Adding upstream version 6.6.15.upstream/6.6.15

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

1 files changed, 814 insertions, 0 deletions

diff --git a/mm/workingset.c b/mm/workingset.c
new file mode 100644
index 0000000000..2559a1f2fc
--- /dev/null
+++ b/mm/workingset.c
@@ -0,0 +1,814 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Workingset detection
+ *
+ * Copyright (C) 2013 Red Hat, Inc., Johannes Weiner
+ */
+
+#include <linux/memcontrol.h>
+#include <linux/mm_inline.h>
+#include <linux/writeback.h>
+#include <linux/shmem_fs.h>
+#include <linux/pagemap.h>
+#include <linux/atomic.h>
+#include <linux/module.h>
+#include <linux/swap.h>
+#include <linux/dax.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+
+/*
+ *		Double CLOCK lists
+ *
+ * Per node, two clock lists are maintained for file pages: the
+ * inactive and the active list.  Freshly faulted pages start out at
+ * the head of the inactive list and page reclaim scans pages from the
+ * tail.  Pages that are accessed multiple times on the inactive list
+ * are promoted to the active list, to protect them from reclaim,
+ * whereas active pages are demoted to the inactive list when the
+ * active list grows too big.
+ *
+ *   fault ------------------------+
+ *                                 |
+ *              +--------------+   |            +-------------+
+ *   reclaim <- |   inactive   | <-+-- demotion |    active   | <--+
+ *              +--------------+                +-------------+    |
+ *                     |                                           |
+ *                     +-------------- promotion ------------------+
+ *
+ *
+ *		Access frequency and refault distance
+ *
+ * A workload is thrashing when its pages are frequently used but they
+ * are evicted from the inactive list every time before another access
+ * would have promoted them to the active list.
+ *
+ * In cases where the average access distance between thrashing pages
+ * is bigger than the size of memory there is nothing that can be
+ * done - the thrashing set could never fit into memory under any
+ * circumstance.
+ *
+ * However, the average access distance could be bigger than the
+ * inactive list, yet smaller than the size of memory.  In this case,
+ * the set could fit into memory if it weren't for the currently
+ * active pages - which may be used more, hopefully less frequently:
+ *
+ *      +-memory available to cache-+
+ *      |                           |
+ *      +-inactive------+-active----+
+ *  a b | c d e f g h i | J K L M N |
+ *      +---------------+-----------+
+ *
+ * It is prohibitively expensive to accurately track access frequency
+ * of pages.  But a reasonable approximation can be made to measure
+ * thrashing on the inactive list, after which refaulting pages can be
+ * activated optimistically to compete with the existing active pages.
+ *
+ * Approximating inactive page access frequency - Observations:
+ *
+ * 1. When a page is accessed for the first time, it is added to the
+ *    head of the inactive list, slides every existing inactive page
+ *    towards the tail by one slot, and pushes the current tail page
+ *    out of memory.
+ *
+ * 2. When a page is accessed for the second time, it is promoted to
+ *    the active list, shrinking the inactive list by one slot.  This
+ *    also slides all inactive pages that were faulted into the cache
+ *    more recently than the activated page towards the tail of the
+ *    inactive list.
+ *
+ * Thus:
+ *
+ * 1. The sum of evictions and activations between any two points in
+ *    time indicate the minimum number of inactive pages accessed in
+ *    between.
+ *
+ * 2. Moving one inactive page N page slots towards the tail of the
+ *    list requires at least N inactive page accesses.
+ *
+ * Combining these:
+ *
+ * 1. When a page is finally evicted from memory, the number of
+ *    inactive pages accessed while the page was in cache is at least
+ *    the number of page slots on the inactive list.
+ *
+ * 2. In addition, measuring the sum of evictions and activations (E)
+ *    at the time of a page's eviction, and comparing it to another
+ *    reading (R) at the time the page faults back into memory tells
+ *    the minimum number of accesses while the page was not cached.
+ *    This is called the refault distance.
