Adding upstream version 5.10.209.upstream/5.10.209upstream

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

1 files changed, 4322 insertions, 0 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
new file mode 100644
index 000000000..51ccd80e7
--- /dev/null
+++ b/mm/vmscan.c
@@ -0,0 +1,4322 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  linux/mm/vmscan.c
+ *
+ *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
+ *
+ *  Swap reorganised 29.12.95, Stephen Tweedie.
+ *  kswapd added: 7.1.96  sct
+ *  Removed kswapd_ctl limits, and swap out as many pages as needed
+ *  to bring the system back to freepages.high: 2.4.97, Rik van Riel.
+ *  Zone aware kswapd started 02/00, Kanoj Sarcar (kanoj@sgi.com).
+ *  Multiqueue VM started 5.8.00, Rik van Riel.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/mm.h>
+#include <linux/sched/mm.h>
+#include <linux/module.h>
+#include <linux/gfp.h>
+#include <linux/kernel_stat.h>
+#include <linux/swap.h>
+#include <linux/pagemap.h>
+#include <linux/init.h>
+#include <linux/highmem.h>
+#include <linux/vmpressure.h>
+#include <linux/vmstat.h>
+#include <linux/file.h>
+#include <linux/writeback.h>
+#include <linux/blkdev.h>
+#include <linux/buffer_head.h>	/* for try_to_release_page(),
+					buffer_heads_over_limit */
+#include <linux/mm_inline.h>
+#include <linux/backing-dev.h>
+#include <linux/rmap.h>
+#include <linux/topology.h>
+#include <linux/cpu.h>
+#include <linux/cpuset.h>
+#include <linux/compaction.h>
+#include <linux/notifier.h>
+#include <linux/rwsem.h>
+#include <linux/delay.h>
+#include <linux/kthread.h>
+#include <linux/freezer.h>
+#include <linux/memcontrol.h>
+#include <linux/delayacct.h>
+#include <linux/sysctl.h>
+#include <linux/oom.h>
+#include <linux/pagevec.h>
+#include <linux/prefetch.h>
+#include <linux/printk.h>
+#include <linux/dax.h>
+#include <linux/psi.h>
+
+#include <asm/tlbflush.h>
+#include <asm/div64.h>
+
+#include <linux/swapops.h>
+#include <linux/balloon_compaction.h>
+
+#include "internal.h"
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/vmscan.h>
+
+struct scan_control {
+	/* How many pages shrink_list() should reclaim */
+	unsigned long nr_to_reclaim;
+
+	/*
+	 * Nodemask of nodes allowed by the caller. If NULL, all nodes
+	 * are scanned.
+	 */
+	nodemask_t	*nodemask;
+
+	/*
+	 * The memory cgroup that hit its limit and as a result is the
+	 * primary target of this reclaim invocation.
+	 */
+	struct mem_cgroup *target_mem_cgroup;
+
+	/*
+	 * Scan pressure balancing between anon and file LRUs
+	 */
+	unsigned long	anon_cost;
+	unsigned long	file_cost;
+
+	/* Can active pages be deactivated as part of reclaim? */
+#define DEACTIVATE_ANON 1
+#define DEACTIVATE_FILE 2
+	unsigned int may_deactivate:2;
+	unsigned int force_deactivate:1;
+	unsigned int skipped_deactivate:1;
+
+	/* Writepage batching in laptop mode; RECLAIM_WRITE */
+	unsigned int may_writepage:1;
+
+	/* Can mapped pages be reclaimed? */
+	unsigned int may_unmap:1;
+
+	/* Can pages be swapped as part of reclaim? */
+	unsigned int may_swap:1;
+
+	/*
+	 * Cgroup memory below memory.low is protected as long as we
+	 * don't threaten to OOM. If any cgroup is reclaimed at
+	 * reduced force or passed over entirely due to its memory.low
+	 * setting (memcg_low_skipped), and nothing is reclaimed as a
+	 * result, then go back for one more cycle that reclaims the protected
+	 * memory (memcg_low_reclaim) to avert OOM.
+	 */
+	unsigned int memcg_low_reclaim:1;
+	unsigned int memcg_low_skipped:1;
+
+	unsigned int hibernation_mode:1;
+
+	/* One of the zones is ready for compaction */
+	unsigned int compaction_ready:1;
+
+	/* There is easily reclaimable cold cache in the current node */
+	unsigned int cache_trim_mode:1;
+
+	/* The file pages on the current node are dangerously low */
+	unsigned int file_is_tiny:1;
+
+	/* Allocation order */
+	s8 order;
+
+	/* Scan (total_size >> priority) pages at once */
+	s8 priority;
+
+	/* The highest zone to isolate pages for reclaim from */
+	s8 reclaim_idx;
+
+	/* This context's GFP mask */
+	gfp_t gfp_mask;
+
+	/* Incremented by the number of inactive pages that were scanned */
+	unsigned long nr_scanned;
+
+	/* Number of pages freed so far during a call to shrink_zones() */
+	unsigned long nr_reclaimed;
+
+	struct {
+		unsigned int dirty;
+		unsigned int unqueued_dirty;
+		unsigned int congested;
+		unsigned int writeback;
+		unsigned int immediate;
+		unsigned int file_taken;
+		unsigned int taken;
+	} nr;
+
+	/* for recording the reclaimed slab by now */
+	struct reclaim_state reclaim_state;
+};
+
+#ifdef ARCH_HAS_PREFETCHW
+#define prefetchw_prev_lru_page(_page, _base, _field)			\
+	do {								\
+		if ((_page)->lru.prev != _base) {			\
+			struct page *prev;				\
+									\
+			prev = lru_to_page(&(_page->lru));		\
+			prefetchw(&prev->_field);			\
+		}							\
+	} while (0)
+#else
+#define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
+#endif
+
+/*
+ * From 0 .. 200.  Higher means more swappy.
+ */
+int vm_swappiness = 60;
+
+static void set_task_reclaim_state(struct task_struct *task,
+				   struct reclaim_state *rs)
+{
+	/* Check for an overwrite */
+	WARN_ON_ONCE(rs && task->reclaim_state);
+
+	/* Check for the nulling of an already-nulled member */
+	WARN_ON_ONCE(!rs && !task->reclaim_state);
+
+	task->reclaim_state = rs;
+}
+
+static LIST_HEAD(shrinker_list);
+static DECLARE_RWSEM(shrinker_rwsem);
+
+#ifdef CONFIG_MEMCG
+/*
+ * We allow subsystems to populate their shrinker-related
+ * LRU lists before register_shrinker_prepared() is called
+ * for the shrinker, since we don't want to impose
+ * restrictions on their internal registration order.
+ * In this case shrink_slab_memcg() may find corresponding
+ * bit is set in the shrinkers map.
+ *
+ * This value is used by the function to detect registering
+ * shrinkers and to skip do_shrink_slab() calls for them.
+ */
+#define SHRINKER_REGISTERING ((struct shrinker *)~0UL)
+
+static DEFINE_IDR(shrinker_idr);
+static int shrinker_nr_max;
+
+static int prealloc_memcg_shrinker(struct shrinker *shrinker)
+{
+	int id, ret = -ENOMEM;
+
+	down_write(&shrinker_rwsem);
+	/* This may call shrinker, so it must use down_read_trylock() */
+	id = idr_alloc(&shrinker_idr, SHRINKER_REGISTERING, 0, 0, GFP_KERNEL);
+	if (id < 0)
+		goto unlock;
+
+	if (id >= shrinker_nr_max) {
+		if (memcg_expand_shrinker_maps(id)) {
+			idr_remove(&shrinker_idr, id);
+			goto unlock;
+		}
+
+		shrinker_nr_max = id + 1;
+	}
+	shrinker->id = id;
+	ret = 0;
+unlock:
+	up_write(&shrinker_rwsem);
+	return ret;
+}
+
+static void unregister_memcg_shrinker(struct shrinker *shrinker)
+{
+	int id = shrinker->id;
+
+	BUG_ON(id < 0);
+
+	down_write(&shrinker_rwsem);
+	idr_remove(&shrinker_idr, id);
+	up_write(&shrinker_rwsem);
+}
+
+static bool cgroup_reclaim(struct scan_control *sc)
+{
+	return sc->target_mem_cgroup;
+}
+
+/**
+ * writeback_throttling_sane - is the usual dirty throttling mechanism available?
+ * @sc: scan_control in question
+ *
+ * The normal page dirty throttling mechanism in balance_dirty_pages() is
+ * completely broken with the legacy memcg and direct stalling in
+ * shrink_page_list() is used for throttling instead, which lacks all the
+ * niceties such as fairness, adaptive pausing, bandwidth proportional
+ * allocation and configurability.
+ *
+ * This function tests whether the vmscan currently in progress can assume
+ * that the normal dirty throttling mechanism is operational.
+ */
+static bool writeback_throttling_sane(struct scan_control *sc)
+{
+	if (!cgroup_reclaim(sc))
+		return true;
+#ifdef CONFIG_CGROUP_WRITEBACK
+	if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
+		return true;
+#endif
+	return false;
+}
+#else
+static int prealloc_memcg_shrinker(struct shrinker *shrinker)
+{
+	return 0;
+}
+
+static void unregister_memcg_shrinker(struct shrinker *shrinker)
+{
+}
+
+static bool cgroup_reclaim(struct scan_control *sc)
+{
+	return false;
+}
+
+static bool writeback_throttling_sane(struct scan_control *sc)
+{
+	return true;
+}
+#endif
+
+/*
+ * This misses isolated pages which are not accounted for to save counters.
+ * As the data only determines if reclaim or compaction continues, it is
+ * not expected that isolated pages will be a dominating factor.
+ */
+unsigned long zone_reclaimable_pages(struct zone *zone)
+{
+	unsigned long nr;
+
+	nr = zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_FILE) +
+		zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_FILE);
+	if (get_nr_swap_pages() > 0)
+		nr += zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_ANON) +
+			zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_ANON);
+
+	return nr;
+}
+
+/**
+ * lruvec_lru_size -  Returns the number of pages on the given LRU list.
+ * @lruvec: lru vector
+ * @lru: lru to use
+ * @zone_idx: zones to consider (use MAX_NR_ZONES for the whole LRU list)
+ */
+unsigned long lruvec_lru_size(struct lruvec *lruvec, enum lru_list lru, int zone_idx)
+{
+	unsigned long size = 0;
+	int zid;
+
+	for (zid = 0; zid <= zone_idx && zid < MAX_NR_ZONES; zid++) {
+		struct zone *zone = &lruvec_pgdat(lruvec)->node_zones[zid];
+
+		if (!managed_zone(zone))
+			continue;
+
+		if (!mem_cgroup_disabled())
+			size += mem_cgroup_get_zone_lru_size(lruvec, lru, zid);
+		else
+			size += zone_page_state(zone, NR_ZONE_LRU_BASE + lru);
+	}
+	return size;
+}
+
+/*
+ * Add a shrinker callback to be called from the vm.
+ */
+int prealloc_shrinker(struct shrinker *shrinker)
+{
+	unsigned int size = sizeof(*shrinker->nr_deferred);
+
+	if (shrinker->flags & SHRINKER_NUMA_AWARE)
+		size *= nr_node_ids;
+
+	shrinker->nr_deferred = kzalloc(size, GFP_KERNEL);
+	if (!shrinker->nr_deferred)
+		return -ENOMEM;
+
+	if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
+		if (prealloc_memcg_shrinker(shrinker))
+			goto free_deferred;
+	}
+
+	return 0;
+
+free_deferred:
+	kfree(shrinker->nr_deferred);
+	shrinker->nr_deferred = NULL;
+	return -ENOMEM;
+}
+
+void free_prealloced_shrinker(struct shrinker *shrinker)
+{
+	if (!shrinker->nr_deferred)
+		return;
+
+	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
+		unregister_memcg_shrinker(shrinker);
+
+	kfree(shrinker->nr_deferred);
+	shrinker->nr_deferred = NULL;
+}
+
+void register_shrinker_prepared(struct shrinker *shrinker)
+{
+	down_write(&shrinker_rwsem);
+	list_add_tail(&shrinker->list, &shrinker_list);
+#ifdef CONFIG_MEMCG
+	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
+		idr_replace(&shrinker_idr, shrinker, shrinker->id);
+#endif
+	up_write(&shrinker_rwsem);
+}
+
+int register_shrinker(struct shrinker *shrinker)
+{
+	int err = prealloc_shrinker(shrinker);
+
+	if (err)
+		return err;
+	register_shrinker_prepared(shrinker);
+	return 0;
+}
+EXPORT_SYMBOL(register_shrinker);
+
+/*
+ * Remove one
+ */
+void unregister_shrinker(struct shrinker *shrinker)
+{
+	if (!shrinker->nr_deferred)
+		return;
+	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
+		unregister_memcg_shrinker(shrinker);
+	down_write(&shrinker_rwsem);
+	list_del(&shrinker->list);
+	up_write(&shrinker_rwsem);
+	kfree(shrinker->nr_deferred);
+	shrinker->nr_deferred = NULL;
+}
+EXPORT_SYMBOL(unregister_shrinker);
+
+#define SHRINK_BATCH 128
+
+static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
+				    struct shrinker *shrinker, int priority)
+{
+	unsigned long freed = 0;
+	unsigned long long delta;
+	long total_scan;
+	long freeable;
+	long nr;
+	long new_nr;
+	int nid = shrinkctl->nid;
+	long batch_size = shrinker->batch ? shrinker->batch
+					  : SHRINK_BATCH;
+	long scanned = 0, next_deferred;
+
+	if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
+		nid = 0;
+
+	freeable = shrinker->count_objects(shrinker, shrinkctl);
+	if (freeable == 0 || freeable == SHRINK_EMPTY)
+		return freeable;
+
+	/*
+	 * copy the current shrinker scan count into a local variable
+	 * and zero it so that other concurrent shrinker invocations
+	 * don't also do this scanning work.
+	 */
+	nr = atomic_long_xchg(&shrinker->nr_deferred[nid], 0);
+
+	total_scan = nr;
+	if (shrinker->seeks) {
+		delta = freeable >> priority;
+		delta *= 4;
+		do_div(delta, shrinker->seeks);
+	} else {
+		/*
+		 * These objects don't require any IO to create. Trim
+		 * them aggressively under memory pressure to keep
+		 * them from causing refetches in the IO caches.
+		 */
+		delta = freeable / 2;
+	}
+
+	total_scan += delta;
+	if (total_scan < 0) {
+		pr_err("shrink_slab: %pS negative objects to delete nr=%ld\n",
+		       shrinker->scan_objects, total_scan);
+		total_scan = freeable;
+		next_deferred = nr;
+	} else
+		next_deferred = total_scan;
+
+	/*
+	 * We need to avoid excessive windup on filesystem shrinkers
+	 * due to large numbers of GFP_NOFS allocations causing the
+	 * shrinkers to return -1 all the time. This results in a large
+	 * nr being built up so when a shrink that can do some work
+	 * comes along it empties the entire cache due to nr >>>
+	 * freeable. This is bad for sustaining a working set in
+	 * memory.
+	 *
+	 * Hence only allow the shrinker to scan the entire cache when
+	 * a large delta change is calculated directly.
+	 */
+	if (delta < freeable / 4)
+		total_scan = min(total_scan, freeable / 2);
+
+	/*
+	 * Avoid risking looping forever due to too large nr value:
+	 * never try to free more than twice the estimate number of
+	 * freeable entries.
+	 */
+	if (total_scan > freeable * 2)
+		total_scan = freeable * 2;
+
+	trace_mm_shrink_slab_start(shrinker, shrinkctl, nr,
+				   freeable, delta, total_scan, priority);
+
+	/*
+	 * Normally, we should not scan less than batch_size objects in one
+	 * pass to avoid too frequent shrinker calls, but if the slab has less
+	 * than batch_size objects in total and we are really tight on memory,
+	 * we will try to reclaim all available objects, otherwise we can end
+	 * up failing allocations although there are plenty of reclaimable
+	 * objects spread over several slabs with usage less than the
+	 * batch_size.
+	 *
+	 * We detect the "tight on memory" situations by looking at the total
+	 * number of objects we want to scan (total_scan). If it is greater
+	 * than the total number of objects on slab (freeable), we must be
+	 * scanning at high prio and therefore should try to reclaim as much as
+	 * possible.
+	 */
+	while (total_scan >= batch_size ||
+	       total_scan >= freeable) {
+		unsigned long ret;
+		unsigned long nr_to_scan = min(batch_size, total_scan);
+
+		shrinkctl->nr_to_scan = nr_to_scan;
+		shrinkctl->nr_scanned = nr_to_scan;
+		ret = shrinker->scan_objects(shrinker, shrinkctl);
+		if (ret == SHRINK_STOP)
+			break;
+		freed += ret;
+
+		count_vm_events(SLABS_SCANNED, shrinkctl->nr_scanned);
+		total_scan -= shrinkctl->nr_scanned;
+		scanned += shrinkctl->nr_scanned;
+
+		cond_resched();
+	}
+
+	if (next_deferred >= scanned)
+		next_deferred -= scanned;
+	else
+		next_deferred = 0;
+	/*
+	 * move the unused scan count back into the shrinker in a
+	 * manner that handles concurrent updates. If we exhausted the
+	 * scan, there is no need to do an update.
+	 */
+	if (next_deferred > 0)
+		new_nr = atomic_long_add_return(next_deferred,
+						&shrinker->nr_deferred[nid]);
+	else
+		new_nr = atomic_long_read(&shrinker->nr_deferred[nid]);
+
+	trace_mm_shrink_slab_end(shrinker, nid, freed, nr, new_nr, total_scan);
+	return freed;
+}
+
+#ifdef CONFIG_MEMCG
+static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
+			struct mem_cgroup *memcg, int priority)
+{
+	struct memcg_shrinker_map *map;
+	unsigned long ret, freed = 0;
+	int i;
+
+	if (!mem_cgroup_online(memcg))
+		return 0;
+
+	if (!down_read_trylock(&shrinker_rwsem))
+		return 0;
+
+	map = rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_map,
+					true);
+	if (unlikely(!map))
+		goto unlock;
+
+	for_each_set_bit(i, map->map, shrinker_nr_max) {
+		struct shrink_control sc = {
+			.gfp_mask = gfp_mask,
+			.nid = nid,
+			.memcg = memcg,
+		};
+		struct shrinker *shrinker;
+
+		shrinker = idr_find(&shrinker_idr, i);
+		if (unlikely(!shrinker || shrinker == SHRINKER_REGISTERING)) {
+			if (!shrinker)
+				clear_bit(i, map->map);
+			continue;
+		}
+
+		/* Call non-slab shrinkers even though kmem is disabled */
+		if (!memcg_kmem_enabled() &&
+		    !(shrinker->flags & SHRINKER_NONSLAB))
+			continue;
+
+		ret = do_shrink_slab(&sc, shrinker, priority);
+		if (ret == SHRINK_EMPTY) {
+			clear_bit(i, map->map);
+			/*
+			 * After the shrinker reported that it had no objects to
+			 * free, but before we cleared the corresponding bit in
+			 * the memcg shrinker map, a new object might have been
+			 * added. To make sure, we have the bit set in this
+			 * case, we invoke the shrinker one more time and reset
+			 * the bit if it reports that it is not empty anymore.
