/*
   * linux/mm/compaction.c
   *
   * Memory compaction for the reduction of external fragmentation. Note that
   * this heavily depends upon page migration to do all the real heavy
   * lifting
   *
   * Copyright IBM Corp. 2007-2010 Mel Gorman <mel@csn.ul.ie>
   */
  #include <linux/swap.h>
  #include <linux/migrate.h>
  #include <linux/compaction.h>
  #include <linux/mm_inline.h>
  #include <linux/backing-dev.h>

  #include <linux/sysctl.h>

  #include <linux/sysfs.h>

  #include <linux/balloon_compaction.h>

  #include <linux/page-isolation.h>

  #include "internal.h"

  #ifdef CONFIG_COMPACTION
  static inline void count_compact_event(enum vm_event_item item)
  {
  	count_vm_event(item);
  }
  
  static inline void count_compact_events(enum vm_event_item item, long delta)
  {
  	count_vm_events(item, delta);
  }
  #else
  #define count_compact_event(item) do { } while (0)
  #define count_compact_events(item, delta) do { } while (0)
  #endif

  #if defined CONFIG_COMPACTION || defined CONFIG_CMA

  #define CREATE_TRACE_POINTS
  #include <trace/events/compaction.h>

  static unsigned long release_freepages(struct list_head *freelist)
  {
  	struct page *page, *next;

  	unsigned long high_pfn = 0;

  
  	list_for_each_entry_safe(page, next, freelist, lru) {

  		unsigned long pfn = page_to_pfn(page);

  		list_del(&page->lru);
  		__free_page(page);

  		if (pfn > high_pfn)
  			high_pfn = pfn;

  	}

  	return high_pfn;

  }

  static void map_pages(struct list_head *list)
  {
  	struct page *page;
  
  	list_for_each_entry(page, list, lru) {
  		arch_alloc_page(page, 0);
  		kernel_map_pages(page, 1, 1);
  	}
  }

  static inline bool migrate_async_suitable(int migratetype)
  {
  	return is_migrate_cma(migratetype) || migratetype == MIGRATE_MOVABLE;
  }

  /*
   * Check that the whole (or subset of) a pageblock given by the interval of
   * [start_pfn, end_pfn) is valid and within the same zone, before scanning it
   * with the migration of free compaction scanner. The scanners then need to
   * use only pfn_valid_within() check for arches that allow holes within
   * pageblocks.
   *
   * Return struct page pointer of start_pfn, or NULL if checks were not passed.
   *
   * It's possible on some configurations to have a setup like node0 node1 node0
   * i.e. it's possible that all pages within a zones range of pages do not
   * belong to a single zone. We assume that a border between node0 and node1
   * can occur within a single pageblock, but not a node0 node1 node0
   * interleaving within a single pageblock. It is therefore sufficient to check
   * the first and last page of a pageblock and avoid checking each individual
   * page in a pageblock.
   */
  static struct page *pageblock_pfn_to_page(unsigned long start_pfn,
  				unsigned long end_pfn, struct zone *zone)
  {
  	struct page *start_page;
  	struct page *end_page;
  
  	/* end_pfn is one past the range we are checking */
  	end_pfn--;
  
  	if (!pfn_valid(start_pfn) || !pfn_valid(end_pfn))
  		return NULL;
  
  	start_page = pfn_to_page(start_pfn);
  
  	if (page_zone(start_page) != zone)
  		return NULL;
  
  	end_page = pfn_to_page(end_pfn);
  
  	/* This gives a shorter code than deriving page_zone(end_page) */
  	if (page_zone_id(start_page) != page_zone_id(end_page))
  		return NULL;
  
  	return start_page;
  }

  #ifdef CONFIG_COMPACTION
  /* Returns true if the pageblock should be scanned for pages to isolate. */
  static inline bool isolation_suitable(struct compact_control *cc,
  					struct page *page)
  {
  	if (cc->ignore_skip_hint)
  		return true;
  
  	return !get_pageblock_skip(page);
  }
  
  /*
   * This function is called to clear all cached information on pageblocks that
   * should be skipped for page isolation when the migrate and free page scanner
   * meet.
   */

  static void __reset_isolation_suitable(struct zone *zone)

  {
  	unsigned long start_pfn = zone->zone_start_pfn;

  	unsigned long end_pfn = zone_end_pfn(zone);

  	unsigned long pfn;

  	zone->compact_cached_migrate_pfn[0] = start_pfn;
  	zone->compact_cached_migrate_pfn[1] = start_pfn;

  	zone->compact_cached_free_pfn = end_pfn;

  	zone->compact_blockskip_flush = false;

  
  	/* Walk the zone and mark every pageblock as suitable for isolation */
  	for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages) {
  		struct page *page;
  
  		cond_resched();
  
  		if (!pfn_valid(pfn))
  			continue;
  
  		page = pfn_to_page(pfn);
  		if (zone != page_zone(page))
  			continue;
  
  		clear_pageblock_skip(page);
  	}
  }

  void reset_isolation_suitable(pg_data_t *pgdat)
  {
  	int zoneid;
  
  	for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
  		struct zone *zone = &pgdat->node_zones[zoneid];
  		if (!populated_zone(zone))
  			continue;
  
  		/* Only flush if a full compaction finished recently */
  		if (zone->compact_blockskip_flush)
  			__reset_isolation_suitable(zone);
  	}
  }

  /*
   * If no pages were isolated then mark this pageblock to be skipped in the

   * future. The information is later cleared by __reset_isolation_suitable().

   */

  static void update_pageblock_skip(struct compact_control *cc,
  			struct page *page, unsigned long nr_isolated,

  			bool migrate_scanner)

  {

  	struct zone *zone = cc->zone;

  	unsigned long pfn;

  
  	if (cc->ignore_skip_hint)
  		return;

  	if (!page)
  		return;

  	if (nr_isolated)
  		return;

  	set_pageblock_skip(page);

  	pfn = page_to_pfn(page);
  
  	/* Update where async and sync compaction should restart */
  	if (migrate_scanner) {

  		if (pfn > zone->compact_cached_migrate_pfn[0])
  			zone->compact_cached_migrate_pfn[0] = pfn;

  		if (cc->mode != MIGRATE_ASYNC &&
  		    pfn > zone->compact_cached_migrate_pfn[1])

  			zone->compact_cached_migrate_pfn[1] = pfn;
  	} else {

  		if (pfn < zone->compact_cached_free_pfn)
  			zone->compact_cached_free_pfn = pfn;

