Adding upstream version 6.1.76.upstream/6.1.76

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 3068 insertions, 0 deletions

diff --git a/mm/compaction.c b/mm/compaction.c
new file mode 100644
index 000000000..8238e8338
--- /dev/null
+++ b/mm/compaction.c
@@ -0,0 +1,3068 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * 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/cpu.h>
+#include <linux/swap.h>
+#include <linux/migrate.h>
+#include <linux/compaction.h>
+#include <linux/mm_inline.h>
+#include <linux/sched/signal.h>
+#include <linux/backing-dev.h>
+#include <linux/sysctl.h>
+#include <linux/sysfs.h>
+#include <linux/page-isolation.h>
+#include <linux/kasan.h>
+#include <linux/kthread.h>
+#include <linux/freezer.h>
+#include <linux/page_owner.h>
+#include <linux/psi.h>
+#include "internal.h"
+
+#ifdef CONFIG_COMPACTION
+/*
+ * Fragmentation score check interval for proactive compaction purposes.
+ */
+#define HPAGE_FRAG_CHECK_INTERVAL_MSEC	(500)
+
+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>
+
+#define block_start_pfn(pfn, order)	round_down(pfn, 1UL << (order))
+#define block_end_pfn(pfn, order)	ALIGN((pfn) + 1, 1UL << (order))
+
+/*
+ * Page order with-respect-to which proactive compaction
+ * calculates external fragmentation, which is used as
+ * the "fragmentation score" of a node/zone.
+ */
+#if defined CONFIG_TRANSPARENT_HUGEPAGE
+#define COMPACTION_HPAGE_ORDER	HPAGE_PMD_ORDER
+#elif defined CONFIG_HUGETLBFS
+#define COMPACTION_HPAGE_ORDER	HUGETLB_PAGE_ORDER
+#else
+#define COMPACTION_HPAGE_ORDER	(PMD_SHIFT - PAGE_SHIFT)
+#endif
+
+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 split_map_pages(struct list_head *list)
+{
+	unsigned int i, order, nr_pages;
+	struct page *page, *next;
+	LIST_HEAD(tmp_list);
+
+	list_for_each_entry_safe(page, next, list, lru) {
+		list_del(&page->lru);
+
+		order = page_private(page);
+		nr_pages = 1 << order;
+
+		post_alloc_hook(page, order, __GFP_MOVABLE);
+		if (order)
+			split_page(page, order);
+
+		for (i = 0; i < nr_pages; i++) {
+			list_add(&page->lru, &tmp_list);
+			page++;
+		}
+	}
+
+	list_splice(&tmp_list, list);
+}
+
+#ifdef CONFIG_COMPACTION
+bool PageMovable(struct page *page)
+{
+	const struct movable_operations *mops;
+
+	VM_BUG_ON_PAGE(!PageLocked(page), page);
+	if (!__PageMovable(page))
+		return false;
+
+	mops = page_movable_ops(page);
+	if (mops)
+		return true;
+
+	return false;
+}
+EXPORT_SYMBOL(PageMovable);
+
+void __SetPageMovable(struct page *page, const struct movable_operations *mops)
+{
+	VM_BUG_ON_PAGE(!PageLocked(page), page);
+	VM_BUG_ON_PAGE((unsigned long)mops & PAGE_MAPPING_MOVABLE, page);
+	page->mapping = (void *)((unsigned long)mops | PAGE_MAPPING_MOVABLE);
+}
+EXPORT_SYMBOL(__SetPageMovable);
+
+void __ClearPageMovable(struct page *page)
+{
+	VM_BUG_ON_PAGE(!PageMovable(page), page);
+	/*
+	 * This page still has the type of a movable page, but it's
+	 * actually not movable any more.
+	 */
+	page->mapping = (void *)PAGE_MAPPING_MOVABLE;
+}
+EXPORT_SYMBOL(__ClearPageMovable);
+
+/* Do not skip compaction more than 64 times */
+#define COMPACT_MAX_DEFER_SHIFT 6
+
+/*
+ * Compaction is deferred when compaction fails to result in a page
+ * allocation success. 1 << compact_defer_shift, compactions are skipped up
+ * to a limit of 1 << COMPACT_MAX_DEFER_SHIFT
+ */
+static void defer_compaction(struct zone *zone, int order)
+{
+	zone->compact_considered = 0;
+	zone->compact_defer_shift++;
+
+	if (order < zone->compact_order_failed)
+		zone->compact_order_failed = order;
+
+	if (zone->compact_defer_shift > COMPACT_MAX_DEFER_SHIFT)
+		zone->compact_defer_shift = COMPACT_MAX_DEFER_SHIFT;
+
+	trace_mm_compaction_defer_compaction(zone, order);
+}
+
+/* Returns true if compaction should be skipped this time */
+static bool compaction_deferred(struct zone *zone, int order)
+{
+	unsigned long defer_limit = 1UL << zone->compact_defer_shift;
+
+	if (order < zone->compact_order_failed)
+		return false;
+
+	/* Avoid possible overflow */
+	if (++zone->compact_considered >= defer_limit) {
+		zone->compact_considered = defer_limit;
+		return false;
+	}
+
+	trace_mm_compaction_deferred(zone, order);
+
+	return true;
+}
+
+/*
+ * Update defer tracking counters after successful compaction of given order,
+ * which means an allocation either succeeded (alloc_success == true) or is
+ * expected to succeed.
+ */
+void compaction_defer_reset(struct zone *zone, int order,
+		bool alloc_success)
+{
+	if (alloc_success) {
+		zone->compact_considered = 0;
+		zone->compact_defer_shift = 0;
+	}
+	if (order >= zone->compact_order_failed)
+		zone->compact_order_failed = order + 1;
+
+	trace_mm_compaction_defer_reset(zone, order);
+}
+
+/* Returns true if restarting compaction after many failures */
+static bool compaction_restarting(struct zone *zone, int order)
+{
+	if (order < zone->compact_order_failed)
+		return false;
+
+	return zone->compact_defer_shift == COMPACT_MAX_DEFER_SHIFT &&
+		zone->compact_considered >= 1UL << zone->compact_defer_shift;
+}
+
+/* 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);
+}
+
+static void reset_cached_positions(struct zone *zone)
+{
+	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 =
+				pageblock_start_pfn(zone_end_pfn(zone) - 1);
+}
+
+/*
+ * Compound pages of >= pageblock_order should consistently be skipped until
+ * released. It is always pointless to compact pages of such order (if they are
+ * migratable), and the pageblocks they occupy cannot contain any free pages.
+ */
+static bool pageblock_skip_persistent(struct page *page)
+{
+	if (!PageCompound(page))
+		return false;
+
+	page = compound_head(page);
+
+	if (compound_order(page) >= pageblock_order)
+		return true;
+
+	return false;
+}
+
+static bool
+__reset_isolation_pfn(struct zone *zone, unsigned long pfn, bool check_source,
+							bool check_target)
+{
+	struct page *page = pfn_to_online_page(pfn);
+	struct page *block_page;
+	struct page *end_page;
+	unsigned long block_pfn;
+
+	if (!page)
+		return false;
+	if (zone != page_zone(page))
+		return false;
+	if (pageblock_skip_persistent(page))
+		return false;
+
+	/*
+	 * If skip is already cleared do no further checking once the
+	 * restart points have been set.
+	 */
+	if (check_source && check_target && !get_pageblock_skip(page))
+		return true;
+
+	/*
+	 * If clearing skip for the target scanner, do not select a
+	 * non-movable pageblock as the starting point.
+	 */
+	if (!check_source && check_target &&
+	    get_pageblock_migratetype(page) != MIGRATE_MOVABLE)
+		return false;
+
+	/* Ensure the start of the pageblock or zone is online and valid */
+	block_pfn = pageblock_start_pfn(pfn);
+	block_pfn = max(block_pfn, zone->zone_start_pfn);
+	block_page = pfn_to_online_page(block_pfn);
+	if (block_page) {
+		page = block_page;
+		pfn = block_pfn;
+	}
+
+	/* Ensure the end of the pageblock or zone is online and valid */
+	block_pfn = pageblock_end_pfn(pfn) - 1;
+	block_pfn = min(block_pfn, zone_end_pfn(zone) - 1);
+	end_page = pfn_to_online_page(block_pfn);
+	if (!end_page)
+		return false;
+
+	/*
+	 * Only clear the hint if a sample indicates there is either a
+	 * free page or an LRU page in the block. One or other condition
+	 * is necessary for the block to be a migration source/target.
+	 */
+	do {
+		if (check_source && PageLRU(page)) {
+			clear_pageblock_skip(page);
+			return true;
+		}
+
+		if (check_target && PageBuddy(page)) {
+			clear_pageblock_skip(page);
+			return true;
+		}
+
+		page += (1 << PAGE_ALLOC_COSTLY_ORDER);
+	} while (page <= end_page);
+
+	return false;
+}
+
+/*
+ * 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 migrate_pfn = zone->zone_start_pfn;
+	unsigned long free_pfn = zone_end_pfn(zone) - 1;
+	unsigned long reset_migrate = free_pfn;
+	unsigned long reset_free = migrate_pfn;
+	bool source_set = false;
+	bool free_set = false;
+
+	if (!zone->compact_blockskip_flush)
+		return;
+
+	zone->compact_blockskip_flush = false;
+
+	/*
+	 * Walk the zone and update pageblock skip information. Source looks
+	 * for PageLRU while target looks for PageBuddy. When the scanner
+	 * is found, both PageBuddy and PageLRU are checked as the pageblock
+	 * is suitable as both source and target.
+	 */
+	for (; migrate_pfn < free_pfn; migrate_pfn += pageblock_nr_pages,
+					free_pfn -= pageblock_nr_pages) {
+		cond_resched();
+
+		/* Update the migrate PFN */
+		if (__reset_isolation_pfn(zone, migrate_pfn, true, source_set) &&
+		    migrate_pfn < reset_migrate) {
+			source_set = true;
+			reset_migrate = migrate_pfn;
+			zone->compact_init_migrate_pfn = reset_migrate;
+			zone->compact_cached_migrate_pfn[0] = reset_migrate;
+			zone->compact_cached_migrate_pfn[1] = reset_migrate;
+		}
+
+		/* Update the free PFN */
+		if (__reset_isolation_pfn(zone, free_pfn, free_set, true) &&
+		    free_pfn > reset_free) {
+			free_set = true;
+			reset_free = free_pfn;
+			zone->compact_init_free_pfn = reset_free;
+			zone->compact_cached_free_pfn = reset_free;
+		}
+	}
+
+	/* Leave no distance if no suitable block was reset */
+	if (reset_migrate >= reset_free) {
+		zone->compact_cached_migrate_pfn[0] = migrate_pfn;
+		zone->compact_cached_migrate_pfn[1] = migrate_pfn;
+		zone->compact_cached_free_pfn = free_pfn;
+	}
+}
+
+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);
+	}
+}
+
+/*
+ * Sets the pageblock skip bit if it was clear. Note that this is a hint as
+ * locks are not required for read/writers. Returns true if it was already set.