+			 * The memory barrier here pairs with the barrier in
+			 * memcg_set_shrinker_bit():
+			 *
+			 * list_lru_add()     shrink_slab_memcg()
+			 *   list_add_tail()    clear_bit()
+			 *   <MB>               <MB>
+			 *   set_bit()          do_shrink_slab()
+			 */
+			smp_mb__after_atomic();
+			ret = do_shrink_slab(&sc, shrinker, priority);
+			if (ret == SHRINK_EMPTY)
+				ret = 0;
+			else
+				memcg_set_shrinker_bit(memcg, nid, i);
+		}
+		freed += ret;
+
+		if (rwsem_is_contended(&shrinker_rwsem)) {
+			freed = freed ? : 1;
+			break;
+		}
+	}
+unlock:
+	up_read(&shrinker_rwsem);
+	return freed;
+}
+#else /* CONFIG_MEMCG */
+static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
+			struct mem_cgroup *memcg, int priority)
+{
+	return 0;
+}
+#endif /* CONFIG_MEMCG */
+
+/**
+ * shrink_slab - shrink slab caches
+ * @gfp_mask: allocation context
+ * @nid: node whose slab caches to target
+ * @memcg: memory cgroup whose slab caches to target
+ * @priority: the reclaim priority
+ *
+ * Call the shrink functions to age shrinkable caches.
+ *
+ * @nid is passed along to shrinkers with SHRINKER_NUMA_AWARE set,
+ * unaware shrinkers will receive a node id of 0 instead.
+ *
+ * @memcg specifies the memory cgroup to target. Unaware shrinkers
+ * are called only if it is the root cgroup.
+ *
+ * @priority is sc->priority, we take the number of objects and >> by priority
+ * in order to get the scan target.
+ *
+ * Returns the number of reclaimed slab objects.
+ */
+static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
+				 struct mem_cgroup *memcg,
+				 int priority)
+{
+	unsigned long ret, freed = 0;
+	struct shrinker *shrinker;
+
+	/*
+	 * The root memcg might be allocated even though memcg is disabled
+	 * via "cgroup_disable=memory" boot parameter.  This could make
+	 * mem_cgroup_is_root() return false, then just run memcg slab
+	 * shrink, but skip global shrink.  This may result in premature
+	 * oom.
+	 */
+	if (!mem_cgroup_disabled() && !mem_cgroup_is_root(memcg))
+		return shrink_slab_memcg(gfp_mask, nid, memcg, priority);
+
+	if (!down_read_trylock(&shrinker_rwsem))
+		goto out;
+
+	list_for_each_entry(shrinker, &shrinker_list, list) {
+		struct shrink_control sc = {
+			.gfp_mask = gfp_mask,
+			.nid = nid,
+			.memcg = memcg,
+		};
+
+		ret = do_shrink_slab(&sc, shrinker, priority);
+		if (ret == SHRINK_EMPTY)
+			ret = 0;
+		freed += ret;
+		/*
+		 * Bail out if someone want to register a new shrinker to
+		 * prevent the registration from being stalled for long periods
+		 * by parallel ongoing shrinking.
+		 */
+		if (rwsem_is_contended(&shrinker_rwsem)) {
+			freed = freed ? : 1;
+			break;
+		}
+	}
+
+	up_read(&shrinker_rwsem);
+out:
+	cond_resched();
+	return freed;
+}
+
+void drop_slab_node(int nid)
+{
+	unsigned long freed;
+
+	do {
+		struct mem_cgroup *memcg = NULL;
+
+		if (fatal_signal_pending(current))
+			return;
+
+		freed = 0;
+		memcg = mem_cgroup_iter(NULL, NULL, NULL);
+		do {
+			freed += shrink_slab(GFP_KERNEL, nid, memcg, 0);
+		} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
+	} while (freed > 10);
+}
+
+void drop_slab(void)
+{
+	int nid;
+
+	for_each_online_node(nid)
+		drop_slab_node(nid);
+}
+
+static inline int is_page_cache_freeable(struct page *page)
+{
+	/*
+	 * A freeable page cache page is referenced only by the caller
+	 * that isolated the page, the page cache and optional buffer
+	 * heads at page->private.
+	 */
+	int page_cache_pins = thp_nr_pages(page);
+	return page_count(page) - page_has_private(page) == 1 + page_cache_pins;
+}
+
+static int may_write_to_inode(struct inode *inode)
+{
+	if (current->flags & PF_SWAPWRITE)
+		return 1;
+	if (!inode_write_congested(inode))
+		return 1;
+	if (inode_to_bdi(inode) == current->backing_dev_info)
+		return 1;
+	return 0;
+}
+
+/*
+ * We detected a synchronous write error writing a page out.  Probably
+ * -ENOSPC.  We need to propagate that into the address_space for a subsequent
+ * fsync(), msync() or close().
+ *
+ * The tricky part is that after writepage we cannot touch the mapping: nothing
+ * prevents it from being freed up.  But we have a ref on the page and once
+ * that page is locked, the mapping is pinned.
+ *
+ * We're allowed to run sleeping lock_page() here because we know the caller has
+ * __GFP_FS.
+ */
+static void handle_write_error(struct address_space *mapping,
+				struct page *page, int error)
+{
+	lock_page(page);
+	if (page_mapping(page) == mapping)
+		mapping_set_error(mapping, error);
+	unlock_page(page);
+}
+
+/* possible outcome of pageout() */
+typedef enum {
+	/* failed to write page out, page is locked */
+	PAGE_KEEP,
+	/* move page to the active list, page is locked */
+	PAGE_ACTIVATE,
+	/* page has been sent to the disk successfully, page is unlocked */
+	PAGE_SUCCESS,
+	/* page is clean and locked */
+	PAGE_CLEAN,
+} pageout_t;
+
+/*
+ * pageout is called by shrink_page_list() for each dirty page.
+ * Calls ->writepage().
+ */
+static pageout_t pageout(struct page *page, struct address_space *mapping)
+{
+	/*
+	 * If the page is dirty, only perform writeback if that write
+	 * will be non-blocking.  To prevent this allocation from being
+	 * stalled by pagecache activity.  But note that there may be
+	 * stalls if we need to run get_block().  We could test
+	 * PagePrivate for that.
+	 *
+	 * If this process is currently in __generic_file_write_iter() against
+	 * this page's queue, we can perform writeback even if that
+	 * will block.
+	 *
+	 * If the page is swapcache, write it back even if that would
+	 * block, for some throttling. This happens by accident, because
+	 * swap_backing_dev_info is bust: it doesn't reflect the
+	 * congestion state of the swapdevs.  Easy to fix, if needed.
+	 */
+	if (!is_page_cache_freeable(page))
+		return PAGE_KEEP;
+	if (!mapping) {
+		/*
+		 * Some data journaling orphaned pages can have
+		 * page->mapping == NULL while being dirty with clean buffers.
+		 */
+		if (page_has_private(page)) {
+			if (try_to_free_buffers(page)) {
+				ClearPageDirty(page);
+				pr_info("%s: orphaned page\n", __func__);
+				return PAGE_CLEAN;
+			}
+		}
+		return PAGE_KEEP;
+	}
+	if (mapping->a_ops->writepage == NULL)
+		return PAGE_ACTIVATE;
+	if (!may_write_to_inode(mapping->host))
+		return PAGE_KEEP;
+
+	if (clear_page_dirty_for_io(page)) {
+		int res;
+		struct writeback_control wbc = {
+			.sync_mode = WB_SYNC_NONE,
+			.nr_to_write = SWAP_CLUSTER_MAX,
+			.range_start = 0,
+			.range_end = LLONG_MAX,
+			.for_reclaim = 1,
+		};
+
+		SetPageReclaim(page);
+		res = mapping->a_ops->writepage(page, &wbc);
+		if (res < 0)
+			handle_write_error(mapping, page, res);
+		if (res == AOP_WRITEPAGE_ACTIVATE) {
+			ClearPageReclaim(page);
+			return PAGE_ACTIVATE;
+		}
+
+		if (!PageWriteback(page)) {
+			/* synchronous write or broken a_ops? */
+			ClearPageReclaim(page);
+		}
+		trace_mm_vmscan_writepage(page);
+		inc_node_page_state(page, NR_VMSCAN_WRITE);
+		return PAGE_SUCCESS;
+	}
+
+	return PAGE_CLEAN;
+}
+
+/*
+ * Same as remove_mapping, but if the page is removed from the mapping, it
+ * gets returned with a refcount of 0.
+ */
+static int __remove_mapping(struct address_space *mapping, struct page *page,
+			    bool reclaimed, struct mem_cgroup *target_memcg)
+{
+	unsigned long flags;
+	int refcount;
+	void *shadow = NULL;
+
+	BUG_ON(!PageLocked(page));
+	BUG_ON(mapping != page_mapping(page));
+
+	xa_lock_irqsave(&mapping->i_pages, flags);
+	/*
+	 * The non racy check for a busy page.
+	 *
+	 * Must be careful with the order of the tests. When someone has
+	 * a ref to the page, it may be possible that they dirty it then
+	 * drop the reference. So if PageDirty is tested before page_count
+	 * here, then the following race may occur:
+	 *
+	 * get_user_pages(&page);
+	 * [user mapping goes away]
+	 * write_to(page);
+	 *				!PageDirty(page)    [good]
+	 * SetPageDirty(page);
+	 * put_page(page);
+	 *				!page_count(page)   [good, discard it]
+	 *
+	 * [oops, our write_to data is lost]
+	 *
+	 * Reversing the order of the tests ensures such a situation cannot
+	 * escape unnoticed. The smp_rmb is needed to ensure the page->flags
+	 * load is not satisfied before that of page->_refcount.
+	 *
+	 * Note that if SetPageDirty is always performed via set_page_dirty,
+	 * and thus under the i_pages lock, then this ordering is not required.
+	 */
+	refcount = 1 + compound_nr(page);
+	if (!page_ref_freeze(page, refcount))
+		goto cannot_free;
+	/* note: atomic_cmpxchg in page_ref_freeze provides the smp_rmb */
+	if (unlikely(PageDirty(page))) {
+		page_ref_unfreeze(page, refcount);
+		goto cannot_free;
+	}
+
+	if (PageSwapCache(page)) {
+		swp_entry_t swap = { .val = page_private(page) };
+		mem_cgroup_swapout(page, swap);
+		if (reclaimed && !mapping_exiting(mapping))
+			shadow = workingset_eviction(page, target_memcg);
+		__delete_from_swap_cache(page, swap, shadow);
+		xa_unlock_irqrestore(&mapping->i_pages, flags);
+		put_swap_page(page, swap);
+	} else {
+		void (*freepage)(struct page *);
+
+		freepage = mapping->a_ops->freepage;
+		/*
+		 * Remember a shadow entry for reclaimed file cache in
+		 * order to detect refaults, thus thrashing, later on.
+		 *
+		 * But don't store shadows in an address space that is
+		 * already exiting.  This is not just an optimization,
+		 * inode reclaim needs to empty out the radix tree or
+		 * the nodes are lost.  Don't plant shadows behind its
+		 * back.
+		 *
+		 * We also don't store shadows for DAX mappings because the
+		 * only page cache pages found in these are zero pages
+		 * covering holes, and because we don't want to mix DAX
+		 * exceptional entries and shadow exceptional entries in the
+		 * same address_space.
+		 */
+		if (reclaimed && page_is_file_lru(page) &&
+		    !mapping_exiting(mapping) && !dax_mapping(mapping))
+			shadow = workingset_eviction(page, target_memcg);
+		__delete_from_page_cache(page, shadow);
+		xa_unlock_irqrestore(&mapping->i_pages, flags);
+
+		if (freepage != NULL)
+			freepage(page);
+	}
+
+	return 1;
+
+cannot_free:
+	xa_unlock_irqrestore(&mapping->i_pages, flags);
+	return 0;
+}
+
+/*
+ * Attempt to detach a locked page from its ->mapping.  If it is dirty or if
+ * someone else has a ref on the page, abort and return 0.  If it was
+ * successfully detached, return 1.  Assumes the caller has a single ref on
+ * this page.
+ */
+int remove_mapping(struct address_space *mapping, struct page *page)
+{
+	if (__remove_mapping(mapping, page, false, NULL)) {
+		/*
+		 * Unfreezing the refcount with 1 rather than 2 effectively
+		 * drops the pagecache ref for us without requiring another
+		 * atomic operation.
+		 */
+		page_ref_unfreeze(page, 1);
+		return 1;
+	}
+	return 0;
+}
+
+/**
+ * putback_lru_page - put previously isolated page onto appropriate LRU list
+ * @page: page to be put back to appropriate lru list
+ *
+ * Add previously isolated @page to appropriate LRU list.
+ * Page may still be unevictable for other reasons.
+ *
+ * lru_lock must not be held, interrupts must be enabled.
+ */
+void putback_lru_page(struct page *page)
+{
+	lru_cache_add(page);
+	put_page(page);		/* drop ref from isolate */
+}
+
+enum page_references {
+	PAGEREF_RECLAIM,
+	PAGEREF_RECLAIM_CLEAN,
+	PAGEREF_KEEP,
+	PAGEREF_ACTIVATE,
+};
+
+static enum page_references page_check_references(struct page *page,
+						  struct scan_control *sc)
+{
+	int referenced_ptes, referenced_page;
+	unsigned long vm_flags;
+
+	referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup,
+					  &vm_flags);
+	referenced_page = TestClearPageReferenced(page);
+
+	/*
+	 * Mlock lost the isolation race with us.  Let try_to_unmap()
+	 * move the page to the unevictable list.
+	 */
+	if (vm_flags & VM_LOCKED)
+		return PAGEREF_RECLAIM;
+
+	if (referenced_ptes) {
+		/*
+		 * All mapped pages start out with page table
+		 * references from the instantiating fault, so we need
+		 * to look twice if a mapped file page is used more
+		 * than once.
+		 *
+		 * Mark it and spare it for another trip around the
+		 * inactive list.  Another page table reference will
+		 * lead to its activation.
+		 *
+		 * Note: the mark is set for activated pages as well
+		 * so that recently deactivated but used pages are
+		 * quickly recovered.
+		 */
+		SetPageReferenced(page);
+
+		if (referenced_page || referenced_ptes > 1)
+			return PAGEREF_ACTIVATE;
+
+		/*
+		 * Activate file-backed executable pages after first usage.
+		 */
+		if ((vm_flags & VM_EXEC) && !PageSwapBacked(page))
+			return PAGEREF_ACTIVATE;
+
+		return PAGEREF_KEEP;
+	}
+
+	/* Reclaim if clean, defer dirty pages to writeback */
+	if (referenced_page && !PageSwapBacked(page))
+		return PAGEREF_RECLAIM_CLEAN;
+
+	return PAGEREF_RECLAIM;
+}
+
+/* Check if a page is dirty or under writeback */
+static void page_check_dirty_writeback(struct page *page,
+				       bool *dirty, bool *writeback)
+{
+	struct address_space *mapping;
+
+	/*
+	 * Anonymous pages are not handled by flushers and must be written
+	 * from reclaim context. Do not stall reclaim based on them
+	 */
+	if (!page_is_file_lru(page) ||
+	    (PageAnon(page) && !PageSwapBacked(page))) {
+		*dirty = false;
+		*writeback = false;
+		return;
+	}
+
+	/* By default assume that the page flags are accurate */
+	*dirty = PageDirty(page);
+	*writeback = PageWriteback(page);
+
+	/* Verify dirty/writeback state if the filesystem supports it */
+	if (!page_has_private(page))
+		return;
+
+	mapping = page_mapping(page);
+	if (mapping && mapping->a_ops->is_dirty_writeback)
+		mapping->a_ops->is_dirty_writeback(page, dirty, writeback);
+}
+
+/*
+ * shrink_page_list() returns the number of reclaimed pages
+ */
+static unsigned int shrink_page_list(struct list_head *page_list,
+				     struct pglist_data *pgdat,
+				     struct scan_control *sc,
+				     struct reclaim_stat *stat,
+				     bool ignore_references)
+{
+	LIST_HEAD(ret_pages);
+	LIST_HEAD(free_pages);
+	unsigned int nr_reclaimed = 0;
+	unsigned int pgactivate = 0;
+
+	memset(stat, 0, sizeof(*stat));
+	cond_resched();
+
+	while (!list_empty(page_list)) {
+		struct address_space *mapping;
+		struct page *page;
+		enum page_references references = PAGEREF_RECLAIM;
+		bool dirty, writeback, may_enter_fs;
+		unsigned int nr_pages;
+
+		cond_resched();
+
+		page = lru_to_page(page_list);
+		list_del(&page->lru);
+
+		if (!trylock_page(page))
+			goto keep;
+
+		VM_BUG_ON_PAGE(PageActive(page), page);
+
+		nr_pages = compound_nr(page);
+
+		/* Account the number of base pages even though THP */
+		sc->nr_scanned += nr_pages;
+
+		if (unlikely(!page_evictable(page)))
+			goto activate_locked;
+
+		if (!sc->may_unmap && page_mapped(page))
+			goto keep_locked;
+
+		may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
+			(PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
+
+		/*
+		 * The number of dirty pages determines if a node is marked
+		 * reclaim_congested which affects wait_iff_congested. kswapd
+		 * will stall and start writing pages if the tail of the LRU
+		 * is all dirty unqueued pages.
+		 */
+		page_check_dirty_writeback(page, &dirty, &writeback);
+		if (dirty || writeback)
+			stat->nr_dirty++;
+
+		if (dirty && !writeback)
+			stat->nr_unqueued_dirty++;
+
+		/*
+		 * Treat this page as congested if the underlying BDI is or if
+		 * pages are cycling through the LRU so quickly that the
+		 * pages marked for immediate reclaim are making it to the
+		 * end of the LRU a second time.
+		 */
+		mapping = page_mapping(page);
+		if (((dirty || writeback) && mapping &&
+		     inode_write_congested(mapping->host)) ||
+		    (writeback && PageReclaim(page)))
+			stat->nr_congested++;
+
+		/*
+		 * If a page at the tail of the LRU is under writeback, there
+		 * are three cases to consider.
+		 *
+		 * 1) If reclaim is encountering an excessive number of pages
+		 *    under writeback and this page is both under writeback and
+		 *    PageReclaim then it indicates that pages are being queued
+		 *    for IO but are being recycled through the LRU before the
+		 *    IO can complete. Waiting on the page itself risks an
+		 *    indefinite stall if it is impossible to writeback the
+		 *    page due to IO error or disconnected storage so instead
+		 *    note that the LRU is being scanned too quickly and the
+		 *    caller can stall after page list has been processed.