  	}

  }
  #else
  static inline bool isolation_suitable(struct compact_control *cc,
  					struct page *page)
  {
  	return true;
  }

  static void update_pageblock_skip(struct compact_control *cc,
  			struct page *page, unsigned long nr_isolated,

  			bool migrate_scanner)

  {
  }
  #endif /* CONFIG_COMPACTION */

  /*
   * Compaction requires the taking of some coarse locks that are potentially
   * very heavily contended. For async compaction, back out if the lock cannot
   * be taken immediately. For sync compaction, spin on the lock if needed.
   *
   * Returns true if the lock is held
   * Returns false if the lock is not held and compaction should abort
   */
  static bool compact_trylock_irqsave(spinlock_t *lock, unsigned long *flags,
  						struct compact_control *cc)

  {

  	if (cc->mode == MIGRATE_ASYNC) {
  		if (!spin_trylock_irqsave(lock, *flags)) {
  			cc->contended = COMPACT_CONTENDED_LOCK;
  			return false;
  		}
  	} else {
  		spin_lock_irqsave(lock, *flags);
  	}

  	return true;

  }

  /*

   * Compaction requires the taking of some coarse locks that are potentially

   * very heavily contended. The lock should be periodically unlocked to avoid
   * having disabled IRQs for a long time, even when there is nobody waiting on
   * the lock. It might also be that allowing the IRQs will result in
   * need_resched() becoming true. If scheduling is needed, async compaction
   * aborts. Sync compaction schedules.
   * Either compaction type will also abort if a fatal signal is pending.
   * In either case if the lock was locked, it is dropped and not regained.

   *

   * Returns true if compaction should abort due to fatal signal pending, or
   *		async compaction due to need_resched()
   * Returns false when compaction can continue (sync compaction might have
   *		scheduled)

   */

  static bool compact_unlock_should_abort(spinlock_t *lock,
  		unsigned long flags, bool *locked, struct compact_control *cc)

  {

  	if (*locked) {
  		spin_unlock_irqrestore(lock, flags);
  		*locked = false;
  	}

  	if (fatal_signal_pending(current)) {
  		cc->contended = COMPACT_CONTENDED_SCHED;
  		return true;
  	}

  	if (need_resched()) {

  		if (cc->mode == MIGRATE_ASYNC) {

  			cc->contended = COMPACT_CONTENDED_SCHED;
  			return true;

  		}

  		cond_resched();

  	}

  	return false;

  }

  /*
   * Aside from avoiding lock contention, compaction also periodically checks
   * need_resched() and either schedules in sync compaction or aborts async

   * compaction. This is similar to what compact_unlock_should_abort() does, but

   * is used where no lock is concerned.
   *
   * Returns false when no scheduling was needed, or sync compaction scheduled.
   * Returns true when async compaction should abort.
   */
  static inline bool compact_should_abort(struct compact_control *cc)
  {
  	/* async compaction aborts if contended */
  	if (need_resched()) {
  		if (cc->mode == MIGRATE_ASYNC) {

  			cc->contended = COMPACT_CONTENDED_SCHED;

  			return true;
  		}
  
  		cond_resched();
  	}
  
  	return false;
  }

  /* Returns true if the page is within a block suitable for migration to */
  static bool suitable_migration_target(struct page *page)
  {

  	/* If the page is a large free page, then disallow migration */

  	if (PageBuddy(page)) {
  		/*
  		 * We are checking page_order without zone->lock taken. But
  		 * the only small danger is that we skip a potentially suitable
  		 * pageblock, so it's not worth to check order for valid range.
  		 */
  		if (page_order_unsafe(page) >= pageblock_order)
  			return false;
  	}

  
  	/* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */

  	if (migrate_async_suitable(get_pageblock_migratetype(page)))

  		return true;
  
  	/* Otherwise skip the block */
  	return false;
  }

  /*

   * Isolate free pages onto a private freelist. If @strict is true, will abort
   * returning 0 on any invalid PFNs or non-free pages inside of the pageblock
   * (even though it may still end up isolating some pages).

   */

  static unsigned long isolate_freepages_block(struct compact_control *cc,

  				unsigned long *start_pfn,

  				unsigned long end_pfn,
  				struct list_head *freelist,
  				bool strict)

  {

  	int nr_scanned = 0, total_isolated = 0;

  	struct page *cursor, *valid_page = NULL;

  	unsigned long flags = 0;

  	bool locked = false;

  	unsigned long blockpfn = *start_pfn;

  	cursor = pfn_to_page(blockpfn);

  	/* Isolate free pages. */

  	for (; blockpfn < end_pfn; blockpfn++, cursor++) {
  		int isolated, i;
  		struct page *page = cursor;

  		/*
  		 * Periodically drop the lock (if held) regardless of its
  		 * contention, to give chance to IRQs. Abort if fatal signal
  		 * pending or async compaction detects need_resched()
  		 */
  		if (!(blockpfn % SWAP_CLUSTER_MAX)
  		    && compact_unlock_should_abort(&cc->zone->lock, flags,
  								&locked, cc))
  			break;

  		nr_scanned++;

  		if (!pfn_valid_within(blockpfn))

  			goto isolate_fail;

  		if (!valid_page)
  			valid_page = page;

  		if (!PageBuddy(page))

  			goto isolate_fail;

  
  		/*

  		 * If we already hold the lock, we can skip some rechecking.
  		 * Note that if we hold the lock now, checked_pageblock was
  		 * already set in some previous iteration (or strict is true),
  		 * so it is correct to skip the suitable migration target
  		 * recheck as well.

  		 */

  		if (!locked) {
  			/*
  			 * The zone lock must be held to isolate freepages.
  			 * Unfortunately this is a very coarse lock and can be
  			 * heavily contended if there are parallel allocations
  			 * or parallel compactions. For async compaction do not
  			 * spin on the lock and we acquire the lock as late as
  			 * possible.
  			 */

  			locked = compact_trylock_irqsave(&cc->zone->lock,
  								&flags, cc);

  			if (!locked)
  				break;

  			/* Recheck this is a buddy page under lock */
  			if (!PageBuddy(page))
  				goto isolate_fail;
  		}

  
  		/* Found a free page, break it into order-0 pages */
  		isolated = split_free_page(page);
  		total_isolated += isolated;
  		for (i = 0; i < isolated; i++) {
  			list_add(&page->lru, freelist);
  			page++;
  		}
  
  		/* If a page was split, advance to the end of it */
  		if (isolated) {
  			blockpfn += isolated - 1;
  			cursor += isolated - 1;

  			continue;

  		}

  
  isolate_fail:
  		if (strict)
  			break;
  		else
  			continue;

