762                          * Without lock, we cannot be sure that what we got is
 763                          * a valid page order. Consider only values in the
 764                          * valid order range to prevent low_pfn overflow.
 765                          */
 766                         if (freepage_order > 0 && freepage_order < MAX_ORDER)
 767                                 low_pfn += (1UL << freepage_order) - 1;
 768                         continue;
 769                 }
 770
 771                 /*
 772                  * Regardless of being on LRU, compound pages such as THP and
 773                  * hugetlbfs are not to be compacted. We can potentially save
 774                  * a lot of iterations if we skip them at once. The check is
 775                  * racy, but we can consider only valid values and the only
 776                  * danger is skipping too much.
 777                  */
 778                 if (PageCompound(page)) {
 779                         unsigned int comp_order = compound_order(page);
 780
 781                         if (likely(comp_order < MAX_ORDER))
 782                                 low_pfn += (1UL << comp_order) - 1;
 783
 784                         goto isolate_fail;
 785                 }
 786
 787                 /*
 788                  * Check may be lockless but that's ok as we recheck later.
 789                  * It's possible to migrate LRU and non-lru movable pages.
 790                  * Skip any other type of page
 791                  */
 792                 if (!PageLRU(page)) {
 793                         /*
 794                          * __PageMovable can return false positive so we need
 795                          * to verify it under page_lock.
 796                          */
 797                         if (unlikely(__PageMovable(page)) &&
 798                                         !PageIsolated(page)) {
 799                                 if (locked) {
 800                                         spin_unlock_irqrestore(zone_lru_lock(zone),
 801                                                                         flags);
 802                                         locked = false;
 803                                 }
 804
 805                                 if (isolate_movable_page(page, isolate_mode))
 806                                         goto isolate_success;
 807                         }
 808
 809                         goto isolate_fail;
 810                 }
 811
 812                 /*
 813                  * Migration will fail if an anonymous page is pinned in memory,
 814                  * so avoid taking lru_lock and isolating it unnecessarily in an
 815                  * admittedly racy check.
 816                  */
 817                 if (!page_mapping(page) &&
 818                     page_count(page) > page_mapcount(page))
 819                         goto isolate_fail;
 820
 821                 /*
 822                  * Only allow to migrate anonymous pages in GFP_NOFS context
 823                  * because those do not depend on fs locks.
 824                  */
 825                 if (!(cc->gfp_mask & __GFP_FS) && page_mapping(page))
 826                         goto isolate_fail;
 827
 828                 /* If we already hold the lock, we can skip some rechecking */
 829                 if (!locked) {
 830                         locked = compact_trylock_irqsave(zone_lru_lock(zone),
 831                                                                 &flags, cc);
 832                         if (!locked)
 833                                 break;
 834
 835                         /* Recheck PageLRU and PageCompound under lock */
 836                         if (!PageLRU(page))
 837                                 goto isolate_fail;
 838
 839                         /*
 840                          * Page become compound since the non-locked check,
 841                          * and it's on LRU. It can only be a THP so the order
 842                          * is safe to read and it's 0 for tail pages.
 843                          */
 844                         if (unlikely(PageCompound(page))) {
 845                                 low_pfn += (1UL << compound_order(page)) - 1;
 846                                 goto isolate_fail;
 847                         }
 848                 }
 849
 850                 lruvec = mem_cgroup_page_lruvec(page, zone->zone_pgdat);
 851
 852                 /* Try isolate the page */
 853                 if (__isolate_lru_page(page, isolate_mode) != 0)
 854                         goto isolate_fail;
 855
 856                 VM_BUG_ON_PAGE(PageCompound(page), page);
 857
 858                 /* Successfully isolated */
 859                 del_page_from_lru_list(page, lruvec, page_lru(page));
 860                 inc_node_page_state(page,
 861                                 NR_ISOLATED_ANON + page_is_file_cache(page));
 862
 863 isolate_success:
 864                 list_add(&page->lru, &cc->migratepages);
 865                 cc->nr_migratepages++;
 866                 nr_isolated++;
 867
 868                 /*
 869                  * Record where we could have freed pages by migration and not
 870                  * yet flushed them to buddy allocator.
 871                  * - this is the lowest page that was isolated and likely be
 872                  * then freed by migration.
 873                  */
 874                 if (!cc->last_migrated_pfn)
 875                         cc->last_migrated_pfn = low_pfn;
 876
 877                 /* Avoid isolating too much */
 878                 if (cc->nr_migratepages == COMPACT_CLUSTER_MAX) {
 879                         ++low_pfn;
 880                         break;
 881                 }
 882
 883                 continue;
 884 isolate_fail:
 885                 if (!skip_on_failure)
 886                         continue;
 887
 888                 /*
 889                  * We have isolated some pages, but then failed. Release them
 890                  * instead of migrating, as we cannot form the cc->order buddy
 891                  * page anyway.
 892                  */
 893                 if (nr_isolated) {
 894                         if (locked) {
 895                                 spin_unlock_irqrestore(zone_lru_lock(zone), flags);
 896                                 locked = false;
 897                         }
 898                         putback_movable_pages(&cc->migratepages);
 899                         cc->nr_migratepages = 0;
 900                         cc->last_migrated_pfn = 0;
 901                         nr_isolated = 0;
 902                 }
 903
 904                 if (low_pfn < next_skip_pfn) {
 905                         low_pfn = next_skip_pfn - 1;
 906                         /*
 907                          * The check near the loop beginning would have updated
 908                          * next_skip_pfn too, but this is a bit simpler.
 909                          */
 910                         next_skip_pfn += 1UL << cc->order;
 911                 }
 912         }
 913
 914         /*
 915          * The PageBuddy() check could have potentially brought us outside
 916          * the range to be scanned.
 917          */
 918         if (unlikely(low_pfn > end_pfn))
 919                 low_pfn = end_pfn;
 920
 921         if (locked)
 922                 spin_unlock_irqrestore(zone_lru_lock(zone), flags);
 923
 924         /*
 925          * Update the pageblock-skip information and cached scanner pfn,
 926          * if the whole pageblock was scanned without isolating any page.