+ */
+static bool test_and_set_skip(struct compact_control *cc, struct page *page,
+							unsigned long pfn)
+{
+	bool skip;
+
+	/* Do no update if skip hint is being ignored */
+	if (cc->ignore_skip_hint)
+		return false;
+
+	if (!pageblock_aligned(pfn))
+		return false;
+
+	skip = get_pageblock_skip(page);
+	if (!skip && !cc->no_set_skip_hint)
+		set_pageblock_skip(page);
+
+	return skip;
+}
+
+static void update_cached_migrate(struct compact_control *cc, unsigned long pfn)
+{
+	struct zone *zone = cc->zone;
+
+	pfn = pageblock_end_pfn(pfn);
+
+	/* Set for isolation rather than compaction */
+	if (cc->no_set_skip_hint)
+		return;
+
+	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;
+}
+
+/*
+ * 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 pfn)
+{
+	struct zone *zone = cc->zone;
+
+	if (cc->no_set_skip_hint)
+		return;
+
+	if (!page)
+		return;
+
+	set_pageblock_skip(page);
+
+	/* Update where async and sync compaction should restart */
+	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 inline bool pageblock_skip_persistent(struct page *page)
+{
+	return false;
+}
+
+static inline void update_pageblock_skip(struct compact_control *cc,
+			struct page *page, unsigned long pfn)
+{
+}
+
+static void update_cached_migrate(struct compact_control *cc, unsigned long pfn)
+{
+}
+
+static bool test_and_set_skip(struct compact_control *cc, struct page *page,
+							unsigned long pfn)
+{
+	return false;
+}
+#endif /* CONFIG_COMPACTION */
+
+/*
+ * Compaction requires the taking of some coarse locks that are potentially
+ * very heavily contended. For async compaction, trylock and record if the
+ * lock is contended. The lock will still be acquired but compaction will
+ * abort when the current block is finished regardless of success rate.
+ * Sync compaction acquires the lock.
+ *
+ * Always returns true which makes it easier to track lock state in callers.
+ */
+static bool compact_lock_irqsave(spinlock_t *lock, unsigned long *flags,
+						struct compact_control *cc)
+	__acquires(lock)
+{
+	/* Track if the lock is contended in async mode */
+	if (cc->mode == MIGRATE_ASYNC && !cc->contended) {
+		if (spin_trylock_irqsave(lock, *flags))
+			return true;
+
+		cc->contended = true;
+	}
+
+	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, 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.
+ * Returns false when compaction can continue.
+ */
+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 = true;
+		return true;
+	}
+
+	cond_resched();
+
+	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,
+				unsigned int stride,
+				bool strict)
+{
+	int nr_scanned = 0, total_isolated = 0;
+	struct page *cursor;
+	unsigned long flags = 0;
+	bool locked = false;
+	unsigned long blockpfn = *start_pfn;
+	unsigned int order;
+
+	/* Strict mode is for isolation, speed is secondary */
+	if (strict)
+		stride = 1;
+
+	cursor = pfn_to_page(blockpfn);
+
+	/* Isolate free pages. */
+	for (; blockpfn < end_pfn; blockpfn += stride, cursor += stride) {
+		int isolated;
+		struct page *page = cursor;
+
+		/*
+		 * Periodically drop the lock (if held) regardless of its
+		 * contention, to give chance to IRQs. Abort if fatal signal
+		 * pending.
+		 */
+		if (!(blockpfn % COMPACT_CLUSTER_MAX)
+		    && compact_unlock_should_abort(&cc->zone->lock, flags,
+								&locked, cc))
+			break;
+
+		nr_scanned++;
+
+		/*
+		 * For compound pages such as THP and hugetlbfs, we can save
+		 * potentially a lot of iterations if we skip them at once.
+		 * The check is racy, but we can consider only valid values
+		 * and the only danger is skipping too much.
+		 */
+		if (PageCompound(page)) {
+			const unsigned int order = compound_order(page);
+
+			if (likely(order < MAX_ORDER)) {
+				blockpfn += (1UL << order) - 1;
+				cursor += (1UL << order) - 1;
+			}
+			goto isolate_fail;
+		}
+
+		if (!PageBuddy(page))
+			goto isolate_fail;
+
+		/* If we already hold the lock, we can skip some rechecking. */
+		if (!locked) {
+			locked = compact_lock_irqsave(&cc->zone->lock,
+								&flags, cc);
+
+			/* Recheck this is a buddy page under lock */
+			if (!PageBuddy(page))
+				goto isolate_fail;
+		}
+
+		/* Found a free page, will break it into order-0 pages */
+		order = buddy_order(page);
+		isolated = __isolate_free_page(page, order);
+		if (!isolated)
+			break;
+		set_page_private(page, order);
+
+		nr_scanned += isolated - 1;
+		total_isolated += isolated;
+		cc->nr_freepages += isolated;
+		list_add_tail(&page->lru, freelist);
+
+		if (!strict && cc->nr_migratepages <= cc->nr_freepages) {
+			blockpfn += isolated;
+			break;
+		}
+		/* Advance to the end of split page */
+		blockpfn += isolated - 1;
+		cursor += isolated - 1;
+		continue;
+
+isolate_fail:
+		if (strict)
+			break;
+		else
+			continue;
+
+	}
+
+	if (locked)
+		spin_unlock_irqrestore(&cc->zone->lock, flags);
+
+	/*
+	 * There is a tiny chance that we have read bogus compound_order(),
+	 * so be careful to not go outside of the pageblock.
+	 */
+	if (unlikely(blockpfn > end_pfn))
+		blockpfn = end_pfn;
+
+	trace_mm_compaction_isolate_freepages(*start_pfn, blockpfn,
+					nr_scanned, total_isolated);
+
+	/* Record how far we have got within the block */
+	*start_pfn = blockpfn;
+
+	/*
+	 * 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;
+
+	cc->total_free_scanned += nr_scanned;
+	if (total_isolated)
+		count_compact_events(COMPACTISOLATED, total_isolated);
+	return total_isolated;
+}
+
+/**
+ * isolate_freepages_range() - isolate free pages.
+ * @cc:        Compaction control structure.
+ * @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_start_pfn, block_end_pfn;
+	LIST_HEAD(freelist);
+
+	pfn = start_pfn;
+	block_start_pfn = pageblock_start_pfn(pfn);
+	if (block_start_pfn < cc->zone->zone_start_pfn)
+		block_start_pfn = cc->zone->zone_start_pfn;
+	block_end_pfn = pageblock_end_pfn(pfn);
+
+	for (; pfn < end_pfn; pfn += isolated,
+				block_start_pfn = block_end_pfn,
+				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_start_pfn = pageblock_start_pfn(pfn);
+			block_end_pfn = pageblock_end_pfn(pfn);
+			block_end_pfn = min(block_end_pfn, end_pfn);
+		}
+
+		if (!pageblock_pfn_to_page(block_start_pfn,
+					block_end_pfn, cc->zone))
+			break;
+
+		isolated = isolate_freepages_block(cc, &isolate_start_pfn,
+					block_end_pfn, &freelist, 0, 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).
+		 */
+	}
+
+	/* __isolate_free_page() does not map the pages */
+	split_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;
+}
+
+/* Similar to reclaim, but different enough that they don't share logic */
+static bool too_many_isolated(pg_data_t *pgdat)
+{
+	bool too_many;
+
+	unsigned long active, inactive, isolated;
+
+	inactive = node_page_state(pgdat, NR_INACTIVE_FILE) +
+			node_page_state(pgdat, NR_INACTIVE_ANON);
+	active = node_page_state(pgdat, NR_ACTIVE_FILE) +
+			node_page_state(pgdat, NR_ACTIVE_ANON);
+	isolated = node_page_state(pgdat, NR_ISOLATED_FILE) +
+			node_page_state(pgdat, NR_ISOLATED_ANON);
+
+	too_many = isolated > (inactive + active) / 2;
+	if (!too_many)
+		wake_throttle_isolated(pgdat);
+
+	return too_many;
+}
+
+/**
+ * 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
+ * @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 errno, like -EAGAIN or -EINTR in case e.g signal pending or congestion,
+ * -ENOMEM in case we could not allocate a page, or 0.
+ * cc->migrate_pfn will contain the next pfn to scan.
+ *
+ * The pages are isolated on cc->migratepages list (not required to be empty),
+ * and cc->nr_migratepages is updated accordingly.
+ */
+static int
+isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
+			unsigned long end_pfn, isolate_mode_t mode)
+{
+	pg_data_t *pgdat = cc->zone->zone_pgdat;
+	unsigned long nr_scanned = 0, nr_isolated = 0;
+	struct lruvec *lruvec;
+	unsigned long flags = 0;
+	struct lruvec *locked = NULL;
+	struct page *page = NULL, *valid_page = NULL;
+	struct address_space *mapping;
+	unsigned long start_pfn = low_pfn;
+	bool skip_on_failure = false;
+	unsigned long next_skip_pfn = 0;
+	bool skip_updated = false;
+	int ret = 0;
+
+	cc->migrate_pfn = low_pfn;
+
+	/*
+	 * 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(pgdat))) {
+		/* stop isolation if there are still pages not migrated */
+		if (cc->nr_migratepages)
+			return -EAGAIN;
+
+		/* async migration should just abort */
+		if (cc->mode == MIGRATE_ASYNC)
+			return -EAGAIN;
+
+		reclaim_throttle(pgdat, VMSCAN_THROTTLE_ISOLATED);
+
+		if (fatal_signal_pending(current))
+			return -EINTR;
+	}
+
+	cond_resched();
+
+	if (cc->direct_compaction && (cc->mode == MIGRATE_ASYNC)) {
+		skip_on_failure = true;
+		next_skip_pfn = block_end_pfn(low_pfn, cc->order);
+	}
+
+	/* Time to isolate some pages for migration */
+	for (; low_pfn < end_pfn; low_pfn++) {
+
+		if (skip_on_failure && low_pfn >= next_skip_pfn) {
+			/*
+			 * We have isolated all migration candidates in the
+			 * previous order-aligned block, and did not skip it due
+			 * to failure. We should migrate the pages now and
+			 * hopefully succeed compaction.
+			 */
+			if (nr_isolated)
+				break;
+
+			/*
+			 * We failed to isolate in the previous order-aligned
+			 * block. Set the new boundary to the end of the
+			 * current block. Note we can't simply increase
+			 * next_skip_pfn by 1 << order, as low_pfn might have
+			 * been incremented by a higher number due to skipping
+			 * a compound or a high-order buddy page in the
+			 * previous loop iteration.
+			 */
+			next_skip_pfn = block_end_pfn(low_pfn, cc->order);
+		}
+
+		/*
+		 * Periodically drop the lock (if held) regardless of its
+		 * contention, to give chance to IRQs. Abort completely if
+		 * a fatal signal is pending.
+		 */
+		if (!(low_pfn % COMPACT_CLUSTER_MAX)) {
+			if (locked) {
+				unlock_page_lruvec_irqrestore(locked, flags);
+				locked = NULL;
+			}
+
+			if (fatal_signal_pending(current)) {
+				cc->contended = true;
+				ret = -EINTR;
+
+				goto fatal_pending;
+			}
+
+			cond_resched();
+		}
+
+		nr_scanned++;
+
+		page = pfn_to_page(low_pfn);
+
+		/*
+		 * Check if the pageblock has already been marked skipped.
