1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * linux/mm/compaction.c
   4 *
   5 * Memory compaction for the reduction of external fragmentation. Note that
   6 * this heavily depends upon page migration to do all the real heavy
   7 * lifting
   8 *
   9 * Copyright IBM Corp. 2007-2010 Mel Gorman <mel@csn.ul.ie>
  10 */
  11#include <linux/cpu.h>
  12#include <linux/swap.h>
  13#include <linux/migrate.h>
  14#include <linux/compaction.h>
  15#include <linux/mm_inline.h>
  16#include <linux/sched/signal.h>
  17#include <linux/backing-dev.h>
  18#include <linux/sysctl.h>
  19#include <linux/sysfs.h>
  20#include <linux/page-isolation.h>
  21#include <linux/kasan.h>
  22#include <linux/kthread.h>
  23#include <linux/freezer.h>
  24#include <linux/page_owner.h>
  25#include "internal.h"
  26
  27#ifdef CONFIG_COMPACTION
  28static inline void count_compact_event(enum vm_event_item item)
  29{
  30	count_vm_event(item);
  31}
  32
  33static inline void count_compact_events(enum vm_event_item item, long delta)
  34{
  35	count_vm_events(item, delta);
  36}
  37#else
  38#define count_compact_event(item) do { } while (0)
  39#define count_compact_events(item, delta) do { } while (0)
  40#endif
  41
  42#if defined CONFIG_COMPACTION || defined CONFIG_CMA
  43
  44#define CREATE_TRACE_POINTS
  45#include <trace/events/compaction.h>
  46
  47#define block_start_pfn(pfn, order)	round_down(pfn, 1UL << (order))
  48#define block_end_pfn(pfn, order)	ALIGN((pfn) + 1, 1UL << (order))
  49#define pageblock_start_pfn(pfn)	block_start_pfn(pfn, pageblock_order)
  50#define pageblock_end_pfn(pfn)		block_end_pfn(pfn, pageblock_order)
  51
  52static unsigned long release_freepages(struct list_head *freelist)
  53{
  54	struct page *page, *next;
  55	unsigned long high_pfn = 0;
  56
  57	list_for_each_entry_safe(page, next, freelist, lru) {
  58		unsigned long pfn = page_to_pfn(page);
  59		list_del(&page->lru);
  60		__free_page(page);
  61		if (pfn > high_pfn)
  62			high_pfn = pfn;
  63	}
  64
  65	return high_pfn;
  66}
  67
  68static void map_pages(struct list_head *list)
  69{
  70	unsigned int i, order, nr_pages;
  71	struct page *page, *next;
  72	LIST_HEAD(tmp_list);
  73
  74	list_for_each_entry_safe(page, next, list, lru) {
  75		list_del(&page->lru);
  76
  77		order = page_private(page);
  78		nr_pages = 1 << order;
  79
  80		post_alloc_hook(page, order, __GFP_MOVABLE);
  81		if (order)
  82			split_page(page, order);
  83
  84		for (i = 0; i < nr_pages; i++) {
  85			list_add(&page->lru, &tmp_list);
  86			page++;
  87		}
  88	}
  89
  90	list_splice(&tmp_list, list);
  91}
  92
  93#ifdef CONFIG_COMPACTION
  94
  95int PageMovable(struct page *page)
  96{
  97	struct address_space *mapping;
  98
  99	VM_BUG_ON_PAGE(!PageLocked(page), page);
 100	if (!__PageMovable(page))
 101		return 0;
 102
 103	mapping = page_mapping(page);
 104	if (mapping && mapping->a_ops && mapping->a_ops->isolate_page)
 105		return 1;
 106
 107	return 0;
 108}
 109EXPORT_SYMBOL(PageMovable);
 110
 111void __SetPageMovable(struct page *page, struct address_space *mapping)
 112{
 113	VM_BUG_ON_PAGE(!PageLocked(page), page);
 114	VM_BUG_ON_PAGE((unsigned long)mapping & PAGE_MAPPING_MOVABLE, page);
 115	page->mapping = (void *)((unsigned long)mapping | PAGE_MAPPING_MOVABLE);
 116}
 117EXPORT_SYMBOL(__SetPageMovable);
 118
 119void __ClearPageMovable(struct page *page)
 120{
 121	VM_BUG_ON_PAGE(!PageLocked(page), page);
 122	VM_BUG_ON_PAGE(!PageMovable(page), page);
 123	/*
 124	 * Clear registered address_space val with keeping PAGE_MAPPING_MOVABLE
 125	 * flag so that VM can catch up released page by driver after isolation.
 126	 * With it, VM migration doesn't try to put it back.
 127	 */
 128	page->mapping = (void *)((unsigned long)page->mapping &
 129				PAGE_MAPPING_MOVABLE);
 130}
 131EXPORT_SYMBOL(__ClearPageMovable);
 132
 133/* Do not skip compaction more than 64 times */
 134#define COMPACT_MAX_DEFER_SHIFT 6
 135
 136/*
 137 * Compaction is deferred when compaction fails to result in a page
 138 * allocation success. 1 << compact_defer_limit compactions are skipped up
 139 * to a limit of 1 << COMPACT_MAX_DEFER_SHIFT
 140 */
 141void defer_compaction(struct zone *zone, int order)
 142{
 143	zone->compact_considered = 0;
 144	zone->compact_defer_shift++;
 145
 146	if (order < zone->compact_order_failed)
 147		zone->compact_order_failed = order;
 148
 149	if (zone->compact_defer_shift > COMPACT_MAX_DEFER_SHIFT)
 150		zone->compact_defer_shift = COMPACT_MAX_DEFER_SHIFT;
 151
 152	trace_mm_compaction_defer_compaction(zone, order);
 153}
 154
 155/* Returns true if compaction should be skipped this time */
 156bool compaction_deferred(struct zone *zone, int order)
 157{
 158	unsigned long defer_limit = 1UL << zone->compact_defer_shift;
 159
 160	if (order < zone->compact_order_failed)
 161		return false;
 162
 163	/* Avoid possible overflow */
 164	if (++zone->compact_considered > defer_limit)
 165		zone->compact_considered = defer_limit;
 166
 167	if (zone->compact_considered >= defer_limit)
 168		return false;
 169
 170	trace_mm_compaction_deferred(zone, order);
 171
 172	return true;
 173}
 174
 175/*
 176 * Update defer tracking counters after successful compaction of given order,
 177 * which means an allocation either succeeded (alloc_success == true) or is
 178 * expected to succeed.
 179 */
 180void compaction_defer_reset(struct zone *zone, int order,
 181		bool alloc_success)
 182{
 183	if (alloc_success) {
 184		zone->compact_considered = 0;
 185		zone->compact_defer_shift = 0;
 186	}
 187	if (order >= zone->compact_order_failed)
 188		zone->compact_order_failed = order + 1;
 189
 190	trace_mm_compaction_defer_reset(zone, order);
 191}
 192
 193/* Returns true if restarting compaction after many failures */
 194bool compaction_restarting(struct zone *zone, int order)
 195{
 196	if (order < zone->compact_order_failed)
 197		return false;
 198
 199	return zone->compact_defer_shift == COMPACT_MAX_DEFER_SHIFT &&
 200		zone->compact_considered >= 1UL << zone->compact_defer_shift;
 201}
 202
 203/* Returns true if the pageblock should be scanned for pages to isolate. */
 204static inline bool isolation_suitable(struct compact_control *cc,
 205					struct page *page)
 206{
 207	if (cc->ignore_skip_hint)
 208		return true;
 209
 210	return !get_pageblock_skip(page);
 211}
 212
 213static void reset_cached_positions(struct zone *zone)
 214{
 215	zone->compact_cached_migrate_pfn[0] = zone->zone_start_pfn;
 216	zone->compact_cached_migrate_pfn[1] = zone->zone_start_pfn;
 217	zone->compact_cached_free_pfn =
 218				pageblock_start_pfn(zone_end_pfn(zone) - 1);
 219}
 220
 221/*
 222 * Compound pages of >= pageblock_order should consistenly be skipped until
 223 * released. It is always pointless to compact pages of such order (if they are
 224 * migratable), and the pageblocks they occupy cannot contain any free pages.
 225 */
 226static bool pageblock_skip_persistent(struct page *page)
 227{
 228	if (!PageCompound(page))
 229		return false;
 230
 231	page = compound_head(page);
 232
 233	if (compound_order(page) >= pageblock_order)
 234		return true;
 235
 236	return false;
 237}
 238
 239/*
 240 * This function is called to clear all cached information on pageblocks that
 241 * should be skipped for page isolation when the migrate and free page scanner
 242 * meet.
 243 */
 244static void __reset_isolation_suitable(struct zone *zone)
 245{
 246	unsigned long start_pfn = zone->zone_start_pfn;
 247	unsigned long end_pfn = zone_end_pfn(zone);
 248	unsigned long pfn;
 249
 250	zone->compact_blockskip_flush = false;
 251
 252	/* Walk the zone and mark every pageblock as suitable for isolation */
 253	for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages) {
 254		struct page *page;
 255
 256		cond_resched();
 257
 258		page = pfn_to_online_page(pfn);
 259		if (!page)
 260			continue;
 261		if (zone != page_zone(page))
 262			continue;
 263		if (pageblock_skip_persistent(page))
 264			continue;
 265
 266		clear_pageblock_skip(page);
 267	}
 268
 269	reset_cached_positions(zone);
 270}
 271
 272void reset_isolation_suitable(pg_data_t *pgdat)
 273{
 274	int zoneid;
 275
 276	for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
 277		struct zone *zone = &pgdat->node_zones[zoneid];
 278		if (!populated_zone(zone))
 279			continue;
 280
 281		/* Only flush if a full compaction finished recently */
 282		if (zone->compact_blockskip_flush)
 283			__reset_isolation_suitable(zone);
 284	}
 285}
 286
 287/*
 288 * If no pages were isolated then mark this pageblock to be skipped in the
 289 * future. The information is later cleared by __reset_isolation_suitable().
 290 */
 291static void update_pageblock_skip(struct compact_control *cc,
 292			struct page *page, unsigned long nr_isolated,
 293			bool migrate_scanner)
 294{
 295	struct zone *zone = cc->zone;
 296	unsigned long pfn;
 297
 298	if (cc->no_set_skip_hint)
 299		return;
 300
 301	if (!page)
 302		return;
 303
 304	if (nr_isolated)
 305		return;
 306
 307	set_pageblock_skip(page);
 308
 309	pfn = page_to_pfn(page);
 310
 311	/* Update where async and sync compaction should restart */
 312	if (migrate_scanner) {
 313		if (pfn > zone->compact_cached_migrate_pfn[0])
 314			zone->compact_cached_migrate_pfn[0] = pfn;
 315		if (cc->mode != MIGRATE_ASYNC &&
 316		    pfn > zone->compact_cached_migrate_pfn[1])
 317			zone->compact_cached_migrate_pfn[1] = pfn;
 318	} else {
 319		if (pfn < zone->compact_cached_free_pfn)
 320			zone->compact_cached_free_pfn = pfn;
 321	}
 322}
 323#else
 324static inline bool isolation_suitable(struct compact_control *cc,
 325					struct page *page)
 326{
 327	return true;
 328}
 329
 330static inline bool pageblock_skip_persistent(struct page *page)
 331{
 332	return false;
 333}
 334
 335static inline void update_pageblock_skip(struct compact_control *cc,
 336			struct page *page, unsigned long nr_isolated,
 337			bool migrate_scanner)
 338{
 