 927          */
 928         if (low_pfn == end_pfn)
 929                 update_pageblock_skip(cc, valid_page, nr_isolated, true);
 930
 931         trace_mm_compaction_isolate_migratepages(start_pfn, low_pfn,
 932                                                 nr_scanned, nr_isolated);
 933
 934         count_compact_events(COMPACTMIGRATE_SCANNED, nr_scanned);
 935         if (nr_isolated)
 936                 count_compact_events(COMPACTISOLATED, nr_isolated);
 937
 938         return low_pfn;
 939 }
 940
 941 /**
 942  * isolate_migratepages_range() - isolate migrate-able pages in a PFN range
 943  * @cc:        Compaction control structure.
 944  * @start_pfn: The first PFN to start isolating.
 945  * @end_pfn:   The one-past-last PFN.
 946  *
 947  * Returns zero if isolation fails fatally due to e.g. pending signal.
 948  * Otherwise, function returns one-past-the-last PFN of isolated page
 949  * (which may be greater than end_pfn if end fell in a middle of a THP page).
 950  */
 951 unsigned long
 952 isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn,
 953                                                         unsigned long end_pfn)
 954 {
 955         unsigned long pfn, block_start_pfn, block_end_pfn;
 956
 957         /* Scan block by block. First and last block may be incomplete */
 958         pfn = start_pfn;
 959         block_start_pfn = pageblock_start_pfn(pfn);
 960         if (block_start_pfn < cc->zone->zone_start_pfn)
 961                 block_start_pfn = cc->zone->zone_start_pfn;
 962         block_end_pfn = pageblock_end_pfn(pfn);
 963
 964         for (; pfn < end_pfn; pfn = block_end_pfn,
 965                                 block_start_pfn = block_end_pfn,
 966                                 block_end_pfn += pageblock_nr_pages) {
 967
 968                 block_end_pfn = min(block_end_pfn, end_pfn);
 969
 970                 if (!pageblock_pfn_to_page(block_start_pfn,
 971                                         block_end_pfn, cc->zone))
 972                         continue;
 973
 974                 pfn = isolate_migratepages_block(cc, pfn, block_end_pfn,
 975                                                         ISOLATE_UNEVICTABLE);
 976
 977                 if (!pfn)
 978                         break;
 979
 980                 if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
 981                         break;
 982         }
 983
 984         return pfn;
 985 }
 986
 987 #endif /* CONFIG_COMPACTION || CONFIG_CMA */
 988 #ifdef CONFIG_COMPACTION
 989
 990 /* Returns true if the page is within a block suitable for migration to */
 991 static bool suitable_migration_target(struct compact_control *cc,
 992                                                         struct page *page)
 993 {
 994         if (cc->ignore_block_suitable)
 995                 return true;
 996
 997         /* If the page is a large free page, then disallow migration */
 998         if (PageBuddy(page)) {
 999                 /*
1000                  * We are checking page_order without zone->lock taken. But
1001                  * the only small danger is that we skip a potentially suitable
1002                  * pageblock, so it's not worth to check order for valid range.
1003                  */
1004                 if (page_order_unsafe(page) >= pageblock_order)
1005                         return false;
1006         }
1007
1008         /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
1009         if (migrate_async_suitable(get_pageblock_migratetype(page)))
1010                 return true;
1011
1012         /* Otherwise skip the block */
1013         return false;
1014 }
1015
1016 /*
1017  * Test whether the free scanner has reached the same or lower pageblock than
1018  * the migration scanner, and compaction should thus terminate.
1019  */
1020 static inline bool compact_scanners_met(struct compact_control *cc)
1021 {
1022         return (cc->free_pfn >> pageblock_order)
1023                 <= (cc->migrate_pfn >> pageblock_order);
1024 }
1025
1026 /*
1027  * Based on information in the current compact_control, find blocks
1028  * suitable for isolating free pages from and then isolate them.
1029  */
1030 static void isolate_freepages(struct compact_control *cc)
1031 {
1032         struct zone *zone = cc->zone;
1033         struct page *page;
1034         unsigned long block_start_pfn;  /* start of current pageblock */
1035         unsigned long isolate_start_pfn; /* exact pfn we start at */
1036         unsigned long block_end_pfn;    /* end of current pageblock */
1037         unsigned long low_pfn;       /* lowest pfn scanner is able to scan */
1038         struct list_head *freelist = &cc->freepages;
1039
1040         /*
1041          * Initialise the free scanner. The starting point is where we last
1042          * successfully isolated from, zone-cached value, or the end of the
1043          * zone when isolating for the first time. For looping we also need
1044          * this pfn aligned down to the pageblock boundary, because we do
1045          * block_start_pfn -= pageblock_nr_pages in the for loop.
1046          * For ending point, take care when isolating in last pageblock of a
1047          * a zone which ends in the middle of a pageblock.
1048          * The low boundary is the end of the pageblock the migration scanner
1049          * is using.
1050          */
1051         isolate_start_pfn = cc->free_pfn;
1052         block_start_pfn = pageblock_start_pfn(cc->free_pfn);
1053         block_end_pfn = min(block_start_pfn + pageblock_nr_pages,
1054                                                 zone_end_pfn(zone));
1055         low_pfn = pageblock_end_pfn(cc->migrate_pfn);
1056
1057         /*
1058          * Isolate free pages until enough are available to migrate the
1059          * pages on cc->migratepages. We stop searching if the migrate
1060          * and free page scanners meet or enough free pages are isolated.
1061          */
1062         for (; block_start_pfn >= low_pfn;
1063                                 block_end_pfn = block_start_pfn,
1064                                 block_start_pfn -= pageblock_nr_pages,
1065                                 isolate_start_pfn = block_start_pfn) {
1066                 /*
1067                  * This can iterate a massively long zone without finding any
1068                  * suitable migration targets, so periodically check if we need
1069                  * to schedule, or even abort async compaction.
1070                  */
1071                 if (!(block_start_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages))
1072                                                 && compact_should_abort(cc))
1073                         break;
1074
1075                 page = pageblock_pfn_to_page(block_start_pfn, block_end_pfn,
1076                                                                         zone);
1077                 if (!page)
1078                         continue;
1079
1080                 /* Check the block is suitable for migration */
1081                 if (!suitable_migration_target(cc, page))
1082                         continue;
1083
1084                 /* If isolation recently failed, do not retry */
1085                 if (!isolation_suitable(cc, page))
1086                         continue;
1087
1088                 /* Found a block suitable for isolating free pages from. */
1089                 isolate_freepages_block(cc, &isolate_start_pfn, block_end_pfn,
1090                                         freelist, false);
1091
1092                 /*
1093                  * If we isolated enough freepages, or aborted due to lock
1094                  * contention, terminate.