  	}

  	/* Record how far we have got within the block */
  	*start_pfn = blockpfn;

  	trace_mm_compaction_isolate_freepages(nr_scanned, total_isolated);

  
  	/*
  	 * If strict isolation is requested by CMA then check that all the
  	 * pages requested were isolated. If there were any failures, 0 is
  	 * returned and CMA will fail.
  	 */

  	if (strict && blockpfn < end_pfn)

  		total_isolated = 0;
  
  	if (locked)
  		spin_unlock_irqrestore(&cc->zone->lock, flags);

  	/* Update the pageblock-skip if the whole pageblock was scanned */
  	if (blockpfn == end_pfn)

  		update_pageblock_skip(cc, valid_page, total_isolated, false);

  	count_compact_events(COMPACTFREE_SCANNED, nr_scanned);

  	if (total_isolated)

  		count_compact_events(COMPACTISOLATED, total_isolated);

  	return total_isolated;
  }

  /**
   * isolate_freepages_range() - isolate free pages.
   * @start_pfn: The first PFN to start isolating.
   * @end_pfn:   The one-past-last PFN.
   *
   * Non-free pages, invalid PFNs, or zone boundaries within the
   * [start_pfn, end_pfn) range are considered errors, cause function to
   * undo its actions and return zero.
   *
   * Otherwise, function returns one-past-the-last PFN of isolated page
   * (which may be greater then end_pfn if end fell in a middle of
   * a free page).
   */

  unsigned long

  isolate_freepages_range(struct compact_control *cc,
  			unsigned long start_pfn, unsigned long end_pfn)

  {

  	unsigned long isolated, pfn, block_end_pfn;

  	LIST_HEAD(freelist);

  	pfn = start_pfn;
  	block_end_pfn = ALIGN(pfn + 1, pageblock_nr_pages);
  
  	for (; pfn < end_pfn; pfn += isolated,
  				block_end_pfn += pageblock_nr_pages) {

  		/* Protect pfn from changing by isolate_freepages_block */
  		unsigned long isolate_start_pfn = pfn;

  		block_end_pfn = min(block_end_pfn, end_pfn);

  		/*
  		 * pfn could pass the block_end_pfn if isolated freepage
  		 * is more than pageblock order. In this case, we adjust
  		 * scanning range to right one.
  		 */
  		if (pfn >= block_end_pfn) {
  			block_end_pfn = ALIGN(pfn + 1, pageblock_nr_pages);
  			block_end_pfn = min(block_end_pfn, end_pfn);
  		}

  		if (!pageblock_pfn_to_page(pfn, block_end_pfn, cc->zone))
  			break;

  		isolated = isolate_freepages_block(cc, &isolate_start_pfn,
  						block_end_pfn, &freelist, true);

  
  		/*
  		 * In strict mode, isolate_freepages_block() returns 0 if
  		 * there are any holes in the block (ie. invalid PFNs or
  		 * non-free pages).
  		 */
  		if (!isolated)
  			break;
  
  		/*
  		 * If we managed to isolate pages, it is always (1 << n) *
  		 * pageblock_nr_pages for some non-negative n.  (Max order
  		 * page may span two pageblocks).
  		 */
  	}
  
  	/* split_free_page does not map the pages */
  	map_pages(&freelist);
  
  	if (pfn < end_pfn) {
  		/* Loop terminated early, cleanup. */
  		release_freepages(&freelist);
  		return 0;
  	}
  
  	/* We don't use freelists for anything. */
  	return pfn;
  }

  /* Update the number of anon and file isolated pages in the zone */

  static void acct_isolated(struct zone *zone, struct compact_control *cc)

  {
  	struct page *page;

  	unsigned int count[2] = { 0, };

  	if (list_empty(&cc->migratepages))
  		return;

  	list_for_each_entry(page, &cc->migratepages, lru)
  		count[!!page_is_file_cache(page)]++;

  	mod_zone_page_state(zone, NR_ISOLATED_ANON, count[0]);
  	mod_zone_page_state(zone, NR_ISOLATED_FILE, count[1]);

  }
  
  /* Similar to reclaim, but different enough that they don't share logic */
  static bool too_many_isolated(struct zone *zone)
  {

  	unsigned long active, inactive, isolated;

  
  	inactive = zone_page_state(zone, NR_INACTIVE_FILE) +
  					zone_page_state(zone, NR_INACTIVE_ANON);

  	active = zone_page_state(zone, NR_ACTIVE_FILE) +
  					zone_page_state(zone, NR_ACTIVE_ANON);

  	isolated = zone_page_state(zone, NR_ISOLATED_FILE) +
  					zone_page_state(zone, NR_ISOLATED_ANON);

  	return isolated > (inactive + active) / 2;

  }

  /**

   * isolate_migratepages_block() - isolate all migrate-able pages within
   *				  a single pageblock

   * @cc:		Compaction control structure.

   * @low_pfn:	The first PFN to isolate
   * @end_pfn:	The one-past-the-last PFN to isolate, within same pageblock
   * @isolate_mode: Isolation mode to be used.

   *
   * Isolate all pages that can be migrated from the range specified by

   * [low_pfn, end_pfn). The range is expected to be within same pageblock.
   * Returns zero if there is a fatal signal pending, otherwise PFN of the
   * first page that was not scanned (which may be both less, equal to or more
   * than end_pfn).

   *

   * The pages are isolated on cc->migratepages list (not required to be empty),
   * and cc->nr_migratepages is updated accordingly. The cc->migrate_pfn field
   * is neither read nor updated.

   */

  static unsigned long
  isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
  			unsigned long end_pfn, isolate_mode_t isolate_mode)

  {

  	struct zone *zone = cc->zone;

  	unsigned long nr_scanned = 0, nr_isolated = 0;

  	struct list_head *migratelist = &cc->migratepages;

  	struct lruvec *lruvec;

  	unsigned long flags = 0;

  	bool locked = false;

  	struct page *page = NULL, *valid_page = NULL;

  	/*
  	 * Ensure that there are not too many pages isolated from the LRU
  	 * list by either parallel reclaimers or compaction. If there are,
  	 * delay for some time until fewer pages are isolated
  	 */
  	while (unlikely(too_many_isolated(zone))) {

  		/* async migration should just abort */

  		if (cc->mode == MIGRATE_ASYNC)

  			return 0;

  		congestion_wait(BLK_RW_ASYNC, HZ/10);
  
  		if (fatal_signal_pending(current))

  			return 0;

  	}

  	if (compact_should_abort(cc))
  		return 0;

  	/* Time to isolate some pages for migration */

  	for (; low_pfn < end_pfn; low_pfn++) {

  		/*
  		 * Periodically drop the lock (if held) regardless of its
  		 * contention, to give chance to IRQs. Abort async compaction
  		 * if contended.
  		 */
  		if (!(low_pfn % SWAP_CLUSTER_MAX)
  		    && compact_unlock_should_abort(&zone->lru_lock, flags,
  								&locked, cc))
  			break;

  		if (!pfn_valid_within(low_pfn))
  			continue;

  		nr_scanned++;

  		page = pfn_to_page(low_pfn);

  		if (!valid_page)
  			valid_page = page;

  		/*

  		 * Skip if free. We read page order here without zone lock
  		 * which is generally unsafe, but the race window is small and
  		 * the worst thing that can happen is that we skip some
  		 * potential isolation targets.