+		 *
+		 * 2) Global or new memcg reclaim encounters a page that is
+		 *    not marked for immediate reclaim, or the caller does not
+		 *    have __GFP_FS (or __GFP_IO if it's simply going to swap,
+		 *    not to fs). In this case mark the page for immediate
+		 *    reclaim and continue scanning.
+		 *
+		 *    Require may_enter_fs because we would wait on fs, which
+		 *    may not have submitted IO yet. And the loop driver might
+		 *    enter reclaim, and deadlock if it waits on a page for
+		 *    which it is needed to do the write (loop masks off
+		 *    __GFP_IO|__GFP_FS for this reason); but more thought
+		 *    would probably show more reasons.
+		 *
+		 * 3) Legacy memcg encounters a page that is already marked
+		 *    PageReclaim. memcg does not have any dirty pages
+		 *    throttling so we could easily OOM just because too many
+		 *    pages are in writeback and there is nothing else to
+		 *    reclaim. Wait for the writeback to complete.
+		 *
+		 * In cases 1) and 2) we activate the pages to get them out of
+		 * the way while we continue scanning for clean pages on the
+		 * inactive list and refilling from the active list. The
+		 * observation here is that waiting for disk writes is more
+		 * expensive than potentially causing reloads down the line.
+		 * Since they're marked for immediate reclaim, they won't put
+		 * memory pressure on the cache working set any longer than it
+		 * takes to write them to disk.
+		 */
+		if (PageWriteback(page)) {
+			/* Case 1 above */
+			if (current_is_kswapd() &&
+			    PageReclaim(page) &&
+			    test_bit(PGDAT_WRITEBACK, &pgdat->flags)) {
+				stat->nr_immediate++;
+				goto activate_locked;
+
+			/* Case 2 above */
+			} else if (writeback_throttling_sane(sc) ||
+			    !PageReclaim(page) || !may_enter_fs) {
+				/*
+				 * This is slightly racy - end_page_writeback()
+				 * might have just cleared PageReclaim, then
+				 * setting PageReclaim here end up interpreted
+				 * as PageReadahead - but that does not matter
+				 * enough to care.  What we do want is for this
+				 * page to have PageReclaim set next time memcg
+				 * reclaim reaches the tests above, so it will
+				 * then wait_on_page_writeback() to avoid OOM;
+				 * and it's also appropriate in global reclaim.
+				 */
+				SetPageReclaim(page);
+				stat->nr_writeback++;
+				goto activate_locked;
+
+			/* Case 3 above */
+			} else {
+				unlock_page(page);
+				wait_on_page_writeback(page);
+				/* then go back and try same page again */
+				list_add_tail(&page->lru, page_list);
+				continue;
+			}
+		}
+
+		if (!ignore_references)
+			references = page_check_references(page, sc);
+
+		switch (references) {
+		case PAGEREF_ACTIVATE:
+			goto activate_locked;
+		case PAGEREF_KEEP:
+			stat->nr_ref_keep += nr_pages;
+			goto keep_locked;
+		case PAGEREF_RECLAIM:
+		case PAGEREF_RECLAIM_CLEAN:
+			; /* try to reclaim the page below */
+		}
+
+		/*
+		 * Anonymous process memory has backing store?
+		 * Try to allocate it some swap space here.
+		 * Lazyfree page could be freed directly
+		 */
+		if (PageAnon(page) && PageSwapBacked(page)) {
+			if (!PageSwapCache(page)) {
+				if (!(sc->gfp_mask & __GFP_IO))
+					goto keep_locked;
+				if (page_maybe_dma_pinned(page))
+					goto keep_locked;
+				if (PageTransHuge(page)) {
+					/* cannot split THP, skip it */
+					if (!can_split_huge_page(page, NULL))
+						goto activate_locked;
+					/*
+					 * Split pages without a PMD map right
+					 * away. Chances are some or all of the
+					 * tail pages can be freed without IO.
+					 */
+					if (!compound_mapcount(page) &&
+					    split_huge_page_to_list(page,
+								    page_list))
+						goto activate_locked;
+				}
+				if (!add_to_swap(page)) {
+					if (!PageTransHuge(page))
+						goto activate_locked_split;
+					/* Fallback to swap normal pages */
+					if (split_huge_page_to_list(page,
+								    page_list))
+						goto activate_locked;
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+					count_vm_event(THP_SWPOUT_FALLBACK);
+#endif
+					if (!add_to_swap(page))
+						goto activate_locked_split;
+				}
+
+				may_enter_fs = true;
+
+				/* Adding to swap updated mapping */
+				mapping = page_mapping(page);
+			}
+		} else if (unlikely(PageTransHuge(page))) {
+			/* Split file THP */
+			if (split_huge_page_to_list(page, page_list))
+				goto keep_locked;
+		}
+
+		/*
+		 * THP may get split above, need minus tail pages and update
+		 * nr_pages to avoid accounting tail pages twice.
+		 *
+		 * The tail pages that are added into swap cache successfully
+		 * reach here.
+		 */
+		if ((nr_pages > 1) && !PageTransHuge(page)) {
+			sc->nr_scanned -= (nr_pages - 1);
+			nr_pages = 1;
+		}
+
+		/*
+		 * The page is mapped into the page tables of one or more
+		 * processes. Try to unmap it here.
+		 */
+		if (page_mapped(page)) {
+			enum ttu_flags flags = TTU_BATCH_FLUSH;
+			bool was_swapbacked = PageSwapBacked(page);
+
+			if (unlikely(PageTransHuge(page)))
+				flags |= TTU_SPLIT_HUGE_PMD;
+
+			if (!try_to_unmap(page, flags)) {
+				stat->nr_unmap_fail += nr_pages;
+				if (!was_swapbacked && PageSwapBacked(page))
+					stat->nr_lazyfree_fail += nr_pages;
+				goto activate_locked;
+			}
+		}
+
+		if (PageDirty(page)) {
+			/*
+			 * Only kswapd can writeback filesystem pages
+			 * to avoid risk of stack overflow. But avoid
+			 * injecting inefficient single-page IO into
+			 * flusher writeback as much as possible: only
+			 * write pages when we've encountered many
+			 * dirty pages, and when we've already scanned
+			 * the rest of the LRU for clean pages and see
+			 * the same dirty pages again (PageReclaim).
+			 */
+			if (page_is_file_lru(page) &&
+			    (!current_is_kswapd() || !PageReclaim(page) ||
+			     !test_bit(PGDAT_DIRTY, &pgdat->flags))) {
+				/*
+				 * Immediately reclaim when written back.
+				 * Similar in principal to deactivate_page()
+				 * except we already have the page isolated
+				 * and know it's dirty
+				 */
+				inc_node_page_state(page, NR_VMSCAN_IMMEDIATE);
+				SetPageReclaim(page);
+
+				goto activate_locked;
+			}
+
+			if (references == PAGEREF_RECLAIM_CLEAN)
+				goto keep_locked;
+			if (!may_enter_fs)
+				goto keep_locked;
+			if (!sc->may_writepage)
+				goto keep_locked;
+
+			/*
+			 * Page is dirty. Flush the TLB if a writable entry
+			 * potentially exists to avoid CPU writes after IO
+			 * starts and then write it out here.
+			 */
+			try_to_unmap_flush_dirty();
+			switch (pageout(page, mapping)) {
+			case PAGE_KEEP:
+				goto keep_locked;
+			case PAGE_ACTIVATE:
+				goto activate_locked;
+			case PAGE_SUCCESS:
+				stat->nr_pageout += thp_nr_pages(page);
+
+				if (PageWriteback(page))
+					goto keep;
+				if (PageDirty(page))
+					goto keep;
+
+				/*
+				 * A synchronous write - probably a ramdisk.  Go
+				 * ahead and try to reclaim the page.
+				 */
+				if (!trylock_page(page))
+					goto keep;
+				if (PageDirty(page) || PageWriteback(page))
+					goto keep_locked;
+				mapping = page_mapping(page);
+			case PAGE_CLEAN:
+				; /* try to free the page below */
+			}
+		}
+
+		/*
+		 * If the page has buffers, try to free the buffer mappings
+		 * associated with this page. If we succeed we try to free
+		 * the page as well.
+		 *
+		 * We do this even if the page is PageDirty().
+		 * try_to_release_page() does not perform I/O, but it is
+		 * possible for a page to have PageDirty set, but it is actually
+		 * clean (all its buffers are clean).  This happens if the
+		 * buffers were written out directly, with submit_bh(). ext3
+		 * will do this, as well as the blockdev mapping.
+		 * try_to_release_page() will discover that cleanness and will
+		 * drop the buffers and mark the page clean - it can be freed.
+		 *
+		 * Rarely, pages can have buffers and no ->mapping.  These are
+		 * the pages which were not successfully invalidated in
+		 * truncate_complete_page().  We try to drop those buffers here
+		 * and if that worked, and the page is no longer mapped into
+		 * process address space (page_count == 1) it can be freed.
+		 * Otherwise, leave the page on the LRU so it is swappable.
+		 */
+		if (page_has_private(page)) {
+			if (!try_to_release_page(page, sc->gfp_mask))
+				goto activate_locked;
+			if (!mapping && page_count(page) == 1) {
+				unlock_page(page);
+				if (put_page_testzero(page))
+					goto free_it;
+				else {
+					/*
+					 * rare race with speculative reference.
+					 * the speculative reference will free
+					 * this page shortly, so we may
+					 * increment nr_reclaimed here (and
+					 * leave it off the LRU).
+					 */
+					nr_reclaimed++;
+					continue;
+				}
+			}
+		}
+
+		if (PageAnon(page) && !PageSwapBacked(page)) {
+			/* follow __remove_mapping for reference */
+			if (!page_ref_freeze(page, 1))
+				goto keep_locked;
+			if (PageDirty(page)) {
+				page_ref_unfreeze(page, 1);
+				goto keep_locked;
+			}
+
+			count_vm_event(PGLAZYFREED);
+			count_memcg_page_event(page, PGLAZYFREED);
+		} else if (!mapping || !__remove_mapping(mapping, page, true,
+							 sc->target_mem_cgroup))
+			goto keep_locked;
+
+		unlock_page(page);
+free_it:
+		/*
+		 * THP may get swapped out in a whole, need account
+		 * all base pages.
+		 */
+		nr_reclaimed += nr_pages;
+
+		/*
+		 * Is there need to periodically free_page_list? It would
+		 * appear not as the counts should be low
+		 */
+		if (unlikely(PageTransHuge(page)))
+			destroy_compound_page(page);
+		else
+			list_add(&page->lru, &free_pages);
+		continue;
+
+activate_locked_split:
+		/*
+		 * The tail pages that are failed to add into swap cache
+		 * reach here.  Fixup nr_scanned and nr_pages.
+		 */
+		if (nr_pages > 1) {
+			sc->nr_scanned -= (nr_pages - 1);
+			nr_pages = 1;
+		}
+activate_locked:
+		/* Not a candidate for swapping, so reclaim swap space. */
+		if (PageSwapCache(page) && (mem_cgroup_swap_full(page) ||
+						PageMlocked(page)))
+			try_to_free_swap(page);
+		VM_BUG_ON_PAGE(PageActive(page), page);
+		if (!PageMlocked(page)) {
+			int type = page_is_file_lru(page);
+			SetPageActive(page);
+			stat->nr_activate[type] += nr_pages;
+			count_memcg_page_event(page, PGACTIVATE);
+		}
+keep_locked:
+		unlock_page(page);
+keep:
+		list_add(&page->lru, &ret_pages);
+		VM_BUG_ON_PAGE(PageLRU(page) || PageUnevictable(page), page);
+	}
+
+	pgactivate = stat->nr_activate[0] + stat->nr_activate[1];
+
+	mem_cgroup_uncharge_list(&free_pages);
+	try_to_unmap_flush();
+	free_unref_page_list(&free_pages);
+
+	list_splice(&ret_pages, page_list);
+	count_vm_events(PGACTIVATE, pgactivate);
+
+	return nr_reclaimed;
+}
+
+unsigned int reclaim_clean_pages_from_list(struct zone *zone,
+					    struct list_head *page_list)
+{
+	struct scan_control sc = {
+		.gfp_mask = GFP_KERNEL,
+		.priority = DEF_PRIORITY,
+		.may_unmap = 1,
+	};
+	struct reclaim_stat stat;
+	unsigned int nr_reclaimed;
+	struct page *page, *next;
+	LIST_HEAD(clean_pages);
+
+	list_for_each_entry_safe(page, next, page_list, lru) {
+		if (page_is_file_lru(page) && !PageDirty(page) &&
+		    !__PageMovable(page) && !PageUnevictable(page)) {
+			ClearPageActive(page);
+			list_move(&page->lru, &clean_pages);
+		}
+	}
+
+	nr_reclaimed = shrink_page_list(&clean_pages, zone->zone_pgdat, &sc,
+					&stat, true);
+	list_splice(&clean_pages, page_list);
+	mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE,
+			    -(long)nr_reclaimed);
+	/*
+	 * Since lazyfree pages are isolated from file LRU from the beginning,
+	 * they will rotate back to anonymous LRU in the end if it failed to
+	 * discard so isolated count will be mismatched.
+	 * Compensate the isolated count for both LRU lists.
+	 */
+	mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_ANON,
+			    stat.nr_lazyfree_fail);
+	mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE,
+			    -(long)stat.nr_lazyfree_fail);
+	return nr_reclaimed;
+}
+
+/*
+ * Attempt to remove the specified page from its LRU.  Only take this page
+ * if it is of the appropriate PageActive status.  Pages which are being
+ * freed elsewhere are also ignored.
+ *
+ * page:	page to consider
+ * mode:	one of the LRU isolation modes defined above
+ *
+ * returns 0 on success, -ve errno on failure.
+ */
+int __isolate_lru_page(struct page *page, isolate_mode_t mode)
+{
+	int ret = -EINVAL;
+
+	/* Only take pages on the LRU. */
+	if (!PageLRU(page))
+		return ret;
+
+	/* Compaction should not handle unevictable pages but CMA can do so */
+	if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE))
+		return ret;
+
+	ret = -EBUSY;
+
+	/*
+	 * To minimise LRU disruption, the caller can indicate that it only
+	 * wants to isolate pages it will be able to operate on without
+	 * blocking - clean pages for the most part.
+	 *
+	 * ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages
+	 * that it is possible to migrate without blocking
+	 */
+	if (mode & ISOLATE_ASYNC_MIGRATE) {
+		/* All the caller can do on PageWriteback is block */
+		if (PageWriteback(page))
+			return ret;
+
+		if (PageDirty(page)) {
+			struct address_space *mapping;
+			bool migrate_dirty;
+
+			/*
+			 * Only pages without mappings or that have a
+			 * ->migratepage 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))
+				return ret;
+
+			mapping = page_mapping(page);
+			migrate_dirty = !mapping || mapping->a_ops->migratepage;
+			unlock_page(page);
+			if (!migrate_dirty)
+				return ret;
+		}
+	}
+
+	if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
+		return ret;
+
+	if (likely(get_page_unless_zero(page))) {
+		/*
+		 * 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.
+		 */
+		ClearPageLRU(page);
+		ret = 0;
+	}
+
+	return ret;
+}
+
+
+/*
+ * Update LRU sizes after isolating pages. The LRU size updates must
+ * be complete before mem_cgroup_update_lru_size due to a sanity check.
+ */
+static __always_inline void update_lru_sizes(struct lruvec *lruvec,
+			enum lru_list lru, unsigned long *nr_zone_taken)
+{
+	int zid;
+
+	for (zid = 0; zid < MAX_NR_ZONES; zid++) {
+		if (!nr_zone_taken[zid])
+			continue;
+
+		update_lru_size(lruvec, lru, zid, -nr_zone_taken[zid]);
+	}
+
+}
+
+/**
+ * pgdat->lru_lock is heavily contended.  Some of the functions that
+ * shrink the lists perform better by taking out a batch of pages
+ * and working on them outside the LRU lock.
+ *
+ * For pagecache intensive workloads, this function is the hottest
+ * spot in the kernel (apart from copy_*_user functions).
+ *
+ * Appropriate locks must be held before calling this function.
+ *
+ * @nr_to_scan:	The number of eligible pages to look through on the list.
+ * @lruvec:	The LRU vector to pull pages from.
+ * @dst:	The temp list to put pages on to.
+ * @nr_scanned:	The number of pages that were scanned.
+ * @sc:		The scan_control struct for this reclaim session
+ * @lru:	LRU list id for isolating
+ *
+ * returns how many pages were moved onto *@dst.
+ */
+static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
+		struct lruvec *lruvec, struct list_head *dst,
+		unsigned long *nr_scanned, struct scan_control *sc,
+		enum lru_list lru)
+{
+	struct list_head *src = &lruvec->lists[lru];
+	unsigned long nr_taken = 0;
+	unsigned long nr_zone_taken[MAX_NR_ZONES] = { 0 };
+	unsigned long nr_skipped[MAX_NR_ZONES] = { 0, };
+	unsigned long skipped = 0;
+	unsigned long scan, total_scan, nr_pages;
+	LIST_HEAD(pages_skipped);
+	isolate_mode_t mode = (sc->may_unmap ? 0 : ISOLATE_UNMAPPED);
+
+	total_scan = 0;
+	scan = 0;
+	while (scan < nr_to_scan && !list_empty(src)) {
+		struct page *page;
+
+		page = lru_to_page(src);
+		prefetchw_prev_lru_page(page, src, flags);
+
+		VM_BUG_ON_PAGE(!PageLRU(page), page);
+
+		nr_pages = compound_nr(page);
+		total_scan += nr_pages;
+
+		if (page_zonenum(page) > sc->reclaim_idx) {
+			list_move(&page->lru, &pages_skipped);
+			nr_skipped[page_zonenum(page)] += nr_pages;
+			continue;
+		}
+
+		/*
+		 * Do not count skipped pages because that makes the function
+		 * return with no isolated pages if the LRU mostly contains
+		 * ineligible pages.  This causes the VM to not reclaim any
+		 * pages, triggering a premature OOM.
+		 *
+		 * Account all tail pages of THP.  This would not cause
+		 * premature OOM since __isolate_lru_page() returns -EBUSY
+		 * only when the page is being freed somewhere else.
+		 */
+		scan += nr_pages;
+		switch (__isolate_lru_page(page, mode)) {
+		case 0:
+			nr_taken += nr_pages;
+			nr_zone_taken[page_zonenum(page)] += nr_pages;
+			list_move(&page->lru, dst);
+			break;
+
+		case -EBUSY:
+			/* else it is being freed elsewhere */
+			list_move(&page->lru, src);
+			continue;
+
+		default:
+			BUG();
+		}
+	}
+
+	/*
+	 * Splice any skipped pages to the start of the LRU list. Note that
+	 * this disrupts the LRU order when reclaiming for lower zones but
+	 * we cannot splice to the tail. If we did then the SWAP_CLUSTER_MAX
+	 * scanning would soon rescan the same pages to skip and put the
+	 * system at risk of premature OOM.