1095                  */
1096                 if ((cc->nr_freepages >= cc->nr_migratepages)
1097                                                         || cc->contended) {
1098                         if (isolate_start_pfn >= block_end_pfn) {
1099                                 /*
1100                                  * Restart at previous pageblock if more
1101                                  * freepages can be isolated next time.
1102                                  */
1103                                 isolate_start_pfn =
1104                                         block_start_pfn - pageblock_nr_pages;
1105                         }
1106                         break;
1107                 } else if (isolate_start_pfn < block_end_pfn) {
1108                         /*
1109                          * If isolation failed early, do not continue
1110                          * needlessly.
1111                          */
1112                         break;
1113                 }
1114         }
1115
1116         /* __isolate_free_page() does not map the pages */
1117         map_pages(freelist);
1118
1119         /*
1120          * Record where the free scanner will restart next time. Either we
1121          * broke from the loop and set isolate_start_pfn based on the last
1122          * call to isolate_freepages_block(), or we met the migration scanner
1123          * and the loop terminated due to isolate_start_pfn < low_pfn
1124          */
1125         cc->free_pfn = isolate_start_pfn;
1126 }
1127
1128 /*
1129  * This is a migrate-callback that "allocates" freepages by taking pages
1130  * from the isolated freelists in the block we are migrating to.
1131  */
1132 static struct page *compaction_alloc(struct page *migratepage,
1133                                         unsigned long data,
1134                                         int **result)
1135 {
1136         struct compact_control *cc = (struct compact_control *)data;
1137         struct page *freepage;
1138
1139         /*
1140          * Isolate free pages if necessary, and if we are not aborting due to
1141          * contention.
1142          */
1143         if (list_empty(&cc->freepages)) {
1144                 if (!cc->contended)
1145                         isolate_freepages(cc);
1146
1147                 if (list_empty(&cc->freepages))
1148                         return NULL;
1149         }
1150
1151         freepage = list_entry(cc->freepages.next, struct page, lru);
1152         list_del(&freepage->lru);
1153         cc->nr_freepages--;
1154
1155         return freepage;
1156 }
1157
1158 /*
1159  * This is a migrate-callback that "frees" freepages back to the isolated
1160  * freelist.  All pages on the freelist are from the same zone, so there is no
1161  * special handling needed for NUMA.
1162  */
1163 static void compaction_free(struct page *page, unsigned long data)
1164 {
1165         struct compact_control *cc = (struct compact_control *)data;
1166
1167         list_add(&page->lru, &cc->freepages);
1168         cc->nr_freepages++;
1169 }
1170
1171 /* possible outcome of isolate_migratepages */
1172 typedef enum {
1173         ISOLATE_ABORT,          /* Abort compaction now */
1174         ISOLATE_NONE,           /* No pages isolated, continue scanning */
1175         ISOLATE_SUCCESS,        /* Pages isolated, migrate */
1176 } isolate_migrate_t;
1177
1178 /*
1179  * Allow userspace to control policy on scanning the unevictable LRU for
1180  * compactable pages.
1181  */
1182 int sysctl_compact_unevictable_allowed __read_mostly = 1;
1183
1184 /*
1185  * Isolate all pages that can be migrated from the first suitable block,
1186  * starting at the block pointed to by the migrate scanner pfn within
1187  * compact_control.
1188  */
1189 static isolate_migrate_t isolate_migratepages(struct zone *zone,
1190                                         struct compact_control *cc)
1191 {
1192         unsigned long block_start_pfn;
1193         unsigned long block_end_pfn;
1194         unsigned long low_pfn;
1195         struct page *page;
1196         const isolate_mode_t isolate_mode =
1197                 (sysctl_compact_unevictable_allowed ? ISOLATE_UNEVICTABLE : 0) |
1198                 (cc->mode != MIGRATE_SYNC ? ISOLATE_ASYNC_MIGRATE : 0);
1199
1200         /*
1201          * Start at where we last stopped, or beginning of the zone as
1202          * initialized by compact_zone()
1203          */
1204         low_pfn = cc->migrate_pfn;
1205         block_start_pfn = pageblock_start_pfn(low_pfn);
1206         if (block_start_pfn < zone->zone_start_pfn)
1207                 block_start_pfn = zone->zone_start_pfn;
1208
1209         /* Only scan within a pageblock boundary */
1210         block_end_pfn = pageblock_end_pfn(low_pfn);
1211
1212         /*
1213          * Iterate over whole pageblocks until we find the first suitable.
1214          * Do not cross the free scanner.
1215          */
1216         for (; block_end_pfn <= cc->free_pfn;
1217                         low_pfn = block_end_pfn,
1218                         block_start_pfn = block_end_pfn,
1219                         block_end_pfn += pageblock_nr_pages) {
1220
1221                 /*
1222                  * This can potentially iterate a massively long zone with
1223                  * many pageblocks unsuitable, so periodically check if we
1224                  * need to schedule, or even abort async compaction.
1225                  */
1226                 if (!(low_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages))
1227                                                 && compact_should_abort(cc))
1228                         break;
1229
1230                 page = pageblock_pfn_to_page(block_start_pfn, block_end_pfn,
1231                                                                         zone);
1232                 if (!page)
1233                         continue;
1234
1235                 /* If isolation recently failed, do not retry */
1236                 if (!isolation_suitable(cc, page))
1237                         continue;
1238
1239                 /*
1240                  * For async compaction, also only scan in MOVABLE blocks.
1241                  * Async compaction is optimistic to see if the minimum amount
1242                  * of work satisfies the allocation.
1243                  */
1244                 if (cc->mode == MIGRATE_ASYNC &&
1245                     !migrate_async_suitable(get_pageblock_migratetype(page)))
1246                         continue;
1247
1248                 /* Perform the isolation */
1249                 low_pfn = isolate_migratepages_block(cc, low_pfn,
1250                                                 block_end_pfn, isolate_mode);
1251
1252                 if (!low_pfn || cc->contended)
1253                         return ISOLATE_ABORT;
1254
1255                 /*
1256                  * Either we isolated something and proceed with migration. Or
1257                  * we failed and compact_zone should decide if we should
1258                  * continue or not.