+		 * Only the aligned PFN is checked as the caller isolates
+		 * COMPACT_CLUSTER_MAX at a time so the second call must
+		 * not falsely conclude that the block should be skipped.
+		 */
+		if (!valid_page && pageblock_aligned(low_pfn)) {
+			if (!isolation_suitable(cc, page)) {
+				low_pfn = end_pfn;
+				page = NULL;
+				goto isolate_abort;
+			}
+			valid_page = page;
+		}
+
+		if (PageHuge(page) && cc->alloc_contig) {
+			ret = isolate_or_dissolve_huge_page(page, &cc->migratepages);
+
+			/*
+			 * Fail isolation in case isolate_or_dissolve_huge_page()
+			 * reports an error. In case of -ENOMEM, abort right away.
+			 */
+			if (ret < 0) {
+				 /* Do not report -EBUSY down the chain */
+				if (ret == -EBUSY)
+					ret = 0;
+				low_pfn += compound_nr(page) - 1;
+				goto isolate_fail;
+			}
+
+			if (PageHuge(page)) {
+				/*
+				 * Hugepage was successfully isolated and placed
+				 * on the cc->migratepages list.
+				 */
+				low_pfn += compound_nr(page) - 1;
+				goto isolate_success_no_list;
+			}
+
+			/*
+			 * Ok, the hugepage was dissolved. Now these pages are
+			 * Buddy and cannot be re-allocated because they are
+			 * isolated. Fall-through as the check below handles
+			 * Buddy pages.
+			 */
+		}
+
+		/*
+		 * 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 = buddy_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;
+		}
+
+		/*
+		 * Regardless of being on LRU, compound pages such as THP and
+		 * hugetlbfs are not to be compacted unless we are attempting
+		 * an allocation much larger than the huge page size (eg CMA).
+		 * We can potentially save a lot of iterations if we skip them
+		 * at once. The check is racy, but we can consider only valid
+		 * values and the only danger is skipping too much.
+		 */
+		if (PageCompound(page) && !cc->alloc_contig) {
+			const unsigned int order = compound_order(page);
+
+			if (likely(order < MAX_ORDER))
+				low_pfn += (1UL << order) - 1;
+			goto isolate_fail;
+		}
+
+		/*
+		 * Check may be lockless but that's ok as we recheck later.
+		 * It's possible to migrate LRU and non-lru movable pages.
+		 * Skip any other type of page
+		 */
+		if (!PageLRU(page)) {
+			/*
+			 * __PageMovable can return false positive so we need
+			 * to verify it under page_lock.
+			 */
+			if (unlikely(__PageMovable(page)) &&
+					!PageIsolated(page)) {
+				if (locked) {
+					unlock_page_lruvec_irqrestore(locked, flags);
+					locked = NULL;
+				}
+
+				if (!isolate_movable_page(page, mode))
+					goto isolate_success;
+			}
+
+			goto isolate_fail;
+		}
+
+		/*
+		 * Be careful not to clear PageLRU until after we're
+		 * sure the page is not being freed elsewhere -- the
+		 * page release code relies on it.
+		 */
+		if (unlikely(!get_page_unless_zero(page)))
+			goto isolate_fail;
+
+		/*
+		 * 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.
+		 */
+		mapping = page_mapping(page);
+		if (!mapping && (page_count(page) - 1) > total_mapcount(page))
+			goto isolate_fail_put;
+
+		/*
+		 * Only allow to migrate anonymous pages in GFP_NOFS context
+		 * because those do not depend on fs locks.
+		 */
+		if (!(cc->gfp_mask & __GFP_FS) && mapping)
+			goto isolate_fail_put;
+
+		/* Only take pages on LRU: a check now makes later tests safe */
+		if (!PageLRU(page))
+			goto isolate_fail_put;
+
+		/* Compaction might skip unevictable pages but CMA takes them */
+		if (!(mode & ISOLATE_UNEVICTABLE) && PageUnevictable(page))
+			goto isolate_fail_put;
+
+		/*
+		 * To minimise LRU disruption, the caller can indicate with
+		 * ISOLATE_ASYNC_MIGRATE that it only wants to isolate pages
+		 * it will be able to migrate without blocking - clean pages
+		 * for the most part.  PageWriteback would require blocking.
+		 */
+		if ((mode & ISOLATE_ASYNC_MIGRATE) && PageWriteback(page))
+			goto isolate_fail_put;
+
+		if ((mode & ISOLATE_ASYNC_MIGRATE) && PageDirty(page)) {
+			bool migrate_dirty;
+
+			/*
+			 * Only pages without mappings or that have a
+			 * ->migrate_folio callback are possible to migrate
+			 * without blocking. However, we can be racing with
+			 * truncation so it's necessary to lock the page
+			 * to stabilise the mapping as truncation holds
+			 * the page lock until after the page is removed
+			 * from the page cache.
+			 */
+			if (!trylock_page(page))
+				goto isolate_fail_put;
+
+			mapping = page_mapping(page);
+			migrate_dirty = !mapping ||
+					mapping->a_ops->migrate_folio;
+			unlock_page(page);
+			if (!migrate_dirty)
+				goto isolate_fail_put;
+		}
+
+		/* Try isolate the page */
+		if (!TestClearPageLRU(page))
+			goto isolate_fail_put;
+
+		lruvec = folio_lruvec(page_folio(page));
+
+		/* If we already hold the lock, we can skip some rechecking */
+		if (lruvec != locked) {
+			if (locked)
+				unlock_page_lruvec_irqrestore(locked, flags);
+
+			compact_lock_irqsave(&lruvec->lru_lock, &flags, cc);
+			locked = lruvec;
+
+			lruvec_memcg_debug(lruvec, page_folio(page));
+
+			/* Try get exclusive access under lock */
+			if (!skip_updated) {
+				skip_updated = true;
+				if (test_and_set_skip(cc, page, low_pfn))
+					goto isolate_abort;
+			}
+
+			/*
+			 * Page become compound since the non-locked check,
+			 * and it's on LRU. It can only be a THP so the order
+			 * is safe to read and it's 0 for tail pages.
+			 */
+			if (unlikely(PageCompound(page) && !cc->alloc_contig)) {
+				low_pfn += compound_nr(page) - 1;
+				SetPageLRU(page);
+				goto isolate_fail_put;
+			}
+		}
+
+		/* The whole page is taken off the LRU; skip the tail pages. */
+		if (PageCompound(page))
+			low_pfn += compound_nr(page) - 1;
+
+		/* Successfully isolated */
+		del_page_from_lru_list(page, lruvec);
+		mod_node_page_state(page_pgdat(page),
+				NR_ISOLATED_ANON + page_is_file_lru(page),
+				thp_nr_pages(page));
+
+isolate_success:
+		list_add(&page->lru, &cc->migratepages);
+isolate_success_no_list:
+		cc->nr_migratepages += compound_nr(page);
+		nr_isolated += compound_nr(page);
+		nr_scanned += compound_nr(page) - 1;
+
+		/*
+		 * Avoid isolating too much unless this block is being
+		 * rescanned (e.g. dirty/writeback pages, parallel allocation)
+		 * or a lock is contended. For contention, isolate quickly to
+		 * potentially remove one source of contention.
+		 */
+		if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX &&
+		    !cc->rescan && !cc->contended) {
+			++low_pfn;
+			break;
+		}
+
+		continue;
+
+isolate_fail_put:
+		/* Avoid potential deadlock in freeing page under lru_lock */
+		if (locked) {
+			unlock_page_lruvec_irqrestore(locked, flags);
+			locked = NULL;
+		}
+		put_page(page);
+
+isolate_fail:
+		if (!skip_on_failure && ret != -ENOMEM)
+			continue;
+
+		/*
+		 * We have isolated some pages, but then failed. Release them
+		 * instead of migrating, as we cannot form the cc->order buddy
+		 * page anyway.
+		 */
+		if (nr_isolated) {
+			if (locked) {
+				unlock_page_lruvec_irqrestore(locked, flags);
+				locked = NULL;
+			}
+			putback_movable_pages(&cc->migratepages);
+			cc->nr_migratepages = 0;
+			nr_isolated = 0;
+		}
+
+		if (low_pfn < next_skip_pfn) {
+			low_pfn = next_skip_pfn - 1;
+			/*
+			 * The check near the loop beginning would have updated
+			 * next_skip_pfn too, but this is a bit simpler.
+			 */
+			next_skip_pfn += 1UL << cc->order;
+		}
+
+		if (ret == -ENOMEM)
+			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;
+
+	page = NULL;
+
+isolate_abort:
+	if (locked)
+		unlock_page_lruvec_irqrestore(locked, flags);
+	if (page) {
+		SetPageLRU(page);
+		put_page(page);
+	}
+
+	/*
+	 * Updated the cached scanner pfn once the pageblock has been scanned
+	 * Pages will either be migrated in which case there is no point
+	 * scanning in the near future or migration failed in which case the
+	 * failure reason may persist. The block is marked for skipping if
+	 * there were no pages isolated in the block or if the block is
+	 * rescanned twice in a row.
+	 */
+	if (low_pfn == end_pfn && (!nr_isolated || cc->rescan)) {
+		if (valid_page && !skip_updated)
+			set_pageblock_skip(valid_page);
+		update_cached_migrate(cc, low_pfn);
+	}
+
+	trace_mm_compaction_isolate_migratepages(start_pfn, low_pfn,
+						nr_scanned, nr_isolated);
+
+fatal_pending:
+	cc->total_migrate_scanned += nr_scanned;
+	if (nr_isolated)
+		count_compact_events(COMPACTISOLATED, nr_isolated);
+
+	cc->migrate_pfn = low_pfn;
+
+	return ret;
+}
+
+/**
+ * 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 -EAGAIN when contented, -EINTR in case of a signal pending, -ENOMEM
+ * in case we could not allocate a page, or 0.
