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