1259                  */
1260                 break;
1261         }
1262
1263         /* Record where migration scanner will be restarted. */
1264         cc->migrate_pfn = low_pfn;
1265
1266         return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE;
1267 }
1268
1269 /*
1270  * order == -1 is expected when compacting via
1271  * /proc/sys/vm/compact_memory
1272  */
1273 static inline bool is_via_compact_memory(int order)
1274 {
1275         return order == -1;
1276 }
1277
1278 static enum compact_result __compact_finished(struct zone *zone, struct compact_control *cc,
1279                             const int migratetype)
1280 {
1281         unsigned int order;
1282         unsigned long watermark;
1283
1284         if (cc->contended || fatal_signal_pending(current))
1285                 return COMPACT_CONTENDED;
1286
1287         /* Compaction run completes if the migrate and free scanner meet */
1288         if (compact_scanners_met(cc)) {
1289                 /* Let the next compaction start anew. */
1290                 reset_cached_positions(zone);
1291
1292                 /*
1293                  * Mark that the PG_migrate_skip information should be cleared
1294                  * by kswapd when it goes to sleep. kcompactd does not set the
1295                  * flag itself as the decision to be clear should be directly
1296                  * based on an allocation request.
1297                  */
1298                 if (cc->direct_compaction)
1299                         zone->compact_blockskip_flush = true;
1300
1301                 if (cc->whole_zone)
1302                         return COMPACT_COMPLETE;
1303                 else
1304                         return COMPACT_PARTIAL_SKIPPED;
1305         }
1306
1307         if (is_via_compact_memory(cc->order))
1308                 return COMPACT_CONTINUE;
1309
1310         /* Compaction run is not finished if the watermark is not met */
1311         watermark = zone->watermark[cc->alloc_flags & ALLOC_WMARK_MASK];
1312
1313         if (!zone_watermark_ok(zone, cc->order, watermark, cc->classzone_idx,
1314                                                         cc->alloc_flags))
1315                 return COMPACT_CONTINUE;
1316
1317         /* Direct compactor: Is a suitable page free? */
1318         for (order = cc->order; order < MAX_ORDER; order++) {
1319                 struct free_area *area = &zone->free_area[order];
1320                 bool can_steal;
1321
1322                 /* Job done if page is free of the right migratetype */
1323                 if (!list_empty(&area->free_list[migratetype]))
1324                         return COMPACT_SUCCESS;
1325
1326 #ifdef CONFIG_CMA
1327                 /* MIGRATE_MOVABLE can fallback on MIGRATE_CMA */
1328                 if (migratetype == MIGRATE_MOVABLE &&
1329                         !list_empty(&area->free_list[MIGRATE_CMA]))
1330                         return COMPACT_SUCCESS;
1331 #endif
1332                 /*
1333                  * Job done if allocation would steal freepages from
1334                  * other migratetype buddy lists.
1335                  */
1336                 if (find_suitable_fallback(area, order, migratetype,
1337                                                 true, &can_steal) != -1)
1338                         return COMPACT_SUCCESS;
1339         }
1340
1341         return COMPACT_NO_SUITABLE_PAGE;
1342 }
1343
1344 static enum compact_result compact_finished(struct zone *zone,
1345                         struct compact_control *cc,
1346                         const int migratetype)
1347 {
1348         int ret;
1349
1350         ret = __compact_finished(zone, cc, migratetype);
1351         trace_mm_compaction_finished(zone, cc->order, ret);
1352         if (ret == COMPACT_NO_SUITABLE_PAGE)
1353                 ret = COMPACT_CONTINUE;
1354
1355         return ret;
1356 }
1357
1358 /*
1359  * compaction_suitable: Is this suitable to run compaction on this zone now?
1360  * Returns
1361  *   COMPACT_SKIPPED  - If there are too few free pages for compaction
1362  *   COMPACT_SUCCESS  - If the allocation would succeed without compaction
1363  *   COMPACT_CONTINUE - If compaction should run now
1364  */
1365 static enum compact_result __compaction_suitable(struct zone *zone, int order,
1366                                         unsigned int alloc_flags,
1367                                         int classzone_idx,
1368                                         unsigned long wmark_target)
1369 {
1370         unsigned long watermark;
1371
1372         if (is_via_compact_memory(order))
1373                 return COMPACT_CONTINUE;
1374
1375         watermark = zone->watermark[alloc_flags & ALLOC_WMARK_MASK];
1376         /*
1377          * If watermarks for high-order allocation are already met, there
1378          * should be no need for compaction at all.
1379          */
1380         if (zone_watermark_ok(zone, order, watermark, classzone_idx,
1381                                                                 alloc_flags))
1382                 return COMPACT_SUCCESS;
1383
1384         /*
1385          * Watermarks for order-0 must be met for compaction to be able to
1386          * isolate free pages for migration targets. This means that the
1387          * watermark and alloc_flags have to match, or be more pessimistic than
1388          * the check in __isolate_free_page(). We don't use the direct
1389          * compactor's alloc_flags, as they are not relevant for freepage
1390          * isolation. We however do use the direct compactor's classzone_idx to
1391          * skip over zones where lowmem reserves would prevent allocation even
1392          * if compaction succeeds.
1393          * For costly orders, we require low watermark instead of min for
1394          * compaction to proceed to increase its chances.
1395          * ALLOC_CMA is used, as pages in CMA pageblocks are considered
1396          * suitable migration targets
1397          */
1398         watermark = (order > PAGE_ALLOC_COSTLY_ORDER) ?