 339}
 340#endif /* CONFIG_COMPACTION */
 341
 342/*
 343 * Compaction requires the taking of some coarse locks that are potentially
 344 * very heavily contended. For async compaction, back out if the lock cannot
 345 * be taken immediately. For sync compaction, spin on the lock if needed.
 346 *
 347 * Returns true if the lock is held
 348 * Returns false if the lock is not held and compaction should abort
 349 */
 350static bool compact_trylock_irqsave(spinlock_t *lock, unsigned long *flags,
 351						struct compact_control *cc)
 352{
 353	if (cc->mode == MIGRATE_ASYNC) {
 354		if (!spin_trylock_irqsave(lock, *flags)) {
 355			cc->contended = true;
 356			return false;
 357		}
 358	} else {
 359		spin_lock_irqsave(lock, *flags);
 360	}
 361
 362	return true;
 363}
 364
 365/*
 366 * Compaction requires the taking of some coarse locks that are potentially
 367 * very heavily contended. The lock should be periodically unlocked to avoid
 368 * having disabled IRQs for a long time, even when there is nobody waiting on
 369 * the lock. It might also be that allowing the IRQs will result in
 370 * need_resched() becoming true. If scheduling is needed, async compaction
 371 * aborts. Sync compaction schedules.
 372 * Either compaction type will also abort if a fatal signal is pending.
 373 * In either case if the lock was locked, it is dropped and not regained.
 374 *
 375 * Returns true if compaction should abort due to fatal signal pending, or
 376 *		async compaction due to need_resched()
 377 * Returns false when compaction can continue (sync compaction might have
 378 *		scheduled)
 379 */
 380static bool compact_unlock_should_abort(spinlock_t *lock,
 381		unsigned long flags, bool *locked, struct compact_control *cc)
 382{
 383	if (*locked) {
 384		spin_unlock_irqrestore(lock, flags);
 385		*locked = false;
 386	}
 387
 388	if (fatal_signal_pending(current)) {
 389		cc->contended = true;
 390		return true;
 391	}
 392
 393	if (need_resched()) {
 394		if (cc->mode == MIGRATE_ASYNC) {
 395			cc->contended = true;
 396			return true;
 397		}
 398		cond_resched();
 399	}
 400
 401	return false;
 402}
 403
 404/*
 405 * Aside from avoiding lock contention, compaction also periodically checks
 406 * need_resched() and either schedules in sync compaction or aborts async
 407 * compaction. This is similar to what compact_unlock_should_abort() does, but
 408 * is used where no lock is concerned.
 409 *
 410 * Returns false when no scheduling was needed, or sync compaction scheduled.
 411 * Returns true when async compaction should abort.
 412 */
 413static inline bool compact_should_abort(struct compact_control *cc)
 414{
 415	/* async compaction aborts if contended */
 416	if (need_resched()) {
 417		if (cc->mode == MIGRATE_ASYNC) {
 418			cc->contended = true;
 419			return true;
 420		}
 421
 422		cond_resched();
 423	}
 424
 425	return false;
 426}
 427
 428/*
 429 * Isolate free pages onto a private freelist. If @strict is true, will abort
 430 * returning 0 on any invalid PFNs or non-free pages inside of the pageblock
 431 * (even though it may still end up isolating some pages).
 432 */
 433static unsigned long isolate_freepages_block(struct compact_control *cc,
 434				unsigned long *start_pfn,
 435				unsigned long end_pfn,
 436				struct list_head *freelist,
 437				bool strict)
 438{
 439	int nr_scanned = 0, total_isolated = 0;
 440	struct page *cursor, *valid_page = NULL;
 441	unsigned long flags = 0;
 442	bool locked = false;
 443	unsigned long blockpfn = *start_pfn;
 444	unsigned int order;
 445
 446	cursor = pfn_to_page(blockpfn);
 447
 448	/* Isolate free pages. */
 449	for (; blockpfn < end_pfn; blockpfn++, cursor++) {
 450		int isolated;
 451		struct page *page = cursor;
 452
 453		/*
 454		 * Periodically drop the lock (if held) regardless of its
 455		 * contention, to give chance to IRQs. Abort if fatal signal
 456		 * pending or async compaction detects need_resched()
 457		 */
 458		if (!(blockpfn % SWAP_CLUSTER_MAX)
 459		    && compact_unlock_should_abort(&cc->zone->lock, flags,
 460								&locked, cc))
 461			break;
 462
 463		nr_scanned++;
 464		if (!pfn_valid_within(blockpfn))
 465			goto isolate_fail;
 466
 467		if (!valid_page)
 468			valid_page = page;
 469
 470		/*
 471		 * For compound pages such as THP and hugetlbfs, we can save
 472		 * potentially a lot of iterations if we skip them at once.
 473		 * The check is racy, but we can consider only valid values
 474		 * and the only danger is skipping too much.
 475		 */
 476		if (PageCompound(page)) {
 477			const unsigned int order = compound_order(page);
 478
 479			if (likely(order < MAX_ORDER)) {
 480				blockpfn += (1UL << order) - 1;
 481				cursor += (1UL << order) - 1;
 482			}
 483			goto isolate_fail;
 484		}
 
 485
 486		if (!PageBuddy(page))
 487			goto isolate_fail;
 488
 489		/*
 490		 * If we already hold the lock, we can skip some rechecking.
 491		 * Note that if we hold the lock now, checked_pageblock was
 492		 * already set in some previous iteration (or strict is true),
 493		 * so it is correct to skip the suitable migration target
 494		 * recheck as well.
 495		 */
 496		if (!locked) {
 497			/*
 498			 * The zone lock must be held to isolate freepages.
 499			 * Unfortunately this is a very coarse lock and can be
 500			 * heavily contended if there are parallel allocations
 501			 * or parallel compactions. For async compaction do not
 502			 * spin on the lock and we acquire the lock as late as
 503			 * possible.
 504			 */
 505			locked = compact_trylock_irqsave(&cc->zone->lock,
 506								&flags, cc);
 507			if (!locked)
 508				break;
 509
 510			/* Recheck this is a buddy page under lock */
 511			if (!PageBuddy(page))
 512				goto isolate_fail;
 513		}
 514
 515		/* Found a free page, will break it into order-0 pages */
 516		order = page_order(page);
 517		isolated = __isolate_free_page(page, order);
 518		if (!isolated)
 519			break;
 520		set_page_private(page, order);
 521
 522		total_isolated += isolated;
 523		cc->nr_freepages += isolated;
 524		list_add_tail(&page->lru, freelist);
 525
 526		if (!strict && cc->nr_migratepages <= cc->nr_freepages) {
 527			blockpfn += isolated;
 528			break;
 529		}
 530		/* Advance to the end of split page */
 531		blockpfn += isolated - 1;
 532		cursor += isolated - 1;
 533		continue;
 534
 535isolate_fail:
 536		if (strict)
 537			break;
 538		else
 539			continue;
 540
 
 
 
 
 
 541	}
 542
 543	if (locked)
 544		spin_unlock_irqrestore(&cc->zone->lock, flags);
 545
 546	/*
 547	 * There is a tiny chance that we have read bogus compound_order(),
 548	 * so be careful to not go outside of the pageblock.
 549	 */
 550	if (unlikely(blockpfn > end_pfn))
 551		blockpfn = end_pfn;
 552
 553	trace_mm_compaction_isolate_freepages(*start_pfn, blockpfn,
 554					nr_scanned, total_isolated);
 555
 556	/* Record how far we have got within the block */
 557	*start_pfn = blockpfn;
 558
 559	/*
 560	 * If strict isolation is requested by CMA then check that all the
 561	 * pages requested were isolated. If there were any failures, 0 is
 562	 * returned and CMA will fail.
 563	 */
 564	if (strict && blockpfn < end_pfn)
 565		total_isolated = 0;
 566
 567	/* Update the pageblock-skip if the whole pageblock was scanned */
 568	if (blockpfn == end_pfn)
 569		update_pageblock_skip(cc, valid_page, total_isolated, false);
 570
 571	cc->total_free_scanned += nr_scanned;
 572	if (total_isolated)
 573		count_compact_events(COMPACTISOLATED, total_isolated);
 574	return total_isolated;
 575}
 576
 577/**
 578 * isolate_freepages_range() - isolate free pages.
 579 * @cc:        Compaction control structure.
 580 * @start_pfn: The first PFN to start isolating.
 581 * @end_pfn:   The one-past-last PFN.
 582 *
 583 * Non-free pages, invalid PFNs, or zone boundaries within the
 584 * [start_pfn, end_pfn) range are considered errors, cause function to
 585 * undo its actions and return zero.
 586 *
 587 * Otherwise, function returns one-past-the-last PFN of isolated page
 588 * (which may be greater then end_pfn if end fell in a middle of
 589 * a free page).
 590 */
 591unsigned long
 592isolate_freepages_range(struct compact_control *cc,
 593			unsigned long start_pfn, unsigned long end_pfn)
 594{
 595	unsigned long isolated, pfn, block_start_pfn, block_end_pfn;
 