+	 */
+	if (!list_empty(&pages_skipped)) {
+		int zid;
+
+		list_splice(&pages_skipped, src);
+		for (zid = 0; zid < MAX_NR_ZONES; zid++) {
+			if (!nr_skipped[zid])
+				continue;
+
+			__count_zid_vm_events(PGSCAN_SKIP, zid, nr_skipped[zid]);
+			skipped += nr_skipped[zid];
+		}
+	}
+	*nr_scanned = total_scan;
+	trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan,
+				    total_scan, skipped, nr_taken, mode, lru);
+	update_lru_sizes(lruvec, lru, nr_zone_taken);
+	return nr_taken;
+}
+
+/**
+ * isolate_lru_page - tries to isolate a page from its LRU list
+ * @page: page to isolate from its LRU list
+ *
+ * Isolates a @page from an LRU list, clears PageLRU and adjusts the
+ * vmstat statistic corresponding to whatever LRU list the page was on.
+ *
+ * Returns 0 if the page was removed from an LRU list.
+ * Returns -EBUSY if the page was not on an LRU list.
+ *
+ * The returned page will have PageLRU() cleared.  If it was found on
+ * the active list, it will have PageActive set.  If it was found on
+ * the unevictable list, it will have the PageUnevictable bit set. That flag
+ * may need to be cleared by the caller before letting the page go.
+ *
+ * The vmstat statistic corresponding to the list on which the page was
+ * found will be decremented.
+ *
+ * Restrictions:
+ *
+ * (1) Must be called with an elevated refcount on the page. This is a
+ *     fundamental difference from isolate_lru_pages (which is called
+ *     without a stable reference).
+ * (2) the lru_lock must not be held.
+ * (3) interrupts must be enabled.
+ */
+int isolate_lru_page(struct page *page)
+{
+	int ret = -EBUSY;
+
+	VM_BUG_ON_PAGE(!page_count(page), page);
+	WARN_RATELIMIT(PageTail(page), "trying to isolate tail page");
+
+	if (PageLRU(page)) {
+		pg_data_t *pgdat = page_pgdat(page);
+		struct lruvec *lruvec;
+
+		spin_lock_irq(&pgdat->lru_lock);
+		lruvec = mem_cgroup_page_lruvec(page, pgdat);
+		if (PageLRU(page)) {
+			int lru = page_lru(page);
+			get_page(page);
+			ClearPageLRU(page);
+			del_page_from_lru_list(page, lruvec, lru);
+			ret = 0;
+		}
+		spin_unlock_irq(&pgdat->lru_lock);
+	}
+	return ret;
+}
+
+/*
+ * A direct reclaimer may isolate SWAP_CLUSTER_MAX pages from the LRU list and
+ * then get rescheduled. When there are massive number of tasks doing page
+ * allocation, such sleeping direct reclaimers may keep piling up on each CPU,
+ * the LRU list will go small and be scanned faster than necessary, leading to
+ * unnecessary swapping, thrashing and OOM.
+ */
+static int too_many_isolated(struct pglist_data *pgdat, int file,
+		struct scan_control *sc)
+{
+	unsigned long inactive, isolated;
+
+	if (current_is_kswapd())
+		return 0;
+
+	if (!writeback_throttling_sane(sc))
+		return 0;
+
+	if (file) {
+		inactive = node_page_state(pgdat, NR_INACTIVE_FILE);
+		isolated = node_page_state(pgdat, NR_ISOLATED_FILE);
+	} else {
+		inactive = node_page_state(pgdat, NR_INACTIVE_ANON);
+		isolated = node_page_state(pgdat, NR_ISOLATED_ANON);
+	}
+
+	/*
+	 * GFP_NOIO/GFP_NOFS callers are allowed to isolate more pages, so they
+	 * won't get blocked by normal direct-reclaimers, forming a circular
+	 * deadlock.
+	 */
+	if ((sc->gfp_mask & (__GFP_IO | __GFP_FS)) == (__GFP_IO | __GFP_FS))
+		inactive >>= 3;
+
+	return isolated > inactive;
+}
+
+/*
+ * This moves pages from @list to corresponding LRU list.
+ *
+ * We move them the other way if the page is referenced by one or more
+ * processes, from rmap.
+ *
+ * If the pages are mostly unmapped, the processing is fast and it is
+ * appropriate to hold zone_lru_lock across the whole operation.  But if
+ * the pages are mapped, the processing is slow (page_referenced()) so we
+ * should drop zone_lru_lock around each page.  It's impossible to balance
+ * this, so instead we remove the pages from the LRU while processing them.
+ * It is safe to rely on PG_active against the non-LRU pages in here because
+ * nobody will play with that bit on a non-LRU page.
+ *
+ * The downside is that we have to touch page->_refcount against each page.
+ * But we had to alter page->flags anyway.
+ *
+ * Returns the number of pages moved to the given lruvec.
+ */
+
+static unsigned noinline_for_stack move_pages_to_lru(struct lruvec *lruvec,
+						     struct list_head *list)
+{
+	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
+	int nr_pages, nr_moved = 0;
+	LIST_HEAD(pages_to_free);
+	struct page *page;
+	enum lru_list lru;
+
+	while (!list_empty(list)) {
+		page = lru_to_page(list);
+		VM_BUG_ON_PAGE(PageLRU(page), page);
+		if (unlikely(!page_evictable(page))) {
+			list_del(&page->lru);
+			spin_unlock_irq(&pgdat->lru_lock);
+			putback_lru_page(page);
+			spin_lock_irq(&pgdat->lru_lock);
+			continue;
+		}
+		lruvec = mem_cgroup_page_lruvec(page, pgdat);
+
+		SetPageLRU(page);
+		lru = page_lru(page);
+
+		nr_pages = thp_nr_pages(page);
+		update_lru_size(lruvec, lru, page_zonenum(page), nr_pages);
+		list_move(&page->lru, &lruvec->lists[lru]);
+
+		if (put_page_testzero(page)) {
+			__ClearPageLRU(page);
+			__ClearPageActive(page);
+			del_page_from_lru_list(page, lruvec, lru);
+
+			if (unlikely(PageCompound(page))) {
+				spin_unlock_irq(&pgdat->lru_lock);
+				destroy_compound_page(page);
+				spin_lock_irq(&pgdat->lru_lock);
+			} else
+				list_add(&page->lru, &pages_to_free);
+		} else {
+			nr_moved += nr_pages;
+			if (PageActive(page))
+				workingset_age_nonresident(lruvec, nr_pages);
+		}
+	}
+
+	/*
+	 * To save our caller's stack, now use input list for pages to free.
+	 */
+	list_splice(&pages_to_free, list);
+
+	return nr_moved;
+}
+
+/*
+ * If a kernel thread (such as nfsd for loop-back mounts) services
+ * a backing device by writing to the page cache it sets PF_LOCAL_THROTTLE.
+ * In that case we should only throttle if the backing device it is
+ * writing to is congested.  In other cases it is safe to throttle.
+ */
+static int current_may_throttle(void)
+{
+	return !(current->flags & PF_LOCAL_THROTTLE) ||
+		current->backing_dev_info == NULL ||
+		bdi_write_congested(current->backing_dev_info);
+}
+
+/*
+ * shrink_inactive_list() is a helper for shrink_node().  It returns the number
+ * of reclaimed pages
+ */
+static noinline_for_stack unsigned long
+shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
+		     struct scan_control *sc, enum lru_list lru)
+{
+	LIST_HEAD(page_list);
+	unsigned long nr_scanned;
+	unsigned int nr_reclaimed = 0;
+	unsigned long nr_taken;
+	struct reclaim_stat stat;
+	bool file = is_file_lru(lru);
+	enum vm_event_item item;
+	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
+	bool stalled = false;
+
+	while (unlikely(too_many_isolated(pgdat, file, sc))) {
+		if (stalled)
+			return 0;
+
+		/* wait a bit for the reclaimer. */
+		msleep(100);
+		stalled = true;
+
+		/* We are about to die and free our memory. Return now. */
+		if (fatal_signal_pending(current))
+			return SWAP_CLUSTER_MAX;
+	}
+
+	lru_add_drain();
+
+	spin_lock_irq(&pgdat->lru_lock);
+
+	nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list,
+				     &nr_scanned, sc, lru);
+
+	__mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, nr_taken);
+	item = current_is_kswapd() ? PGSCAN_KSWAPD : PGSCAN_DIRECT;
+	if (!cgroup_reclaim(sc))
+		__count_vm_events(item, nr_scanned);
+	__count_memcg_events(lruvec_memcg(lruvec), item, nr_scanned);
+	__count_vm_events(PGSCAN_ANON + file, nr_scanned);
+
+	spin_unlock_irq(&pgdat->lru_lock);
+
+	if (nr_taken == 0)
+		return 0;
+
+	nr_reclaimed = shrink_page_list(&page_list, pgdat, sc, &stat, false);
+
+	spin_lock_irq(&pgdat->lru_lock);
+
+	move_pages_to_lru(lruvec, &page_list);
+
+	__mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken);
+	lru_note_cost(lruvec, file, stat.nr_pageout);
+	item = current_is_kswapd() ? PGSTEAL_KSWAPD : PGSTEAL_DIRECT;
+	if (!cgroup_reclaim(sc))
+		__count_vm_events(item, nr_reclaimed);
+	__count_memcg_events(lruvec_memcg(lruvec), item, nr_reclaimed);
+	__count_vm_events(PGSTEAL_ANON + file, nr_reclaimed);
+
+	spin_unlock_irq(&pgdat->lru_lock);
+
+	mem_cgroup_uncharge_list(&page_list);
+	free_unref_page_list(&page_list);
+
+	/*
+	 * If dirty pages are scanned that are not queued for IO, it
+	 * implies that flushers are not doing their job. This can
+	 * happen when memory pressure pushes dirty pages to the end of
+	 * the LRU before the dirty limits are breached and the dirty
+	 * data has expired. It can also happen when the proportion of
+	 * dirty pages grows not through writes but through memory
+	 * pressure reclaiming all the clean cache. And in some cases,
+	 * the flushers simply cannot keep up with the allocation
+	 * rate. Nudge the flusher threads in case they are asleep.
+	 */
+	if (stat.nr_unqueued_dirty == nr_taken)
+		wakeup_flusher_threads(WB_REASON_VMSCAN);
+
+	sc->nr.dirty += stat.nr_dirty;
+	sc->nr.congested += stat.nr_congested;
+	sc->nr.unqueued_dirty += stat.nr_unqueued_dirty;
+	sc->nr.writeback += stat.nr_writeback;
+	sc->nr.immediate += stat.nr_immediate;
+	sc->nr.taken += nr_taken;
+	if (file)
+		sc->nr.file_taken += nr_taken;
+
+	trace_mm_vmscan_lru_shrink_inactive(pgdat->node_id,
+			nr_scanned, nr_reclaimed, &stat, sc->priority, file);
+	return nr_reclaimed;
+}
+
+static void shrink_active_list(unsigned long nr_to_scan,
+			       struct lruvec *lruvec,
+			       struct scan_control *sc,
+			       enum lru_list lru)
+{
+	unsigned long nr_taken;
+	unsigned long nr_scanned;
+	unsigned long vm_flags;
+	LIST_HEAD(l_hold);	/* The pages which were snipped off */
+	LIST_HEAD(l_active);
+	LIST_HEAD(l_inactive);
+	struct page *page;
+	unsigned nr_deactivate, nr_activate;
+	unsigned nr_rotated = 0;
+	int file = is_file_lru(lru);
+	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
+
+	lru_add_drain();
+
+	spin_lock_irq(&pgdat->lru_lock);
+
+	nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold,
+				     &nr_scanned, sc, lru);
+
+	__mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, nr_taken);
+
+	if (!cgroup_reclaim(sc))
+		__count_vm_events(PGREFILL, nr_scanned);
+	__count_memcg_events(lruvec_memcg(lruvec), PGREFILL, nr_scanned);
+
+	spin_unlock_irq(&pgdat->lru_lock);
+
+	while (!list_empty(&l_hold)) {
+		cond_resched();
+		page = lru_to_page(&l_hold);
+		list_del(&page->lru);
+
+		if (unlikely(!page_evictable(page))) {
+			putback_lru_page(page);
+			continue;
+		}
+
+		if (unlikely(buffer_heads_over_limit)) {
+			if (page_has_private(page) && trylock_page(page)) {
+				if (page_has_private(page))
+					try_to_release_page(page, 0);
+				unlock_page(page);
+			}
+		}
+
+		if (page_referenced(page, 0, sc->target_mem_cgroup,
+				    &vm_flags)) {
+			/*
+			 * Identify referenced, file-backed active pages and
+			 * give them one more trip around the active list. So
+			 * that executable code get better chances to stay in
+			 * memory under moderate memory pressure.  Anon pages
+			 * are not likely to be evicted by use-once streaming
+			 * IO, plus JVM can create lots of anon VM_EXEC pages,
+			 * so we ignore them here.
+			 */
+			if ((vm_flags & VM_EXEC) && page_is_file_lru(page)) {
+				nr_rotated += thp_nr_pages(page);
+				list_add(&page->lru, &l_active);
+				continue;
+			}
+		}
+
+		ClearPageActive(page);	/* we are de-activating */
+		SetPageWorkingset(page);
+		list_add(&page->lru, &l_inactive);
+	}
+
+	/*
+	 * Move pages back to the lru list.
+	 */
+	spin_lock_irq(&pgdat->lru_lock);
+
+	nr_activate = move_pages_to_lru(lruvec, &l_active);
+	nr_deactivate = move_pages_to_lru(lruvec, &l_inactive);
+	/* Keep all free pages in l_active list */
+	list_splice(&l_inactive, &l_active);
+
+	__count_vm_events(PGDEACTIVATE, nr_deactivate);
+	__count_memcg_events(lruvec_memcg(lruvec), PGDEACTIVATE, nr_deactivate);
+
+	__mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken);
+	spin_unlock_irq(&pgdat->lru_lock);
+
+	mem_cgroup_uncharge_list(&l_active);
+	free_unref_page_list(&l_active);
+	trace_mm_vmscan_lru_shrink_active(pgdat->node_id, nr_taken, nr_activate,
+			nr_deactivate, nr_rotated, sc->priority, file);
+}
+
+unsigned long reclaim_pages(struct list_head *page_list)
+{
+	int nid = NUMA_NO_NODE;
+	unsigned int nr_reclaimed = 0;
+	LIST_HEAD(node_page_list);
+	struct reclaim_stat dummy_stat;
+	struct page *page;
+	struct scan_control sc = {
+		.gfp_mask = GFP_KERNEL,
+		.priority = DEF_PRIORITY,
+		.may_writepage = 1,
+		.may_unmap = 1,
+		.may_swap = 1,
+	};
+
+	while (!list_empty(page_list)) {
+		page = lru_to_page(page_list);
+		if (nid == NUMA_NO_NODE) {
+			nid = page_to_nid(page);
+			INIT_LIST_HEAD(&node_page_list);
+		}
+
+		if (nid == page_to_nid(page)) {
+			ClearPageActive(page);
+			list_move(&page->lru, &node_page_list);
+			continue;
+		}
+
+		nr_reclaimed += shrink_page_list(&node_page_list,
+						NODE_DATA(nid),
+						&sc, &dummy_stat, false);
+		while (!list_empty(&node_page_list)) {
+			page = lru_to_page(&node_page_list);
+			list_del(&page->lru);
+			putback_lru_page(page);
+		}
+
+		nid = NUMA_NO_NODE;
+	}
+
+	if (!list_empty(&node_page_list)) {
+		nr_reclaimed += shrink_page_list(&node_page_list,
+						NODE_DATA(nid),
+						&sc, &dummy_stat, false);
+		while (!list_empty(&node_page_list)) {
+			page = lru_to_page(&node_page_list);
+			list_del(&page->lru);
+			putback_lru_page(page);
+		}
+	}
+
+	return nr_reclaimed;
+}
+
+static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
+				 struct lruvec *lruvec, struct scan_control *sc)
+{
+	if (is_active_lru(lru)) {
+		if (sc->may_deactivate & (1 << is_file_lru(lru)))
+			shrink_active_list(nr_to_scan, lruvec, sc, lru);
+		else
+			sc->skipped_deactivate = 1;
+		return 0;
+	}
+
+	return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
+}
+
+/*
+ * The inactive anon list should be small enough that the VM never has
+ * to do too much work.
+ *
+ * The inactive file list should be small enough to leave most memory
+ * to the established workingset on the scan-resistant active list,
+ * but large enough to avoid thrashing the aggregate readahead window.
+ *
+ * Both inactive lists should also be large enough that each inactive
+ * page has a chance to be referenced again before it is reclaimed.
+ *
+ * If that fails and refaulting is observed, the inactive list grows.
+ *
+ * The inactive_ratio is the target ratio of ACTIVE to INACTIVE pages
+ * on this LRU, maintained by the pageout code. An inactive_ratio
+ * of 3 means 3:1 or 25% of the pages are kept on the inactive list.
+ *
+ * total     target    max
+ * memory    ratio     inactive
+ * -------------------------------------
+ *   10MB       1         5MB
+ *  100MB       1        50MB
+ *    1GB       3       250MB
+ *   10GB      10       0.9GB
+ *  100GB      31         3GB
+ *    1TB     101        10GB
+ *   10TB     320        32GB
+ */
+static bool inactive_is_low(struct lruvec *lruvec, enum lru_list inactive_lru)
+{
+	enum lru_list active_lru = inactive_lru + LRU_ACTIVE;
+	unsigned long inactive, active;
+	unsigned long inactive_ratio;
+	unsigned long gb;
+
+	inactive = lruvec_page_state(lruvec, NR_LRU_BASE + inactive_lru);
+	active = lruvec_page_state(lruvec, NR_LRU_BASE + active_lru);
+
+	gb = (inactive + active) >> (30 - PAGE_SHIFT);
+	if (gb)
+		inactive_ratio = int_sqrt(10 * gb);
+	else
+		inactive_ratio = 1;
+
+	return inactive * inactive_ratio < active;
+}
+
+enum scan_balance {
+	SCAN_EQUAL,
+	SCAN_FRACT,
+	SCAN_ANON,
+	SCAN_FILE,
+};
+
+/*
+ * Determine how aggressively the anon and file LRU lists should be
+ * scanned.  The relative value of each set of LRU lists is determined
+ * by looking at the fraction of the pages scanned we did rotate back
+ * onto the active list instead of evict.