+ */
+int
+isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn,
+							unsigned long end_pfn)
+{
+	unsigned long pfn, block_start_pfn, block_end_pfn;
+	int ret = 0;
+
+	/* Scan block by block. First and last block may be incomplete */
+	pfn = start_pfn;
+	block_start_pfn = pageblock_start_pfn(pfn);
+	if (block_start_pfn < cc->zone->zone_start_pfn)
+		block_start_pfn = cc->zone->zone_start_pfn;
+	block_end_pfn = pageblock_end_pfn(pfn);
+
+	for (; pfn < end_pfn; pfn = block_end_pfn,
+				block_start_pfn = block_end_pfn,
+				block_end_pfn += pageblock_nr_pages) {
+
+		block_end_pfn = min(block_end_pfn, end_pfn);
+
+		if (!pageblock_pfn_to_page(block_start_pfn,
+					block_end_pfn, cc->zone))
+			continue;
+
+		ret = isolate_migratepages_block(cc, pfn, block_end_pfn,
+						 ISOLATE_UNEVICTABLE);
+
+		if (ret)
+			break;
+
+		if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX)
+			break;
+	}
+
+	return ret;
+}
+
+#endif /* CONFIG_COMPACTION || CONFIG_CMA */
+#ifdef CONFIG_COMPACTION
+
+static bool suitable_migration_source(struct compact_control *cc,
+							struct page *page)
+{
+	int block_mt;
+
+	if (pageblock_skip_persistent(page))
+		return false;
+
+	if ((cc->mode != MIGRATE_ASYNC) || !cc->direct_compaction)
+		return true;
+
+	block_mt = get_pageblock_migratetype(page);
+
+	if (cc->migratetype == MIGRATE_MOVABLE)
+		return is_migrate_movable(block_mt);
+	else
+		return block_mt == cc->migratetype;
+}
+
+/* Returns true if the page is within a block suitable for migration to */
+static bool suitable_migration_target(struct compact_control *cc,
+							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 (buddy_order_unsafe(page) >= pageblock_order)
+			return false;
+	}
+
+	if (cc->ignore_block_suitable)
+		return true;
+
+	/* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
+	if (is_migrate_movable(get_pageblock_migratetype(page)))
+		return true;
+
+	/* Otherwise skip the block */
+	return false;
+}
+
+static inline unsigned int
+freelist_scan_limit(struct compact_control *cc)
+{
+	unsigned short shift = BITS_PER_LONG - 1;
+
+	return (COMPACT_CLUSTER_MAX >> min(shift, cc->fast_search_fail)) + 1;
+}
+
+/*
+ * Test whether the free scanner has reached the same or lower pageblock than
+ * the migration scanner, and compaction should thus terminate.
+ */
+static inline bool compact_scanners_met(struct compact_control *cc)
+{
+	return (cc->free_pfn >> pageblock_order)
+		<= (cc->migrate_pfn >> pageblock_order);
+}
+
+/*
+ * Used when scanning for a suitable migration target which scans freelists
+ * in reverse. Reorders the list such as the unscanned pages are scanned
+ * first on the next iteration of the free scanner
+ */
+static void
+move_freelist_head(struct list_head *freelist, struct page *freepage)
+{
+	LIST_HEAD(sublist);
+
+	if (!list_is_last(freelist, &freepage->lru)) {
+		list_cut_before(&sublist, freelist, &freepage->lru);
+		list_splice_tail(&sublist, freelist);
+	}
+}
+
+/*
+ * Similar to move_freelist_head except used by the migration scanner
+ * when scanning forward. It's possible for these list operations to
+ * move against each other if they search the free list exactly in
+ * lockstep.
+ */
+static void
+move_freelist_tail(struct list_head *freelist, struct page *freepage)
+{
+	LIST_HEAD(sublist);
+
+	if (!list_is_first(freelist, &freepage->lru)) {
+		list_cut_position(&sublist, freelist, &freepage->lru);
+		list_splice_tail(&sublist, freelist);
+	}
+}
+
+static void
+fast_isolate_around(struct compact_control *cc, unsigned long pfn)
+{
+	unsigned long start_pfn, end_pfn;
+	struct page *page;
+
+	/* Do not search around if there are enough pages already */
+	if (cc->nr_freepages >= cc->nr_migratepages)
+		return;
+
+	/* Minimise scanning during async compaction */
+	if (cc->direct_compaction && cc->mode == MIGRATE_ASYNC)
+		return;
+
+	/* Pageblock boundaries */
+	start_pfn = max(pageblock_start_pfn(pfn), cc->zone->zone_start_pfn);
+	end_pfn = min(pageblock_end_pfn(pfn), zone_end_pfn(cc->zone));
+
+	page = pageblock_pfn_to_page(start_pfn, end_pfn, cc->zone);
+	if (!page)
+		return;
+
+	isolate_freepages_block(cc, &start_pfn, end_pfn, &cc->freepages, 1, false);
+
+	/* Skip this pageblock in the future as it's full or nearly full */
+	if (cc->nr_freepages < cc->nr_migratepages)
+		set_pageblock_skip(page);
+
+	return;
+}
+
+/* Search orders in round-robin fashion */
+static int next_search_order(struct compact_control *cc, int order)
+{
+	order--;
+	if (order < 0)
+		order = cc->order - 1;
+
+	/* Search wrapped around? */
+	if (order == cc->search_order) {
+		cc->search_order--;
+		if (cc->search_order < 0)
+			cc->search_order = cc->order - 1;
+		return -1;
+	}
+
+	return order;
+}
+
+static unsigned long
+fast_isolate_freepages(struct compact_control *cc)
+{
+	unsigned int limit = max(1U, freelist_scan_limit(cc) >> 1);
+	unsigned int nr_scanned = 0;
+	unsigned long low_pfn, min_pfn, highest = 0;
+	unsigned long nr_isolated = 0;
+	unsigned long distance;
+	struct page *page = NULL;
+	bool scan_start = false;
+	int order;
+
+	/* Full compaction passes in a negative order */
+	if (cc->order <= 0)
+		return cc->free_pfn;
+
+	/*
+	 * If starting the scan, use a deeper search and use the highest
+	 * PFN found if a suitable one is not found.
+	 */
+	if (cc->free_pfn >= cc->zone->compact_init_free_pfn) {
+		limit = pageblock_nr_pages >> 1;
+		scan_start = true;
+	}
+
+	/*
+	 * Preferred point is in the top quarter of the scan space but take
+	 * a pfn from the top half if the search is problematic.
+	 */
+	distance = (cc->free_pfn - cc->migrate_pfn);
+	low_pfn = pageblock_start_pfn(cc->free_pfn - (distance >> 2));
+	min_pfn = pageblock_start_pfn(cc->free_pfn - (distance >> 1));
+
+	if (WARN_ON_ONCE(min_pfn > low_pfn))
+		low_pfn = min_pfn;
+
+	/*
+	 * Search starts from the last successful isolation order or the next
+	 * order to search after a previous failure
+	 */
+	cc->search_order = min_t(unsigned int, cc->order - 1, cc->search_order);
+
+	for (order = cc->search_order;
+	     !page && order >= 0;
+	     order = next_search_order(cc, order)) {
+		struct free_area *area = &cc->zone->free_area[order];
+		struct list_head *freelist;
+		struct page *freepage;
+		unsigned long flags;
+		unsigned int order_scanned = 0;
+		unsigned long high_pfn = 0;
+
+		if (!area->nr_free)
+			continue;
+
+		spin_lock_irqsave(&cc->zone->lock, flags);
+		freelist = &area->free_list[MIGRATE_MOVABLE];
+		list_for_each_entry_reverse(freepage, freelist, lru) {
+			unsigned long pfn;
+
+			order_scanned++;
+			nr_scanned++;
+			pfn = page_to_pfn(freepage);
+
+			if (pfn >= highest)
+				highest = max(pageblock_start_pfn(pfn),
+					      cc->zone->zone_start_pfn);
+
+			if (pfn >= low_pfn) {
+				cc->fast_search_fail = 0;
+				cc->search_order = order;
+				page = freepage;
+				break;
+			}
+
+			if (pfn >= min_pfn && pfn > high_pfn) {
+				high_pfn = pfn;
+
+				/* Shorten the scan if a candidate is found */
+				limit >>= 1;
+			}
+
+			if (order_scanned >= limit)
+				break;
+		}
+
+		/* Use a minimum pfn if a preferred one was not found */
+		if (!page && high_pfn) {
+			page = pfn_to_page(high_pfn);
+
+			/* Update freepage for the list reorder below */
+			freepage = page;
+		}
+
+		/* Reorder to so a future search skips recent pages */
+		move_freelist_head(freelist, freepage);
+
+		/* Isolate the page if available */
+		if (page) {
+			if (__isolate_free_page(page, order)) {
+				set_page_private(page, order);
+				nr_isolated = 1 << order;
+				nr_scanned += nr_isolated - 1;
+				cc->nr_freepages += nr_isolated;
+				list_add_tail(&page->lru, &cc->freepages);
+				count_compact_events(COMPACTISOLATED, nr_isolated);
+			} else {
+				/* If isolation fails, abort the search */
+				order = cc->search_order + 1;
+				page = NULL;
+			}
+		}
+
+		spin_unlock_irqrestore(&cc->zone->lock, flags);
+
+		/*
+		 * Smaller scan on next order so the total scan is related
+		 * to freelist_scan_limit.
+		 */
+		if (order_scanned >= limit)
+			limit = max(1U, limit >> 1);
+	}
+
+	if (!page) {
+		cc->fast_search_fail++;
+		if (scan_start) {
+			/*
+			 * Use the highest PFN found above min. If one was
+			 * not found, be pessimistic for direct compaction
+			 * and use the min mark.
+			 */
+			if (highest >= min_pfn) {
+				page = pfn_to_page(highest);
+				cc->free_pfn = highest;
+			} else {
+				if (cc->direct_compaction && pfn_valid(min_pfn)) {
+					page = pageblock_pfn_to_page(min_pfn,
+						min(pageblock_end_pfn(min_pfn),
+						    zone_end_pfn(cc->zone)),
+						cc->zone);
+					cc->free_pfn = min_pfn;
+				}
+			}
+		}
+	}
+
+	if (highest && highest >= cc->zone->compact_cached_free_pfn) {
+		highest -= pageblock_nr_pages;
+		cc->zone->compact_cached_free_pfn = highest;
+	}
+
+	cc->total_free_scanned += nr_scanned;
+	if (!page)
+		return cc->free_pfn;
+
+	low_pfn = page_to_pfn(page);
+	fast_isolate_around(cc, low_pfn);
+	return low_pfn;
+}
+
+/*
+ * 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 */
+	struct list_head *freelist = &cc->freepages;
+	unsigned int stride;
+
+	/* Try a small search of the free lists for a candidate */
+	fast_isolate_freepages(cc);
+	if (cc->nr_freepages)
+		goto splitmap;
+
+	/*
+	 * 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
+	 * 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 = pageblock_start_pfn(isolate_start_pfn);
+	block_end_pfn = min(block_start_pfn + pageblock_nr_pages,
+						zone_end_pfn(zone));
+	low_pfn = pageblock_end_pfn(cc->migrate_pfn);
+	stride = cc->mode == MIGRATE_ASYNC ? COMPACT_CLUSTER_MAX : 1;
+
+	/*
+	 * 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;
+				block_end_pfn = block_start_pfn,
+				block_start_pfn -= pageblock_nr_pages,
+				isolate_start_pfn = block_start_pfn) {
+		unsigned long nr_isolated;
+
+		/*
+		 * This can iterate a massively long zone without finding any
+		 * suitable migration targets, so periodically check resched.
+		 */
+		if (!(block_start_pfn % (COMPACT_CLUSTER_MAX * pageblock_nr_pages)))
+			cond_resched();
+
+		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(cc, page))
+			continue;
+
+		/* If isolation recently failed, do not retry */
+		if (!isolation_suitable(cc, page))
+			continue;
+
+		/* Found a block suitable for isolating free pages from. */
+		nr_isolated = isolate_freepages_block(cc, &isolate_start_pfn,
+					block_end_pfn, freelist, stride, false);
+
+		/* Update the skip hint if the full pageblock was scanned */
+		if (isolate_start_pfn == block_end_pfn)
+			update_pageblock_skip(cc, page, block_start_pfn);
+
+		/* Are enough freepages isolated? */
+		if (cc->nr_freepages >= cc->nr_migratepages) {
+			if (isolate_start_pfn >= block_end_pfn) {
+				/*
+				 * Restart at previous pageblock if more
+				 * freepages can be isolated next time.