 596	LIST_HEAD(freelist);
 597
 598	pfn = start_pfn;
 599	block_start_pfn = pageblock_start_pfn(pfn);
 600	if (block_start_pfn < cc->zone->zone_start_pfn)
 601		block_start_pfn = cc->zone->zone_start_pfn;
 602	block_end_pfn = pageblock_end_pfn(pfn);
 603
 604	for (; pfn < end_pfn; pfn += isolated,
 605				block_start_pfn = block_end_pfn,
 606				block_end_pfn += pageblock_nr_pages) {
 607		/* Protect pfn from changing by isolate_freepages_block */
 608		unsigned long isolate_start_pfn = pfn;
 609
 610		block_end_pfn = min(block_end_pfn, end_pfn);
 
 
 611
 612		/*
 613		 * pfn could pass the block_end_pfn if isolated freepage
 614		 * is more than pageblock order. In this case, we adjust
 615		 * scanning range to right one.
 616		 */
 617		if (pfn >= block_end_pfn) {
 618			block_start_pfn = pageblock_start_pfn(pfn);
 619			block_end_pfn = pageblock_end_pfn(pfn);
 620			block_end_pfn = min(block_end_pfn, end_pfn);
 621		}
 622
 623		if (!pageblock_pfn_to_page(block_start_pfn,
 624					block_end_pfn, cc->zone))
 625			break;
 626
 627		isolated = isolate_freepages_block(cc, &isolate_start_pfn,
 628						block_end_pfn, &freelist, true);
 
 
 629
 630		/*
 631		 * In strict mode, isolate_freepages_block() returns 0 if
 632		 * there are any holes in the block (ie. invalid PFNs or
 633		 * non-free pages).
 634		 */
 635		if (!isolated)
 636			break;
 637
 638		/*
 639		 * If we managed to isolate pages, it is always (1 << n) *
 640		 * pageblock_nr_pages for some non-negative n.  (Max order
 641		 * page may span two pageblocks).
 642		 */
 643	}
 644
 645	/* __isolate_free_page() does not map the pages */
 646	map_pages(&freelist);
 647
 648	if (pfn < end_pfn) {
 649		/* Loop terminated early, cleanup. */
 650		release_freepages(&freelist);
 651		return 0;
 652	}
 653
 654	/* We don't use freelists for anything. */
 655	return pfn;
 656}
 657
 
 
 
 
 
 
 
 
 
 
 
 
 
 658/* Similar to reclaim, but different enough that they don't share logic */
 659static bool too_many_isolated(struct zone *zone)
 660{
 661	unsigned long active, inactive, isolated;
 662
 663	inactive = node_page_state(zone->zone_pgdat, NR_INACTIVE_FILE) +
 664			node_page_state(zone->zone_pgdat, NR_INACTIVE_ANON);
 665	active = node_page_state(zone->zone_pgdat, NR_ACTIVE_FILE) +
 666			node_page_state(zone->zone_pgdat, NR_ACTIVE_ANON);
 667	isolated = node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE) +
 668			node_page_state(zone->zone_pgdat, NR_ISOLATED_ANON);
 669
 670	return isolated > (inactive + active) / 2;
 671}
 672
 673/**
 674 * isolate_migratepages_block() - isolate all migrate-able pages within
 675 *				  a single pageblock
 676 * @cc:		Compaction control structure.
 677 * @low_pfn:	The first PFN to isolate
 678 * @end_pfn:	The one-past-the-last PFN to isolate, within same pageblock
 679 * @isolate_mode: Isolation mode to be used.
 680 *
 681 * Isolate all pages that can be migrated from the range specified by
 682 * [low_pfn, end_pfn). The range is expected to be within same pageblock.
 683 * Returns zero if there is a fatal signal pending, otherwise PFN of the
 684 * first page that was not scanned (which may be both less, equal to or more
 685 * than end_pfn).
 686 *
 687 * The pages are isolated on cc->migratepages list (not required to be empty),
 688 * and cc->nr_migratepages is updated accordingly. The cc->migrate_pfn field
 689 * is neither read nor updated.
 
 
 690 */
 691static unsigned long
 692isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 693			unsigned long end_pfn, isolate_mode_t isolate_mode)
 694{
 695	struct zone *zone = cc->zone;
 696	unsigned long nr_scanned = 0, nr_isolated = 0;
 
 
 697	struct lruvec *lruvec;
 698	unsigned long flags = 0;
 699	bool locked = false;
 700	struct page *page = NULL, *valid_page = NULL;
 701	unsigned long start_pfn = low_pfn;
 702	bool skip_on_failure = false;
 703	unsigned long next_skip_pfn = 0;
 704
 705	/*
 706	 * Ensure that there are not too many pages isolated from the LRU
 707	 * list by either parallel reclaimers or compaction. If there are,
 708	 * delay for some time until fewer pages are isolated
 709	 */
 710	while (unlikely(too_many_isolated(zone))) {
 711		/* async migration should just abort */
 712		if (cc->mode == MIGRATE_ASYNC)
 713			return 0;
 714
 715		congestion_wait(BLK_RW_ASYNC, HZ/10);
 716
 717		if (fatal_signal_pending(current))
 718			return 0;
 719	}
 720
 721	if (compact_should_abort(cc))
 722		return 0;
 723
 724	if (cc->direct_compaction && (cc->mode == MIGRATE_ASYNC)) {
 725		skip_on_failure = true;
 726		next_skip_pfn = block_end_pfn(low_pfn, cc->order);
 727	}
 728
 729	/* Time to isolate some pages for migration */
 
 
 730	for (; low_pfn < end_pfn; low_pfn++) {
 
 
 731
 732		if (skip_on_failure && low_pfn >= next_skip_pfn) {
 733			/*
 734			 * We have isolated all migration candidates in the
 735			 * previous order-aligned block, and did not skip it due
 736			 * to failure. We should migrate the pages now and
 737			 * hopefully succeed compaction.
 738			 */
 739			if (nr_isolated)
 
 
 
 740				break;
 741
 742			/*
 743			 * We failed to isolate in the previous order-aligned
 744			 * block. Set the new boundary to the end of the
 745			 * current block. Note we can't simply increase
 746			 * next_skip_pfn by 1 << order, as low_pfn might have
 747			 * been incremented by a higher number due to skipping
 748			 * a compound or a high-order buddy page in the
 749			 * previous loop iteration.
 750			 */
 751			next_skip_pfn = block_end_pfn(low_pfn, cc->order);
 752		}
 753
 754		/*
 755		 * Periodically drop the lock (if held) regardless of its
 756		 * contention, to give chance to IRQs. Abort async compaction
 757		 * if contended.
 758		 */
 759		if (!(low_pfn % SWAP_CLUSTER_MAX)
 760		    && compact_unlock_should_abort(zone_lru_lock(zone), flags,
 761								&locked, cc))
 762			break;
 
 
 
 763
 764		if (!pfn_valid_within(low_pfn))
 765			goto isolate_fail;
 766		nr_scanned++;
 767
 768		page = pfn_to_page(low_pfn);
 769
 770		if (!valid_page)
 771			valid_page = page;
 772
 773		/*
 774		 * Skip if free. We read page order here without zone lock
 775		 * which is generally unsafe, but the race window is small and
 776		 * the worst thing that can happen is that we skip some
 777		 * potential isolation targets.
 778		 */
 779		if (PageBuddy(page)) {
 780			unsigned long freepage_order = page_order_unsafe(page);
 781
 782			/*
 783			 * Without lock, we cannot be sure that what we got is
 784			 * a valid page order. Consider only values in the
 785			 * valid order range to prevent low_pfn overflow.
 786			 */
 787			if (freepage_order > 0 && freepage_order < MAX_ORDER)
 788				low_pfn += (1UL << freepage_order) - 1;
 789			continue;
 790		}
 791
 792		/*
 793		 * Regardless of being on LRU, compound pages such as THP and
 794		 * hugetlbfs are not to be compacted. We can potentially save
 795		 * a lot of iterations if we skip them at once. The check is
 796		 * racy, but we can consider only valid values and the only
 797		 * danger is skipping too much.
 798		 */
 799		if (PageCompound(page)) {
 800			const unsigned int order = compound_order(page);
 801
 802			if (likely(order < MAX_ORDER))
 803				low_pfn += (1UL << order) - 1;
 804			goto isolate_fail;
 805		}
 806
 807		/*
 808		 * Check may be lockless but that's ok as we recheck later.
 809		 * It's possible to migrate LRU and non-lru movable pages.
 810		 * Skip any other type of page
 811		 */
 812		if (!PageLRU(page)) {
 813			/*
 814			 * __PageMovable can return false positive so we need
 815			 * to verify it under page_lock.
 816			 */
 817			if (unlikely(__PageMovable(page)) &&
 818					!PageIsolated(page)) {
 819				if (locked) {
 820					spin_unlock_irqrestore(zone_lru_lock(zone),
 821									flags);
 822					locked = false;
 823				}
 824
 825				if (!isolate_movable_page(page, isolate_mode))
 826					goto isolate_success;
 827			}
 828
 829			goto isolate_fail;
 830		}
 831
 832		/*
 833		 * Migration will fail if an anonymous page is pinned in memory,
 834		 * so avoid taking lru_lock and isolating it unnecessarily in an
 835		 * admittedly racy check.
 836		 */
 837		if (!page_mapping(page) &&
 838		    page_count(page) > page_mapcount(page))
 839			goto isolate_fail;
 840
 841		/*
 842		 * Only allow to migrate anonymous pages in GFP_NOFS context
 843		 * because those do not depend on fs locks.
 