+ *
+ * nr[0] = anon inactive pages to scan; nr[1] = anon active pages to scan
+ * nr[2] = file inactive pages to scan; nr[3] = file active pages to scan
+ */
+static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
+			   unsigned long *nr)
+{
+	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
+	unsigned long anon_cost, file_cost, total_cost;
+	int swappiness = mem_cgroup_swappiness(memcg);
+	u64 fraction[ANON_AND_FILE];
+	u64 denominator = 0;	/* gcc */
+	enum scan_balance scan_balance;
+	unsigned long ap, fp;
+	enum lru_list lru;
+
+	/* If we have no swap space, do not bother scanning anon pages. */
+	if (!sc->may_swap || mem_cgroup_get_nr_swap_pages(memcg) <= 0) {
+		scan_balance = SCAN_FILE;
+		goto out;
+	}
+
+	/*
+	 * Global reclaim will swap to prevent OOM even with no
+	 * swappiness, but memcg users want to use this knob to
+	 * disable swapping for individual groups completely when
+	 * using the memory controller's swap limit feature would be
+	 * too expensive.
+	 */
+	if (cgroup_reclaim(sc) && !swappiness) {
+		scan_balance = SCAN_FILE;
+		goto out;
+	}
+
+	/*
+	 * Do not apply any pressure balancing cleverness when the
+	 * system is close to OOM, scan both anon and file equally
+	 * (unless the swappiness setting disagrees with swapping).
+	 */
+	if (!sc->priority && swappiness) {
+		scan_balance = SCAN_EQUAL;
+		goto out;
+	}
+
+	/*
+	 * If the system is almost out of file pages, force-scan anon.
+	 */
+	if (sc->file_is_tiny) {
+		scan_balance = SCAN_ANON;
+		goto out;
+	}
+
+	/*
+	 * If there is enough inactive page cache, we do not reclaim
+	 * anything from the anonymous working right now.
+	 */
+	if (sc->cache_trim_mode) {
+		scan_balance = SCAN_FILE;
+		goto out;
+	}
+
+	scan_balance = SCAN_FRACT;
+	/*
+	 * Calculate the pressure balance between anon and file pages.
+	 *
+	 * The amount of pressure we put on each LRU is inversely
+	 * proportional to the cost of reclaiming each list, as
+	 * determined by the share of pages that are refaulting, times
+	 * the relative IO cost of bringing back a swapped out
+	 * anonymous page vs reloading a filesystem page (swappiness).
+	 *
+	 * Although we limit that influence to ensure no list gets
+	 * left behind completely: at least a third of the pressure is
+	 * applied, before swappiness.
+	 *
+	 * With swappiness at 100, anon and file have equal IO cost.
+	 */
+	total_cost = sc->anon_cost + sc->file_cost;
+	anon_cost = total_cost + sc->anon_cost;
+	file_cost = total_cost + sc->file_cost;
+	total_cost = anon_cost + file_cost;
+
+	ap = swappiness * (total_cost + 1);
+	ap /= anon_cost + 1;
+
+	fp = (200 - swappiness) * (total_cost + 1);
+	fp /= file_cost + 1;
+
+	fraction[0] = ap;
+	fraction[1] = fp;
+	denominator = ap + fp;
+out:
+	for_each_evictable_lru(lru) {
+		int file = is_file_lru(lru);
+		unsigned long lruvec_size;
+		unsigned long low, min;
+		unsigned long scan;
+
+		lruvec_size = lruvec_lru_size(lruvec, lru, sc->reclaim_idx);
+		mem_cgroup_protection(sc->target_mem_cgroup, memcg,
+				      &min, &low);
+
+		if (min || low) {
+			/*
+			 * Scale a cgroup's reclaim pressure by proportioning
+			 * its current usage to its memory.low or memory.min
+			 * setting.
+			 *
+			 * This is important, as otherwise scanning aggression
+			 * becomes extremely binary -- from nothing as we
+			 * approach the memory protection threshold, to totally
+			 * nominal as we exceed it.  This results in requiring
+			 * setting extremely liberal protection thresholds. It
+			 * also means we simply get no protection at all if we
+			 * set it too low, which is not ideal.
+			 *
+			 * If there is any protection in place, we reduce scan
+			 * pressure by how much of the total memory used is
+			 * within protection thresholds.
+			 *
+			 * There is one special case: in the first reclaim pass,
+			 * we skip over all groups that are within their low
+			 * protection. If that fails to reclaim enough pages to
+			 * satisfy the reclaim goal, we come back and override
+			 * the best-effort low protection. However, we still
+			 * ideally want to honor how well-behaved groups are in
+			 * that case instead of simply punishing them all
+			 * equally. As such, we reclaim them based on how much
+			 * memory they are using, reducing the scan pressure
+			 * again by how much of the total memory used is under
+			 * hard protection.
+			 */
+			unsigned long cgroup_size = mem_cgroup_size(memcg);
+			unsigned long protection;
+
+			/* memory.low scaling, make sure we retry before OOM */
+			if (!sc->memcg_low_reclaim && low > min) {
+				protection = low;
+				sc->memcg_low_skipped = 1;
+			} else {
+				protection = min;
+			}
+
+			/* Avoid TOCTOU with earlier protection check */
+			cgroup_size = max(cgroup_size, protection);
+
+			scan = lruvec_size - lruvec_size * protection /
+				(cgroup_size + 1);
+
+			/*
+			 * Minimally target SWAP_CLUSTER_MAX pages to keep
+			 * reclaim moving forwards, avoiding decrementing
+			 * sc->priority further than desirable.
+			 */
+			scan = max(scan, SWAP_CLUSTER_MAX);
+		} else {
+			scan = lruvec_size;
+		}
+
+		scan >>= sc->priority;
+
+		/*
+		 * If the cgroup's already been deleted, make sure to
+		 * scrape out the remaining cache.
+		 */
+		if (!scan && !mem_cgroup_online(memcg))
+			scan = min(lruvec_size, SWAP_CLUSTER_MAX);
+
+		switch (scan_balance) {
+		case SCAN_EQUAL:
+			/* Scan lists relative to size */
+			break;
+		case SCAN_FRACT:
+			/*
+			 * Scan types proportional to swappiness and
+			 * their relative recent reclaim efficiency.
+			 * Make sure we don't miss the last page on
+			 * the offlined memory cgroups because of a
+			 * round-off error.
+			 */
+			scan = mem_cgroup_online(memcg) ?
+			       div64_u64(scan * fraction[file], denominator) :
+			       DIV64_U64_ROUND_UP(scan * fraction[file],
+						  denominator);
+			break;
+		case SCAN_FILE:
+		case SCAN_ANON:
+			/* Scan one type exclusively */
+			if ((scan_balance == SCAN_FILE) != file)
+				scan = 0;
+			break;
+		default:
+			/* Look ma, no brain */
+			BUG();
+		}
+
+		nr[lru] = scan;
+	}
+}
+
+static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
+{
+	unsigned long nr[NR_LRU_LISTS];
+	unsigned long targets[NR_LRU_LISTS];
+	unsigned long nr_to_scan;
+	enum lru_list lru;
+	unsigned long nr_reclaimed = 0;
+	unsigned long nr_to_reclaim = sc->nr_to_reclaim;
+	bool proportional_reclaim;
+	struct blk_plug plug;
+
+	get_scan_count(lruvec, sc, nr);
+
+	/* Record the original scan target for proportional adjustments later */
+	memcpy(targets, nr, sizeof(nr));
+
+	/*
+	 * Global reclaiming within direct reclaim at DEF_PRIORITY is a normal
+	 * event that can occur when there is little memory pressure e.g.
+	 * multiple streaming readers/writers. Hence, we do not abort scanning
+	 * when the requested number of pages are reclaimed when scanning at
+	 * DEF_PRIORITY on the assumption that the fact we are direct
+	 * reclaiming implies that kswapd is not keeping up and it is best to
+	 * do a batch of work at once. For memcg reclaim one check is made to
+	 * abort proportional reclaim if either the file or anon lru has already
+	 * dropped to zero at the first pass.
+	 */
+	proportional_reclaim = (!cgroup_reclaim(sc) && !current_is_kswapd() &&
+				sc->priority == DEF_PRIORITY);
+
+	blk_start_plug(&plug);
+	while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
+					nr[LRU_INACTIVE_FILE]) {
+		unsigned long nr_anon, nr_file, percentage;
+		unsigned long nr_scanned;
+
+		for_each_evictable_lru(lru) {
+			if (nr[lru]) {
+				nr_to_scan = min(nr[lru], SWAP_CLUSTER_MAX);
+				nr[lru] -= nr_to_scan;
+
+				nr_reclaimed += shrink_list(lru, nr_to_scan,
+							    lruvec, sc);
+			}
+		}
+
+		cond_resched();
+
+		if (nr_reclaimed < nr_to_reclaim || proportional_reclaim)
+			continue;
+
+		/*
+		 * For kswapd and memcg, reclaim at least the number of pages
+		 * requested. Ensure that the anon and file LRUs are scanned
+		 * proportionally what was requested by get_scan_count(). We
+		 * stop reclaiming one LRU and reduce the amount scanning
+		 * proportional to the original scan target.
+		 */
+		nr_file = nr[LRU_INACTIVE_FILE] + nr[LRU_ACTIVE_FILE];
+		nr_anon = nr[LRU_INACTIVE_ANON] + nr[LRU_ACTIVE_ANON];
+
+		/*
+		 * It's just vindictive to attack the larger once the smaller
+		 * has gone to zero.  And given the way we stop scanning the
+		 * smaller below, this makes sure that we only make one nudge
+		 * towards proportionality once we've got nr_to_reclaim.
+		 */
+		if (!nr_file || !nr_anon)
+			break;
+
+		if (nr_file > nr_anon) {
+			unsigned long scan_target = targets[LRU_INACTIVE_ANON] +
+						targets[LRU_ACTIVE_ANON] + 1;
+			lru = LRU_BASE;
+			percentage = nr_anon * 100 / scan_target;
+		} else {
+			unsigned long scan_target = targets[LRU_INACTIVE_FILE] +
+						targets[LRU_ACTIVE_FILE] + 1;
+			lru = LRU_FILE;
+			percentage = nr_file * 100 / scan_target;
+		}
+
+		/* Stop scanning the smaller of the LRU */
+		nr[lru] = 0;
+		nr[lru + LRU_ACTIVE] = 0;
+
+		/*
+		 * Recalculate the other LRU scan count based on its original
+		 * scan target and the percentage scanning already complete
+		 */
+		lru = (lru == LRU_FILE) ? LRU_BASE : LRU_FILE;
+		nr_scanned = targets[lru] - nr[lru];
+		nr[lru] = targets[lru] * (100 - percentage) / 100;
+		nr[lru] -= min(nr[lru], nr_scanned);
+
+		lru += LRU_ACTIVE;
+		nr_scanned = targets[lru] - nr[lru];
+		nr[lru] = targets[lru] * (100 - percentage) / 100;
+		nr[lru] -= min(nr[lru], nr_scanned);
+	}
+	blk_finish_plug(&plug);
+	sc->nr_reclaimed += nr_reclaimed;
+
+	/*
+	 * Even if we did not try to evict anon pages at all, we want to
+	 * rebalance the anon lru active/inactive ratio.
+	 */
+	if (total_swap_pages && inactive_is_low(lruvec, LRU_INACTIVE_ANON))
+		shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
+				   sc, LRU_ACTIVE_ANON);
+}
+
+/* Use reclaim/compaction for costly allocs or under memory pressure */
+static bool in_reclaim_compaction(struct scan_control *sc)
+{
+	if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
+			(sc->order > PAGE_ALLOC_COSTLY_ORDER ||
+			 sc->priority < DEF_PRIORITY - 2))
+		return true;
+
+	return false;
+}
+
+/*
+ * Reclaim/compaction is used for high-order allocation requests. It reclaims
+ * order-0 pages before compacting the zone. should_continue_reclaim() returns
+ * true if more pages should be reclaimed such that when the page allocator
+ * calls try_to_compact_pages() that it will have enough free pages to succeed.
+ * It will give up earlier than that if there is difficulty reclaiming pages.
+ */
+static inline bool should_continue_reclaim(struct pglist_data *pgdat,
+					unsigned long nr_reclaimed,
+					struct scan_control *sc)
+{
+	unsigned long pages_for_compaction;
+	unsigned long inactive_lru_pages;
+	int z;
+
+	/* If not in reclaim/compaction mode, stop */
+	if (!in_reclaim_compaction(sc))
+		return false;
+
+	/*
+	 * Stop if we failed to reclaim any pages from the last SWAP_CLUSTER_MAX
+	 * number of pages that were scanned. This will return to the caller
+	 * with the risk reclaim/compaction and the resulting allocation attempt
+	 * fails. In the past we have tried harder for __GFP_RETRY_MAYFAIL
+	 * allocations through requiring that the full LRU list has been scanned
+	 * first, by assuming that zero delta of sc->nr_scanned means full LRU
+	 * scan, but that approximation was wrong, and there were corner cases
+	 * where always a non-zero amount of pages were scanned.
+	 */
+	if (!nr_reclaimed)
+		return false;
+
+	/* If compaction would go ahead or the allocation would succeed, stop */
+	for (z = 0; z <= sc->reclaim_idx; z++) {
+		struct zone *zone = &pgdat->node_zones[z];
+		if (!managed_zone(zone))
+			continue;
+
+		switch (compaction_suitable(zone, sc->order, 0, sc->reclaim_idx)) {
+		case COMPACT_SUCCESS:
+		case COMPACT_CONTINUE:
+			return false;
+		default:
+			/* check next zone */
+			;
+		}
+	}
+
+	/*
+	 * If we have not reclaimed enough pages for compaction and the
+	 * inactive lists are large enough, continue reclaiming
+	 */
+	pages_for_compaction = compact_gap(sc->order);
+	inactive_lru_pages = node_page_state(pgdat, NR_INACTIVE_FILE);
+	if (get_nr_swap_pages() > 0)
+		inactive_lru_pages += node_page_state(pgdat, NR_INACTIVE_ANON);
+
+	return inactive_lru_pages > pages_for_compaction;
+}
+
+static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc)
+{
+	struct mem_cgroup *target_memcg = sc->target_mem_cgroup;
+	struct mem_cgroup *memcg;
+
+	memcg = mem_cgroup_iter(target_memcg, NULL, NULL);
+	do {
+		struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat);
+		unsigned long reclaimed;
+		unsigned long scanned;
+
+		/*
+		 * This loop can become CPU-bound when target memcgs
+		 * aren't eligible for reclaim - either because they
+		 * don't have any reclaimable pages, or because their
+		 * memory is explicitly protected. Avoid soft lockups.
+		 */
+		cond_resched();
+
+		mem_cgroup_calculate_protection(target_memcg, memcg);
+
+		if (mem_cgroup_below_min(memcg)) {
+			/*
+			 * Hard protection.
+			 * If there is no reclaimable memory, OOM.
+			 */
+			continue;
+		} else if (mem_cgroup_below_low(memcg)) {
+			/*
+			 * Soft protection.
+			 * Respect the protection only as long as
+			 * there is an unprotected supply
+			 * of reclaimable memory from other cgroups.
+			 */
+			if (!sc->memcg_low_reclaim) {
+				sc->memcg_low_skipped = 1;
+				continue;
+			}
+			memcg_memory_event(memcg, MEMCG_LOW);
+		}
+
+		reclaimed = sc->nr_reclaimed;
+		scanned = sc->nr_scanned;
+
+		shrink_lruvec(lruvec, sc);
+
+		shrink_slab(sc->gfp_mask, pgdat->node_id, memcg,
+			    sc->priority);
+
+		/* Record the group's reclaim efficiency */
+		vmpressure(sc->gfp_mask, memcg, false,
+			   sc->nr_scanned - scanned,
+			   sc->nr_reclaimed - reclaimed);
+
+	} while ((memcg = mem_cgroup_iter(target_memcg, memcg, NULL)));
+}
+
+static void shrink_node(pg_data_t *pgdat, struct scan_control *sc)
+{
+	struct reclaim_state *reclaim_state = current->reclaim_state;
+	unsigned long nr_reclaimed, nr_scanned;
+	struct lruvec *target_lruvec;
+	bool reclaimable = false;
+	unsigned long file;
+
+	target_lruvec = mem_cgroup_lruvec(sc->target_mem_cgroup, pgdat);
+
+again:
+	memset(&sc->nr, 0, sizeof(sc->nr));
+
+	nr_reclaimed = sc->nr_reclaimed;
+	nr_scanned = sc->nr_scanned;
+
+	/*
+	 * Determine the scan balance between anon and file LRUs.
+	 */
+	spin_lock_irq(&pgdat->lru_lock);
+	sc->anon_cost = target_lruvec->anon_cost;
+	sc->file_cost = target_lruvec->file_cost;
+	spin_unlock_irq(&pgdat->lru_lock);
+
+	/*
+	 * Target desirable inactive:active list ratios for the anon
+	 * and file LRU lists.
+	 */
+	if (!sc->force_deactivate) {
+		unsigned long refaults;
+
+		refaults = lruvec_page_state(target_lruvec,
+				WORKINGSET_ACTIVATE_ANON);
+		if (refaults != target_lruvec->refaults[0] ||
+			inactive_is_low(target_lruvec, LRU_INACTIVE_ANON))
+			sc->may_deactivate |= DEACTIVATE_ANON;
+		else
+			sc->may_deactivate &= ~DEACTIVATE_ANON;
+
+		/*
+		 * When refaults are being observed, it means a new
+		 * workingset is being established. Deactivate to get
+		 * rid of any stale active pages quickly.
+		 */
+		refaults = lruvec_page_state(target_lruvec,
+				WORKINGSET_ACTIVATE_FILE);
+		if (refaults != target_lruvec->refaults[1] ||
+		    inactive_is_low(target_lruvec, LRU_INACTIVE_FILE))
+			sc->may_deactivate |= DEACTIVATE_FILE;
+		else
+			sc->may_deactivate &= ~DEACTIVATE_FILE;
+	} else
+		sc->may_deactivate = DEACTIVATE_ANON | DEACTIVATE_FILE;
+
+	/*
+	 * If we have plenty of inactive file pages that aren't
+	 * thrashing, try to reclaim those first before touching
+	 * anonymous pages.
+	 */
+	file = lruvec_page_state(target_lruvec, NR_INACTIVE_FILE);
+	if (file >> sc->priority && !(sc->may_deactivate & DEACTIVATE_FILE))
+		sc->cache_trim_mode = 1;
+	else
+		sc->cache_trim_mode = 0;
+
+	/*
+	 * Prevent the reclaimer from falling into the cache trap: as
+	 * cache pages start out inactive, every cache fault will tip
+	 * the scan balance towards the file LRU.  And as the file LRU
+	 * shrinks, so does the window for rotation from references.
+	 * This means we have a runaway feedback loop where a tiny
+	 * thrashing file LRU becomes infinitely more attractive than
+	 * anon pages.  Try to detect this based on file LRU size.