+				 */
+				isolate_start_pfn =
+					block_start_pfn - pageblock_nr_pages;
+			}
+			break;
+		} else if (isolate_start_pfn < block_end_pfn) {
+			/*
+			 * If isolation failed early, do not continue
+			 * needlessly.
+			 */
+			break;
+		}
+
+		/* Adjust stride depending on isolation */
+		if (nr_isolated) {
+			stride = 1;
+			continue;
+		}
+		stride = min_t(unsigned int, COMPACT_CLUSTER_MAX, stride << 1);
+	}
+
+	/*
+	 * Record where the free scanner will restart next time. Either we
+	 * broke from the loop and set isolate_start_pfn based on the last
+	 * call to isolate_freepages_block(), or we met the migration scanner
+	 * and the loop terminated due to isolate_start_pfn < low_pfn
+	 */
+	cc->free_pfn = isolate_start_pfn;
+
+splitmap:
+	/* __isolate_free_page() does not map the pages */
+	split_map_pages(freelist);
+}
+
+/*
+ * 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)
+{
+	struct compact_control *cc = (struct compact_control *)data;
+	struct page *freepage;
+
+	if (list_empty(&cc->freepages)) {
+		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;
+
+/*
+ * Allow userspace to control policy on scanning the unevictable LRU for
+ * compactable pages.
+ */
+int sysctl_compact_unevictable_allowed __read_mostly = CONFIG_COMPACT_UNEVICTABLE_DEFAULT;
+
+static inline void
+update_fast_start_pfn(struct compact_control *cc, unsigned long pfn)
+{
+	if (cc->fast_start_pfn == ULONG_MAX)
+		return;
+
+	if (!cc->fast_start_pfn)
+		cc->fast_start_pfn = pfn;
+
+	cc->fast_start_pfn = min(cc->fast_start_pfn, pfn);
+}
+
+static inline unsigned long
+reinit_migrate_pfn(struct compact_control *cc)
+{
+	if (!cc->fast_start_pfn || cc->fast_start_pfn == ULONG_MAX)
+		return cc->migrate_pfn;
+
+	cc->migrate_pfn = cc->fast_start_pfn;
+	cc->fast_start_pfn = ULONG_MAX;
+
+	return cc->migrate_pfn;
+}
+
+/*
+ * Briefly search the free lists for a migration source that already has
+ * some free pages to reduce the number of pages that need migration
+ * before a pageblock is free.
+ */
+static unsigned long fast_find_migrateblock(struct compact_control *cc)
+{
+	unsigned int limit = freelist_scan_limit(cc);
+	unsigned int nr_scanned = 0;
+	unsigned long distance;
+	unsigned long pfn = cc->migrate_pfn;
+	unsigned long high_pfn;
+	int order;
+	bool found_block = false;
+
+	/* Skip hints are relied on to avoid repeats on the fast search */
+	if (cc->ignore_skip_hint)
+		return pfn;
+
+	/*
+	 * If the migrate_pfn is not at the start of a zone or the start
+	 * of a pageblock then assume this is a continuation of a previous
+	 * scan restarted due to COMPACT_CLUSTER_MAX.
+	 */
+	if (pfn != cc->zone->zone_start_pfn && pfn != pageblock_start_pfn(pfn))
+		return pfn;
+
+	/*
+	 * For smaller orders, just linearly scan as the number of pages
+	 * to migrate should be relatively small and does not necessarily
+	 * justify freeing up a large block for a small allocation.
+	 */
+	if (cc->order <= PAGE_ALLOC_COSTLY_ORDER)
+		return pfn;
+
+	/*
+	 * Only allow kcompactd and direct requests for movable pages to
+	 * quickly clear out a MOVABLE pageblock for allocation. This
+	 * reduces the risk that a large movable pageblock is freed for
+	 * an unmovable/reclaimable small allocation.
+	 */
+	if (cc->direct_compaction && cc->migratetype != MIGRATE_MOVABLE)
+		return pfn;
+
+	/*
+	 * When starting the migration scanner, pick any pageblock within the
+	 * first half of the search space. Otherwise try and pick a pageblock
+	 * within the first eighth to reduce the chances that a migration
+	 * target later becomes a source.
+	 */
+	distance = (cc->free_pfn - cc->migrate_pfn) >> 1;
+	if (cc->migrate_pfn != cc->zone->zone_start_pfn)
+		distance >>= 2;
+	high_pfn = pageblock_start_pfn(cc->migrate_pfn + distance);
+
+	for (order = cc->order - 1;
+	     order >= PAGE_ALLOC_COSTLY_ORDER && !found_block && nr_scanned < limit;
+	     order--) {
+		struct free_area *area = &cc->zone->free_area[order];
+		struct list_head *freelist;
+		unsigned long flags;
+		struct page *freepage;
+
+		if (!area->nr_free)
+			continue;
+
+		spin_lock_irqsave(&cc->zone->lock, flags);
+		freelist = &area->free_list[MIGRATE_MOVABLE];
+		list_for_each_entry(freepage, freelist, lru) {
+			unsigned long free_pfn;
+
+			if (nr_scanned++ >= limit) {
+				move_freelist_tail(freelist, freepage);
+				break;
+			}
+
+			free_pfn = page_to_pfn(freepage);
+			if (free_pfn < high_pfn) {
+				/*
+				 * Avoid if skipped recently. Ideally it would
+				 * move to the tail but even safe iteration of
+				 * the list assumes an entry is deleted, not
+				 * reordered.
+				 */
+				if (get_pageblock_skip(freepage))
+					continue;
+
+				/* Reorder to so a future search skips recent pages */
+				move_freelist_tail(freelist, freepage);
+
+				update_fast_start_pfn(cc, free_pfn);
+				pfn = pageblock_start_pfn(free_pfn);
+				if (pfn < cc->zone->zone_start_pfn)
+					pfn = cc->zone->zone_start_pfn;
+				cc->fast_search_fail = 0;
+				found_block = true;
+				set_pageblock_skip(freepage);
+				break;
+			}
+		}
+		spin_unlock_irqrestore(&cc->zone->lock, flags);
+	}
+
+	cc->total_migrate_scanned += nr_scanned;
+
+	/*
+	 * If fast scanning failed then use a cached entry for a page block
+	 * that had free pages as the basis for starting a linear scan.
+	 */
+	if (!found_block) {
+		cc->fast_search_fail++;
+		pfn = reinit_migrate_pfn(cc);
+	}
+	return pfn;
+}
+
+/*
+ * 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 compact_control *cc)
+{
+	unsigned long block_start_pfn;
+	unsigned long block_end_pfn;
+	unsigned long low_pfn;
+	struct page *page;
+	const isolate_mode_t isolate_mode =
+		(sysctl_compact_unevictable_allowed ? ISOLATE_UNEVICTABLE : 0) |
+		(cc->mode != MIGRATE_SYNC ? ISOLATE_ASYNC_MIGRATE : 0);
+	bool fast_find_block;
+
+	/*
+	 * Start at where we last stopped, or beginning of the zone as
+	 * initialized by compact_zone(). The first failure will use
+	 * the lowest PFN as the starting point for linear scanning.
+	 */
+	low_pfn = fast_find_migrateblock(cc);
+	block_start_pfn = pageblock_start_pfn(low_pfn);
+	if (block_start_pfn < cc->zone->zone_start_pfn)
+		block_start_pfn = cc->zone->zone_start_pfn;
+
+	/*
+	 * fast_find_migrateblock marks a pageblock skipped so to avoid
+	 * the isolation_suitable check below, check whether the fast
+	 * search was successful.
+	 */
+	fast_find_block = low_pfn != cc->migrate_pfn && !cc->fast_search_fail;
+
+	/* Only scan within a pageblock boundary */
+	block_end_pfn = pageblock_end_pfn(low_pfn);
+
+	/*
+	 * Iterate over whole pageblocks until we find the first suitable.
+	 * Do not cross the free scanner.
+	 */
+	for (; block_end_pfn <= cc->free_pfn;
+			fast_find_block = false,
+			cc->migrate_pfn = low_pfn = block_end_pfn,
+			block_start_pfn = block_end_pfn,
+			block_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.
+		 */
+		if (!(low_pfn % (COMPACT_CLUSTER_MAX * pageblock_nr_pages)))
+			cond_resched();
+
+		page = pageblock_pfn_to_page(block_start_pfn,
+						block_end_pfn, cc->zone);
+		if (!page)
+			continue;
+
+		/*
+		 * If isolation recently failed, do not retry. Only check the
+		 * pageblock once. COMPACT_CLUSTER_MAX causes a pageblock
+		 * to be visited multiple times. Assume skip was checked
+		 * before making it "skip" so other compaction instances do
+		 * not scan the same block.
+		 */
+		if (pageblock_aligned(low_pfn) &&
+		    !fast_find_block && !isolation_suitable(cc, page))
+			continue;
+
+		/*
+		 * For async direct compaction, only scan the pageblocks of the
+		 * same migratetype without huge pages. Async direct compaction
+		 * is optimistic to see if the minimum amount of work satisfies
+		 * the allocation. The cached PFN is updated as it's possible
+		 * that all remaining blocks between source and target are
+		 * unsuitable and the compaction scanners fail to meet.
+		 */
+		if (!suitable_migration_source(cc, page)) {
+			update_cached_migrate(cc, block_end_pfn);
+			continue;
+		}
+
+		/* Perform the isolation */
+		if (isolate_migratepages_block(cc, low_pfn, block_end_pfn,
+						isolate_mode))
+			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;
+	}
+
+	return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE;
+}
+
+/*
+ * order == -1 is expected when compacting via
+ * /proc/sys/vm/compact_memory
+ */
+static inline bool is_via_compact_memory(int order)
+{
+	return order == -1;
+}
+
+/*
+ * Determine whether kswapd is (or recently was!) running on this node.
+ *
+ * pgdat_kswapd_lock() pins pgdat->kswapd, so a concurrent kswapd_stop() can't
+ * zero it.
+ */
+static bool kswapd_is_running(pg_data_t *pgdat)
+{
+	bool running;
+
+	pgdat_kswapd_lock(pgdat);
+	running = pgdat->kswapd && task_is_running(pgdat->kswapd);
+	pgdat_kswapd_unlock(pgdat);
+
+	return running;
+}
+
+/*
+ * A zone's fragmentation score is the external fragmentation wrt to the
+ * COMPACTION_HPAGE_ORDER. It returns a value in the range [0, 100].
+ */
+static unsigned int fragmentation_score_zone(struct zone *zone)
+{
+	return extfrag_for_order(zone, COMPACTION_HPAGE_ORDER);
+}
+
+/*
+ * A weighted zone's fragmentation score is the external fragmentation
+ * wrt to the COMPACTION_HPAGE_ORDER scaled by the zone's size. It
+ * returns a value in the range [0, 100].