1399                                 low_wmark_pages(zone) : min_wmark_pages(zone);
1400         watermark += compact_gap(order);
1401         if (!__zone_watermark_ok(zone, 0, watermark, classzone_idx,
1402                                                 ALLOC_CMA, wmark_target))
1403                 return COMPACT_SKIPPED;
1404
1405         return COMPACT_CONTINUE;
1406 }
1407
1408 enum compact_result compaction_suitable(struct zone *zone, int order,
1409                                         unsigned int alloc_flags,
1410                                         int classzone_idx)
1411 {
1412         enum compact_result ret;
1413         int fragindex;
1414
1415         ret = __compaction_suitable(zone, order, alloc_flags, classzone_idx,
1416                                     zone_page_state(zone, NR_FREE_PAGES));
1417         /*
1418          * fragmentation index determines if allocation failures are due to
1419          * low memory or external fragmentation
1420          *
1421          * index of -1000 would imply allocations might succeed depending on
1422          * watermarks, but we already failed the high-order watermark check
1423          * index towards 0 implies failure is due to lack of memory
1424          * index towards 1000 implies failure is due to fragmentation
1425          *
1426          * Only compact if a failure would be due to fragmentation. Also
1427          * ignore fragindex for non-costly orders where the alternative to
1428          * a successful reclaim/compaction is OOM. Fragindex and the
1429          * vm.extfrag_threshold sysctl is meant as a heuristic to prevent
1430          * excessive compaction for costly orders, but it should not be at the
1431          * expense of system stability.
1432          */
1433         if (ret == COMPACT_CONTINUE && (order > PAGE_ALLOC_COSTLY_ORDER)) {
1434                 fragindex = fragmentation_index(zone, order);
1435                 if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
1436                         ret = COMPACT_NOT_SUITABLE_ZONE;
1437         }
1438
1439         trace_mm_compaction_suitable(zone, order, ret);
1440         if (ret == COMPACT_NOT_SUITABLE_ZONE)
1441                 ret = COMPACT_SKIPPED;
1442
1443         return ret;
1444 }
1445
1446 bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
1447                 int alloc_flags)
1448 {
1449         struct zone *zone;
1450         struct zoneref *z;
1451
1452         /*
1453          * Make sure at least one zone would pass __compaction_suitable if we continue
1454          * retrying the reclaim.
1455          */
1456         for_each_zone_zonelist_nodemask(zone, z, ac->zonelist, ac->high_zoneidx,
1457                                         ac->nodemask) {
1458                 unsigned long available;
1459                 enum compact_result compact_result;
1460
1461                 /*
1462                  * Do not consider all the reclaimable memory because we do not
1463                  * want to trash just for a single high order allocation which
1464                  * is even not guaranteed to appear even if __compaction_suitable
1465                  * is happy about the watermark check.
1466                  */
1467                 available = zone_reclaimable_pages(zone) / order;
1468                 available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
1469                 compact_result = __compaction_suitable(zone, order, alloc_flags,
1470                                 ac_classzone_idx(ac), available);
1471                 if (compact_result != COMPACT_SKIPPED)
1472                         return true;
1473         }
1474
1475         return false;
1476 }
1477
1478 static enum compact_result compact_zone(struct zone *zone, struct compact_control *cc)
1479 {
1480         enum compact_result ret;
1481         unsigned long start_pfn = zone->zone_start_pfn;
1482         unsigned long end_pfn = zone_end_pfn(zone);
1483         const int migratetype = gfpflags_to_migratetype(cc->gfp_mask);
1484         const bool sync = cc->mode != MIGRATE_ASYNC;
1485
1486         ret = compaction_suitable(zone, cc->order, cc->alloc_flags,
1487                                                         cc->classzone_idx);
1488         /* Compaction is likely to fail */
1489         if (ret == COMPACT_SUCCESS || ret == COMPACT_SKIPPED)
1490                 return ret;
1491
1492         /* huh, compaction_suitable is returning something unexpected */
1493         VM_BUG_ON(ret != COMPACT_CONTINUE);
1494
1495         /*
1496          * Clear pageblock skip if there were failures recently and compaction
1497          * is about to be retried after being deferred.
1498          */
1499         if (compaction_restarting(zone, cc->order))
1500                 __reset_isolation_suitable(zone);
1501
1502         /*
1503          * Setup to move all movable pages to the end of the zone. Used cached
1504          * information on where the scanners should start (unless we explicitly
1505          * want to compact the whole zone), but check that it is initialised
1506          * by ensuring the values are within zone boundaries.
1507          */
1508         if (cc->whole_zone) {
1509                 cc->migrate_pfn = start_pfn;
1510                 cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
1511         } else {
1512                 cc->migrate_pfn = zone->compact_cached_migrate_pfn[sync];
1513                 cc->free_pfn = zone->compact_cached_free_pfn;
1514                 if (cc->free_pfn < start_pfn || cc->free_pfn >= end_pfn) {
1515                         cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
1516                         zone->compact_cached_free_pfn = cc->free_pfn;
1517                 }
1518                 if (cc->migrate_pfn < start_pfn || cc->migrate_pfn >= end_pfn) {
1519                         cc->migrate_pfn = start_pfn;
1520                         zone->compact_cached_migrate_pfn[0] = cc->migrate_pfn;
1521                         zone->compact_cached_migrate_pfn[1] = cc->migrate_pfn;
1522                 }
1523
1524                 if (cc->migrate_pfn == start_pfn)
1525                         cc->whole_zone = true;
1526         }
1527
1528         cc->last_migrated_pfn = 0;
1529
1530         trace_mm_compaction_begin(start_pfn, cc->migrate_pfn,
1531                                 cc->free_pfn, end_pfn, sync);
1532
1533         migrate_prep_local();
1534
1535         while ((ret = compact_finished(zone, cc, migratetype)) ==
1536                                                 COMPACT_CONTINUE) {
1537                 int err;
1538
1539                 switch (isolate_migratepages(zone, cc)) {
1540                 case ISOLATE_ABORT:
1541                         ret = COMPACT_CONTENDED;
1542                         putback_movable_pages(&cc->migratepages);
1543                         cc->nr_migratepages = 0;
1544                         goto out;
1545                 case ISOLATE_NONE:
1546                         /*
1547                          * We haven't isolated and migrated anything, but
1548                          * there might still be unflushed migrations from
1549                          * previous cc->order aligned block.
1550                          */
1551                         goto check_drain;
1552                 case ISOLATE_SUCCESS:
1553                         ;
1554                 }
1555
1556                 err = migrate_pages(&cc->migratepages, compaction_alloc,
1557                                 compaction_free, (unsigned long)cc, cc->mode,
1558                                 MR_COMPACTION);
1559
1560                 trace_mm_compaction_migratepages(cc->nr_migratepages, err,
1561                                                         &cc->migratepages);
1562
1563                 /* All pages were either migrated or will be released */
1564                 cc->nr_migratepages = 0;
1565                 if (err) {
1566                         putback_movable_pages(&cc->migratepages);
1567                         /*
1568                          * migrate_pages() may return -ENOMEM when scanners meet
1569                          * and we want compact_finished() to detect it
1570                          */
1571                         if (err == -ENOMEM && !compact_scanners_met(cc)) {
1572                                 ret = COMPACT_CONTENDED;
1573                                 goto out;
1574                         }
1575                         /*
1576                          * We failed to migrate at least one page in the current
1577                          * order-aligned block, so skip the rest of it.