  		 */

  		if (PageBuddy(page)) {
  			unsigned long freepage_order = page_order_unsafe(page);
  
  			/*
  			 * Without lock, we cannot be sure that what we got is
  			 * a valid page order. Consider only values in the
  			 * valid order range to prevent low_pfn overflow.
  			 */
  			if (freepage_order > 0 && freepage_order < MAX_ORDER)
  				low_pfn += (1UL << freepage_order) - 1;

  			continue;

  		}

  		/*

  		 * Check may be lockless but that's ok as we recheck later.
  		 * It's possible to migrate LRU pages and balloon pages
  		 * Skip any other type of page
  		 */
  		if (!PageLRU(page)) {
  			if (unlikely(balloon_page_movable(page))) {

  				if (balloon_page_isolate(page)) {

  					/* Successfully isolated */

  					goto isolate_success;

  				}
  			}

  			continue;

  		}

  
  		/*

  		 * PageLRU is set. lru_lock normally excludes isolation
  		 * splitting and collapsing (collapsing has already happened
  		 * if PageLRU is set) but the lock is not necessarily taken
  		 * here and it is wasteful to take it just to check transhuge.
  		 * Check TransHuge without lock and skip the whole pageblock if
  		 * it's either a transhuge or hugetlbfs page, as calling
  		 * compound_order() without preventing THP from splitting the
  		 * page underneath us may return surprising results.

  		 */
  		if (PageTransHuge(page)) {

  			if (!locked)

  				low_pfn = ALIGN(low_pfn + 1,
  						pageblock_nr_pages) - 1;
  			else
  				low_pfn += (1 << compound_order(page)) - 1;

  			continue;
  		}

  		/*
  		 * Migration will fail if an anonymous page is pinned in memory,
  		 * so avoid taking lru_lock and isolating it unnecessarily in an
  		 * admittedly racy check.
  		 */
  		if (!page_mapping(page) &&
  		    page_count(page) > page_mapcount(page))
  			continue;

  		/* If we already hold the lock, we can skip some rechecking */
  		if (!locked) {

  			locked = compact_trylock_irqsave(&zone->lru_lock,
  								&flags, cc);

  			if (!locked)
  				break;

  			/* Recheck PageLRU and PageTransHuge under lock */
  			if (!PageLRU(page))
  				continue;
  			if (PageTransHuge(page)) {
  				low_pfn += (1 << compound_order(page)) - 1;
  				continue;
  			}

  		}

  		lruvec = mem_cgroup_page_lruvec(page, zone);

  		/* Try isolate the page */

  		if (__isolate_lru_page(page, isolate_mode) != 0)

  			continue;

  		VM_BUG_ON_PAGE(PageTransCompound(page), page);

  		/* Successfully isolated */

  		del_page_from_lru_list(page, lruvec, page_lru(page));

  
  isolate_success:

  		list_add(&page->lru, migratelist);

  		cc->nr_migratepages++;

  		nr_isolated++;

  
  		/* Avoid isolating too much */

  		if (cc->nr_migratepages == COMPACT_CLUSTER_MAX) {
  			++low_pfn;

  			break;

  		}

  	}

  	/*
  	 * The PageBuddy() check could have potentially brought us outside
  	 * the range to be scanned.
  	 */
  	if (unlikely(low_pfn > end_pfn))
  		low_pfn = end_pfn;

  	if (locked)
  		spin_unlock_irqrestore(&zone->lru_lock, flags);

  	/*
  	 * Update the pageblock-skip information and cached scanner pfn,
  	 * if the whole pageblock was scanned without isolating any page.

  	 */

  	if (low_pfn == end_pfn)

  		update_pageblock_skip(cc, valid_page, nr_isolated, true);

  	trace_mm_compaction_isolate_migratepages(nr_scanned, nr_isolated);

  	count_compact_events(COMPACTMIGRATE_SCANNED, nr_scanned);

  	if (nr_isolated)

  		count_compact_events(COMPACTISOLATED, nr_isolated);

  	return low_pfn;
  }

  /**
   * isolate_migratepages_range() - isolate migrate-able pages in a PFN range
   * @cc:        Compaction control structure.
   * @start_pfn: The first PFN to start isolating.
   * @end_pfn:   The one-past-last PFN.
   *
   * Returns zero if isolation fails fatally due to e.g. pending signal.
   * Otherwise, function returns one-past-the-last PFN of isolated page
   * (which may be greater than end_pfn if end fell in a middle of a THP page).
   */
  unsigned long
  isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn,
  							unsigned long end_pfn)
  {
  	unsigned long pfn, block_end_pfn;
  
  	/* Scan block by block. First and last block may be incomplete */
  	pfn = start_pfn;
  	block_end_pfn = ALIGN(pfn + 1, pageblock_nr_pages);
  
  	for (; pfn < end_pfn; pfn = block_end_pfn,
  				block_end_pfn += pageblock_nr_pages) {
  
  		block_end_pfn = min(block_end_pfn, end_pfn);

  		if (!pageblock_pfn_to_page(pfn, block_end_pfn, cc->zone))

  			continue;
  
  		pfn = isolate_migratepages_block(cc, pfn, block_end_pfn,
  							ISOLATE_UNEVICTABLE);
  
  		/*
  		 * In case of fatal failure, release everything that might
  		 * have been isolated in the previous iteration, and signal
  		 * the failure back to caller.
  		 */
  		if (!pfn) {
  			putback_movable_pages(&cc->migratepages);
  			cc->nr_migratepages = 0;
  			break;
  		}

  
  		if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
  			break;

  	}
  	acct_isolated(cc->zone, cc);
  
  	return pfn;
  }

  #endif /* CONFIG_COMPACTION || CONFIG_CMA */
  #ifdef CONFIG_COMPACTION

  /*

   * Based on information in the current compact_control, find blocks
   * suitable for isolating free pages from and then isolate them.