+ *
+ * Because the first access of the page was the fault and the second
+ * access the refault, we combine the in-cache distance with the
+ * out-of-cache distance to get the complete minimum access distance
+ * of this page:
+ *
+ *      NR_inactive + (R - E)
+ *
+ * And knowing the minimum access distance of a page, we can easily
+ * tell if the page would be able to stay in cache assuming all page
+ * slots in the cache were available:
+ *
+ *   NR_inactive + (R - E) <= NR_inactive + NR_active
+ *
+ * If we have swap we should consider about NR_inactive_anon and
+ * NR_active_anon, so for page cache and anonymous respectively:
+ *
+ *   NR_inactive_file + (R - E) <= NR_inactive_file + NR_active_file
+ *   + NR_inactive_anon + NR_active_anon
+ *
+ *   NR_inactive_anon + (R - E) <= NR_inactive_anon + NR_active_anon
+ *   + NR_inactive_file + NR_active_file
+ *
+ * Which can be further simplified to:
+ *
+ *   (R - E) <= NR_active_file + NR_inactive_anon + NR_active_anon
+ *
+ *   (R - E) <= NR_active_anon + NR_inactive_file + NR_active_file
+ *
+ * Put into words, the refault distance (out-of-cache) can be seen as
+ * a deficit in inactive list space (in-cache).  If the inactive list
+ * had (R - E) more page slots, the page would not have been evicted
+ * in between accesses, but activated instead.  And on a full system,
+ * the only thing eating into inactive list space is active pages.
+ *
+ *
+ *		Refaulting inactive pages
+ *
+ * All that is known about the active list is that the pages have been
+ * accessed more than once in the past.  This means that at any given
+ * time there is actually a good chance that pages on the active list
+ * are no longer in active use.
+ *
+ * So when a refault distance of (R - E) is observed and there are at
+ * least (R - E) pages in the userspace workingset, the refaulting page
+ * is activated optimistically in the hope that (R - E) pages are actually
+ * used less frequently than the refaulting page - or even not used at
+ * all anymore.
+ *
+ * That means if inactive cache is refaulting with a suitable refault
+ * distance, we assume the cache workingset is transitioning and put
+ * pressure on the current workingset.
+ *
+ * If this is wrong and demotion kicks in, the pages which are truly
+ * used more frequently will be reactivated while the less frequently
+ * used once will be evicted from memory.
+ *
+ * But if this is right, the stale pages will be pushed out of memory
+ * and the used pages get to stay in cache.
+ *
+ *		Refaulting active pages
+ *
+ * If on the other hand the refaulting pages have recently been
+ * deactivated, it means that the active list is no longer protecting
+ * actively used cache from reclaim. The cache is NOT transitioning to
+ * a different workingset; the existing workingset is thrashing in the
+ * space allocated to the page cache.
+ *
+ *
+ *		Implementation
+ *
+ * For each node's LRU lists, a counter for inactive evictions and
+ * activations is maintained (node->nonresident_age).
+ *
+ * On eviction, a snapshot of this counter (along with some bits to
+ * identify the node) is stored in the now empty page cache
+ * slot of the evicted page.  This is called a shadow entry.
+ *
+ * On cache misses for which there are shadow entries, an eligible
+ * refault distance will immediately activate the refaulting page.
+ */
+
+#define WORKINGSET_SHIFT 1
+#define EVICTION_SHIFT	((BITS_PER_LONG - BITS_PER_XA_VALUE) +	\
+			 WORKINGSET_SHIFT + NODES_SHIFT + \
+			 MEM_CGROUP_ID_SHIFT)
+#define EVICTION_MASK	(~0UL >> EVICTION_SHIFT)
+
+/*
+ * Eviction timestamps need to be able to cover the full range of
+ * actionable refaults. However, bits are tight in the xarray
+ * entry, and after storing the identifier for the lruvec there might
+ * not be enough left to represent every single actionable refault. In
+ * that case, we have to sacrifice granularity for distance, and group
+ * evictions into coarser buckets by shaving off lower timestamp bits.