 844		 */
 845		if (!(cc->gfp_mask & __GFP_FS) && page_mapping(page))
 846			goto isolate_fail;
 847
 848		/* If we already hold the lock, we can skip some rechecking */
 849		if (!locked) {
 850			locked = compact_trylock_irqsave(zone_lru_lock(zone),
 851								&flags, cc);
 852			if (!locked)
 853				break;
 854
 855			/* Recheck PageLRU and PageCompound under lock */
 856			if (!PageLRU(page))
 857				goto isolate_fail;
 858
 859			/*
 860			 * Page become compound since the non-locked check,
 861			 * and it's on LRU. It can only be a THP so the order
 862			 * is safe to read and it's 0 for tail pages.
 863			 */
 864			if (unlikely(PageCompound(page))) {
 865				low_pfn += (1UL << compound_order(page)) - 1;
 866				goto isolate_fail;
 867			}
 868		}
 869
 870		lruvec = mem_cgroup_page_lruvec(page, zone->zone_pgdat);
 
 
 
 871
 872		/* Try isolate the page */
 873		if (__isolate_lru_page(page, isolate_mode) != 0)
 874			goto isolate_fail;
 875
 876		VM_BUG_ON_PAGE(PageCompound(page), page);
 877
 878		/* Successfully isolated */
 879		del_page_from_lru_list(page, lruvec, page_lru(page));
 880		inc_node_page_state(page,
 881				NR_ISOLATED_ANON + page_is_file_cache(page));
 882
 883isolate_success:
 884		list_add(&page->lru, &cc->migratepages);
 885		cc->nr_migratepages++;
 886		nr_isolated++;
 887
 888		/*
 889		 * Record where we could have freed pages by migration and not
 890		 * yet flushed them to buddy allocator.
 891		 * - this is the lowest page that was isolated and likely be
 892		 * then freed by migration.
 893		 */
 894		if (!cc->last_migrated_pfn)
 895			cc->last_migrated_pfn = low_pfn;
 896
 897		/* Avoid isolating too much */
 898		if (cc->nr_migratepages == COMPACT_CLUSTER_MAX) {
 899			++low_pfn;
 900			break;
 901		}
 902
 903		continue;
 904isolate_fail:
 905		if (!skip_on_failure)
 906			continue;
 907
 908		/*
 909		 * We have isolated some pages, but then failed. Release them
 910		 * instead of migrating, as we cannot form the cc->order buddy
 911		 * page anyway.
 912		 */
 913		if (nr_isolated) {
 914			if (locked) {
 915				spin_unlock_irqrestore(zone_lru_lock(zone), flags);
 916				locked = false;
 917			}
 918			putback_movable_pages(&cc->migratepages);
 919			cc->nr_migratepages = 0;
 920			cc->last_migrated_pfn = 0;
 921			nr_isolated = 0;
 922		}
 923
 924		if (low_pfn < next_skip_pfn) {
 925			low_pfn = next_skip_pfn - 1;
 926			/*
 927			 * The check near the loop beginning would have updated
 928			 * next_skip_pfn too, but this is a bit simpler.
 929			 */
 930			next_skip_pfn += 1UL << cc->order;
 931		}
 932	}
 933
 934	/*
 935	 * The PageBuddy() check could have potentially brought us outside
 936	 * the range to be scanned.
 937	 */
 938	if (unlikely(low_pfn > end_pfn))
 939		low_pfn = end_pfn;
 940
 941	if (locked)
 942		spin_unlock_irqrestore(zone_lru_lock(zone), flags);
 943
 944	/*
 945	 * Update the pageblock-skip information and cached scanner pfn,
 946	 * if the whole pageblock was scanned without isolating any page.
 947	 */
 948	if (low_pfn == end_pfn)
 949		update_pageblock_skip(cc, valid_page, nr_isolated, true);
 950
 951	trace_mm_compaction_isolate_migratepages(start_pfn, low_pfn,
 952						nr_scanned, nr_isolated);
 953
 954	cc->total_migrate_scanned += nr_scanned;
 955	if (nr_isolated)
 956		count_compact_events(COMPACTISOLATED, nr_isolated);
 957
 958	return low_pfn;
 959}
 960
 961/**
 962 * isolate_migratepages_range() - isolate migrate-able pages in a PFN range
 963 * @cc:        Compaction control structure.
 964 * @start_pfn: The first PFN to start isolating.
 965 * @end_pfn:   The one-past-last PFN.
 966 *
 967 * Returns zero if isolation fails fatally due to e.g. pending signal.
 968 * Otherwise, function returns one-past-the-last PFN of isolated page
 969 * (which may be greater than end_pfn if end fell in a middle of a THP page).
 970 */
 971unsigned long
 972isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn,
 973							unsigned long end_pfn)
 974{
 975	unsigned long pfn, block_start_pfn, block_end_pfn;
 976
 977	/* Scan block by block. First and last block may be incomplete */
 978	pfn = start_pfn;
 979	block_start_pfn = pageblock_start_pfn(pfn);
 980	if (block_start_pfn < cc->zone->zone_start_pfn)
 981		block_start_pfn = cc->zone->zone_start_pfn;
 982	block_end_pfn = pageblock_end_pfn(pfn);
 983
 984	for (; pfn < end_pfn; pfn = block_end_pfn,
 985				block_start_pfn = block_end_pfn,
 986				block_end_pfn += pageblock_nr_pages) {
 987
 988		block_end_pfn = min(block_end_pfn, end_pfn);
 989
 990		if (!pageblock_pfn_to_page(block_start_pfn,
 991					block_end_pfn, cc->zone))
 992			continue;
 993
 994		pfn = isolate_migratepages_block(cc, pfn, block_end_pfn,
 995							ISOLATE_UNEVICTABLE);
 996
 997		if (!pfn)
 998			break;
 999
1000		if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
1001			break;
1002	}
1003
1004	return pfn;
1005}
1006
1007#endif /* CONFIG_COMPACTION || CONFIG_CMA */
1008#ifdef CONFIG_COMPACTION
1009
1010static bool suitable_migration_source(struct compact_control *cc,
1011							struct page *page)
1012{
1013	int block_mt;
1014
1015	if ((cc->mode != MIGRATE_ASYNC) || !cc->direct_compaction)
1016		return true;
1017
1018	block_mt = get_pageblock_migratetype(page);
1019
1020	if (cc->migratetype == MIGRATE_MOVABLE)
1021		return is_migrate_movable(block_mt);
1022	else
1023		return block_mt == cc->migratetype;
1024}
1025
1026/* Returns true if the page is within a block suitable for migration to */
1027static bool suitable_migration_target(struct compact_control *cc,
1028							struct page *page)
1029{
1030	/* If the page is a large free page, then disallow migration */
1031	if (PageBuddy(page)) {
1032		/*
1033		 * We are checking page_order without zone->lock taken. But
1034		 * the only small danger is that we skip a potentially suitable
1035		 * pageblock, so it's not worth to check order for valid range.
1036		 */
1037		if (page_order_unsafe(page) >= pageblock_order)
1038			return false;
1039	}
1040
1041	if (cc->ignore_block_suitable)
 
1042		return true;
1043
1044	/* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
1045	if (is_migrate_movable(get_pageblock_migratetype(page)))
1046		return true;
1047
1048	/* Otherwise skip the block */
1049	return false;
1050}
1051
1052/*
1053 * Test whether the free scanner has reached the same or lower pageblock than
1054 * the migration scanner, and compaction should thus terminate.
1055 */
1056static inline bool compact_scanners_met(struct compact_control *cc)
1057{
1058	return (cc->free_pfn >> pageblock_order)
1059		<= (cc->migrate_pfn >> pageblock_order);
1060}
1061
1062/*
1063 * Based on information in the current compact_control, find blocks
1064 * suitable for isolating free pages from and then isolate them.
1065 */
1066static void isolate_freepages(struct compact_control *cc)
 
1067{
1068	struct zone *zone = cc->zone;
1069	struct page *page;
1070	unsigned long block_start_pfn;	/* start of current pageblock */
1071	unsigned long isolate_start_pfn; /* exact pfn we start at */
1072	unsigned long block_end_pfn;	/* end of current pageblock */
1073	unsigned long low_pfn;	     /* lowest pfn scanner is able to scan */
1074	struct list_head *freelist = &cc->freepages;
1075
1076	/*
1077	 * Initialise the free scanner. The starting point is where we last
1078	 * successfully isolated from, zone-cached value, or the end of the
1079	 * zone when isolating for the first time. For looping we also need
1080	 * this pfn aligned down to the pageblock boundary, because we do
1081	 * block_start_pfn -= pageblock_nr_pages in the for loop.
1082	 * For ending point, take care when isolating in last pageblock of a
1083	 * a zone which ends in the middle of a pageblock.
1084	 * The low boundary is the end of the pageblock the migration scanner
1085	 * is using.
1086	 */
1087	isolate_start_pfn = cc->free_pfn;
1088	block_start_pfn = pageblock_start_pfn(cc->free_pfn);
1089	block_end_pfn = min(block_start_pfn + pageblock_nr_pages,
1090						zone_end_pfn(zone));
1091	low_pfn = pageblock_end_pfn(cc->migrate_pfn);
 
 
 
 
 
 
1092
1093	/*
1094	 * Isolate free pages until enough are available to migrate the
1095	 * pages on cc->migratepages. We stop searching if the migrate
1096	 * and free page scanners meet or enough free pages are isolated.
1097	 */
1098	for (; block_start_pfn >= low_pfn;
1099				block_end_pfn = block_start_pfn,
1100				block_start_pfn -= pageblock_nr_pages,
1101				isolate_start_pfn = block_start_pfn) {
1102		/*
1103		 * This can iterate a massively long zone without finding any
1104		 * suitable migration targets, so periodically check if we need
1105		 * to schedule, or even abort async compaction.
1106		 */
1107		if (!(block_start_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages))
1108						&& compact_should_abort(cc))
1109			break;
1110
1111		page = pageblock_pfn_to_page(block_start_pfn, block_end_pfn,
1112									zone);
1113		if (!page)
1114			continue;
1115
1116		/* Check the block is suitable for migration */
1117		if (!suitable_migration_target(cc, page))
 
 
 
 
 
 
 
1118			continue;
1119
1120		/* If isolation recently failed, do not retry */
1121		if (!isolation_suitable(cc, page))
1122			continue;
1123
1124		/* Found a block suitable for isolating free pages from. */
1125		isolate_freepages_block(cc, &isolate_start_pfn, block_end_pfn,
1126					freelist, false);
1127
1128		/*
1129		 * If we isolated enough freepages, or aborted due to lock
1130		 * contention, terminate.
 