   */

  static void isolate_freepages(struct compact_control *cc)

  {

  	struct zone *zone = cc->zone;

  	struct page *page;

  	unsigned long block_start_pfn;	/* start of current pageblock */

  	unsigned long isolate_start_pfn; /* exact pfn we start at */

  	unsigned long block_end_pfn;	/* end of current pageblock */
  	unsigned long low_pfn;	     /* lowest pfn scanner is able to scan */

  	int nr_freepages = cc->nr_freepages;
  	struct list_head *freelist = &cc->freepages;

  	/*
  	 * Initialise the free scanner. The starting point is where we last

  	 * successfully isolated from, zone-cached value, or the end of the

  	 * zone when isolating for the first time. For looping we also need
  	 * this pfn aligned down to the pageblock boundary, because we do

  	 * block_start_pfn -= pageblock_nr_pages in the for loop.
  	 * For ending point, take care when isolating in last pageblock of a
  	 * a zone which ends in the middle of a pageblock.

  	 * The low boundary is the end of the pageblock the migration scanner
  	 * is using.

  	 */

  	isolate_start_pfn = cc->free_pfn;

  	block_start_pfn = cc->free_pfn & ~(pageblock_nr_pages-1);
  	block_end_pfn = min(block_start_pfn + pageblock_nr_pages,
  						zone_end_pfn(zone));

  	low_pfn = ALIGN(cc->migrate_pfn + 1, pageblock_nr_pages);

  	/*

  	 * Isolate free pages until enough are available to migrate the
  	 * pages on cc->migratepages. We stop searching if the migrate
  	 * and free page scanners meet or enough free pages are isolated.
  	 */

  	for (; block_start_pfn >= low_pfn && cc->nr_migratepages > nr_freepages;
  				block_end_pfn = block_start_pfn,

  				block_start_pfn -= pageblock_nr_pages,
  				isolate_start_pfn = block_start_pfn) {

  		unsigned long isolated;

  		/*
  		 * This can iterate a massively long zone without finding any
  		 * suitable migration targets, so periodically check if we need

  		 * to schedule, or even abort async compaction.

  		 */

  		if (!(block_start_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages))
  						&& compact_should_abort(cc))
  			break;

  		page = pageblock_pfn_to_page(block_start_pfn, block_end_pfn,
  									zone);
  		if (!page)

  			continue;
  
  		/* Check the block is suitable for migration */

  		if (!suitable_migration_target(page))

  			continue;

  		/* If isolation recently failed, do not retry */
  		if (!isolation_suitable(cc, page))
  			continue;

  		/* Found a block suitable for isolating free pages from. */
  		isolated = isolate_freepages_block(cc, &isolate_start_pfn,

  					block_end_pfn, freelist, false);

  		nr_freepages += isolated;

  
  		/*

  		 * Remember where the free scanner should restart next time,
  		 * which is where isolate_freepages_block() left off.
  		 * But if it scanned the whole pageblock, isolate_start_pfn
  		 * now points at block_end_pfn, which is the start of the next
  		 * pageblock.
  		 * In that case we will however want to restart at the start
  		 * of the previous pageblock.
  		 */
  		cc->free_pfn = (isolate_start_pfn < block_end_pfn) ?
  				isolate_start_pfn :
  				block_start_pfn - pageblock_nr_pages;
  
  		/*

  		 * isolate_freepages_block() might have aborted due to async
  		 * compaction being contended
  		 */
  		if (cc->contended)
  			break;

  	}
  
  	/* split_free_page does not map the pages */
  	map_pages(freelist);

  	/*
  	 * If we crossed the migrate scanner, we want to keep it that way
  	 * so that compact_finished() may detect this
  	 */

  	if (block_start_pfn < low_pfn)

  		cc->free_pfn = cc->migrate_pfn;

  	cc->nr_freepages = nr_freepages;

  }
  
  /*
   * This is a migrate-callback that "allocates" freepages by taking pages
   * from the isolated freelists in the block we are migrating to.
   */
  static struct page *compaction_alloc(struct page *migratepage,
  					unsigned long data,
  					int **result)
  {
  	struct compact_control *cc = (struct compact_control *)data;
  	struct page *freepage;

  	/*
  	 * Isolate free pages if necessary, and if we are not aborting due to
  	 * contention.
  	 */

  	if (list_empty(&cc->freepages)) {

  		if (!cc->contended)

  			isolate_freepages(cc);

  
  		if (list_empty(&cc->freepages))
  			return NULL;
  	}
  
  	freepage = list_entry(cc->freepages.next, struct page, lru);
  	list_del(&freepage->lru);
  	cc->nr_freepages--;
  
  	return freepage;
  }
  
  /*

   * This is a migrate-callback that "frees" freepages back to the isolated
   * freelist.  All pages on the freelist are from the same zone, so there is no
   * special handling needed for NUMA.
   */
  static void compaction_free(struct page *page, unsigned long data)
  {
  	struct compact_control *cc = (struct compact_control *)data;
  
  	list_add(&page->lru, &cc->freepages);
  	cc->nr_freepages++;
  }

  /* possible outcome of isolate_migratepages */
  typedef enum {
  	ISOLATE_ABORT,		/* Abort compaction now */
  	ISOLATE_NONE,		/* No pages isolated, continue scanning */
  	ISOLATE_SUCCESS,	/* Pages isolated, migrate */
  } isolate_migrate_t;
  
  /*

   * Isolate all pages that can be migrated from the first suitable block,
   * starting at the block pointed to by the migrate scanner pfn within
   * compact_control.

   */
  static isolate_migrate_t isolate_migratepages(struct zone *zone,
  					struct compact_control *cc)
  {
  	unsigned long low_pfn, end_pfn;

  	struct page *page;
  	const isolate_mode_t isolate_mode =
  		(cc->mode == MIGRATE_ASYNC ? ISOLATE_ASYNC_MIGRATE : 0);

  	/*
  	 * Start at where we last stopped, or beginning of the zone as
  	 * initialized by compact_zone()
  	 */
  	low_pfn = cc->migrate_pfn;

  
  	/* Only scan within a pageblock boundary */

  	end_pfn = ALIGN(low_pfn + 1, pageblock_nr_pages);

  	/*
  	 * Iterate over whole pageblocks until we find the first suitable.
  	 * Do not cross the free scanner.
  	 */
  	for (; end_pfn <= cc->free_pfn;
  			low_pfn = end_pfn, end_pfn += pageblock_nr_pages) {