+	 */
+	if (!cgroup_reclaim(sc)) {
+		unsigned long total_high_wmark = 0;
+		unsigned long free, anon;
+		int z;
+
+		free = sum_zone_node_page_state(pgdat->node_id, NR_FREE_PAGES);
+		file = node_page_state(pgdat, NR_ACTIVE_FILE) +
+			   node_page_state(pgdat, NR_INACTIVE_FILE);
+
+		for (z = 0; z < MAX_NR_ZONES; z++) {
+			struct zone *zone = &pgdat->node_zones[z];
+			if (!managed_zone(zone))
+				continue;
+
+			total_high_wmark += high_wmark_pages(zone);
+		}
+
+		/*
+		 * Consider anon: if that's low too, this isn't a
+		 * runaway file reclaim problem, but rather just
+		 * extreme pressure. Reclaim as per usual then.
+		 */
+		anon = node_page_state(pgdat, NR_INACTIVE_ANON);
+
+		sc->file_is_tiny =
+			file + free <= total_high_wmark &&
+			!(sc->may_deactivate & DEACTIVATE_ANON) &&
+			anon >> sc->priority;
+	}
+
+	shrink_node_memcgs(pgdat, sc);
+
+	if (reclaim_state) {
+		sc->nr_reclaimed += reclaim_state->reclaimed_slab;
+		reclaim_state->reclaimed_slab = 0;
+	}
+
+	/* Record the subtree's reclaim efficiency */
+	vmpressure(sc->gfp_mask, sc->target_mem_cgroup, true,
+		   sc->nr_scanned - nr_scanned,
+		   sc->nr_reclaimed - nr_reclaimed);
+
+	if (sc->nr_reclaimed - nr_reclaimed)
+		reclaimable = true;
+
+	if (current_is_kswapd()) {
+		/*
+		 * If reclaim is isolating dirty pages under writeback,
+		 * it implies that the long-lived page allocation rate
+		 * is exceeding the page laundering rate. Either the
+		 * global limits are not being effective at throttling
+		 * processes due to the page distribution throughout
+		 * zones or there is heavy usage of a slow backing
+		 * device. The only option is to throttle from reclaim
+		 * context which is not ideal as there is no guarantee
+		 * the dirtying process is throttled in the same way
+		 * balance_dirty_pages() manages.
+		 *
+		 * Once a node is flagged PGDAT_WRITEBACK, kswapd will
+		 * count the number of pages under pages flagged for
+		 * immediate reclaim and stall if any are encountered
+		 * in the nr_immediate check below.
+		 */
+		if (sc->nr.writeback && sc->nr.writeback == sc->nr.taken)
+			set_bit(PGDAT_WRITEBACK, &pgdat->flags);
+
+		/* Allow kswapd to start writing pages during reclaim.*/
+		if (sc->nr.unqueued_dirty == sc->nr.file_taken)
+			set_bit(PGDAT_DIRTY, &pgdat->flags);
+
+		/*
+		 * If kswapd scans pages marked for immediate
+		 * reclaim and under writeback (nr_immediate), it
+		 * implies that pages are cycling through the LRU
+		 * faster than they are written so also forcibly stall.
+		 */
+		if (sc->nr.immediate)
+			congestion_wait(BLK_RW_ASYNC, HZ/10);
+	}
+
+	/*
+	 * Tag a node/memcg as congested if all the dirty pages
+	 * scanned were backed by a congested BDI and
+	 * wait_iff_congested will stall.
+	 *
+	 * Legacy memcg will stall in page writeback so avoid forcibly
+	 * stalling in wait_iff_congested().
+	 */
+	if ((current_is_kswapd() ||
+	     (cgroup_reclaim(sc) && writeback_throttling_sane(sc))) &&
+	    sc->nr.dirty && sc->nr.dirty == sc->nr.congested)
+		set_bit(LRUVEC_CONGESTED, &target_lruvec->flags);
+
+	/*
+	 * Stall direct reclaim for IO completions if underlying BDIs
+	 * and node is congested. Allow kswapd to continue until it
+	 * starts encountering unqueued dirty pages or cycling through
+	 * the LRU too quickly.
+	 */
+	if (!current_is_kswapd() && current_may_throttle() &&
+	    !sc->hibernation_mode &&
+	    test_bit(LRUVEC_CONGESTED, &target_lruvec->flags))
+		wait_iff_congested(BLK_RW_ASYNC, HZ/10);
+
+	if (should_continue_reclaim(pgdat, sc->nr_reclaimed - nr_reclaimed,
+				    sc))
+		goto again;
+
+	/*
+	 * Kswapd gives up on balancing particular nodes after too
+	 * many failures to reclaim anything from them and goes to
+	 * sleep. On reclaim progress, reset the failure counter. A
+	 * successful direct reclaim run will revive a dormant kswapd.
+	 */
+	if (reclaimable)
+		pgdat->kswapd_failures = 0;
+}
+
+/*
+ * Returns true if compaction should go ahead for a costly-order request, or
+ * the allocation would already succeed without compaction. Return false if we
+ * should reclaim first.
+ */
+static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
+{
+	unsigned long watermark;
+	enum compact_result suitable;
+
+	suitable = compaction_suitable(zone, sc->order, 0, sc->reclaim_idx);
+	if (suitable == COMPACT_SUCCESS)
+		/* Allocation should succeed already. Don't reclaim. */
+		return true;
+	if (suitable == COMPACT_SKIPPED)
+		/* Compaction cannot yet proceed. Do reclaim. */
+		return false;
+
+	/*
+	 * Compaction is already possible, but it takes time to run and there
+	 * are potentially other callers using the pages just freed. So proceed
+	 * with reclaim to make a buffer of free pages available to give
+	 * compaction a reasonable chance of completing and allocating the page.
+	 * Note that we won't actually reclaim the whole buffer in one attempt
+	 * as the target watermark in should_continue_reclaim() is lower. But if
+	 * we are already above the high+gap watermark, don't reclaim at all.
+	 */
+	watermark = high_wmark_pages(zone) + compact_gap(sc->order);
+
+	return zone_watermark_ok_safe(zone, 0, watermark, sc->reclaim_idx);
+}
+
+/*
+ * This is the direct reclaim path, for page-allocating processes.  We only
+ * try to reclaim pages from zones which will satisfy the caller's allocation
+ * request.
+ *
+ * If a zone is deemed to be full of pinned pages then just give it a light
+ * scan then give up on it.
+ */
+static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
+{
+	struct zoneref *z;
+	struct zone *zone;
+	unsigned long nr_soft_reclaimed;
+	unsigned long nr_soft_scanned;
+	gfp_t orig_mask;
+	pg_data_t *last_pgdat = NULL;
+
+	/*
+	 * If the number of buffer_heads in the machine exceeds the maximum
+	 * allowed level, force direct reclaim to scan the highmem zone as
+	 * highmem pages could be pinning lowmem pages storing buffer_heads
+	 */
+	orig_mask = sc->gfp_mask;
+	if (buffer_heads_over_limit) {
+		sc->gfp_mask |= __GFP_HIGHMEM;
+		sc->reclaim_idx = gfp_zone(sc->gfp_mask);
+	}
+
+	for_each_zone_zonelist_nodemask(zone, z, zonelist,
+					sc->reclaim_idx, sc->nodemask) {
+		/*
+		 * Take care memory controller reclaiming has small influence
+		 * to global LRU.
+		 */
+		if (!cgroup_reclaim(sc)) {
+			if (!cpuset_zone_allowed(zone,
+						 GFP_KERNEL | __GFP_HARDWALL))
+				continue;
+
+			/*
+			 * If we already have plenty of memory free for
+			 * compaction in this zone, don't free any more.
+			 * Even though compaction is invoked for any
+			 * non-zero order, only frequent costly order
+			 * reclamation is disruptive enough to become a
+			 * noticeable problem, like transparent huge
+			 * page allocations.
+			 */
+			if (IS_ENABLED(CONFIG_COMPACTION) &&
+			    sc->order > PAGE_ALLOC_COSTLY_ORDER &&
+			    compaction_ready(zone, sc)) {
+				sc->compaction_ready = true;
+				continue;
+			}
+
+			/*
+			 * Shrink each node in the zonelist once. If the
+			 * zonelist is ordered by zone (not the default) then a
+			 * node may be shrunk multiple times but in that case
+			 * the user prefers lower zones being preserved.
+			 */
+			if (zone->zone_pgdat == last_pgdat)
+				continue;
+
+			/*
+			 * This steals pages from memory cgroups over softlimit
+			 * and returns the number of reclaimed pages and
+			 * scanned pages. This works for global memory pressure
+			 * and balancing, not for a memcg's limit.
+			 */
+			nr_soft_scanned = 0;
+			nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone->zone_pgdat,
+						sc->order, sc->gfp_mask,
+						&nr_soft_scanned);
+			sc->nr_reclaimed += nr_soft_reclaimed;
+			sc->nr_scanned += nr_soft_scanned;
+			/* need some check for avoid more shrink_zone() */
+		}
+
+		/* See comment about same check for global reclaim above */
+		if (zone->zone_pgdat == last_pgdat)
+			continue;
+		last_pgdat = zone->zone_pgdat;
+		shrink_node(zone->zone_pgdat, sc);
+	}
+
+	/*
+	 * Restore to original mask to avoid the impact on the caller if we
+	 * promoted it to __GFP_HIGHMEM.
+	 */
+	sc->gfp_mask = orig_mask;
+}
+
+static void snapshot_refaults(struct mem_cgroup *target_memcg, pg_data_t *pgdat)
+{
+	struct lruvec *target_lruvec;
+	unsigned long refaults;
+
+	target_lruvec = mem_cgroup_lruvec(target_memcg, pgdat);
+	refaults = lruvec_page_state(target_lruvec, WORKINGSET_ACTIVATE_ANON);
+	target_lruvec->refaults[0] = refaults;
+	refaults = lruvec_page_state(target_lruvec, WORKINGSET_ACTIVATE_FILE);
+	target_lruvec->refaults[1] = refaults;
+}
+
+/*
+ * This is the main entry point to direct page reclaim.
+ *
+ * If a full scan of the inactive list fails to free enough memory then we
+ * are "out of memory" and something needs to be killed.
+ *
+ * If the caller is !__GFP_FS then the probability of a failure is reasonably
+ * high - the zone may be full of dirty or under-writeback pages, which this
+ * caller can't do much about.  We kick the writeback threads and take explicit
+ * naps in the hope that some of these pages can be written.  But if the
+ * allocating task holds filesystem locks which prevent writeout this might not
+ * work, and the allocation attempt will fail.
+ *
+ * returns:	0, if no pages reclaimed
+ * 		else, the number of pages reclaimed
+ */
+static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
+					  struct scan_control *sc)
+{
+	int initial_priority = sc->priority;
+	pg_data_t *last_pgdat;
+	struct zoneref *z;
+	struct zone *zone;
+retry:
+	delayacct_freepages_start();
+
+	if (!cgroup_reclaim(sc))
+		__count_zid_vm_events(ALLOCSTALL, sc->reclaim_idx, 1);
+
+	do {
+		vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
+				sc->priority);
+		sc->nr_scanned = 0;
+		shrink_zones(zonelist, sc);
+
+		if (sc->nr_reclaimed >= sc->nr_to_reclaim)
+			break;
+
+		if (sc->compaction_ready)
+			break;
+
+		/*
+		 * If we're getting trouble reclaiming, start doing
+		 * writepage even in laptop mode.
+		 */
+		if (sc->priority < DEF_PRIORITY - 2)
+			sc->may_writepage = 1;
+	} while (--sc->priority >= 0);
+
+	last_pgdat = NULL;
+	for_each_zone_zonelist_nodemask(zone, z, zonelist, sc->reclaim_idx,
+					sc->nodemask) {
+		if (zone->zone_pgdat == last_pgdat)
+			continue;
+		last_pgdat = zone->zone_pgdat;
+
+		snapshot_refaults(sc->target_mem_cgroup, zone->zone_pgdat);
+
+		if (cgroup_reclaim(sc)) {
+			struct lruvec *lruvec;
+
+			lruvec = mem_cgroup_lruvec(sc->target_mem_cgroup,
+						   zone->zone_pgdat);
+			clear_bit(LRUVEC_CONGESTED, &lruvec->flags);
+		}
+	}
+
+	delayacct_freepages_end();
+
+	if (sc->nr_reclaimed)
+		return sc->nr_reclaimed;
+
+	/* Aborted reclaim to try compaction? don't OOM, then */
+	if (sc->compaction_ready)
+		return 1;
+
+	/*
+	 * We make inactive:active ratio decisions based on the node's
+	 * composition of memory, but a restrictive reclaim_idx or a
+	 * memory.low cgroup setting can exempt large amounts of
+	 * memory from reclaim. Neither of which are very common, so
+	 * instead of doing costly eligibility calculations of the
+	 * entire cgroup subtree up front, we assume the estimates are
+	 * good, and retry with forcible deactivation if that fails.
+	 */
+	if (sc->skipped_deactivate) {
+		sc->priority = initial_priority;
+		sc->force_deactivate = 1;
+		sc->skipped_deactivate = 0;
+		goto retry;
+	}
+
+	/* Untapped cgroup reserves?  Don't OOM, retry. */
+	if (sc->memcg_low_skipped) {
+		sc->priority = initial_priority;
+		sc->force_deactivate = 0;
+		sc->memcg_low_reclaim = 1;
+		sc->memcg_low_skipped = 0;
+		goto retry;
+	}
+
+	return 0;
+}
+
+static bool allow_direct_reclaim(pg_data_t *pgdat)
+{
+	struct zone *zone;
+	unsigned long pfmemalloc_reserve = 0;
+	unsigned long free_pages = 0;
+	int i;
+	bool wmark_ok;
+
+	if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES)
+		return true;
+
+	for (i = 0; i <= ZONE_NORMAL; i++) {
+		zone = &pgdat->node_zones[i];
+		if (!managed_zone(zone))
+			continue;
+
+		if (!zone_reclaimable_pages(zone))
+			continue;
+
+		pfmemalloc_reserve += min_wmark_pages(zone);
+		free_pages += zone_page_state(zone, NR_FREE_PAGES);
+	}
+
+	/* If there are no reserves (unexpected config) then do not throttle */
+	if (!pfmemalloc_reserve)
+		return true;
+
+	wmark_ok = free_pages > pfmemalloc_reserve / 2;
+
+	/* kswapd must be awake if processes are being throttled */
+	if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) {
+		if (READ_ONCE(pgdat->kswapd_highest_zoneidx) > ZONE_NORMAL)
+			WRITE_ONCE(pgdat->kswapd_highest_zoneidx, ZONE_NORMAL);
+
+		wake_up_interruptible(&pgdat->kswapd_wait);
+	}
+
+	return wmark_ok;
+}
+
+/*
+ * Throttle direct reclaimers if backing storage is backed by the network
+ * and the PFMEMALLOC reserve for the preferred node is getting dangerously
+ * depleted. kswapd will continue to make progress and wake the processes
+ * when the low watermark is reached.
+ *
+ * Returns true if a fatal signal was delivered during throttling. If this
+ * happens, the page allocator should not consider triggering the OOM killer.
+ */
+static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
+					nodemask_t *nodemask)
+{
+	struct zoneref *z;
+	struct zone *zone;
+	pg_data_t *pgdat = NULL;
+
+	/*
+	 * Kernel threads should not be throttled as they may be indirectly
+	 * responsible for cleaning pages necessary for reclaim to make forward
+	 * progress. kjournald for example may enter direct reclaim while
+	 * committing a transaction where throttling it could forcing other
+	 * processes to block on log_wait_commit().
+	 */
+	if (current->flags & PF_KTHREAD)
+		goto out;
+
+	/*
+	 * If a fatal signal is pending, this process should not throttle.
+	 * It should return quickly so it can exit and free its memory
+	 */
+	if (fatal_signal_pending(current))
+		goto out;
+
+	/*
+	 * Check if the pfmemalloc reserves are ok by finding the first node
+	 * with a usable ZONE_NORMAL or lower zone. The expectation is that
+	 * GFP_KERNEL will be required for allocating network buffers when
+	 * swapping over the network so ZONE_HIGHMEM is unusable.
+	 *
+	 * Throttling is based on the first usable node and throttled processes
+	 * wait on a queue until kswapd makes progress and wakes them. There
+	 * is an affinity then between processes waking up and where reclaim
+	 * progress has been made assuming the process wakes on the same node.
+	 * More importantly, processes running on remote nodes will not compete
+	 * for remote pfmemalloc reserves and processes on different nodes
+	 * should make reasonable progress.
+	 */
+	for_each_zone_zonelist_nodemask(zone, z, zonelist,
+					gfp_zone(gfp_mask), nodemask) {
+		if (zone_idx(zone) > ZONE_NORMAL)
+			continue;
+
+		/* Throttle based on the first usable node */
+		pgdat = zone->zone_pgdat;
+		if (allow_direct_reclaim(pgdat))
+			goto out;
+		break;
+	}
+
+	/* If no zone was usable by the allocation flags then do not throttle */
+	if (!pgdat)
+		goto out;
+
+	/* Account for the throttling */
+	count_vm_event(PGSCAN_DIRECT_THROTTLE);
+
+	/*
+	 * If the caller cannot enter the filesystem, it's possible that it
+	 * is due to the caller holding an FS lock or performing a journal
+	 * transaction in the case of a filesystem like ext[3|4]. In this case,
+	 * it is not safe to block on pfmemalloc_wait as kswapd could be
+	 * blocked waiting on the same lock. Instead, throttle for up to a
+	 * second before continuing.
+	 */
+	if (!(gfp_mask & __GFP_FS)) {
+		wait_event_interruptible_timeout(pgdat->pfmemalloc_wait,
+			allow_direct_reclaim(pgdat), HZ);
+
+		goto check_pending;
+	}
+
+	/* Throttle until kswapd wakes the process */
+	wait_event_killable(zone->zone_pgdat->pfmemalloc_wait,
+		allow_direct_reclaim(pgdat));
+
+check_pending:
+	if (fatal_signal_pending(current))
+		return true;
+
+out:
+	return false;
+}
+
+unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
+				gfp_t gfp_mask, nodemask_t *nodemask)
+{
+	unsigned long nr_reclaimed;
+	struct scan_control sc = {
+		.nr_to_reclaim = SWAP_CLUSTER_MAX,
+		.gfp_mask = current_gfp_context(gfp_mask),
+		.reclaim_idx = gfp_zone(gfp_mask),
+		.order = order,
+		.nodemask = nodemask,
+		.priority = DEF_PRIORITY,
+		.may_writepage = !laptop_mode,
+		.may_unmap = 1,
+		.may_swap = 1,
+	};
+
+	/*
+	 * scan_control uses s8 fields for order, priority, and reclaim_idx.
+	 * Confirm they are large enough for max values.