 
1131		 */
1132		if ((cc->nr_freepages >= cc->nr_migratepages)
1133							|| cc->contended) {
1134			if (isolate_start_pfn >= block_end_pfn) {
1135				/*
1136				 * Restart at previous pageblock if more
1137				 * freepages can be isolated next time.
1138				 */
1139				isolate_start_pfn =
1140					block_start_pfn - pageblock_nr_pages;
1141			}
1142			break;
1143		} else if (isolate_start_pfn < block_end_pfn) {
1144			/*
1145			 * If isolation failed early, do not continue
1146			 * needlessly.
1147			 */
1148			break;
1149		}
 
 
 
 
 
 
 
 
 
1150	}
1151
1152	/* __isolate_free_page() does not map the pages */
1153	map_pages(freelist);
1154
1155	/*
1156	 * Record where the free scanner will restart next time. Either we
1157	 * broke from the loop and set isolate_start_pfn based on the last
1158	 * call to isolate_freepages_block(), or we met the migration scanner
1159	 * and the loop terminated due to isolate_start_pfn < low_pfn
1160	 */
1161	cc->free_pfn = isolate_start_pfn;
1162}
1163
1164/*
1165 * This is a migrate-callback that "allocates" freepages by taking pages
1166 * from the isolated freelists in the block we are migrating to.
1167 */
1168static struct page *compaction_alloc(struct page *migratepage,
1169					unsigned long data)
 
1170{
1171	struct compact_control *cc = (struct compact_control *)data;
1172	struct page *freepage;
1173
1174	/*
1175	 * Isolate free pages if necessary, and if we are not aborting due to
1176	 * contention.
1177	 */
1178	if (list_empty(&cc->freepages)) {
1179		if (!cc->contended)
1180			isolate_freepages(cc);
1181
1182		if (list_empty(&cc->freepages))
1183			return NULL;
1184	}
1185
1186	freepage = list_entry(cc->freepages.next, struct page, lru);
1187	list_del(&freepage->lru);
1188	cc->nr_freepages--;
1189
1190	return freepage;
1191}
1192
1193/*
1194 * This is a migrate-callback that "frees" freepages back to the isolated
1195 * freelist.  All pages on the freelist are from the same zone, so there is no
1196 * special handling needed for NUMA.
1197 */
1198static void compaction_free(struct page *page, unsigned long data)
1199{
1200	struct compact_control *cc = (struct compact_control *)data;
 
 
 
 
 
 
 
1201
1202	list_add(&page->lru, &cc->freepages);
1203	cc->nr_freepages++;
1204}
1205
1206/* possible outcome of isolate_migratepages */
1207typedef enum {
1208	ISOLATE_ABORT,		/* Abort compaction now */
1209	ISOLATE_NONE,		/* No pages isolated, continue scanning */
1210	ISOLATE_SUCCESS,	/* Pages isolated, migrate */
1211} isolate_migrate_t;
1212
1213/*
1214 * Allow userspace to control policy on scanning the unevictable LRU for
1215 * compactable pages.
1216 */
1217int sysctl_compact_unevictable_allowed __read_mostly = 1;
1218
1219/*
1220 * Isolate all pages that can be migrated from the first suitable block,
1221 * starting at the block pointed to by the migrate scanner pfn within
1222 * compact_control.
1223 */
1224static isolate_migrate_t isolate_migratepages(struct zone *zone,
1225					struct compact_control *cc)
1226{
1227	unsigned long block_start_pfn;
1228	unsigned long block_end_pfn;
1229	unsigned long low_pfn;
1230	struct page *page;
1231	const isolate_mode_t isolate_mode =
1232		(sysctl_compact_unevictable_allowed ? ISOLATE_UNEVICTABLE : 0) |
1233		(cc->mode != MIGRATE_SYNC ? ISOLATE_ASYNC_MIGRATE : 0);
1234
1235	/*
1236	 * Start at where we last stopped, or beginning of the zone as
1237	 * initialized by compact_zone()
1238	 */
1239	low_pfn = cc->migrate_pfn;
1240	block_start_pfn = pageblock_start_pfn(low_pfn);
1241	if (block_start_pfn < zone->zone_start_pfn)
1242		block_start_pfn = zone->zone_start_pfn;
1243
1244	/* Only scan within a pageblock boundary */
1245	block_end_pfn = pageblock_end_pfn(low_pfn);
1246
1247	/*
1248	 * Iterate over whole pageblocks until we find the first suitable.
1249	 * Do not cross the free scanner.
1250	 */
1251	for (; block_end_pfn <= cc->free_pfn;
1252			low_pfn = block_end_pfn,
1253			block_start_pfn = block_end_pfn,
1254			block_end_pfn += pageblock_nr_pages) {
1255
1256		/*
1257		 * This can potentially iterate a massively long zone with
1258		 * many pageblocks unsuitable, so periodically check if we
1259		 * need to schedule, or even abort async compaction.
1260		 */
1261		if (!(low_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages))
1262						&& compact_should_abort(cc))
1263			break;
1264
1265		page = pageblock_pfn_to_page(block_start_pfn, block_end_pfn,
1266									zone);
1267		if (!page)
1268			continue;
1269
1270		/* If isolation recently failed, do not retry */
1271		if (!isolation_suitable(cc, page))
1272			continue;
1273
1274		/*
1275		 * For async compaction, also only scan in MOVABLE blocks.
1276		 * Async compaction is optimistic to see if the minimum amount
1277		 * of work satisfies the allocation.
1278		 */
1279		if (!suitable_migration_source(cc, page))
1280			continue;
1281
1282		/* Perform the isolation */
1283		low_pfn = isolate_migratepages_block(cc, low_pfn,
1284						block_end_pfn, isolate_mode);
1285
1286		if (!low_pfn || cc->contended)
1287			return ISOLATE_ABORT;
1288
1289		/*
1290		 * Either we isolated something and proceed with migration. Or
1291		 * we failed and compact_zone should decide if we should
1292		 * continue or not.
1293		 */
1294		break;
1295	}
1296
1297	/* Record where migration scanner will be restarted. */
 
 
 
 
1298	cc->migrate_pfn = low_pfn;
1299
1300	return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE;
1301}
1302
1303/*
1304 * order == -1 is expected when compacting via
1305 * /proc/sys/vm/compact_memory
1306 */
1307static inline bool is_via_compact_memory(int order)
1308{
1309	return order == -1;
1310}
1311
1312static enum compact_result __compact_finished(struct zone *zone,
1313						struct compact_control *cc)
1314{
1315	unsigned int order;
1316	const int migratetype = cc->migratetype;
1317
1318	if (cc->contended || fatal_signal_pending(current))
1319		return COMPACT_CONTENDED;
1320
1321	/* Compaction run completes if the migrate and free scanner meet */
1322	if (compact_scanners_met(cc)) {
1323		/* Let the next compaction start anew. */
1324		reset_cached_positions(zone);
1325
1326		/*
1327		 * Mark that the PG_migrate_skip information should be cleared
1328		 * by kswapd when it goes to sleep. kcompactd does not set the
1329		 * flag itself as the decision to be clear should be directly
1330		 * based on an allocation request.
1331		 */
1332		if (cc->direct_compaction)
1333			zone->compact_blockskip_flush = true;
1334
1335		if (cc->whole_zone)
1336			return COMPACT_COMPLETE;
1337		else
1338			return COMPACT_PARTIAL_SKIPPED;
1339	}
1340
1341	if (is_via_compact_memory(cc->order))
1342		return COMPACT_CONTINUE;
1343
1344	if (cc->finishing_block) {
1345		/*
1346		 * We have finished the pageblock, but better check again that
1347		 * we really succeeded.
1348		 */
1349		if (IS_ALIGNED(cc->migrate_pfn, pageblock_nr_pages))
1350			cc->finishing_block = false;
1351		else
1352			return COMPACT_CONTINUE;
1353	}
1354
1355	/* Direct compactor: Is a suitable page free? */
1356	for (order = cc->order; order < MAX_ORDER; order++) {
1357		struct free_area *area = &zone->free_area[order];
1358		bool can_steal;
1359
1360		/* Job done if page is free of the right migratetype */
1361		if (!list_empty(&area->free_list[migratetype]))
1362			return COMPACT_SUCCESS;
1363
1364#ifdef CONFIG_CMA
1365		/* MIGRATE_MOVABLE can fallback on MIGRATE_CMA */
1366		if (migratetype == MIGRATE_MOVABLE &&
1367			!list_empty(&area->free_list[MIGRATE_CMA]))
1368			return COMPACT_SUCCESS;
1369#endif
1370		/*
1371		 * Job done if allocation would steal freepages from
1372		 * other migratetype buddy lists.
1373		 */
1374		if (find_suitable_fallback(area, order, migratetype,
1375						true, &can_steal) != -1) {
1376
1377			/* movable pages are OK in any pageblock */
1378			if (migratetype == MIGRATE_MOVABLE)
1379				return COMPACT_SUCCESS;
1380
1381			/*
1382			 * We are stealing for a non-movable allocation. Make
1383			 * sure we finish compacting the current pageblock
1384			 * first so it is as free as possible and we won't
1385			 * have to steal another one soon. This only applies
1386			 * to sync compaction, as async compaction operates
1387			 * on pageblocks of the same migratetype.
1388			 */
1389			if (cc->mode == MIGRATE_ASYNC ||
1390					IS_ALIGNED(cc->migrate_pfn,
1391							pageblock_nr_pages)) {
1392				return COMPACT_SUCCESS;
1393			}
1394
1395			cc->finishing_block = true;
1396			return COMPACT_CONTINUE;
1397		}
1398	}
1399
1400	return COMPACT_NO_SUITABLE_PAGE;
1401}
1402
1403static enum compact_result compact_finished(struct zone *zone,
1404			struct compact_control *cc)
1405{
1406	int ret;
1407
1408	ret = __compact_finished(zone, cc);
1409	trace_mm_compaction_finished(zone, cc->order, ret);
1410	if (ret == COMPACT_NO_SUITABLE_PAGE)
1411		ret = COMPACT_CONTINUE;
1412
1413	return ret;
1414}
1415
1416/*
1417 * compaction_suitable: Is this suitable to run compaction on this zone now?
1418 * Returns
1419 *   COMPACT_SKIPPED  - If there are too few free pages for compaction
1420 *   COMPACT_SUCCESS  - If the allocation would succeed without compaction
1421 *   COMPACT_CONTINUE - If compaction should run now
1422 */
1423static enum compact_result __compaction_suitable(struct zone *zone, int order,
1424					unsigned int alloc_flags,
1425					int classzone_idx,
1426					unsigned long wmark_target)
1427{
 