  		/*
  		 * This can potentially iterate a massively long zone with
  		 * many pageblocks unsuitable, so periodically check if we
  		 * need to schedule, or even abort async compaction.
  		 */
  		if (!(low_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages))
  						&& compact_should_abort(cc))
  			break;

  		page = pageblock_pfn_to_page(low_pfn, end_pfn, zone);
  		if (!page)

  			continue;

  		/* If isolation recently failed, do not retry */
  		if (!isolation_suitable(cc, page))
  			continue;
  
  		/*
  		 * For async compaction, also only scan in MOVABLE blocks.
  		 * Async compaction is optimistic to see if the minimum amount
  		 * of work satisfies the allocation.
  		 */
  		if (cc->mode == MIGRATE_ASYNC &&
  		    !migrate_async_suitable(get_pageblock_migratetype(page)))
  			continue;
  
  		/* Perform the isolation */
  		low_pfn = isolate_migratepages_block(cc, low_pfn, end_pfn,
  								isolate_mode);
  
  		if (!low_pfn || cc->contended)
  			return ISOLATE_ABORT;
  
  		/*
  		 * Either we isolated something and proceed with migration. Or
  		 * we failed and compact_zone should decide if we should
  		 * continue or not.
  		 */
  		break;
  	}
  
  	acct_isolated(zone, cc);

  	/*
  	 * Record where migration scanner will be restarted. If we end up in
  	 * the same pageblock as the free scanner, make the scanners fully
  	 * meet so that compact_finished() terminates compaction.
  	 */
  	cc->migrate_pfn = (end_pfn <= cc->free_pfn) ? low_pfn : cc->free_pfn;

  	return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE;

  }

  static int compact_finished(struct zone *zone, struct compact_control *cc,
  			    const int migratetype)

  {

  	unsigned int order;

  	unsigned long watermark;

  	if (cc->contended || fatal_signal_pending(current))

  		return COMPACT_PARTIAL;

  	/* Compaction run completes if the migrate and free scanner meet */

  	if (cc->free_pfn <= cc->migrate_pfn) {

  		/* Let the next compaction start anew. */

  		zone->compact_cached_migrate_pfn[0] = zone->zone_start_pfn;
  		zone->compact_cached_migrate_pfn[1] = zone->zone_start_pfn;

  		zone->compact_cached_free_pfn = zone_end_pfn(zone);

  		/*
  		 * Mark that the PG_migrate_skip information should be cleared
  		 * by kswapd when it goes to sleep. kswapd does not set the
  		 * flag itself as the decision to be clear should be directly
  		 * based on an allocation request.
  		 */
  		if (!current_is_kswapd())
  			zone->compact_blockskip_flush = true;

  		return COMPACT_COMPLETE;

  	}

  	/*
  	 * order == -1 is expected when compacting via
  	 * /proc/sys/vm/compact_memory
  	 */

  	if (cc->order == -1)
  		return COMPACT_CONTINUE;

  	/* Compaction run is not finished if the watermark is not met */
  	watermark = low_wmark_pages(zone);

  	if (!zone_watermark_ok(zone, cc->order, watermark, cc->classzone_idx,
  							cc->alloc_flags))

  		return COMPACT_CONTINUE;

  	/* Direct compactor: Is a suitable page free? */

  	for (order = cc->order; order < MAX_ORDER; order++) {
  		struct free_area *area = &zone->free_area[order];
  
  		/* Job done if page is free of the right migratetype */

  		if (!list_empty(&area->free_list[migratetype]))

  			return COMPACT_PARTIAL;
  
  		/* Job done if allocation would set block type */
  		if (cc->order >= pageblock_order && area->nr_free)

  			return COMPACT_PARTIAL;
  	}

  	return COMPACT_CONTINUE;
  }

  /*
   * compaction_suitable: Is this suitable to run compaction on this zone now?
   * Returns
   *   COMPACT_SKIPPED  - If there are too few free pages for compaction
   *   COMPACT_PARTIAL  - If the allocation would succeed without compaction
   *   COMPACT_CONTINUE - If compaction should run now
   */

  unsigned long compaction_suitable(struct zone *zone, int order,
  					int alloc_flags, int classzone_idx)

  {
  	int fragindex;
  	unsigned long watermark;
  
  	/*

  	 * order == -1 is expected when compacting via
  	 * /proc/sys/vm/compact_memory
  	 */
  	if (order == -1)
  		return COMPACT_CONTINUE;

  	watermark = low_wmark_pages(zone);
  	/*
  	 * If watermarks for high-order allocation are already met, there
  	 * should be no need for compaction at all.
  	 */
  	if (zone_watermark_ok(zone, order, watermark, classzone_idx,
  								alloc_flags))
  		return COMPACT_PARTIAL;

  	/*

  	 * Watermarks for order-0 must be met for compaction. Note the 2UL.
  	 * This is because during migration, copies of pages need to be
  	 * allocated and for a short time, the footprint is higher
  	 */

  	watermark += (2UL << order);
  	if (!zone_watermark_ok(zone, 0, watermark, classzone_idx, alloc_flags))

  		return COMPACT_SKIPPED;
  
  	/*
  	 * fragmentation index determines if allocation failures are due to
  	 * low memory or external fragmentation
  	 *

  	 * index of -1000 would imply allocations might succeed depending on
  	 * watermarks, but we already failed the high-order watermark check

  	 * index towards 0 implies failure is due to lack of memory
  	 * index towards 1000 implies failure is due to fragmentation
  	 *
  	 * Only compact if a failure would be due to fragmentation.
  	 */
  	fragindex = fragmentation_index(zone, order);
  	if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
  		return COMPACT_SKIPPED;

  	return COMPACT_CONTINUE;
  }

  static int compact_zone(struct zone *zone, struct compact_control *cc)
  {
  	int ret;

  	unsigned long start_pfn = zone->zone_start_pfn;

  	unsigned long end_pfn = zone_end_pfn(zone);

  	const int migratetype = gfpflags_to_migratetype(cc->gfp_mask);

  	const bool sync = cc->mode != MIGRATE_ASYNC;

  	unsigned long last_migrated_pfn = 0;

  	ret = compaction_suitable(zone, cc->order, cc->alloc_flags,
  							cc->classzone_idx);

  	switch (ret) {
  	case COMPACT_PARTIAL:
  	case COMPACT_SKIPPED:
  		/* Compaction is likely to fail */
  		return ret;
  	case COMPACT_CONTINUE:
  		/* Fall through to compaction */
  		;
  	}

  	/*

  	 * Clear pageblock skip if there were failures recently and compaction
  	 * is about to be retried after being deferred. kswapd does not do
  	 * this reset as it'll reset the cached information when going to sleep.
  	 */
  	if (compaction_restarting(zone, cc->order) && !current_is_kswapd())
  		__reset_isolation_suitable(zone);
  