1578                          */
1579                         if (cc->direct_compaction &&
1580                                                 (cc->mode == MIGRATE_ASYNC)) {
1581                                 cc->migrate_pfn = block_end_pfn(
1582                                                 cc->migrate_pfn - 1, cc->order);
1583                                 /* Draining pcplists is useless in this case */
1584                                 cc->last_migrated_pfn = 0;
1585
1586                         }
1587                 }
1588
1589 check_drain:
1590                 /*
1591                  * Has the migration scanner moved away from the previous
1592                  * cc->order aligned block where we migrated from? If yes,
1593                  * flush the pages that were freed, so that they can merge and
1594                  * compact_finished() can detect immediately if allocation
1595                  * would succeed.
1596                  */
1597                 if (cc->order > 0 && cc->last_migrated_pfn) {
1598                         int cpu;
1599                         unsigned long current_block_start =
1600                                 block_start_pfn(cc->migrate_pfn, cc->order);
1601
1602                         if (cc->last_migrated_pfn < current_block_start) {
1603                                 cpu = get_cpu();
1604                                 lru_add_drain_cpu(cpu);
1605                                 drain_local_pages(zone);
1606                                 put_cpu();
1607                                 /* No more flushing until we migrate again */
1608                                 cc->last_migrated_pfn = 0;
1609                         }
1610                 }
1611
1612         }
1613
1614 out:
1615         /*
1616          * Release free pages and update where the free scanner should restart,
1617          * so we don't leave any returned pages behind in the next attempt.
1618          */
1619         if (cc->nr_freepages > 0) {
1620                 unsigned long free_pfn = release_freepages(&cc->freepages);
1621
1622                 cc->nr_freepages = 0;
1623                 VM_BUG_ON(free_pfn == 0);
1624                 /* The cached pfn is always the first in a pageblock */
1625                 free_pfn = pageblock_start_pfn(free_pfn);
1626                 /*
1627                  * Only go back, not forward. The cached pfn might have been
1628                  * already reset to zone end in compact_finished()
1629                  */
1630                 if (free_pfn > zone->compact_cached_free_pfn)
1631                         zone->compact_cached_free_pfn = free_pfn;
1632         }
1633
1634         trace_mm_compaction_end(start_pfn, cc->migrate_pfn,
1635                                 cc->free_pfn, end_pfn, sync, ret);
1636
1637         return ret;
1638 }
1639
1640 static enum compact_result compact_zone_order(struct zone *zone, int order,
1641                 gfp_t gfp_mask, enum compact_priority prio,
1642                 unsigned int alloc_flags, int classzone_idx)
1643 {
1644         enum compact_result ret;
1645         struct compact_control cc = {
1646                 .nr_freepages = 0,
1647                 .nr_migratepages = 0,
1648                 .order = order,
1649                 .gfp_mask = gfp_mask,
1650                 .zone = zone,
1651                 .mode = (prio == COMPACT_PRIO_ASYNC) ?
1652                                         MIGRATE_ASYNC : MIGRATE_SYNC_LIGHT,
1653                 .alloc_flags = alloc_flags,
1654                 .classzone_idx = classzone_idx,
1655                 .direct_compaction = true,
1656                 .whole_zone = (prio == MIN_COMPACT_PRIORITY),
1657                 .ignore_skip_hint = (prio == MIN_COMPACT_PRIORITY),
1658                 .ignore_block_suitable = (prio == MIN_COMPACT_PRIORITY)
1659         };
1660         INIT_LIST_HEAD(&cc.freepages);
1661         INIT_LIST_HEAD(&cc.migratepages);
1662
1663         ret = compact_zone(zone, &cc);
1664
1665         VM_BUG_ON(!list_empty(&cc.freepages));
1666         VM_BUG_ON(!list_empty(&cc.migratepages));
1667
1668         return ret;
1669 }
1670
1671 int sysctl_extfrag_threshold = 500;
1672
1673 /**
1674  * try_to_compact_pages - Direct compact to satisfy a high-order allocation
1675  * @gfp_mask: The GFP mask of the current allocation
1676  * @order: The order of the current allocation
1677  * @alloc_flags: The allocation flags of the current allocation
1678  * @ac: The context of current allocation
1679  * @mode: The migration mode for async, sync light, or sync migration
1680  *
1681  * This is the main entry point for direct page compaction.
1682  */
1683 enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
1684                 unsigned int alloc_flags, const struct alloc_context *ac,
1685                 enum compact_priority prio)
1686 {
1687         int may_perform_io = gfp_mask & __GFP_IO;
1688         struct zoneref *z;
1689         struct zone *zone;
1690         enum compact_result rc = COMPACT_SKIPPED;
1691
1692         /*
1693          * Check if the GFP flags allow compaction - GFP_NOIO is really
1694          * tricky context because the migration might require IO
1695          */
1696         if (!may_perform_io)
1697                 return COMPACT_SKIPPED;
1698
1699         trace_mm_compaction_try_to_compact_pages(order, gfp_mask, prio);
1700
1701         /* Compact each zone in the list */
1702         for_each_zone_zonelist_nodemask(zone, z, ac->zonelist, ac->high_zoneidx,
1703                                                                 ac->nodemask) {
1704                 enum compact_result status;
1705
1706                 if (prio > MIN_COMPACT_PRIORITY
1707                                         && compaction_deferred(zone, order)) {
1708                         rc = max_t(enum compact_result, COMPACT_DEFERRED, rc);
1709                         continue;
1710                 }
1711
1712                 status = compact_zone_order(zone, order, gfp_mask, prio,
1713                                         alloc_flags, ac_classzone_idx(ac));
1714                 rc = max(status, rc);
1715
1716                 /* The allocation should succeed, stop compacting */
1717                 if (status == COMPACT_SUCCESS) {
1718                         /*
1719                          * We think the allocation will succeed in this zone,
1720                          * but it is not certain, hence the false. The caller
1721                          * will repeat this with true if allocation indeed
1722                          * succeeds in this zone.