+	 */
+	BUILD_BUG_ON(MAX_ORDER > S8_MAX);
+	BUILD_BUG_ON(DEF_PRIORITY > S8_MAX);
+	BUILD_BUG_ON(MAX_NR_ZONES > S8_MAX);
+
+	/*
+	 * Do not enter reclaim if fatal signal was delivered while throttled.
+	 * 1 is returned so that the page allocator does not OOM kill at this
+	 * point.
+	 */
+	if (throttle_direct_reclaim(sc.gfp_mask, zonelist, nodemask))
+		return 1;
+
+	set_task_reclaim_state(current, &sc.reclaim_state);
+	trace_mm_vmscan_direct_reclaim_begin(order, sc.gfp_mask);
+
+	nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
+
+	trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
+	set_task_reclaim_state(current, NULL);
+
+	return nr_reclaimed;
+}
+
+#ifdef CONFIG_MEMCG
+
+/* Only used by soft limit reclaim. Do not reuse for anything else. */
+unsigned long mem_cgroup_shrink_node(struct mem_cgroup *memcg,
+						gfp_t gfp_mask, bool noswap,
+						pg_data_t *pgdat,
+						unsigned long *nr_scanned)
+{
+	struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat);
+	struct scan_control sc = {
+		.nr_to_reclaim = SWAP_CLUSTER_MAX,
+		.target_mem_cgroup = memcg,
+		.may_writepage = !laptop_mode,
+		.may_unmap = 1,
+		.reclaim_idx = MAX_NR_ZONES - 1,
+		.may_swap = !noswap,
+	};
+
+	WARN_ON_ONCE(!current->reclaim_state);
+
+	sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
+			(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
+
+	trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order,
+						      sc.gfp_mask);
+
+	/*
+	 * NOTE: Although we can get the priority field, using it
+	 * here is not a good idea, since it limits the pages we can scan.
+	 * if we don't reclaim here, the shrink_node from balance_pgdat
+	 * will pick up pages from other mem cgroup's as well. We hack
+	 * the priority and make it zero.
+	 */
+	shrink_lruvec(lruvec, &sc);
+
+	trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
+
+	*nr_scanned = sc.nr_scanned;
+
+	return sc.nr_reclaimed;
+}
+
+unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
+					   unsigned long nr_pages,
+					   gfp_t gfp_mask,
+					   bool may_swap)
+{
+	unsigned long nr_reclaimed;
+	unsigned int noreclaim_flag;
+	struct scan_control sc = {
+		.nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
+		.gfp_mask = (current_gfp_context(gfp_mask) & GFP_RECLAIM_MASK) |
+				(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
+		.reclaim_idx = MAX_NR_ZONES - 1,
+		.target_mem_cgroup = memcg,
+		.priority = DEF_PRIORITY,
+		.may_writepage = !laptop_mode,
+		.may_unmap = 1,
+		.may_swap = may_swap,
+	};
+	/*
+	 * Traverse the ZONELIST_FALLBACK zonelist of the current node to put
+	 * equal pressure on all the nodes. This is based on the assumption that
+	 * the reclaim does not bail out early.
+	 */
+	struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
+
+	set_task_reclaim_state(current, &sc.reclaim_state);
+	trace_mm_vmscan_memcg_reclaim_begin(0, sc.gfp_mask);
+	noreclaim_flag = memalloc_noreclaim_save();
+
+	nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
+
+	memalloc_noreclaim_restore(noreclaim_flag);
+	trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
+	set_task_reclaim_state(current, NULL);
+
+	return nr_reclaimed;
+}
+#endif
+
+static void age_active_anon(struct pglist_data *pgdat,
+				struct scan_control *sc)
+{
+	struct mem_cgroup *memcg;
+	struct lruvec *lruvec;
+
+	if (!total_swap_pages)
+		return;
+
+	lruvec = mem_cgroup_lruvec(NULL, pgdat);
+	if (!inactive_is_low(lruvec, LRU_INACTIVE_ANON))
+		return;
+
+	memcg = mem_cgroup_iter(NULL, NULL, NULL);
+	do {
+		lruvec = mem_cgroup_lruvec(memcg, pgdat);
+		shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
+				   sc, LRU_ACTIVE_ANON);
+		memcg = mem_cgroup_iter(NULL, memcg, NULL);
+	} while (memcg);
+}
+
+static bool pgdat_watermark_boosted(pg_data_t *pgdat, int highest_zoneidx)
+{
+	int i;
+	struct zone *zone;
+
+	/*
+	 * Check for watermark boosts top-down as the higher zones
+	 * are more likely to be boosted. Both watermarks and boosts
+	 * should not be checked at the same time as reclaim would
+	 * start prematurely when there is no boosting and a lower
+	 * zone is balanced.
+	 */
+	for (i = highest_zoneidx; i >= 0; i--) {
+		zone = pgdat->node_zones + i;
+		if (!managed_zone(zone))
+			continue;
+
+		if (zone->watermark_boost)
+			return true;
+	}
+
+	return false;
+}
+
+/*
+ * Returns true if there is an eligible zone balanced for the request order
+ * and highest_zoneidx
+ */
+static bool pgdat_balanced(pg_data_t *pgdat, int order, int highest_zoneidx)
+{
+	int i;
+	unsigned long mark = -1;
+	struct zone *zone;
+
+	/*
+	 * Check watermarks bottom-up as lower zones are more likely to
+	 * meet watermarks.
+	 */
+	for (i = 0; i <= highest_zoneidx; i++) {
+		zone = pgdat->node_zones + i;
+
+		if (!managed_zone(zone))
+			continue;
+
+		mark = high_wmark_pages(zone);
+		if (zone_watermark_ok_safe(zone, order, mark, highest_zoneidx))
+			return true;
+	}
+
+	/*
+	 * If a node has no populated zone within highest_zoneidx, it does not
+	 * need balancing by definition. This can happen if a zone-restricted
+	 * allocation tries to wake a remote kswapd.
+	 */
+	if (mark == -1)
+		return true;
+
+	return false;
+}
+
+/* Clear pgdat state for congested, dirty or under writeback. */
+static void clear_pgdat_congested(pg_data_t *pgdat)
+{
+	struct lruvec *lruvec = mem_cgroup_lruvec(NULL, pgdat);
+
+	clear_bit(LRUVEC_CONGESTED, &lruvec->flags);
+	clear_bit(PGDAT_DIRTY, &pgdat->flags);
+	clear_bit(PGDAT_WRITEBACK, &pgdat->flags);
+}
+
+/*
+ * Prepare kswapd for sleeping. This verifies that there are no processes
+ * waiting in throttle_direct_reclaim() and that watermarks have been met.
+ *
+ * Returns true if kswapd is ready to sleep
+ */
+static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order,
+				int highest_zoneidx)
+{
+	/*
+	 * The throttled processes are normally woken up in balance_pgdat() as
+	 * soon as allow_direct_reclaim() is true. But there is a potential
+	 * race between when kswapd checks the watermarks and a process gets
+	 * throttled. There is also a potential race if processes get
+	 * throttled, kswapd wakes, a large process exits thereby balancing the
+	 * zones, which causes kswapd to exit balance_pgdat() before reaching
+	 * the wake up checks. If kswapd is going to sleep, no process should
+	 * be sleeping on pfmemalloc_wait, so wake them now if necessary. If
+	 * the wake up is premature, processes will wake kswapd and get
+	 * throttled again. The difference from wake ups in balance_pgdat() is
+	 * that here we are under prepare_to_wait().
+	 */
+	if (waitqueue_active(&pgdat->pfmemalloc_wait))
+		wake_up_all(&pgdat->pfmemalloc_wait);
+
+	/* Hopeless node, leave it to direct reclaim */
+	if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES)
+		return true;
+
+	if (pgdat_balanced(pgdat, order, highest_zoneidx)) {
+		clear_pgdat_congested(pgdat);
+		return true;
+	}
+
+	return false;
+}
+
+/*
+ * kswapd shrinks a node of pages that are at or below the highest usable
+ * zone that is currently unbalanced.
+ *
+ * Returns true if kswapd scanned at least the requested number of pages to
+ * reclaim or if the lack of progress was due to pages under writeback.
+ * This is used to determine if the scanning priority needs to be raised.
+ */
+static bool kswapd_shrink_node(pg_data_t *pgdat,
+			       struct scan_control *sc)
+{
+	struct zone *zone;
+	int z;
+
+	/* Reclaim a number of pages proportional to the number of zones */
+	sc->nr_to_reclaim = 0;
+	for (z = 0; z <= sc->reclaim_idx; z++) {
+		zone = pgdat->node_zones + z;
+		if (!managed_zone(zone))
+			continue;
+
+		sc->nr_to_reclaim += max(high_wmark_pages(zone), SWAP_CLUSTER_MAX);
+	}
+
+	/*
+	 * Historically care was taken to put equal pressure on all zones but
+	 * now pressure is applied based on node LRU order.
+	 */
+	shrink_node(pgdat, sc);
+
+	/*
+	 * Fragmentation may mean that the system cannot be rebalanced for
+	 * high-order allocations. If twice the allocation size has been
+	 * reclaimed then recheck watermarks only at order-0 to prevent
+	 * excessive reclaim. Assume that a process requested a high-order
+	 * can direct reclaim/compact.
+	 */
+	if (sc->order && sc->nr_reclaimed >= compact_gap(sc->order))
+		sc->order = 0;
+
+	return sc->nr_scanned >= sc->nr_to_reclaim;
+}
+
+/*
+ * For kswapd, balance_pgdat() will reclaim pages across a node from zones
+ * that are eligible for use by the caller until at least one zone is
+ * balanced.
+ *
+ * Returns the order kswapd finished reclaiming at.
+ *
+ * kswapd scans the zones in the highmem->normal->dma direction.  It skips
+ * zones which have free_pages > high_wmark_pages(zone), but once a zone is
+ * found to have free_pages <= high_wmark_pages(zone), any page in that zone
+ * or lower is eligible for reclaim until at least one usable zone is
+ * balanced.
+ */
+static int balance_pgdat(pg_data_t *pgdat, int order, int highest_zoneidx)
+{
+	int i;
+	unsigned long nr_soft_reclaimed;
+	unsigned long nr_soft_scanned;
+	unsigned long pflags;
+	unsigned long nr_boost_reclaim;
+	unsigned long zone_boosts[MAX_NR_ZONES] = { 0, };
+	bool boosted;
+	struct zone *zone;
+	struct scan_control sc = {
+		.gfp_mask = GFP_KERNEL,
+		.order = order,
+		.may_unmap = 1,
+	};
+
+	set_task_reclaim_state(current, &sc.reclaim_state);
+	psi_memstall_enter(&pflags);
+	__fs_reclaim_acquire();
+
+	count_vm_event(PAGEOUTRUN);
+
+	/*
+	 * Account for the reclaim boost. Note that the zone boost is left in
+	 * place so that parallel allocations that are near the watermark will
+	 * stall or direct reclaim until kswapd is finished.
+	 */
+	nr_boost_reclaim = 0;
+	for (i = 0; i <= highest_zoneidx; i++) {
+		zone = pgdat->node_zones + i;
+		if (!managed_zone(zone))
+			continue;
+
+		nr_boost_reclaim += zone->watermark_boost;
+		zone_boosts[i] = zone->watermark_boost;
+	}
+	boosted = nr_boost_reclaim;
+
+restart:
+	sc.priority = DEF_PRIORITY;
+	do {
+		unsigned long nr_reclaimed = sc.nr_reclaimed;
+		bool raise_priority = true;
+		bool balanced;
+		bool ret;
+
+		sc.reclaim_idx = highest_zoneidx;
+
+		/*
+		 * If the number of buffer_heads exceeds the maximum allowed
+		 * then consider reclaiming from all zones. This has a dual
+		 * purpose -- on 64-bit systems it is expected that
+		 * buffer_heads are stripped during active rotation. On 32-bit
+		 * systems, highmem pages can pin lowmem memory and shrinking
+		 * buffers can relieve lowmem pressure. Reclaim may still not
+		 * go ahead if all eligible zones for the original allocation
+		 * request are balanced to avoid excessive reclaim from kswapd.
+		 */
+		if (buffer_heads_over_limit) {
+			for (i = MAX_NR_ZONES - 1; i >= 0; i--) {
+				zone = pgdat->node_zones + i;
+				if (!managed_zone(zone))
+					continue;
+
+				sc.reclaim_idx = i;
+				break;
+			}
+		}
+
+		/*
+		 * If the pgdat is imbalanced then ignore boosting and preserve
+		 * the watermarks for a later time and restart. Note that the
+		 * zone watermarks will be still reset at the end of balancing
+		 * on the grounds that the normal reclaim should be enough to
+		 * re-evaluate if boosting is required when kswapd next wakes.
+		 */
+		balanced = pgdat_balanced(pgdat, sc.order, highest_zoneidx);
+		if (!balanced && nr_boost_reclaim) {
+			nr_boost_reclaim = 0;
+			goto restart;
+		}
+
+		/*
+		 * If boosting is not active then only reclaim if there are no
+		 * eligible zones. Note that sc.reclaim_idx is not used as
+		 * buffer_heads_over_limit may have adjusted it.
+		 */
+		if (!nr_boost_reclaim && balanced)
+			goto out;
+
+		/* Limit the priority of boosting to avoid reclaim writeback */
+		if (nr_boost_reclaim && sc.priority == DEF_PRIORITY - 2)
+			raise_priority = false;
+
+		/*
+		 * Do not writeback or swap pages for boosted reclaim. The
+		 * intent is to relieve pressure not issue sub-optimal IO
+		 * from reclaim context. If no pages are reclaimed, the
+		 * reclaim will be aborted.
+		 */
+		sc.may_writepage = !laptop_mode && !nr_boost_reclaim;
+		sc.may_swap = !nr_boost_reclaim;
+
+		/*
+		 * Do some background aging of the anon list, to give
+		 * pages a chance to be referenced before reclaiming. All
+		 * pages are rotated regardless of classzone as this is
+		 * about consistent aging.
+		 */
+		age_active_anon(pgdat, &sc);
+
+		/*
+		 * If we're getting trouble reclaiming, start doing writepage
+		 * even in laptop mode.
+		 */
+		if (sc.priority < DEF_PRIORITY - 2)
+			sc.may_writepage = 1;
+
+		/* Call soft limit reclaim before calling shrink_node. */
+		sc.nr_scanned = 0;
+		nr_soft_scanned = 0;
+		nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(pgdat, sc.order,
+						sc.gfp_mask, &nr_soft_scanned);
+		sc.nr_reclaimed += nr_soft_reclaimed;
+
+		/*
+		 * There should be no need to raise the scanning priority if
+		 * enough pages are already being scanned that that high
+		 * watermark would be met at 100% efficiency.
+		 */
+		if (kswapd_shrink_node(pgdat, &sc))
+			raise_priority = false;
+
+		/*
+		 * If the low watermark is met there is no need for processes
+		 * to be throttled on pfmemalloc_wait as they should not be
+		 * able to safely make forward progress. Wake them
+		 */
+		if (waitqueue_active(&pgdat->pfmemalloc_wait) &&
+				allow_direct_reclaim(pgdat))
+			wake_up_all(&pgdat->pfmemalloc_wait);
+
+		/* Check if kswapd should be suspending */
+		__fs_reclaim_release();
+		ret = try_to_freeze();
+		__fs_reclaim_acquire();
+		if (ret || kthread_should_stop())
+			break;
+
+		/*
+		 * Raise priority if scanning rate is too low or there was no
+		 * progress in reclaiming pages
+		 */
+		nr_reclaimed = sc.nr_reclaimed - nr_reclaimed;
+		nr_boost_reclaim -= min(nr_boost_reclaim, nr_reclaimed);
+
+		/*
+		 * If reclaim made no progress for a boost, stop reclaim as
+		 * IO cannot be queued and it could be an infinite loop in
+		 * extreme circumstances.
+		 */
+		if (nr_boost_reclaim && !nr_reclaimed)
+			break;
+
+		if (raise_priority || !nr_reclaimed)
+			sc.priority--;
+	} while (sc.priority >= 1);
+
+	if (!sc.nr_reclaimed)
+		pgdat->kswapd_failures++;
+
+out:
+	/* If reclaim was boosted, account for the reclaim done in this pass */
+	if (boosted) {
+		unsigned long flags;
+
+		for (i = 0; i <= highest_zoneidx; i++) {
+			if (!zone_boosts[i])
+				continue;
+
+			/* Increments are under the zone lock */
+			zone = pgdat->node_zones + i;
+			spin_lock_irqsave(&zone->lock, flags);
+			zone->watermark_boost -= min(zone->watermark_boost, zone_boosts[i]);
+			spin_unlock_irqrestore(&zone->lock, flags);
+		}
+
+		/*
+		 * As there is now likely space, wakeup kcompact to defragment
+		 * pageblocks.
+		 */
+		wakeup_kcompactd(pgdat, pageblock_order, highest_zoneidx);
+	}
+
+	snapshot_refaults(NULL, pgdat);
+	__fs_reclaim_release();
+	psi_memstall_leave(&pflags);
+	set_task_reclaim_state(current, NULL);
+
+	/*
+	 * Return the order kswapd stopped reclaiming at as
+	 * prepare_kswapd_sleep() takes it into account. If another caller
+	 * entered the allocator slow path while kswapd was awake, order will
+	 * remain at the higher level.
+	 */
+	return sc.order;
+}
+
+/*
+ * The pgdat->kswapd_highest_zoneidx is used to pass the highest zone index to
+ * be reclaimed by kswapd from the waker. If the value is MAX_NR_ZONES which is
+ * not a valid index then either kswapd runs for first time or kswapd couldn't
+ * sleep after previous reclaim attempt (node is still unbalanced). In that
+ * case return the zone index of the previous kswapd reclaim cycle.
+ */
+static enum zone_type kswapd_highest_zoneidx(pg_data_t *pgdat,
+					   enum zone_type prev_highest_zoneidx)
+{
+	enum zone_type curr_idx = READ_ONCE(pgdat->kswapd_highest_zoneidx);
+
+	return curr_idx == MAX_NR_ZONES ? prev_highest_zoneidx : curr_idx;
+}
+
+static void kswapd_try_to_sleep(pg_data_t *pgdat, int alloc_order, int reclaim_order,
+				unsigned int highest_zoneidx)
+{
+	long remaining = 0;
+	DEFINE_WAIT(wait);
+
+	if (freezing(current) || kthread_should_stop())
+		return;
+
+	prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
+
+	/*
+	 * Try to sleep for a short interval. Note that kcompactd will only be
+	 * woken if it is possible to sleep for a short interval. This is
+	 * deliberate on the assumption that if reclaim cannot keep an
+	 * eligible zone balanced that it's also unlikely that compaction will
+	 * succeed.