  	/*

  	 * Setup to move all movable pages to the end of the zone. Used cached
  	 * information on where the scanners should start but check that it
  	 * is initialised by ensuring the values are within zone boundaries.
  	 */

  	cc->migrate_pfn = zone->compact_cached_migrate_pfn[sync];

  	cc->free_pfn = zone->compact_cached_free_pfn;
  	if (cc->free_pfn < start_pfn || cc->free_pfn > end_pfn) {
  		cc->free_pfn = end_pfn & ~(pageblock_nr_pages-1);
  		zone->compact_cached_free_pfn = cc->free_pfn;
  	}
  	if (cc->migrate_pfn < start_pfn || cc->migrate_pfn > end_pfn) {
  		cc->migrate_pfn = start_pfn;

  		zone->compact_cached_migrate_pfn[0] = cc->migrate_pfn;
  		zone->compact_cached_migrate_pfn[1] = cc->migrate_pfn;

  	}

  	trace_mm_compaction_begin(start_pfn, cc->migrate_pfn, cc->free_pfn, end_pfn);

  	migrate_prep_local();

  	while ((ret = compact_finished(zone, cc, migratetype)) ==
  						COMPACT_CONTINUE) {

  		int err;

  		unsigned long isolate_start_pfn = cc->migrate_pfn;

  		switch (isolate_migratepages(zone, cc)) {
  		case ISOLATE_ABORT:
  			ret = COMPACT_PARTIAL;

  			putback_movable_pages(&cc->migratepages);

  			cc->nr_migratepages = 0;

  			goto out;
  		case ISOLATE_NONE:

  			/*
  			 * We haven't isolated and migrated anything, but
  			 * there might still be unflushed migrations from
  			 * previous cc->order aligned block.
  			 */
  			goto check_drain;

  		case ISOLATE_SUCCESS:
  			;
  		}

  		err = migrate_pages(&cc->migratepages, compaction_alloc,

  				compaction_free, (unsigned long)cc, cc->mode,

  				MR_COMPACTION);

  		trace_mm_compaction_migratepages(cc->nr_migratepages, err,
  							&cc->migratepages);

  		/* All pages were either migrated or will be released */
  		cc->nr_migratepages = 0;

  		if (err) {

  			putback_movable_pages(&cc->migratepages);

  			/*
  			 * migrate_pages() may return -ENOMEM when scanners meet
  			 * and we want compact_finished() to detect it
  			 */
  			if (err == -ENOMEM && cc->free_pfn > cc->migrate_pfn) {

  				ret = COMPACT_PARTIAL;
  				goto out;
  			}

  		}

  
  		/*
  		 * Record where we could have freed pages by migration and not
  		 * yet flushed them to buddy allocator. We use the pfn that
  		 * isolate_migratepages() started from in this loop iteration
  		 * - this is the lowest page that could have been isolated and
  		 * then freed by migration.
  		 */
  		if (!last_migrated_pfn)
  			last_migrated_pfn = isolate_start_pfn;
  
  check_drain:
  		/*
  		 * Has the migration scanner moved away from the previous
  		 * cc->order aligned block where we migrated from? If yes,
  		 * flush the pages that were freed, so that they can merge and
  		 * compact_finished() can detect immediately if allocation
  		 * would succeed.
  		 */
  		if (cc->order > 0 && last_migrated_pfn) {
  			int cpu;
  			unsigned long current_block_start =
  				cc->migrate_pfn & ~((1UL << cc->order) - 1);
  
  			if (last_migrated_pfn < current_block_start) {
  				cpu = get_cpu();
  				lru_add_drain_cpu(cpu);
  				drain_local_pages(zone);
  				put_cpu();
  				/* No more flushing until we migrate again */
  				last_migrated_pfn = 0;
  			}
  		}

  	}

  out:

  	/*
  	 * Release free pages and update where the free scanner should restart,
  	 * so we don't leave any returned pages behind in the next attempt.
  	 */
  	if (cc->nr_freepages > 0) {
  		unsigned long free_pfn = release_freepages(&cc->freepages);
  
  		cc->nr_freepages = 0;
  		VM_BUG_ON(free_pfn == 0);
  		/* The cached pfn is always the first in a pageblock */
  		free_pfn &= ~(pageblock_nr_pages-1);
  		/*
  		 * Only go back, not forward. The cached pfn might have been
  		 * already reset to zone end in compact_finished()
  		 */
  		if (free_pfn > zone->compact_cached_free_pfn)
  			zone->compact_cached_free_pfn = free_pfn;
  	}

  	trace_mm_compaction_end(ret);

  	return ret;
  }

  static unsigned long compact_zone_order(struct zone *zone, int order,

  		gfp_t gfp_mask, enum migrate_mode mode, int *contended,
  		int alloc_flags, int classzone_idx)

  {

  	unsigned long ret;

  	struct compact_control cc = {
  		.nr_freepages = 0,
  		.nr_migratepages = 0,
  		.order = order,

  		.gfp_mask = gfp_mask,

  		.zone = zone,

  		.mode = mode,

  		.alloc_flags = alloc_flags,
  		.classzone_idx = classzone_idx,

  	};
  	INIT_LIST_HEAD(&cc.freepages);
  	INIT_LIST_HEAD(&cc.migratepages);

  	ret = compact_zone(zone, &cc);
  
  	VM_BUG_ON(!list_empty(&cc.freepages));
  	VM_BUG_ON(!list_empty(&cc.migratepages));
  
  	*contended = cc.contended;
  	return ret;

  }

  int sysctl_extfrag_threshold = 500;

  /**
   * try_to_compact_pages - Direct compact to satisfy a high-order allocation
   * @zonelist: The zonelist used for the current allocation
   * @order: The order of the current allocation
   * @gfp_mask: The GFP mask of the current allocation
   * @nodemask: The allowed nodes to allocate from

   * @mode: The migration mode for async, sync light, or sync migration

   * @contended: Return value that determines if compaction was aborted due to
   *	       need_resched() or lock contention

   *
   * This is the main entry point for direct page compaction.
   */
  unsigned long try_to_compact_pages(struct zonelist *zonelist,

  			int order, gfp_t gfp_mask, nodemask_t *nodemask,

  			enum migrate_mode mode, int *contended,

  			int alloc_flags, int classzone_idx)