1428	unsigned long watermark;
1429
1430	if (is_via_compact_memory(order))
1431		return COMPACT_CONTINUE;
1432
1433	watermark = zone->watermark[alloc_flags & ALLOC_WMARK_MASK];
1434	/*
1435	 * If watermarks for high-order allocation are already met, there
1436	 * should be no need for compaction at all.
1437	 */
1438	if (zone_watermark_ok(zone, order, watermark, classzone_idx,
1439								alloc_flags))
1440		return COMPACT_SUCCESS;
1441
1442	/*
1443	 * Watermarks for order-0 must be met for compaction to be able to
1444	 * isolate free pages for migration targets. This means that the
1445	 * watermark and alloc_flags have to match, or be more pessimistic than
1446	 * the check in __isolate_free_page(). We don't use the direct
1447	 * compactor's alloc_flags, as they are not relevant for freepage
1448	 * isolation. We however do use the direct compactor's classzone_idx to
1449	 * skip over zones where lowmem reserves would prevent allocation even
1450	 * if compaction succeeds.
1451	 * For costly orders, we require low watermark instead of min for
1452	 * compaction to proceed to increase its chances.
1453	 * ALLOC_CMA is used, as pages in CMA pageblocks are considered
1454	 * suitable migration targets
1455	 */
1456	watermark = (order > PAGE_ALLOC_COSTLY_ORDER) ?
1457				low_wmark_pages(zone) : min_wmark_pages(zone);
1458	watermark += compact_gap(order);
1459	if (!__zone_watermark_ok(zone, 0, watermark, classzone_idx,
1460						ALLOC_CMA, wmark_target))
1461		return COMPACT_SKIPPED;
1462
1463	return COMPACT_CONTINUE;
1464}
1465
1466enum compact_result compaction_suitable(struct zone *zone, int order,
1467					unsigned int alloc_flags,
1468					int classzone_idx)
1469{
1470	enum compact_result ret;
1471	int fragindex;
1472
1473	ret = __compaction_suitable(zone, order, alloc_flags, classzone_idx,
1474				    zone_page_state(zone, NR_FREE_PAGES));
1475	/*
1476	 * fragmentation index determines if allocation failures are due to
1477	 * low memory or external fragmentation
1478	 *
1479	 * index of -1000 would imply allocations might succeed depending on
1480	 * watermarks, but we already failed the high-order watermark check
1481	 * index towards 0 implies failure is due to lack of memory
1482	 * index towards 1000 implies failure is due to fragmentation
1483	 *
1484	 * Only compact if a failure would be due to fragmentation. Also
1485	 * ignore fragindex for non-costly orders where the alternative to
1486	 * a successful reclaim/compaction is OOM. Fragindex and the
1487	 * vm.extfrag_threshold sysctl is meant as a heuristic to prevent
1488	 * excessive compaction for costly orders, but it should not be at the
1489	 * expense of system stability.
1490	 */
1491	if (ret == COMPACT_CONTINUE && (order > PAGE_ALLOC_COSTLY_ORDER)) {
1492		fragindex = fragmentation_index(zone, order);
1493		if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
1494			ret = COMPACT_NOT_SUITABLE_ZONE;
1495	}
1496
1497	trace_mm_compaction_suitable(zone, order, ret);
1498	if (ret == COMPACT_NOT_SUITABLE_ZONE)
1499		ret = COMPACT_SKIPPED;
1500
1501	return ret;
1502}
1503
1504bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
1505		int alloc_flags)
1506{
1507	struct zone *zone;
1508	struct zoneref *z;
1509
1510	/*
1511	 * Make sure at least one zone would pass __compaction_suitable if we continue
1512	 * retrying the reclaim.
1513	 */
1514	for_each_zone_zonelist_nodemask(zone, z, ac->zonelist, ac->high_zoneidx,
1515					ac->nodemask) {
1516		unsigned long available;
1517		enum compact_result compact_result;
1518
1519		/*
1520		 * Do not consider all the reclaimable memory because we do not
1521		 * want to trash just for a single high order allocation which
1522		 * is even not guaranteed to appear even if __compaction_suitable
1523		 * is happy about the watermark check.
1524		 */
1525		available = zone_reclaimable_pages(zone) / order;
1526		available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
1527		compact_result = __compaction_suitable(zone, order, alloc_flags,
1528				ac_classzone_idx(ac), available);
1529		if (compact_result != COMPACT_SKIPPED)
1530			return true;
1531	}
1532
1533	return false;
1534}
1535
1536static enum compact_result compact_zone(struct zone *zone, struct compact_control *cc)
1537{
1538	enum compact_result ret;
1539	unsigned long start_pfn = zone->zone_start_pfn;
1540	unsigned long end_pfn = zone_end_pfn(zone);
1541	const bool sync = cc->mode != MIGRATE_ASYNC;
1542
1543	cc->migratetype = gfpflags_to_migratetype(cc->gfp_mask);
1544	ret = compaction_suitable(zone, cc->order, cc->alloc_flags,
1545							cc->classzone_idx);
1546	/* Compaction is likely to fail */
1547	if (ret == COMPACT_SUCCESS || ret == COMPACT_SKIPPED)
1548		return ret;
1549
1550	/* huh, compaction_suitable is returning something unexpected */
1551	VM_BUG_ON(ret != COMPACT_CONTINUE);
1552
1553	/*
1554	 * Clear pageblock skip if there were failures recently and compaction
1555	 * is about to be retried after being deferred.
1556	 */
1557	if (compaction_restarting(zone, cc->order))
1558		__reset_isolation_suitable(zone);
1559
1560	/*
1561	 * Setup to move all movable pages to the end of the zone. Used cached
1562	 * information on where the scanners should start (unless we explicitly
1563	 * want to compact the whole zone), but check that it is initialised
1564	 * by ensuring the values are within zone boundaries.
1565	 */
1566	if (cc->whole_zone) {
1567		cc->migrate_pfn = start_pfn;
1568		cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
1569	} else {
1570		cc->migrate_pfn = zone->compact_cached_migrate_pfn[sync];
1571		cc->free_pfn = zone->compact_cached_free_pfn;
1572		if (cc->free_pfn < start_pfn || cc->free_pfn >= end_pfn) {
1573			cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
1574			zone->compact_cached_free_pfn = cc->free_pfn;
1575		}
1576		if (cc->migrate_pfn < start_pfn || cc->migrate_pfn >= end_pfn) {
1577			cc->migrate_pfn = start_pfn;
1578			zone->compact_cached_migrate_pfn[0] = cc->migrate_pfn;
1579			zone->compact_cached_migrate_pfn[1] = cc->migrate_pfn;
1580		}
1581
1582		if (cc->migrate_pfn == start_pfn)
1583			cc->whole_zone = true;
1584	}
1585
1586	cc->last_migrated_pfn = 0;
1587
1588	trace_mm_compaction_begin(start_pfn, cc->migrate_pfn,
1589				cc->free_pfn, end_pfn, sync);
1590
1591	migrate_prep_local();
1592
1593	while ((ret = compact_finished(zone, cc)) == COMPACT_CONTINUE) {
 
1594		int err;
1595
1596		switch (isolate_migratepages(zone, cc)) {
1597		case ISOLATE_ABORT:
1598			ret = COMPACT_CONTENDED;
1599			putback_movable_pages(&cc->migratepages);
1600			cc->nr_migratepages = 0;
1601			goto out;
1602		case ISOLATE_NONE:
1603			/*
1604			 * We haven't isolated and migrated anything, but
1605			 * there might still be unflushed migrations from
1606			 * previous cc->order aligned block.
1607			 */
1608			goto check_drain;
1609		case ISOLATE_SUCCESS:
1610			;
1611		}
1612
 