+ *
+ * The scaling factor ensures that proactive compaction focuses on larger
+ * zones like ZONE_NORMAL, rather than smaller, specialized zones like
+ * ZONE_DMA32. For smaller zones, the score value remains close to zero,
+ * and thus never exceeds the high threshold for proactive compaction.
+ */
+static unsigned int fragmentation_score_zone_weighted(struct zone *zone)
+{
+	unsigned long score;
+
+	score = zone->present_pages * fragmentation_score_zone(zone);
+	return div64_ul(score, zone->zone_pgdat->node_present_pages + 1);
+}
+
+/*
+ * The per-node proactive (background) compaction process is started by its
+ * corresponding kcompactd thread when the node's fragmentation score
+ * exceeds the high threshold. The compaction process remains active till
+ * the node's score falls below the low threshold, or one of the back-off
+ * conditions is met.
+ */
+static unsigned int fragmentation_score_node(pg_data_t *pgdat)
+{
+	unsigned int score = 0;
+	int zoneid;
+
+	for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
+		struct zone *zone;
+
+		zone = &pgdat->node_zones[zoneid];
+		score += fragmentation_score_zone_weighted(zone);
+	}
+
+	return score;
+}
+
+static unsigned int fragmentation_score_wmark(pg_data_t *pgdat, bool low)
+{
+	unsigned int wmark_low;
+
+	/*
+	 * Cap the low watermark to avoid excessive compaction
+	 * activity in case a user sets the proactiveness tunable
+	 * close to 100 (maximum).
+	 */
+	wmark_low = max(100U - sysctl_compaction_proactiveness, 5U);
+	return low ? wmark_low : min(wmark_low + 10, 100U);
+}
+
+static bool should_proactive_compact_node(pg_data_t *pgdat)
+{
+	int wmark_high;
+
+	if (!sysctl_compaction_proactiveness || kswapd_is_running(pgdat))
+		return false;
+
+	wmark_high = fragmentation_score_wmark(pgdat, false);
+	return fragmentation_score_node(pgdat) > wmark_high;
+}
+
+static enum compact_result __compact_finished(struct compact_control *cc)
+{
+	unsigned int order;
+	const int migratetype = cc->migratetype;
+	int ret;
+
+	/* Compaction run completes if the migrate and free scanner meet */
+	if (compact_scanners_met(cc)) {
+		/* Let the next compaction start anew. */
+		reset_cached_positions(cc->zone);
+
+		/*
+		 * Mark that the PG_migrate_skip information should be cleared
+		 * by kswapd when it goes to sleep. kcompactd does not set the
+		 * flag itself as the decision to be clear should be directly
+		 * based on an allocation request.
+		 */
+		if (cc->direct_compaction)
+			cc->zone->compact_blockskip_flush = true;
+
+		if (cc->whole_zone)
+			return COMPACT_COMPLETE;
+		else
+			return COMPACT_PARTIAL_SKIPPED;
+	}
+
+	if (cc->proactive_compaction) {
+		int score, wmark_low;
+		pg_data_t *pgdat;
+
+		pgdat = cc->zone->zone_pgdat;
+		if (kswapd_is_running(pgdat))
+			return COMPACT_PARTIAL_SKIPPED;
+
+		score = fragmentation_score_zone(cc->zone);
+		wmark_low = fragmentation_score_wmark(pgdat, true);
+
+		if (score > wmark_low)
+			ret = COMPACT_CONTINUE;
+		else
+			ret = COMPACT_SUCCESS;
+
+		goto out;
+	}
+
+	if (is_via_compact_memory(cc->order))
+		return COMPACT_CONTINUE;
+
+	/*
+	 * Always finish scanning a pageblock to reduce the possibility of
+	 * fallbacks in the future. This is particularly important when
+	 * migration source is unmovable/reclaimable but it's not worth
+	 * special casing.
+	 */
+	if (!pageblock_aligned(cc->migrate_pfn))
+		return COMPACT_CONTINUE;
+
+	/* Direct compactor: Is a suitable page free? */
+	ret = COMPACT_NO_SUITABLE_PAGE;
+	for (order = cc->order; order < MAX_ORDER; order++) {
+		struct free_area *area = &cc->zone->free_area[order];
+		bool can_steal;
+
+		/* Job done if page is free of the right migratetype */
+		if (!free_area_empty(area, migratetype))
+			return COMPACT_SUCCESS;
+
+#ifdef CONFIG_CMA
+		/* MIGRATE_MOVABLE can fallback on MIGRATE_CMA */
+		if (migratetype == MIGRATE_MOVABLE &&
+			!free_area_empty(area, MIGRATE_CMA))
+			return COMPACT_SUCCESS;
+#endif
+		/*
+		 * Job done if allocation would steal freepages from
+		 * other migratetype buddy lists.
+		 */
+		if (find_suitable_fallback(area, order, migratetype,
+						true, &can_steal) != -1)
+			/*
+			 * Movable pages are OK in any pageblock. If we are
+			 * stealing for a non-movable allocation, make sure
+			 * we finish compacting the current pageblock first
+			 * (which is assured by the above migrate_pfn align
+			 * check) so it is as free as possible and we won't
+			 * have to steal another one soon.
+			 */
+			return COMPACT_SUCCESS;
+	}
+
+out:
+	if (cc->contended || fatal_signal_pending(current))
+		ret = COMPACT_CONTENDED;
+
+	return ret;
+}
+
+static enum compact_result compact_finished(struct compact_control *cc)
+{
+	int ret;
+
+	ret = __compact_finished(cc);
+	trace_mm_compaction_finished(cc->zone, cc->order, ret);
+	if (ret == COMPACT_NO_SUITABLE_PAGE)
+		ret = COMPACT_CONTINUE;
+
+	return ret;
+}
+
+static enum compact_result __compaction_suitable(struct zone *zone, int order,
+					unsigned int alloc_flags,
+					int highest_zoneidx,
+					unsigned long wmark_target)
+{
+	unsigned long watermark;
+
+	if (is_via_compact_memory(order))
+		return COMPACT_CONTINUE;
+
+	watermark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK);
+	/*
+	 * 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, highest_zoneidx,
+								alloc_flags))
+		return COMPACT_SUCCESS;
+
+	/*
+	 * Watermarks for order-0 must be met for compaction to be able to
+	 * isolate free pages for migration targets. This means that the
+	 * watermark and alloc_flags have to match, or be more pessimistic than
+	 * the check in __isolate_free_page(). We don't use the direct
+	 * compactor's alloc_flags, as they are not relevant for freepage
+	 * isolation. We however do use the direct compactor's highest_zoneidx
+	 * to skip over zones where lowmem reserves would prevent allocation
+	 * even if compaction succeeds.
+	 * For costly orders, we require low watermark instead of min for
+	 * compaction to proceed to increase its chances.
+	 * ALLOC_CMA is used, as pages in CMA pageblocks are considered
+	 * suitable migration targets
+	 */
+	watermark = (order > PAGE_ALLOC_COSTLY_ORDER) ?
+				low_wmark_pages(zone) : min_wmark_pages(zone);
+	watermark += compact_gap(order);
+	if (!__zone_watermark_ok(zone, 0, watermark, highest_zoneidx,
+						ALLOC_CMA, wmark_target))
+		return COMPACT_SKIPPED;
+
+	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_SUCCESS  - If the allocation would succeed without compaction
+ *   COMPACT_CONTINUE - If compaction should run now
+ */
+enum compact_result compaction_suitable(struct zone *zone, int order,
+					unsigned int alloc_flags,
+					int highest_zoneidx)
+{
+	enum compact_result ret;
+	int fragindex;
+
+	ret = __compaction_suitable(zone, order, alloc_flags, highest_zoneidx,
+				    zone_page_state(zone, NR_FREE_PAGES));
+	/*
+	 * 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. Also
+	 * ignore fragindex for non-costly orders where the alternative to
+	 * a successful reclaim/compaction is OOM. Fragindex and the
+	 * vm.extfrag_threshold sysctl is meant as a heuristic to prevent
+	 * excessive compaction for costly orders, but it should not be at the
+	 * expense of system stability.
+	 */
+	if (ret == COMPACT_CONTINUE && (order > PAGE_ALLOC_COSTLY_ORDER)) {
+		fragindex = fragmentation_index(zone, order);
+		if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
+			ret = COMPACT_NOT_SUITABLE_ZONE;
+	}
+
+	trace_mm_compaction_suitable(zone, order, ret);
+	if (ret == COMPACT_NOT_SUITABLE_ZONE)
+		ret = COMPACT_SKIPPED;
+
+	return ret;
+}
+
+bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
+		int alloc_flags)
+{
+	struct zone *zone;
+	struct zoneref *z;
+
+	/*
+	 * Make sure at least one zone would pass __compaction_suitable if we continue
+	 * retrying the reclaim.
+	 */
+	for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
+				ac->highest_zoneidx, ac->nodemask) {
+		unsigned long available;
+		enum compact_result compact_result;
+
+		/*
+		 * Do not consider all the reclaimable memory because we do not
+		 * want to trash just for a single high order allocation which
+		 * is even not guaranteed to appear even if __compaction_suitable
+		 * is happy about the watermark check.
+		 */
+		available = zone_reclaimable_pages(zone) / order;
+		available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
+		compact_result = __compaction_suitable(zone, order, alloc_flags,
+				ac->highest_zoneidx, available);
+		if (compact_result == COMPACT_CONTINUE)
+			return true;
+	}
+
+	return false;
+}
+
+static enum compact_result
+compact_zone(struct compact_control *cc, struct capture_control *capc)
+{
+	enum compact_result ret;
+	unsigned long start_pfn = cc->zone->zone_start_pfn;
+	unsigned long end_pfn = zone_end_pfn(cc->zone);
+	unsigned long last_migrated_pfn;
+	const bool sync = cc->mode != MIGRATE_ASYNC;
+	bool update_cached;
+	unsigned int nr_succeeded = 0;
+
+	/*
+	 * These counters track activities during zone compaction.  Initialize
+	 * them before compacting a new zone.
+	 */
+	cc->total_migrate_scanned = 0;
+	cc->total_free_scanned = 0;
+	cc->nr_migratepages = 0;
+	cc->nr_freepages = 0;
+	INIT_LIST_HEAD(&cc->freepages);
+	INIT_LIST_HEAD(&cc->migratepages);
+
+	cc->migratetype = gfp_migratetype(cc->gfp_mask);
+	ret = compaction_suitable(cc->zone, cc->order, cc->alloc_flags,
+							cc->highest_zoneidx);
+	/* Compaction is likely to fail */
+	if (ret == COMPACT_SUCCESS || ret == COMPACT_SKIPPED)
+		return ret;
+
+	/* huh, compaction_suitable is returning something unexpected */
+	VM_BUG_ON(ret != COMPACT_CONTINUE);
+
+	/*
+	 * Clear pageblock skip if there were failures recently and compaction
+	 * is about to be retried after being deferred.
+	 */
+	if (compaction_restarting(cc->zone, cc->order))
+		__reset_isolation_suitable(cc->zone);
+
+	/*
+	 * Setup to move all movable pages to the end of the zone. Used cached
+	 * information on where the scanners should start (unless we explicitly
+	 * want to compact the whole zone), but check that it is initialised
+	 * by ensuring the values are within zone boundaries.