+	 */
+	if (prepare_kswapd_sleep(pgdat, reclaim_order, highest_zoneidx)) {
+		/*
+		 * Compaction records what page blocks it recently failed to
+		 * isolate pages from and skips them in the future scanning.
+		 * When kswapd is going to sleep, it is reasonable to assume
+		 * that pages and compaction may succeed so reset the cache.
+		 */
+		reset_isolation_suitable(pgdat);
+
+		/*
+		 * We have freed the memory, now we should compact it to make
+		 * allocation of the requested order possible.
+		 */
+		wakeup_kcompactd(pgdat, alloc_order, highest_zoneidx);
+
+		remaining = schedule_timeout(HZ/10);
+
+		/*
+		 * If woken prematurely then reset kswapd_highest_zoneidx and
+		 * order. The values will either be from a wakeup request or
+		 * the previous request that slept prematurely.
+		 */
+		if (remaining) {
+			WRITE_ONCE(pgdat->kswapd_highest_zoneidx,
+					kswapd_highest_zoneidx(pgdat,
+							highest_zoneidx));
+
+			if (READ_ONCE(pgdat->kswapd_order) < reclaim_order)
+				WRITE_ONCE(pgdat->kswapd_order, reclaim_order);
+		}
+
+		finish_wait(&pgdat->kswapd_wait, &wait);
+		prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
+	}
+
+	/*
+	 * After a short sleep, check if it was a premature sleep. If not, then
+	 * go fully to sleep until explicitly woken up.
+	 */
+	if (!remaining &&
+	    prepare_kswapd_sleep(pgdat, reclaim_order, highest_zoneidx)) {
+		trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
+
+		/*
+		 * vmstat counters are not perfectly accurate and the estimated
+		 * value for counters such as NR_FREE_PAGES can deviate from the
+		 * true value by nr_online_cpus * threshold. To avoid the zone
+		 * watermarks being breached while under pressure, we reduce the
+		 * per-cpu vmstat threshold while kswapd is awake and restore
+		 * them before going back to sleep.
+		 */
+		set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
+
+		if (!kthread_should_stop())
+			schedule();
+
+		set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
+	} else {
+		if (remaining)
+			count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
+		else
+			count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
+	}
+	finish_wait(&pgdat->kswapd_wait, &wait);
+}
+
+/*
+ * The background pageout daemon, started as a kernel thread
+ * from the init process.
+ *
+ * This basically trickles out pages so that we have _some_
+ * free memory available even if there is no other activity
+ * that frees anything up. This is needed for things like routing
+ * etc, where we otherwise might have all activity going on in
+ * asynchronous contexts that cannot page things out.
+ *
+ * If there are applications that are active memory-allocators
+ * (most normal use), this basically shouldn't matter.
+ */
+static int kswapd(void *p)
+{
+	unsigned int alloc_order, reclaim_order;
+	unsigned int highest_zoneidx = MAX_NR_ZONES - 1;
+	pg_data_t *pgdat = (pg_data_t*)p;
+	struct task_struct *tsk = current;
+	const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
+
+	if (!cpumask_empty(cpumask))
+		set_cpus_allowed_ptr(tsk, cpumask);
+
+	/*
+	 * Tell the memory management that we're a "memory allocator",
+	 * and that if we need more memory we should get access to it
+	 * regardless (see "__alloc_pages()"). "kswapd" should
+	 * never get caught in the normal page freeing logic.
+	 *
+	 * (Kswapd normally doesn't need memory anyway, but sometimes
+	 * you need a small amount of memory in order to be able to
+	 * page out something else, and this flag essentially protects
+	 * us from recursively trying to free more memory as we're
+	 * trying to free the first piece of memory in the first place).
+	 */
+	tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
+	set_freezable();
+
+	WRITE_ONCE(pgdat->kswapd_order, 0);
+	WRITE_ONCE(pgdat->kswapd_highest_zoneidx, MAX_NR_ZONES);
+	for ( ; ; ) {
+		bool ret;
+
+		alloc_order = reclaim_order = READ_ONCE(pgdat->kswapd_order);
+		highest_zoneidx = kswapd_highest_zoneidx(pgdat,
+							highest_zoneidx);
+
+kswapd_try_sleep:
+		kswapd_try_to_sleep(pgdat, alloc_order, reclaim_order,
+					highest_zoneidx);
+
+		/* Read the new order and highest_zoneidx */
+		alloc_order = reclaim_order = READ_ONCE(pgdat->kswapd_order);
+		highest_zoneidx = kswapd_highest_zoneidx(pgdat,
+							highest_zoneidx);
+		WRITE_ONCE(pgdat->kswapd_order, 0);
+		WRITE_ONCE(pgdat->kswapd_highest_zoneidx, MAX_NR_ZONES);
+
+		ret = try_to_freeze();
+		if (kthread_should_stop())
+			break;
+
+		/*
+		 * We can speed up thawing tasks if we don't call balance_pgdat
+		 * after returning from the refrigerator
+		 */
+		if (ret)
+			continue;
+
+		/*
+		 * Reclaim begins at the requested order but if a high-order
+		 * reclaim fails then kswapd falls back to reclaiming for
+		 * order-0. If that happens, kswapd will consider sleeping
+		 * for the order it finished reclaiming at (reclaim_order)
+		 * but kcompactd is woken to compact for the original
+		 * request (alloc_order).
+		 */
+		trace_mm_vmscan_kswapd_wake(pgdat->node_id, highest_zoneidx,
+						alloc_order);
+		reclaim_order = balance_pgdat(pgdat, alloc_order,
+						highest_zoneidx);
+		if (reclaim_order < alloc_order)
+			goto kswapd_try_sleep;
+	}
+
+	tsk->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD);
+
+	return 0;
+}
+
+/*
+ * A zone is low on free memory or too fragmented for high-order memory.  If
+ * kswapd should reclaim (direct reclaim is deferred), wake it up for the zone's
+ * pgdat.  It will wake up kcompactd after reclaiming memory.  If kswapd reclaim
+ * has failed or is not needed, still wake up kcompactd if only compaction is
+ * needed.
+ */
+void wakeup_kswapd(struct zone *zone, gfp_t gfp_flags, int order,
+		   enum zone_type highest_zoneidx)
+{
+	pg_data_t *pgdat;
+	enum zone_type curr_idx;
+
+	if (!managed_zone(zone))
+		return;
+
+	if (!cpuset_zone_allowed(zone, gfp_flags))
+		return;
+
+	pgdat = zone->zone_pgdat;
+	curr_idx = READ_ONCE(pgdat->kswapd_highest_zoneidx);
+
+	if (curr_idx == MAX_NR_ZONES || curr_idx < highest_zoneidx)
+		WRITE_ONCE(pgdat->kswapd_highest_zoneidx, highest_zoneidx);
+
+	if (READ_ONCE(pgdat->kswapd_order) < order)
+		WRITE_ONCE(pgdat->kswapd_order, order);
+
+	if (!waitqueue_active(&pgdat->kswapd_wait))
+		return;
+
+	/* Hopeless node, leave it to direct reclaim if possible */
+	if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES ||
+	    (pgdat_balanced(pgdat, order, highest_zoneidx) &&
+	     !pgdat_watermark_boosted(pgdat, highest_zoneidx))) {
+		/*
+		 * There may be plenty of free memory available, but it's too
+		 * fragmented for high-order allocations.  Wake up kcompactd
+		 * and rely on compaction_suitable() to determine if it's
+		 * needed.  If it fails, it will defer subsequent attempts to
+		 * ratelimit its work.
+		 */
+		if (!(gfp_flags & __GFP_DIRECT_RECLAIM))
+			wakeup_kcompactd(pgdat, order, highest_zoneidx);
+		return;
+	}
+
+	trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, highest_zoneidx, order,
+				      gfp_flags);
+	wake_up_interruptible(&pgdat->kswapd_wait);
+}
+
+#ifdef CONFIG_HIBERNATION
+/*
+ * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
+ * freed pages.
+ *
+ * Rather than trying to age LRUs the aim is to preserve the overall
+ * LRU order by reclaiming preferentially
+ * inactive > active > active referenced > active mapped
+ */
+unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
+{
+	struct scan_control sc = {
+		.nr_to_reclaim = nr_to_reclaim,
+		.gfp_mask = GFP_HIGHUSER_MOVABLE,
+		.reclaim_idx = MAX_NR_ZONES - 1,
+		.priority = DEF_PRIORITY,
+		.may_writepage = 1,
+		.may_unmap = 1,
+		.may_swap = 1,
+		.hibernation_mode = 1,
+	};
+	struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
+	unsigned long nr_reclaimed;
+	unsigned int noreclaim_flag;
+
+	fs_reclaim_acquire(sc.gfp_mask);
+	noreclaim_flag = memalloc_noreclaim_save();
+	set_task_reclaim_state(current, &sc.reclaim_state);
+
+	nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
+
+	set_task_reclaim_state(current, NULL);
+	memalloc_noreclaim_restore(noreclaim_flag);
+	fs_reclaim_release(sc.gfp_mask);
+
+	return nr_reclaimed;
+}
+#endif /* CONFIG_HIBERNATION */
+
+/*
+ * This kswapd start function will be called by init and node-hot-add.
+ * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
+ */
+int kswapd_run(int nid)
+{
+	pg_data_t *pgdat = NODE_DATA(nid);
+	int ret = 0;
+
+	if (pgdat->kswapd)
+		return 0;
+
+	pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
+	if (IS_ERR(pgdat->kswapd)) {
+		/* failure at boot is fatal */
+		BUG_ON(system_state < SYSTEM_RUNNING);
+		pr_err("Failed to start kswapd on node %d\n", nid);
+		ret = PTR_ERR(pgdat->kswapd);
+		pgdat->kswapd = NULL;
+	}
+	return ret;
+}
+
+/*
+ * Called by memory hotplug when all memory in a node is offlined.  Caller must
+ * hold mem_hotplug_begin/end().
+ */
+void kswapd_stop(int nid)
+{
+	struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
+
+	if (kswapd) {
+		kthread_stop(kswapd);
+		NODE_DATA(nid)->kswapd = NULL;
+	}
+}
+
+static int __init kswapd_init(void)
+{
+	int nid;
+
+	swap_setup();
+	for_each_node_state(nid, N_MEMORY)
+ 		kswapd_run(nid);
+	return 0;
+}
+
+module_init(kswapd_init)
+
+#ifdef CONFIG_NUMA
+/*
+ * Node reclaim mode
+ *
+ * If non-zero call node_reclaim when the number of free pages falls below
+ * the watermarks.
+ */
+int node_reclaim_mode __read_mostly;
+
+/*
+ * These bit locations are exposed in the vm.zone_reclaim_mode sysctl
+ * ABI.  New bits are OK, but existing bits can never change.
+ */
+#define RECLAIM_ZONE  (1<<0)   /* Run shrink_inactive_list on the zone */
+#define RECLAIM_WRITE (1<<1)   /* Writeout pages during reclaim */
+#define RECLAIM_UNMAP (1<<2)   /* Unmap pages during reclaim */
+
+/*
+ * Priority for NODE_RECLAIM. This determines the fraction of pages
+ * of a node considered for each zone_reclaim. 4 scans 1/16th of
+ * a zone.
+ */
+#define NODE_RECLAIM_PRIORITY 4
+
+/*
+ * Percentage of pages in a zone that must be unmapped for node_reclaim to
+ * occur.
+ */
+int sysctl_min_unmapped_ratio = 1;
+
+/*
+ * If the number of slab pages in a zone grows beyond this percentage then
+ * slab reclaim needs to occur.
+ */
+int sysctl_min_slab_ratio = 5;
+
+static inline unsigned long node_unmapped_file_pages(struct pglist_data *pgdat)
+{
+	unsigned long file_mapped = node_page_state(pgdat, NR_FILE_MAPPED);
+	unsigned long file_lru = node_page_state(pgdat, NR_INACTIVE_FILE) +
+		node_page_state(pgdat, NR_ACTIVE_FILE);
+
+	/*
+	 * It's possible for there to be more file mapped pages than
+	 * accounted for by the pages on the file LRU lists because
+	 * tmpfs pages accounted for as ANON can also be FILE_MAPPED
+	 */
+	return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
+}
+
+/* Work out how many page cache pages we can reclaim in this reclaim_mode */
+static unsigned long node_pagecache_reclaimable(struct pglist_data *pgdat)
+{
+	unsigned long nr_pagecache_reclaimable;
+	unsigned long delta = 0;
+
+	/*
+	 * If RECLAIM_UNMAP is set, then all file pages are considered
+	 * potentially reclaimable. Otherwise, we have to worry about
+	 * pages like swapcache and node_unmapped_file_pages() provides
+	 * a better estimate
+	 */
+	if (node_reclaim_mode & RECLAIM_UNMAP)
+		nr_pagecache_reclaimable = node_page_state(pgdat, NR_FILE_PAGES);
+	else
+		nr_pagecache_reclaimable = node_unmapped_file_pages(pgdat);
+
+	/* If we can't clean pages, remove dirty pages from consideration */
+	if (!(node_reclaim_mode & RECLAIM_WRITE))
+		delta += node_page_state(pgdat, NR_FILE_DIRTY);
+
+	/* Watch for any possible underflows due to delta */
+	if (unlikely(delta > nr_pagecache_reclaimable))
+		delta = nr_pagecache_reclaimable;
+
+	return nr_pagecache_reclaimable - delta;
+}
+
+/*
+ * Try to free up some pages from this node through reclaim.
+ */
+static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
+{
+	/* Minimum pages needed in order to stay on node */
+	const unsigned long nr_pages = 1 << order;
+	struct task_struct *p = current;
+	unsigned int noreclaim_flag;
+	struct scan_control sc = {
+		.nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
+		.gfp_mask = current_gfp_context(gfp_mask),
+		.order = order,
+		.priority = NODE_RECLAIM_PRIORITY,
+		.may_writepage = !!(node_reclaim_mode & RECLAIM_WRITE),
+		.may_unmap = !!(node_reclaim_mode & RECLAIM_UNMAP),
+		.may_swap = 1,
+		.reclaim_idx = gfp_zone(gfp_mask),
+	};
+
+	trace_mm_vmscan_node_reclaim_begin(pgdat->node_id, order,
+					   sc.gfp_mask);
+
+	cond_resched();
+	fs_reclaim_acquire(sc.gfp_mask);
+	/*
+	 * We need to be able to allocate from the reserves for RECLAIM_UNMAP
+	 * and we also need to be able to write out pages for RECLAIM_WRITE
+	 * and RECLAIM_UNMAP.
+	 */
+	noreclaim_flag = memalloc_noreclaim_save();
+	p->flags |= PF_SWAPWRITE;
+	set_task_reclaim_state(p, &sc.reclaim_state);
+
+	if (node_pagecache_reclaimable(pgdat) > pgdat->min_unmapped_pages) {
+		/*
+		 * Free memory by calling shrink node with increasing
+		 * priorities until we have enough memory freed.
+		 */
+		do {
+			shrink_node(pgdat, &sc);
+		} while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
+	}
+
+	set_task_reclaim_state(p, NULL);
+	current->flags &= ~PF_SWAPWRITE;
+	memalloc_noreclaim_restore(noreclaim_flag);
+	fs_reclaim_release(sc.gfp_mask);
+
+	trace_mm_vmscan_node_reclaim_end(sc.nr_reclaimed);
+
+	return sc.nr_reclaimed >= nr_pages;
+}
+
+int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
+{
+	int ret;
+
+	/*
+	 * Node reclaim reclaims unmapped file backed pages and
+	 * slab pages if we are over the defined limits.
+	 *
+	 * A small portion of unmapped file backed pages is needed for
+	 * file I/O otherwise pages read by file I/O will be immediately
+	 * thrown out if the node is overallocated. So we do not reclaim
+	 * if less than a specified percentage of the node is used by
+	 * unmapped file backed pages.
+	 */
+	if (node_pagecache_reclaimable(pgdat) <= pgdat->min_unmapped_pages &&
+	    node_page_state_pages(pgdat, NR_SLAB_RECLAIMABLE_B) <=
+	    pgdat->min_slab_pages)
+		return NODE_RECLAIM_FULL;
+
+	/*
+	 * Do not scan if the allocation should not be delayed.
+	 */
+	if (!gfpflags_allow_blocking(gfp_mask) || (current->flags & PF_MEMALLOC))
+		return NODE_RECLAIM_NOSCAN;
+
+	/*
+	 * Only run node reclaim on the local node or on nodes that do not
+	 * have associated processors. This will favor the local processor
+	 * over remote processors and spread off node memory allocations
+	 * as wide as possible.
+	 */
+	if (node_state(pgdat->node_id, N_CPU) && pgdat->node_id != numa_node_id())
+		return NODE_RECLAIM_NOSCAN;
+
+	if (test_and_set_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags))
+		return NODE_RECLAIM_NOSCAN;
+
+	ret = __node_reclaim(pgdat, gfp_mask, order);
+	clear_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags);
+
+	if (!ret)
+		count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
+
+	return ret;
+}
+#endif
+
+/**
+ * check_move_unevictable_pages - check pages for evictability and move to
+ * appropriate zone lru list
+ * @pvec: pagevec with lru pages to check
+ *
+ * Checks pages for evictability, if an evictable page is in the unevictable
+ * lru list, moves it to the appropriate evictable lru list. This function
+ * should be only used for lru pages.
+ */
+void check_move_unevictable_pages(struct pagevec *pvec)
+{
+	struct lruvec *lruvec;
+	struct pglist_data *pgdat = NULL;
+	int pgscanned = 0;
+	int pgrescued = 0;
+	int i;
+
+	for (i = 0; i < pvec->nr; i++) {
+		struct page *page = pvec->pages[i];
+		struct pglist_data *pagepgdat = page_pgdat(page);
+		int nr_pages;
+
+		if (PageTransTail(page))
+			continue;
+
+		nr_pages = thp_nr_pages(page);
+		pgscanned += nr_pages;
+
+		if (pagepgdat != pgdat) {
+			if (pgdat)
+				spin_unlock_irq(&pgdat->lru_lock);
+			pgdat = pagepgdat;
+			spin_lock_irq(&pgdat->lru_lock);
+		}
+		lruvec = mem_cgroup_page_lruvec(page, pgdat);
+
+		if (!PageLRU(page) || !PageUnevictable(page))
+			continue;
+
+		if (page_evictable(page)) {
+			enum lru_list lru = page_lru_base_type(page);
+
+			VM_BUG_ON_PAGE(PageActive(page), page);
+			ClearPageUnevictable(page);
+			del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE);
+			add_page_to_lru_list(page, lruvec, lru);
+			pgrescued += nr_pages;
+		}
+	}
+
+	if (pgdat) {
+		__count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
+		__count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
+		spin_unlock_irq(&pgdat->lru_lock);
+	}
+}
+EXPORT_SYMBOL_GPL(check_move_unevictable_pages);