1723                          */
1724                         compaction_defer_reset(zone, order, false);
1725
1726                         break;
1727                 }
1728
1729                 if (prio != COMPACT_PRIO_ASYNC && (status == COMPACT_COMPLETE ||
1730                                         status == COMPACT_PARTIAL_SKIPPED))
1731                         /*
1732                          * We think that allocation won't succeed in this zone
1733                          * so we defer compaction there. If it ends up
1734                          * succeeding after all, it will be reset.
1735                          */
1736                         defer_compaction(zone, order);
1737
1738                 /*
1739                  * We might have stopped compacting due to need_resched() in
1740                  * async compaction, or due to a fatal signal detected. In that
1741                  * case do not try further zones
1742                  */
1743                 if ((prio == COMPACT_PRIO_ASYNC && need_resched())
1744                                         || fatal_signal_pending(current))
1745                         break;
1746         }
1747
1748         return rc;
1749 }
1750
1751
1752 /* Compact all zones within a node */
1753 static void compact_node(int nid)
1754 {
1755         pg_data_t *pgdat = NODE_DATA(nid);
1756         int zoneid;
1757         struct zone *zone;
1758         struct compact_control cc = {
1759                 .order = -1,
1760                 .mode = MIGRATE_SYNC,
1761                 .ignore_skip_hint = true,
1762                 .whole_zone = true,
1763                 .gfp_mask = GFP_KERNEL,
1764         };
1765
1766
1767         for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
1768
1769                 zone = &pgdat->node_zones[zoneid];
1770                 if (!populated_zone(zone))
1771                         continue;
1772
1773                 cc.nr_freepages = 0;
1774                 cc.nr_migratepages = 0;
1775                 cc.zone = zone;
1776                 INIT_LIST_HEAD(&cc.freepages);
1777                 INIT_LIST_HEAD(&cc.migratepages);
1778
1779                 compact_zone(zone, &cc);
1780
1781                 VM_BUG_ON(!list_empty(&cc.freepages));
1782                 VM_BUG_ON(!list_empty(&cc.migratepages));
1783         }
1784 }
1785
1786 /* Compact all nodes in the system */
1787 static void compact_nodes(void)
1788 {
1789         int nid;
1790
1791         /* Flush pending updates to the LRU lists */
1792         lru_add_drain_all();
1793
1794         for_each_online_node(nid)
1795                 compact_node(nid);
1796 }
1797
1798 /* The written value is actually unused, all memory is compacted */
1799 int sysctl_compact_memory;
1800
1801 /*
1802  * This is the entry point for compacting all nodes via
1803  * /proc/sys/vm/compact_memory
1804  */
1805 int sysctl_compaction_handler(struct ctl_table *table, int write,
1806                         void __user *buffer, size_t *length, loff_t *ppos)
1807 {
1808         if (write)
1809                 compact_nodes();
1810
1811         return 0;
1812 }
1813
1814 int sysctl_extfrag_handler(struct ctl_table *table, int write,
1815                         void __user *buffer, size_t *length, loff_t *ppos)
1816 {
1817         proc_dointvec_minmax(table, write, buffer, length, ppos);
1818
1819         return 0;
1820 }
1821
1822 #if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
1823 static ssize_t sysfs_compact_node(struct device *dev,
1824                         struct device_attribute *attr,
1825                         const char *buf, size_t count)
1826 {
1827         int nid = dev->id;
1828
1829         if (nid >= 0 && nid < nr_node_ids && node_online(nid)) {
1830                 /* Flush pending updates to the LRU lists */
1831                 lru_add_drain_all();
1832
1833                 compact_node(nid);
1834         }
1835
1836         return count;
1837 }
1838 static DEVICE_ATTR(compact, S_IWUSR, NULL, sysfs_compact_node);
1839
1840 int compaction_register_node(struct node *node)
1841 {
1842         return device_create_file(&node->dev, &dev_attr_compact);
1843 }
1844
1845 void compaction_unregister_node(struct node *node)
1846 {
1847         return device_remove_file(&node->dev, &dev_attr_compact);
1848 }
1849 #endif /* CONFIG_SYSFS && CONFIG_NUMA */
1850
1851 static inline bool kcompactd_work_requested(pg_data_t *pgdat)
1852 {
1853         return pgdat->kcompactd_max_order > 0 || kthread_should_stop();
1854 }
1855
1856 static bool kcompactd_node_suitable(pg_data_t *pgdat)
1857 {
1858         int zoneid;
1859         struct zone *zone;
1860         enum zone_type classzone_idx = pgdat->kcompactd_classzone_idx;
1861
1862         for (zoneid = 0; zoneid <= classzone_idx; zoneid++) {
1863                 zone = &pgdat->node_zones[zoneid];
1864
1865                 if (!populated_zone(zone))
1866                         continue;
1867
1868                 if (compaction_suitable(zone, pgdat->kcompactd_max_order, 0,
1869                                         classzone_idx) == COMPACT_CONTINUE)
1870                         return true;
1871         }
1872
1873         return false;
1874 }
1875
1876 static void kcompactd_do_work(pg_data_t *pgdat)
1877 {
1878         /*
1879          * With no special task, compact all zones so that a page of requested
1880          * order is allocatable.