1613		err = migrate_pages(&cc->migratepages, compaction_alloc,
1614				compaction_free, (unsigned long)cc, cc->mode,
1615				MR_COMPACTION);
 
 
 
 
 
 
 
 
 
1616
1617		trace_mm_compaction_migratepages(cc->nr_migratepages, err,
1618							&cc->migratepages);
1619
1620		/* All pages were either migrated or will be released */
1621		cc->nr_migratepages = 0;
1622		if (err) {
1623			putback_movable_pages(&cc->migratepages);
1624			/*
1625			 * migrate_pages() may return -ENOMEM when scanners meet
1626			 * and we want compact_finished() to detect it
1627			 */
1628			if (err == -ENOMEM && !compact_scanners_met(cc)) {
1629				ret = COMPACT_CONTENDED;
1630				goto out;
1631			}
1632			/*
1633			 * We failed to migrate at least one page in the current
1634			 * order-aligned block, so skip the rest of it.
1635			 */
1636			if (cc->direct_compaction &&
1637						(cc->mode == MIGRATE_ASYNC)) {
1638				cc->migrate_pfn = block_end_pfn(
1639						cc->migrate_pfn - 1, cc->order);
1640				/* Draining pcplists is useless in this case */
1641				cc->last_migrated_pfn = 0;
1642
1643			}
1644		}
1645
1646check_drain:
1647		/*
1648		 * Has the migration scanner moved away from the previous
1649		 * cc->order aligned block where we migrated from? If yes,
1650		 * flush the pages that were freed, so that they can merge and
1651		 * compact_finished() can detect immediately if allocation
1652		 * would succeed.
1653		 */
1654		if (cc->order > 0 && cc->last_migrated_pfn) {
1655			int cpu;
1656			unsigned long current_block_start =
1657				block_start_pfn(cc->migrate_pfn, cc->order);
1658
1659			if (cc->last_migrated_pfn < current_block_start) {
1660				cpu = get_cpu();
1661				lru_add_drain_cpu(cpu);
1662				drain_local_pages(zone);
1663				put_cpu();
1664				/* No more flushing until we migrate again */
1665				cc->last_migrated_pfn = 0;
1666			}
1667		}
1668
1669	}
1670
1671out:
1672	/*
1673	 * Release free pages and update where the free scanner should restart,
1674	 * so we don't leave any returned pages behind in the next attempt.
1675	 */
1676	if (cc->nr_freepages > 0) {
1677		unsigned long free_pfn = release_freepages(&cc->freepages);
1678
1679		cc->nr_freepages = 0;
1680		VM_BUG_ON(free_pfn == 0);
1681		/* The cached pfn is always the first in a pageblock */
1682		free_pfn = pageblock_start_pfn(free_pfn);
1683		/*
1684		 * Only go back, not forward. The cached pfn might have been
1685		 * already reset to zone end in compact_finished()
1686		 */
1687		if (free_pfn > zone->compact_cached_free_pfn)
1688			zone->compact_cached_free_pfn = free_pfn;
1689	}
1690
1691	count_compact_events(COMPACTMIGRATE_SCANNED, cc->total_migrate_scanned);
1692	count_compact_events(COMPACTFREE_SCANNED, cc->total_free_scanned);
1693
1694	trace_mm_compaction_end(start_pfn, cc->migrate_pfn,
1695				cc->free_pfn, end_pfn, sync, ret);
1696
1697	return ret;
1698}
1699
1700static enum compact_result compact_zone_order(struct zone *zone, int order,
1701		gfp_t gfp_mask, enum compact_priority prio,
1702		unsigned int alloc_flags, int classzone_idx)
1703{
1704	enum compact_result ret;
1705	struct compact_control cc = {
1706		.nr_freepages = 0,
1707		.nr_migratepages = 0,
1708		.total_migrate_scanned = 0,
1709		.total_free_scanned = 0,
1710		.order = order,
1711		.gfp_mask = gfp_mask,
1712		.zone = zone,
1713		.mode = (prio == COMPACT_PRIO_ASYNC) ?
1714					MIGRATE_ASYNC :	MIGRATE_SYNC_LIGHT,
1715		.alloc_flags = alloc_flags,
1716		.classzone_idx = classzone_idx,
1717		.direct_compaction = true,
1718		.whole_zone = (prio == MIN_COMPACT_PRIORITY),
1719		.ignore_skip_hint = (prio == MIN_COMPACT_PRIORITY),
1720		.ignore_block_suitable = (prio == MIN_COMPACT_PRIORITY)
1721	};
1722	INIT_LIST_HEAD(&cc.freepages);
1723	INIT_LIST_HEAD(&cc.migratepages);
1724
1725	ret = compact_zone(zone, &cc);
1726
1727	VM_BUG_ON(!list_empty(&cc.freepages));
1728	VM_BUG_ON(!list_empty(&cc.migratepages));
1729
1730	return ret;
1731}
1732
1733int sysctl_extfrag_threshold = 500;
1734
1735/**
1736 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
1737 * @gfp_mask: The GFP mask of the current allocation
1738 * @order: The order of the current allocation
1739 * @alloc_flags: The allocation flags of the current allocation
1740 * @ac: The context of current allocation
1741 * @prio: Determines how hard direct compaction should try to succeed
1742 *
1743 * This is the main entry point for direct page compaction.
1744 */
1745enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
1746		unsigned int alloc_flags, const struct alloc_context *ac,
1747		enum compact_priority prio)
1748{
 
 
1749	int may_perform_io = gfp_mask & __GFP_IO;
1750	struct zoneref *z;
1751	struct zone *zone;
1752	enum compact_result rc = COMPACT_SKIPPED;
1753
1754	/*
1755	 * Check if the GFP flags allow compaction - GFP_NOIO is really
1756	 * tricky context because the migration might require IO
 
1757	 */
1758	if (!may_perform_io)
1759		return COMPACT_SKIPPED;
1760
1761	trace_mm_compaction_try_to_compact_pages(order, gfp_mask, prio);
1762
1763	/* Compact each zone in the list */
1764	for_each_zone_zonelist_nodemask(zone, z, ac->zonelist, ac->high_zoneidx,
1765								ac->nodemask) {
1766		enum compact_result status;
1767
1768		if (prio > MIN_COMPACT_PRIORITY
1769					&& compaction_deferred(zone, order)) {
1770			rc = max_t(enum compact_result, COMPACT_DEFERRED, rc);
1771			continue;
1772		}
1773
1774		status = compact_zone_order(zone, order, gfp_mask, prio,
1775					alloc_flags, ac_classzone_idx(ac));
1776		rc = max(status, rc);
1777
1778		/* The allocation should succeed, stop compacting */
1779		if (status == COMPACT_SUCCESS) {
1780			/*
1781			 * We think the allocation will succeed in this zone,
1782			 * but it is not certain, hence the false. The caller
1783			 * will repeat this with true if allocation indeed
1784			 * succeeds in this zone.
1785			 */
1786			compaction_defer_reset(zone, order, false);
1787
1788			break;
1789		}
1790
1791		if (prio != COMPACT_PRIO_ASYNC && (status == COMPACT_COMPLETE ||
1792					status == COMPACT_PARTIAL_SKIPPED))
1793			/*
1794			 * We think that allocation won't succeed in this zone
1795			 * so we defer compaction there. If it ends up
1796			 * succeeding after all, it will be reset.
1797			 */
1798			defer_compaction(zone, order);
1799
1800		/*
1801		 * We might have stopped compacting due to need_resched() in
1802		 * async compaction, or due to a fatal signal detected. In that
1803		 * case do not try further zones
1804		 */
1805		if ((prio == COMPACT_PRIO_ASYNC && need_resched())
1806					|| fatal_signal_pending(current))
1807			break;
1808	}
1809
1810	return rc;
1811}
1812
1813
1814/* Compact all zones within a node */
1815static void compact_node(int nid)
1816{
1817	pg_data_t *pgdat = NODE_DATA(nid);
1818	int zoneid;
1819	struct zone *zone;
1820	struct compact_control cc = {
1821		.order = -1,
1822		.total_migrate_scanned = 0,
1823		.total_free_scanned = 0,
1824		.mode = MIGRATE_SYNC,
1825		.ignore_skip_hint = true,
1826		.whole_zone = true,
1827		.gfp_mask = GFP_KERNEL,
1828	};
1829
1830
1831	for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
1832
1833		zone = &pgdat->node_zones[zoneid];
1834		if (!populated_zone(zone))
1835			continue;
1836
1837		cc.nr_freepages = 0;
1838		cc.nr_migratepages = 0;
1839		cc.zone = zone;
1840		INIT_LIST_HEAD(&cc.freepages);
1841		INIT_LIST_HEAD(&cc.migratepages);
1842
1843		compact_zone(zone, &cc);
 
 
 
 
 
 
 
 
 
 
 
1844
1845		VM_BUG_ON(!list_empty(&cc.freepages));
1846		VM_BUG_ON(!list_empty(&cc.migratepages));
1847	}
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1848}
1849
1850/* Compact all nodes in the system */
1851static void compact_nodes(void)
1852{
1853	int nid;
1854
1855	/* Flush pending updates to the LRU lists */
1856	lru_add_drain_all();
1857
1858	for_each_online_node(nid)
1859		compact_node(nid);
 