+	 */
+	cc->fast_start_pfn = 0;
+	if (cc->whole_zone) {
+		cc->migrate_pfn = start_pfn;
+		cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
+	} else {
+		cc->migrate_pfn = cc->zone->compact_cached_migrate_pfn[sync];
+		cc->free_pfn = cc->zone->compact_cached_free_pfn;
+		if (cc->free_pfn < start_pfn || cc->free_pfn >= end_pfn) {
+			cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
+			cc->zone->compact_cached_free_pfn = cc->free_pfn;
+		}
+		if (cc->migrate_pfn < start_pfn || cc->migrate_pfn >= end_pfn) {
+			cc->migrate_pfn = start_pfn;
+			cc->zone->compact_cached_migrate_pfn[0] = cc->migrate_pfn;
+			cc->zone->compact_cached_migrate_pfn[1] = cc->migrate_pfn;
+		}
+
+		if (cc->migrate_pfn <= cc->zone->compact_init_migrate_pfn)
+			cc->whole_zone = true;
+	}
+
+	last_migrated_pfn = 0;
+
+	/*
+	 * Migrate has separate cached PFNs for ASYNC and SYNC* migration on
+	 * the basis that some migrations will fail in ASYNC mode. However,
+	 * if the cached PFNs match and pageblocks are skipped due to having
+	 * no isolation candidates, then the sync state does not matter.
+	 * Until a pageblock with isolation candidates is found, keep the
+	 * cached PFNs in sync to avoid revisiting the same blocks.
+	 */
+	update_cached = !sync &&
+		cc->zone->compact_cached_migrate_pfn[0] == cc->zone->compact_cached_migrate_pfn[1];
+
+	trace_mm_compaction_begin(cc, start_pfn, end_pfn, sync);
+
+	/* lru_add_drain_all could be expensive with involving other CPUs */
+	lru_add_drain();
+
+	while ((ret = compact_finished(cc)) == COMPACT_CONTINUE) {
+		int err;
+		unsigned long iteration_start_pfn = cc->migrate_pfn;
+
+		/*
+		 * Avoid multiple rescans which can happen if a page cannot be
+		 * isolated (dirty/writeback in async mode) or if the migrated
+		 * pages are being allocated before the pageblock is cleared.
+		 * The first rescan will capture the entire pageblock for
+		 * migration. If it fails, it'll be marked skip and scanning
+		 * will proceed as normal.
+		 */
+		cc->rescan = false;
+		if (pageblock_start_pfn(last_migrated_pfn) ==
+		    pageblock_start_pfn(iteration_start_pfn)) {
+			cc->rescan = true;
+		}
+
+		switch (isolate_migratepages(cc)) {
+		case ISOLATE_ABORT:
+			ret = COMPACT_CONTENDED;
+			putback_movable_pages(&cc->migratepages);
+			cc->nr_migratepages = 0;
+			goto out;
+		case ISOLATE_NONE:
+			if (update_cached) {
+				cc->zone->compact_cached_migrate_pfn[1] =
+					cc->zone->compact_cached_migrate_pfn[0];
+			}
+
+			/*
+			 * 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:
+			update_cached = false;
+			last_migrated_pfn = iteration_start_pfn;
+		}
+
+		err = migrate_pages(&cc->migratepages, compaction_alloc,
+				compaction_free, (unsigned long)cc, cc->mode,
+				MR_COMPACTION, &nr_succeeded);
+
+		trace_mm_compaction_migratepages(cc, nr_succeeded);
+
+		/* 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 && !compact_scanners_met(cc)) {
+				ret = COMPACT_CONTENDED;
+				goto out;
+			}
+			/*
+			 * We failed to migrate at least one page in the current
+			 * order-aligned block, so skip the rest of it.
+			 */
+			if (cc->direct_compaction &&
+						(cc->mode == MIGRATE_ASYNC)) {
+				cc->migrate_pfn = block_end_pfn(
+						cc->migrate_pfn - 1, cc->order);
+				/* Draining pcplists is useless in this case */
+				last_migrated_pfn = 0;
+			}
+		}
+
+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) {
+			unsigned long current_block_start =
+				block_start_pfn(cc->migrate_pfn, cc->order);
+
+			if (last_migrated_pfn < current_block_start) {
+				lru_add_drain_cpu_zone(cc->zone);
+				/* No more flushing until we migrate again */
+				last_migrated_pfn = 0;
+			}
+		}
+
+		/* Stop if a page has been captured */
+		if (capc && capc->page) {
+			ret = COMPACT_SUCCESS;
+			break;
+		}
+	}
+
+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_start_pfn(free_pfn);
+		/*
+		 * Only go back, not forward. The cached pfn might have been
+		 * already reset to zone end in compact_finished()
+		 */
+		if (free_pfn > cc->zone->compact_cached_free_pfn)
+			cc->zone->compact_cached_free_pfn = free_pfn;
+	}
+
+	count_compact_events(COMPACTMIGRATE_SCANNED, cc->total_migrate_scanned);
+	count_compact_events(COMPACTFREE_SCANNED, cc->total_free_scanned);
+
+	trace_mm_compaction_end(cc, start_pfn, end_pfn, sync, ret);
+
+	return ret;
+}
+
+static enum compact_result compact_zone_order(struct zone *zone, int order,
+		gfp_t gfp_mask, enum compact_priority prio,
+		unsigned int alloc_flags, int highest_zoneidx,
+		struct page **capture)
+{
+	enum compact_result ret;
+	struct compact_control cc = {
+		.order = order,
+		.search_order = order,
+		.gfp_mask = gfp_mask,
+		.zone = zone,
+		.mode = (prio == COMPACT_PRIO_ASYNC) ?
+					MIGRATE_ASYNC :	MIGRATE_SYNC_LIGHT,
+		.alloc_flags = alloc_flags,
+		.highest_zoneidx = highest_zoneidx,
+		.direct_compaction = true,
+		.whole_zone = (prio == MIN_COMPACT_PRIORITY),
+		.ignore_skip_hint = (prio == MIN_COMPACT_PRIORITY),
+		.ignore_block_suitable = (prio == MIN_COMPACT_PRIORITY)
+	};
+	struct capture_control capc = {
+		.cc = &cc,
+		.page = NULL,
+	};
+
+	/*
+	 * Make sure the structs are really initialized before we expose the
+	 * capture control, in case we are interrupted and the interrupt handler
+	 * frees a page.
+	 */
+	barrier();
+	WRITE_ONCE(current->capture_control, &capc);
+
+	ret = compact_zone(&cc, &capc);
+
+	VM_BUG_ON(!list_empty(&cc.freepages));
+	VM_BUG_ON(!list_empty(&cc.migratepages));
+
+	/*
+	 * Make sure we hide capture control first before we read the captured
+	 * page pointer, otherwise an interrupt could free and capture a page
+	 * and we would leak it.
+	 */
+	WRITE_ONCE(current->capture_control, NULL);
+	*capture = READ_ONCE(capc.page);
+	/*
+	 * Technically, it is also possible that compaction is skipped but
+	 * the page is still captured out of luck(IRQ came and freed the page).
+	 * Returning COMPACT_SUCCESS in such cases helps in properly accounting
+	 * the COMPACT[STALL|FAIL] when compaction is skipped.
+	 */
+	if (*capture)
+		ret = COMPACT_SUCCESS;
+
+	return ret;
+}
+
+int sysctl_extfrag_threshold = 500;
+
+/**
+ * try_to_compact_pages - Direct compact to satisfy a high-order allocation
+ * @gfp_mask: The GFP mask of the current allocation
+ * @order: The order of the current allocation
+ * @alloc_flags: The allocation flags of the current allocation
+ * @ac: The context of current allocation
+ * @prio: Determines how hard direct compaction should try to succeed
+ * @capture: Pointer to free page created by compaction will be stored here
+ *
+ * This is the main entry point for direct page compaction.
+ */
+enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
+		unsigned int alloc_flags, const struct alloc_context *ac,
+		enum compact_priority prio, struct page **capture)
+{
+	int may_perform_io = (__force int)(gfp_mask & __GFP_IO);
+	struct zoneref *z;
+	struct zone *zone;
+	enum compact_result rc = COMPACT_SKIPPED;
+
+	/*
+	 * Check if the GFP flags allow compaction - GFP_NOIO is really
+	 * tricky context because the migration might require IO
+	 */
+	if (!may_perform_io)
+		return COMPACT_SKIPPED;
+
+	trace_mm_compaction_try_to_compact_pages(order, gfp_mask, prio);
+
+	/* Compact each zone in the list */
+	for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
+					ac->highest_zoneidx, ac->nodemask) {
+		enum compact_result status;
+
+		if (prio > MIN_COMPACT_PRIORITY
+					&& compaction_deferred(zone, order)) {
+			rc = max_t(enum compact_result, COMPACT_DEFERRED, rc);
+			continue;
+		}
+
+		status = compact_zone_order(zone, order, gfp_mask, prio,
+				alloc_flags, ac->highest_zoneidx, capture);
+		rc = max(status, rc);
+
+		/* The allocation should succeed, stop compacting */
+		if (status == COMPACT_SUCCESS) {
+			/*
+			 * 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);
+
+			break;
+		}
+
+		if (prio != COMPACT_PRIO_ASYNC && (status == COMPACT_COMPLETE ||
+					status == COMPACT_PARTIAL_SKIPPED))
+			/*
+			 * 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
+		 */
+		if ((prio == COMPACT_PRIO_ASYNC && need_resched())
+					|| fatal_signal_pending(current))
+			break;
+	}
+
+	return rc;
+}
+
+/*
+ * Compact all zones within a node till each zone's fragmentation score
+ * reaches within proactive compaction thresholds (as determined by the
+ * proactiveness tunable).
+ *
+ * It is possible that the function returns before reaching score targets
+ * due to various back-off conditions, such as, contention on per-node or
+ * per-zone locks.
+ */
+static void proactive_compact_node(pg_data_t *pgdat)
+{
+	int zoneid;
+	struct zone *zone;
+	struct compact_control cc = {
+		.order = -1,
+		.mode = MIGRATE_SYNC_LIGHT,
+		.ignore_skip_hint = true,
+		.whole_zone = true,
+		.gfp_mask = GFP_KERNEL,
+		.proactive_compaction = true,
+	};
+
+	for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
+		zone = &pgdat->node_zones[zoneid];
+		if (!populated_zone(zone))
+			continue;
+
+		cc.zone = zone;
+
+		compact_zone(&cc, NULL);
+
+		VM_BUG_ON(!list_empty(&cc.freepages));
+		VM_BUG_ON(!list_empty(&cc.migratepages));
+	}
+}
+
+/* Compact all zones within a node */
+static void compact_node(int nid)
+{
+	pg_data_t *pgdat = NODE_DATA(nid);
+	int zoneid;
+	struct zone *zone;
+	struct compact_control cc = {
+		.order = -1,
+		.mode = MIGRATE_SYNC,
+		.ignore_skip_hint = true,
+		.whole_zone = true,
+		.gfp_mask = GFP_KERNEL,
+	};
+
+
+	for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
+
+		zone = &pgdat->node_zones[zoneid];
+		if (!populated_zone(zone))
+			continue;
+
+		cc.zone = zone;
+
+		compact_zone(&cc, NULL);
+
+		VM_BUG_ON(!list_empty(&cc.freepages));
+		VM_BUG_ON(!list_empty(&cc.migratepages));
+	}
+}
+
+/* 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);
+}
+
+/*
+ * Tunable for proactive compaction. It determines how
+ * aggressively the kernel should compact memory in the
+ * background. It takes values in the range [0, 100].