1881          */
1882         int zoneid;
1883         struct zone *zone;
1884         struct compact_control cc = {
1885                 .order = pgdat->kcompactd_max_order,
1886                 .classzone_idx = pgdat->kcompactd_classzone_idx,
1887                 .mode = MIGRATE_SYNC_LIGHT,
1888                 .ignore_skip_hint = true,
1889                 .gfp_mask = GFP_KERNEL,
1890
1891         };
1892         trace_mm_compaction_kcompactd_wake(pgdat->node_id, cc.order,
1893                                                         cc.classzone_idx);
1894         count_vm_event(KCOMPACTD_WAKE);
1895
1896         for (zoneid = 0; zoneid <= cc.classzone_idx; zoneid++) {
1897                 int status;
1898
1899                 zone = &pgdat->node_zones[zoneid];
1900                 if (!populated_zone(zone))
1901                         continue;
1902
1903                 if (compaction_deferred(zone, cc.order))
1904                         continue;
1905
1906                 if (compaction_suitable(zone, cc.order, 0, zoneid) !=
1907                                                         COMPACT_CONTINUE)
1908                         continue;
1909
1910                 cc.nr_freepages = 0;
1911                 cc.nr_migratepages = 0;
1912                 cc.zone = zone;
1913                 INIT_LIST_HEAD(&cc.freepages);
1914                 INIT_LIST_HEAD(&cc.migratepages);
1915
1916                 if (kthread_should_stop())
1917                         return;
1918                 status = compact_zone(zone, &cc);
1919
1920                 if (status == COMPACT_SUCCESS) {
1921                         compaction_defer_reset(zone, cc.order, false);
1922                 } else if (status == COMPACT_PARTIAL_SKIPPED || status == COMPACT_COMPLETE) {
1923                         /*
1924                          * We use sync migration mode here, so we defer like
1925                          * sync direct compaction does.
1926                          */
1927                         defer_compaction(zone, cc.order);
1928                 }
1929
1930                 VM_BUG_ON(!list_empty(&cc.freepages));
1931                 VM_BUG_ON(!list_empty(&cc.migratepages));
1932         }
1933
1934         /*
1935          * Regardless of success, we are done until woken up next. But remember
1936          * the requested order/classzone_idx in case it was higher/tighter than
1937          * our current ones
1938          */
1939         if (pgdat->kcompactd_max_order <= cc.order)
1940                 pgdat->kcompactd_max_order = 0;
1941         if (pgdat->kcompactd_classzone_idx >= cc.classzone_idx)
1942                 pgdat->kcompactd_classzone_idx = pgdat->nr_zones - 1;
1943 }
1944
1945 void wakeup_kcompactd(pg_data_t *pgdat, int order, int classzone_idx)
1946 {
1947         if (!order)
1948                 return;
1949
1950         if (pgdat->kcompactd_max_order < order)
1951                 pgdat->kcompactd_max_order = order;
1952
1953         if (pgdat->kcompactd_classzone_idx > classzone_idx)
1954                 pgdat->kcompactd_classzone_idx = classzone_idx;
1955
1956         if (!waitqueue_active(&pgdat->kcompactd_wait))
1957                 return;
1958
1959         if (!kcompactd_node_suitable(pgdat))
1960                 return;
1961
1962         trace_mm_compaction_wakeup_kcompactd(pgdat->node_id, order,
1963                                                         classzone_idx);
1964         wake_up_interruptible(&pgdat->kcompactd_wait);
1965 }
1966
1967 /*
1968  * The background compaction daemon, started as a kernel thread
1969  * from the init process.
1970  */
1971 static int kcompactd(void *p)
1972 {
1973         pg_data_t *pgdat = (pg_data_t*)p;
1974         struct task_struct *tsk = current;
1975
1976         const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
1977
1978         if (!cpumask_empty(cpumask))
1979                 set_cpus_allowed_ptr(tsk, cpumask);
1980
1981         set_freezable();
1982
1983         pgdat->kcompactd_max_order = 0;
1984         pgdat->kcompactd_classzone_idx = pgdat->nr_zones - 1;
1985
1986         while (!kthread_should_stop()) {
1987                 trace_mm_compaction_kcompactd_sleep(pgdat->node_id);
1988                 wait_event_freezable(pgdat->kcompactd_wait,
1989                                 kcompactd_work_requested(pgdat));
1990
1991                 kcompactd_do_work(pgdat);
1992         }
1993
1994         return 0;
1995 }
1996
1997 /*
1998  * This kcompactd start function will be called by init and node-hot-add.
1999  * On node-hot-add, kcompactd will moved to proper cpus if cpus are hot-added.
2000  */
2001 int kcompactd_run(int nid)
2002 {
2003         pg_data_t *pgdat = NODE_DATA(nid);
2004         int ret = 0;
2005
2006         if (pgdat->kcompactd)
2007                 return 0;
2008
2009         pgdat->kcompactd = kthread_run(kcompactd, pgdat, "kcompactd%d", nid);
2010         if (IS_ERR(pgdat->kcompactd)) {
2011                 pr_err("Failed to start kcompactd on node %d\n", nid);
2012                 ret = PTR_ERR(pgdat->kcompactd);
2013                 pgdat->kcompactd = NULL;
2014         }
2015         return ret;
2016 }
2017
2018 /*
2019  * Called by memory hotplug when all memory in a node is offlined. Caller must
2020  * hold mem_hotplug_begin/end().
2021  */
2022 void kcompactd_stop(int nid)
2023 {
2024         struct task_struct *kcompactd = NODE_DATA(nid)->kcompactd;
2025
2026         if (kcompactd) {
2027                 kthread_stop(kcompactd);
2028                 NODE_DATA(nid)->kcompactd = NULL;
2029         }
2030 }
2031
2032 /*
2033  * It's optimal to keep kcompactd on the same CPUs as their memory, but
2034  * not required for correctness. So if the last cpu in a node goes
2035  * away, we get changed to run anywhere: as the first one comes back,
2036  * restore their cpu bindings.
2037  */
2038 static int kcompactd_cpu_online(unsigned int cpu)
2039 {
2040         int nid;
2041
2042         for_each_node_state(nid, N_MEMORY) {
2043                 pg_data_t *pgdat = NODE_DATA(nid);
2044                 const struct cpumask *mask;
2045
2046                 mask = cpumask_of_node(pgdat->node_id);
2047
2048                 if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
2049                         /* One of our CPUs online: restore mask */
2050                         set_cpus_allowed_ptr(pgdat->kcompactd, mask);
2051         }
2052         return 0;
2053 }
2054
2055 static int __init kcompactd_init(void)
2056 {
2057         int nid;
2058         int ret;
2059
2060         ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
2061                                         "mm/compaction:online",
2062                                         kcompactd_cpu_online, NULL);
2063         if (ret < 0) {
2064                 pr_err("kcompactd: failed to register hotplug callbacks.\n");
2065                 return ret;
2066         }
2067
2068         for_each_node_state(nid, N_MEMORY)
2069                 kcompactd_run(nid);
2070         return 0;
2071 }
2072 subsys_initcall(kcompactd_init)
2073
2074 #endif /* CONFIG_COMPACTION */