 
1860}
1861
1862/* The written value is actually unused, all memory is compacted */
1863int sysctl_compact_memory;
1864
1865/*
1866 * This is the entry point for compacting all nodes via
1867 * /proc/sys/vm/compact_memory
1868 */
1869int sysctl_compaction_handler(struct ctl_table *table, int write,
1870			void __user *buffer, size_t *length, loff_t *ppos)
1871{
1872	if (write)
1873		compact_nodes();
1874
1875	return 0;
1876}
1877
1878int sysctl_extfrag_handler(struct ctl_table *table, int write,
1879			void __user *buffer, size_t *length, loff_t *ppos)
1880{
1881	proc_dointvec_minmax(table, write, buffer, length, ppos);
1882
1883	return 0;
1884}
1885
1886#if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
1887static ssize_t sysfs_compact_node(struct device *dev,
1888			struct device_attribute *attr,
1889			const char *buf, size_t count)
1890{
1891	int nid = dev->id;
1892
1893	if (nid >= 0 && nid < nr_node_ids && node_online(nid)) {
1894		/* Flush pending updates to the LRU lists */
1895		lru_add_drain_all();
1896
1897		compact_node(nid);
1898	}
1899
1900	return count;
1901}
1902static DEVICE_ATTR(compact, S_IWUSR, NULL, sysfs_compact_node);
1903
1904int compaction_register_node(struct node *node)
1905{
1906	return device_create_file(&node->dev, &dev_attr_compact);
1907}
1908
1909void compaction_unregister_node(struct node *node)
1910{
1911	return device_remove_file(&node->dev, &dev_attr_compact);
1912}
1913#endif /* CONFIG_SYSFS && CONFIG_NUMA */
1914
1915static inline bool kcompactd_work_requested(pg_data_t *pgdat)
1916{
1917	return pgdat->kcompactd_max_order > 0 || kthread_should_stop();
1918}
1919
1920static bool kcompactd_node_suitable(pg_data_t *pgdat)
1921{
1922	int zoneid;
1923	struct zone *zone;
1924	enum zone_type classzone_idx = pgdat->kcompactd_classzone_idx;
1925
1926	for (zoneid = 0; zoneid <= classzone_idx; zoneid++) {
1927		zone = &pgdat->node_zones[zoneid];
1928
1929		if (!populated_zone(zone))
1930			continue;
1931
1932		if (compaction_suitable(zone, pgdat->kcompactd_max_order, 0,
1933					classzone_idx) == COMPACT_CONTINUE)
1934			return true;
1935	}
1936
1937	return false;
1938}
1939
1940static void kcompactd_do_work(pg_data_t *pgdat)
1941{
1942	/*
1943	 * With no special task, compact all zones so that a page of requested
1944	 * order is allocatable.
1945	 */
1946	int zoneid;
1947	struct zone *zone;
1948	struct compact_control cc = {
1949		.order = pgdat->kcompactd_max_order,
1950		.total_migrate_scanned = 0,
1951		.total_free_scanned = 0,
1952		.classzone_idx = pgdat->kcompactd_classzone_idx,
1953		.mode = MIGRATE_SYNC_LIGHT,
1954		.ignore_skip_hint = false,
1955		.gfp_mask = GFP_KERNEL,
1956	};
1957	trace_mm_compaction_kcompactd_wake(pgdat->node_id, cc.order,
1958							cc.classzone_idx);
1959	count_compact_event(KCOMPACTD_WAKE);
1960
1961	for (zoneid = 0; zoneid <= cc.classzone_idx; zoneid++) {
1962		int status;
1963
1964		zone = &pgdat->node_zones[zoneid];
1965		if (!populated_zone(zone))
1966			continue;
1967
1968		if (compaction_deferred(zone, cc.order))
1969			continue;
1970
1971		if (compaction_suitable(zone, cc.order, 0, zoneid) !=
1972							COMPACT_CONTINUE)
1973			continue;
1974
1975		cc.nr_freepages = 0;
1976		cc.nr_migratepages = 0;
1977		cc.total_migrate_scanned = 0;
1978		cc.total_free_scanned = 0;
1979		cc.zone = zone;
1980		INIT_LIST_HEAD(&cc.freepages);
1981		INIT_LIST_HEAD(&cc.migratepages);
1982
1983		if (kthread_should_stop())
1984			return;
1985		status = compact_zone(zone, &cc);
1986
1987		if (status == COMPACT_SUCCESS) {
1988			compaction_defer_reset(zone, cc.order, false);
1989		} else if (status == COMPACT_PARTIAL_SKIPPED || status == COMPACT_COMPLETE) {
1990			/*
1991			 * Buddy pages may become stranded on pcps that could
1992			 * otherwise coalesce on the zone's free area for
1993			 * order >= cc.order.  This is ratelimited by the
1994			 * upcoming deferral.
1995			 */
1996			drain_all_pages(zone);
1997
1998			/*
1999			 * We use sync migration mode here, so we defer like
2000			 * sync direct compaction does.
2001			 */
2002			defer_compaction(zone, cc.order);
2003		}
2004
2005		count_compact_events(KCOMPACTD_MIGRATE_SCANNED,
2006				     cc.total_migrate_scanned);
2007		count_compact_events(KCOMPACTD_FREE_SCANNED,
2008				     cc.total_free_scanned);
2009
2010		VM_BUG_ON(!list_empty(&cc.freepages));
2011		VM_BUG_ON(!list_empty(&cc.migratepages));
2012	}
2013
2014	/*
2015	 * Regardless of success, we are done until woken up next. But remember
2016	 * the requested order/classzone_idx in case it was higher/tighter than
2017	 * our current ones
2018	 */
2019	if (pgdat->kcompactd_max_order <= cc.order)
2020		pgdat->kcompactd_max_order = 0;
2021	if (pgdat->kcompactd_classzone_idx >= cc.classzone_idx)
2022		pgdat->kcompactd_classzone_idx = pgdat->nr_zones - 1;
2023}
2024
2025void wakeup_kcompactd(pg_data_t *pgdat, int order, int classzone_idx)
2026{
2027	if (!order)
2028		return;
2029
2030	if (pgdat->kcompactd_max_order < order)
2031		pgdat->kcompactd_max_order = order;
2032
2033	if (pgdat->kcompactd_classzone_idx > classzone_idx)
2034		pgdat->kcompactd_classzone_idx = classzone_idx;
2035
2036	/*
2037	 * Pairs with implicit barrier in wait_event_freezable()
2038	 * such that wakeups are not missed.
2039	 */
2040	if (!wq_has_sleeper(&pgdat->kcompactd_wait))
2041		return;
2042
2043	if (!kcompactd_node_suitable(pgdat))
2044		return;
2045
2046	trace_mm_compaction_wakeup_kcompactd(pgdat->node_id, order,
2047							classzone_idx);
2048	wake_up_interruptible(&pgdat->kcompactd_wait);
2049}
2050
2051/*
2052 * The background compaction daemon, started as a kernel thread
2053 * from the init process.
2054 */
2055static int kcompactd(void *p)
2056{
2057	pg_data_t *pgdat = (pg_data_t*)p;
2058	struct task_struct *tsk = current;
2059
2060	const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
2061
2062	if (!cpumask_empty(cpumask))
2063		set_cpus_allowed_ptr(tsk, cpumask);
2064
2065	set_freezable();
2066
2067	pgdat->kcompactd_max_order = 0;
2068	pgdat->kcompactd_classzone_idx = pgdat->nr_zones - 1;
2069
2070	while (!kthread_should_stop()) {
2071		trace_mm_compaction_kcompactd_sleep(pgdat->node_id);
2072		wait_event_freezable(pgdat->kcompactd_wait,
2073				kcompactd_work_requested(pgdat));
2074
2075		kcompactd_do_work(pgdat);
2076	}
2077
2078	return 0;
2079}
2080
2081/*
2082 * This kcompactd start function will be called by init and node-hot-add.
2083 * On node-hot-add, kcompactd will moved to proper cpus if cpus are hot-added.
2084 */
2085int kcompactd_run(int nid)
2086{
2087	pg_data_t *pgdat = NODE_DATA(nid);
2088	int ret = 0;
2089
2090	if (pgdat->kcompactd)
2091		return 0;
2092
2093	pgdat->kcompactd = kthread_run(kcompactd, pgdat, "kcompactd%d", nid);
2094	if (IS_ERR(pgdat->kcompactd)) {
2095		pr_err("Failed to start kcompactd on node %d\n", nid);
2096		ret = PTR_ERR(pgdat->kcompactd);
2097		pgdat->kcompactd = NULL;
2098	}
2099	return ret;
2100}
2101
2102/*
2103 * Called by memory hotplug when all memory in a node is offlined. Caller must
2104 * hold mem_hotplug_begin/end().
2105 */
2106void kcompactd_stop(int nid)
2107{
2108	struct task_struct *kcompactd = NODE_DATA(nid)->kcompactd;
2109
2110	if (kcompactd) {
2111		kthread_stop(kcompactd);
2112		NODE_DATA(nid)->kcompactd = NULL;
2113	}
2114}
2115
2116/*
2117 * It's optimal to keep kcompactd on the same CPUs as their memory, but
2118 * not required for correctness. So if the last cpu in a node goes
2119 * away, we get changed to run anywhere: as the first one comes back,
2120 * restore their cpu bindings.
2121 */
2122static int kcompactd_cpu_online(unsigned int cpu)
2123{
2124	int nid;
2125
2126	for_each_node_state(nid, N_MEMORY) {
2127		pg_data_t *pgdat = NODE_DATA(nid);
2128		const struct cpumask *mask;
2129
2130		mask = cpumask_of_node(pgdat->node_id);
2131
2132		if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
2133			/* One of our CPUs online: restore mask */
2134			set_cpus_allowed_ptr(pgdat->kcompactd, mask);
2135	}
2136	return 0;
2137}
2138
2139static int __init kcompactd_init(void)
2140{
2141	int nid;
2142	int ret;
2143
2144	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
2145					"mm/compaction:online",
2146					kcompactd_cpu_online, NULL);
2147	if (ret < 0) {
2148		pr_err("kcompactd: failed to register hotplug callbacks.\n");
2149		return ret;
2150	}
2151
2152	for_each_node_state(nid, N_MEMORY)
2153		kcompactd_run(nid);
2154	return 0;
2155}
2156subsys_initcall(kcompactd_init)
2157
2158#endif /* CONFIG_COMPACTION */