  {
  	enum zone_type high_zoneidx = gfp_zone(gfp_mask);
  	int may_enter_fs = gfp_mask & __GFP_FS;
  	int may_perform_io = gfp_mask & __GFP_IO;

  	struct zoneref *z;
  	struct zone *zone;

  	int rc = COMPACT_DEFERRED;

  	int all_zones_contended = COMPACT_CONTENDED_LOCK; /* init for &= op */
  
  	*contended = COMPACT_CONTENDED_NONE;

  	/* Check if the GFP flags allow compaction */

  	if (!order || !may_enter_fs || !may_perform_io)

  		return COMPACT_SKIPPED;

  
  	/* Compact each zone in the list */
  	for_each_zone_zonelist_nodemask(zone, z, zonelist, high_zoneidx,
  								nodemask) {

  		int status;

  		int zone_contended;

  		if (compaction_deferred(zone, order))
  			continue;

  		status = compact_zone_order(zone, order, gfp_mask, mode,

  				&zone_contended, alloc_flags, classzone_idx);

  		rc = max(status, rc);

  		/*
  		 * It takes at least one zone that wasn't lock contended
  		 * to clear all_zones_contended.
  		 */
  		all_zones_contended &= zone_contended;

  		/* If a normal allocation would succeed, stop compacting */

  		if (zone_watermark_ok(zone, order, low_wmark_pages(zone),
  					classzone_idx, alloc_flags)) {

  			/*
  			 * We think the allocation will succeed in this zone,
  			 * but it is not certain, hence the false. The caller
  			 * will repeat this with true if allocation indeed
  			 * succeeds in this zone.
  			 */
  			compaction_defer_reset(zone, order, false);

  			/*
  			 * It is possible that async compaction aborted due to
  			 * need_resched() and the watermarks were ok thanks to
  			 * somebody else freeing memory. The allocation can
  			 * however still fail so we better signal the
  			 * need_resched() contention anyway (this will not
  			 * prevent the allocation attempt).
  			 */
  			if (zone_contended == COMPACT_CONTENDED_SCHED)
  				*contended = COMPACT_CONTENDED_SCHED;
  
  			goto break_loop;
  		}

  		if (mode != MIGRATE_ASYNC && status == COMPACT_COMPLETE) {

  			/*
  			 * We think that allocation won't succeed in this zone
  			 * so we defer compaction there. If it ends up
  			 * succeeding after all, it will be reset.
  			 */
  			defer_compaction(zone, order);
  		}

  
  		/*
  		 * We might have stopped compacting due to need_resched() in
  		 * async compaction, or due to a fatal signal detected. In that
  		 * case do not try further zones and signal need_resched()
  		 * contention.
  		 */
  		if ((zone_contended == COMPACT_CONTENDED_SCHED)
  					|| fatal_signal_pending(current)) {
  			*contended = COMPACT_CONTENDED_SCHED;
  			goto break_loop;
  		}
  
  		continue;
  break_loop:
  		/*
  		 * We might not have tried all the zones, so  be conservative
  		 * and assume they are not all lock contended.
  		 */
  		all_zones_contended = 0;
  		break;

  	}

  	/*
  	 * If at least one zone wasn't deferred or skipped, we report if all
  	 * zones that were tried were lock contended.
  	 */
  	if (rc > COMPACT_SKIPPED && all_zones_contended)
  		*contended = COMPACT_CONTENDED_LOCK;

  	return rc;
  }

  /* Compact all zones within a node */

  static void __compact_pgdat(pg_data_t *pgdat, struct compact_control *cc)

  {
  	int zoneid;

  	struct zone *zone;

  	for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {

  
  		zone = &pgdat->node_zones[zoneid];
  		if (!populated_zone(zone))
  			continue;

  		cc->nr_freepages = 0;
  		cc->nr_migratepages = 0;
  		cc->zone = zone;
  		INIT_LIST_HEAD(&cc->freepages);
  		INIT_LIST_HEAD(&cc->migratepages);

  		if (cc->order == -1 || !compaction_deferred(zone, cc->order))

  			compact_zone(zone, cc);

  		if (cc->order > 0) {

  			if (zone_watermark_ok(zone, cc->order,
  						low_wmark_pages(zone), 0, 0))
  				compaction_defer_reset(zone, cc->order, false);

  		}

  		VM_BUG_ON(!list_empty(&cc->freepages));
  		VM_BUG_ON(!list_empty(&cc->migratepages));

  	}

  }

  void compact_pgdat(pg_data_t *pgdat, int order)

  {
  	struct compact_control cc = {
  		.order = order,

  		.mode = MIGRATE_ASYNC,

  	};

  	if (!order)
  		return;

  	__compact_pgdat(pgdat, &cc);

  }

  static void compact_node(int nid)

  {

  	struct compact_control cc = {
  		.order = -1,

  		.mode = MIGRATE_SYNC,

  		.ignore_skip_hint = true,

  	};

  	__compact_pgdat(NODE_DATA(nid), &cc);

  }

  /* Compact all nodes in the system */

  static void compact_nodes(void)

  {
  	int nid;

  	/* Flush pending updates to the LRU lists */
  	lru_add_drain_all();

  	for_each_online_node(nid)
  		compact_node(nid);

  }
  
  /* The written value is actually unused, all memory is compacted */
  int sysctl_compact_memory;
  
  /* This is the entry point for compacting all nodes via /proc/sys/vm */
  int sysctl_compaction_handler(struct ctl_table *table, int write,
  			void __user *buffer, size_t *length, loff_t *ppos)
  {
  	if (write)

  		compact_nodes();

  
  	return 0;
  }

  int sysctl_extfrag_handler(struct ctl_table *table, int write,
  			void __user *buffer, size_t *length, loff_t *ppos)
  {
  	proc_dointvec_minmax(table, write, buffer, length, ppos);
  
  	return 0;
  }

  #if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)

  static ssize_t sysfs_compact_node(struct device *dev,

  			struct device_attribute *attr,

  			const char *buf, size_t count)
  {

  	int nid = dev->id;
  
  	if (nid >= 0 && nid < nr_node_ids && node_online(nid)) {
  		/* Flush pending updates to the LRU lists */
  		lru_add_drain_all();
  
  		compact_node(nid);
  	}

  
  	return count;
  }

  static DEVICE_ATTR(compact, S_IWUSR, NULL, sysfs_compact_node);

  
  int compaction_register_node(struct node *node)
  {

  	return device_create_file(&node->dev, &dev_attr_compact);

  }
  
  void compaction_unregister_node(struct node *node)
  {

  	return device_remove_file(&node->dev, &dev_attr_compact);

  }
  #endif /* CONFIG_SYSFS && CONFIG_NUMA */

  
  #endif /* CONFIG_COMPACTION */