+ */
+unsigned int __read_mostly sysctl_compaction_proactiveness = 20;
+
+int compaction_proactiveness_sysctl_handler(struct ctl_table *table, int write,
+		void *buffer, size_t *length, loff_t *ppos)
+{
+	int rc, nid;
+
+	rc = proc_dointvec_minmax(table, write, buffer, length, ppos);
+	if (rc)
+		return rc;
+
+	if (write && sysctl_compaction_proactiveness) {
+		for_each_online_node(nid) {
+			pg_data_t *pgdat = NODE_DATA(nid);
+
+			if (pgdat->proactive_compact_trigger)
+				continue;
+
+			pgdat->proactive_compact_trigger = true;
+			wake_up_interruptible(&pgdat->kcompactd_wait);
+		}
+	}
+
+	return 0;
+}
+
+/*
+ * This is the entry point for compacting all nodes via
+ * /proc/sys/vm/compact_memory
+ */
+int sysctl_compaction_handler(struct ctl_table *table, int write,
+			void *buffer, size_t *length, loff_t *ppos)
+{
+	if (write)
+		compact_nodes();
+
+	return 0;
+}
+
+#if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
+static ssize_t compact_store(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_WO(compact);
+
+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 */
+
+static inline bool kcompactd_work_requested(pg_data_t *pgdat)
+{
+	return pgdat->kcompactd_max_order > 0 || kthread_should_stop() ||
+		pgdat->proactive_compact_trigger;
+}
+
+static bool kcompactd_node_suitable(pg_data_t *pgdat)
+{
+	int zoneid;
+	struct zone *zone;
+	enum zone_type highest_zoneidx = pgdat->kcompactd_highest_zoneidx;
+
+	for (zoneid = 0; zoneid <= highest_zoneidx; zoneid++) {
+		zone = &pgdat->node_zones[zoneid];
+
+		if (!populated_zone(zone))
+			continue;
+
+		if (compaction_suitable(zone, pgdat->kcompactd_max_order, 0,
+					highest_zoneidx) == COMPACT_CONTINUE)
+			return true;
+	}
+
+	return false;
+}
+
+static void kcompactd_do_work(pg_data_t *pgdat)
+{
+	/*
+	 * With no special task, compact all zones so that a page of requested
+	 * order is allocatable.
+	 */
+	int zoneid;
+	struct zone *zone;
+	struct compact_control cc = {
+		.order = pgdat->kcompactd_max_order,
+		.search_order = pgdat->kcompactd_max_order,
+		.highest_zoneidx = pgdat->kcompactd_highest_zoneidx,
+		.mode = MIGRATE_SYNC_LIGHT,
+		.ignore_skip_hint = false,
+		.gfp_mask = GFP_KERNEL,
+	};
+	trace_mm_compaction_kcompactd_wake(pgdat->node_id, cc.order,
+							cc.highest_zoneidx);
+	count_compact_event(KCOMPACTD_WAKE);
+
+	for (zoneid = 0; zoneid <= cc.highest_zoneidx; zoneid++) {
+		int status;
+
+		zone = &pgdat->node_zones[zoneid];
+		if (!populated_zone(zone))
+			continue;
+
+		if (compaction_deferred(zone, cc.order))
+			continue;
+
+		if (compaction_suitable(zone, cc.order, 0, zoneid) !=
+							COMPACT_CONTINUE)
+			continue;
+
+		if (kthread_should_stop())
+			return;
+
+		cc.zone = zone;
+		status = compact_zone(&cc, NULL);
+
+		if (status == COMPACT_SUCCESS) {
+			compaction_defer_reset(zone, cc.order, false);
+		} else if (status == COMPACT_PARTIAL_SKIPPED || status == COMPACT_COMPLETE) {
+			/*
+			 * Buddy pages may become stranded on pcps that could
+			 * otherwise coalesce on the zone's free area for
+			 * order >= cc.order.  This is ratelimited by the
+			 * upcoming deferral.
+			 */
+			drain_all_pages(zone);
+
+			/*
+			 * We use sync migration mode here, so we defer like
+			 * sync direct compaction does.
+			 */
+			defer_compaction(zone, cc.order);
+		}
+
+		count_compact_events(KCOMPACTD_MIGRATE_SCANNED,
+				     cc.total_migrate_scanned);
+		count_compact_events(KCOMPACTD_FREE_SCANNED,
+				     cc.total_free_scanned);
+
+		VM_BUG_ON(!list_empty(&cc.freepages));
+		VM_BUG_ON(!list_empty(&cc.migratepages));
+	}
+
+	/*
+	 * Regardless of success, we are done until woken up next. But remember
+	 * the requested order/highest_zoneidx in case it was higher/tighter
+	 * than our current ones
+	 */
+	if (pgdat->kcompactd_max_order <= cc.order)
+		pgdat->kcompactd_max_order = 0;
+	if (pgdat->kcompactd_highest_zoneidx >= cc.highest_zoneidx)
+		pgdat->kcompactd_highest_zoneidx = pgdat->nr_zones - 1;
+}
+
+void wakeup_kcompactd(pg_data_t *pgdat, int order, int highest_zoneidx)
+{
+	if (!order)
+		return;
+
+	if (pgdat->kcompactd_max_order < order)
+		pgdat->kcompactd_max_order = order;
+
+	if (pgdat->kcompactd_highest_zoneidx > highest_zoneidx)
+		pgdat->kcompactd_highest_zoneidx = highest_zoneidx;
+
+	/*
+	 * Pairs with implicit barrier in wait_event_freezable()
+	 * such that wakeups are not missed.
+	 */
+	if (!wq_has_sleeper(&pgdat->kcompactd_wait))
+		return;
+
+	if (!kcompactd_node_suitable(pgdat))
+		return;
+
+	trace_mm_compaction_wakeup_kcompactd(pgdat->node_id, order,
+							highest_zoneidx);
+	wake_up_interruptible(&pgdat->kcompactd_wait);
+}
+
+/*
+ * The background compaction daemon, started as a kernel thread
+ * from the init process.
+ */
+static int kcompactd(void *p)
+{
+	pg_data_t *pgdat = (pg_data_t *)p;
+	struct task_struct *tsk = current;
+	long default_timeout = msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC);
+	long timeout = default_timeout;
+
+	const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
+
+	if (!cpumask_empty(cpumask))
+		set_cpus_allowed_ptr(tsk, cpumask);
+
+	set_freezable();
+
+	pgdat->kcompactd_max_order = 0;
+	pgdat->kcompactd_highest_zoneidx = pgdat->nr_zones - 1;
+
+	while (!kthread_should_stop()) {
+		unsigned long pflags;
+
+		/*
+		 * Avoid the unnecessary wakeup for proactive compaction
+		 * when it is disabled.
+		 */
+		if (!sysctl_compaction_proactiveness)
+			timeout = MAX_SCHEDULE_TIMEOUT;
+		trace_mm_compaction_kcompactd_sleep(pgdat->node_id);
+		if (wait_event_freezable_timeout(pgdat->kcompactd_wait,
+			kcompactd_work_requested(pgdat), timeout) &&
+			!pgdat->proactive_compact_trigger) {
+
+			psi_memstall_enter(&pflags);
+			kcompactd_do_work(pgdat);
+			psi_memstall_leave(&pflags);
+			/*
+			 * Reset the timeout value. The defer timeout from
+			 * proactive compaction is lost here but that is fine
+			 * as the condition of the zone changing substantionally
+			 * then carrying on with the previous defer interval is
+			 * not useful.
+			 */
+			timeout = default_timeout;
+			continue;
+		}
+
+		/*
+		 * Start the proactive work with default timeout. Based
+		 * on the fragmentation score, this timeout is updated.
+		 */
+		timeout = default_timeout;
+		if (should_proactive_compact_node(pgdat)) {
+			unsigned int prev_score, score;
+
+			prev_score = fragmentation_score_node(pgdat);
+			proactive_compact_node(pgdat);
+			score = fragmentation_score_node(pgdat);
+			/*
+			 * Defer proactive compaction if the fragmentation
+			 * score did not go down i.e. no progress made.
+			 */
+			if (unlikely(score >= prev_score))
+				timeout =
+				   default_timeout << COMPACT_MAX_DEFER_SHIFT;
+		}
+		if (unlikely(pgdat->proactive_compact_trigger))
+			pgdat->proactive_compact_trigger = false;
+	}
+
+	return 0;
+}
+
+/*
+ * This kcompactd start function will be called by init and node-hot-add.
+ * On node-hot-add, kcompactd will moved to proper cpus if cpus are hot-added.
+ */
+void kcompactd_run(int nid)
+{
+	pg_data_t *pgdat = NODE_DATA(nid);
+
+	if (pgdat->kcompactd)
+		return;
+
+	pgdat->kcompactd = kthread_run(kcompactd, pgdat, "kcompactd%d", nid);
+	if (IS_ERR(pgdat->kcompactd)) {
+		pr_err("Failed to start kcompactd on node %d\n", nid);
+		pgdat->kcompactd = NULL;
+	}
+}
+
+/*
+ * Called by memory hotplug when all memory in a node is offlined. Caller must
+ * be holding mem_hotplug_begin/done().
+ */
+void kcompactd_stop(int nid)
+{
+	struct task_struct *kcompactd = NODE_DATA(nid)->kcompactd;
+
+	if (kcompactd) {
+		kthread_stop(kcompactd);
+		NODE_DATA(nid)->kcompactd = NULL;
+	}
+}
+
+/*
+ * It's optimal to keep kcompactd on the same CPUs as their memory, but
+ * not required for correctness. So if the last cpu in a node goes
+ * away, we get changed to run anywhere: as the first one comes back,
+ * restore their cpu bindings.
+ */
+static int kcompactd_cpu_online(unsigned int cpu)
+{
+	int nid;
+
+	for_each_node_state(nid, N_MEMORY) {
+		pg_data_t *pgdat = NODE_DATA(nid);
+		const struct cpumask *mask;
+
+		mask = cpumask_of_node(pgdat->node_id);
+
+		if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
+			/* One of our CPUs online: restore mask */
+			if (pgdat->kcompactd)
+				set_cpus_allowed_ptr(pgdat->kcompactd, mask);
+	}
+	return 0;
+}
+
+static int __init kcompactd_init(void)
+{
+	int nid;
+	int ret;
+
+	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
+					"mm/compaction:online",
+					kcompactd_cpu_online, NULL);
+	if (ret < 0) {
+		pr_err("kcompactd: failed to register hotplug callbacks.\n");
+		return ret;
+	}
+
+	for_each_node_state(nid, N_MEMORY)
+		kcompactd_run(nid);
+	return 0;
+}
+subsys_initcall(kcompactd_init)
+
+#endif /* CONFIG_COMPACTION */