+ */
+static unsigned int bucket_order __read_mostly;
+
+static void *pack_shadow(int memcgid, pg_data_t *pgdat, unsigned long eviction,
+			 bool workingset)
+{
+	eviction &= EVICTION_MASK;
+	eviction = (eviction << MEM_CGROUP_ID_SHIFT) | memcgid;
+	eviction = (eviction << NODES_SHIFT) | pgdat->node_id;
+	eviction = (eviction << WORKINGSET_SHIFT) | workingset;
+
+	return xa_mk_value(eviction);
+}
+
+static void unpack_shadow(void *shadow, int *memcgidp, pg_data_t **pgdat,
+			  unsigned long *evictionp, bool *workingsetp)
+{
+	unsigned long entry = xa_to_value(shadow);
+	int memcgid, nid;
+	bool workingset;
+
+	workingset = entry & ((1UL << WORKINGSET_SHIFT) - 1);
+	entry >>= WORKINGSET_SHIFT;
+	nid = entry & ((1UL << NODES_SHIFT) - 1);
+	entry >>= NODES_SHIFT;
+	memcgid = entry & ((1UL << MEM_CGROUP_ID_SHIFT) - 1);
+	entry >>= MEM_CGROUP_ID_SHIFT;
+
+	*memcgidp = memcgid;
+	*pgdat = NODE_DATA(nid);
+	*evictionp = entry;
+	*workingsetp = workingset;
+}
+
+#ifdef CONFIG_LRU_GEN
+
+static void *lru_gen_eviction(struct folio *folio)
+{
+	int hist;
+	unsigned long token;
+	unsigned long min_seq;
+	struct lruvec *lruvec;
+	struct lru_gen_folio *lrugen;
+	int type = folio_is_file_lru(folio);
+	int delta = folio_nr_pages(folio);
+	int refs = folio_lru_refs(folio);
+	int tier = lru_tier_from_refs(refs);
+	struct mem_cgroup *memcg = folio_memcg(folio);
+	struct pglist_data *pgdat = folio_pgdat(folio);
+
+	BUILD_BUG_ON(LRU_GEN_WIDTH + LRU_REFS_WIDTH > BITS_PER_LONG - EVICTION_SHIFT);
+
+	lruvec = mem_cgroup_lruvec(memcg, pgdat);
+	lrugen = &lruvec->lrugen;
+	min_seq = READ_ONCE(lrugen->min_seq[type]);
+	token = (min_seq << LRU_REFS_WIDTH) | max(refs - 1, 0);
+
+	hist = lru_hist_from_seq(min_seq);
+	atomic_long_add(delta, &lrugen->evicted[hist][type][tier]);
+
+	return pack_shadow(mem_cgroup_id(memcg), pgdat, token, refs);
+}
+
+/*
+ * Tests if the shadow entry is for a folio that was recently evicted.
+ * Fills in @lruvec, @token, @workingset with the values unpacked from shadow.
+ */
+static bool lru_gen_test_recent(void *shadow, bool file, struct lruvec **lruvec,
+				unsigned long *token, bool *workingset)
+{
+	int memcg_id;
+	unsigned long min_seq;
+	struct mem_cgroup *memcg;
+	struct pglist_data *pgdat;
+
+	unpack_shadow(shadow, &memcg_id, &pgdat, token, workingset);
+
+	memcg = mem_cgroup_from_id(memcg_id);
+	*lruvec = mem_cgroup_lruvec(memcg, pgdat);
+
+	min_seq = READ_ONCE((*lruvec)->lrugen.min_seq[file]);
+	return (*token >> LRU_REFS_WIDTH) == (min_seq & (EVICTION_MASK >> LRU_REFS_WIDTH));
+}
+
+static void lru_gen_refault(struct folio *folio, void *shadow)
+{
+	bool recent;
+	int hist, tier, refs;
+	bool workingset;
+	unsigned long token;
+	struct lruvec *lruvec;
+	struct lru_gen_folio *lrugen;
+	int type = folio_is_file_lru(folio);
+	int delta = folio_nr_pages(folio);
+
+	rcu_read_lock();
+
+	recent = lru_gen_test_recent(shadow, type, &lruvec, &token, &workingset);
+	if (lruvec != folio_lruvec(folio))
+		goto unlock;
+
+	mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + type, delta);
+
+	if (!recent)
+		goto unlock;
+
+	lrugen = &lruvec->lrugen;
+
+	hist = lru_hist_from_seq(READ_ONCE(lrugen->min_seq[type]));
+	/* see the comment in folio_lru_refs() */
+	refs = (token & (BIT(LRU_REFS_WIDTH) - 1)) + workingset;
+	tier = lru_tier_from_refs(refs);
+
+	atomic_long_add(delta, &lrugen->refaulted[hist][type][tier]);
+	mod_lruvec_state(lruvec, WORKINGSET_ACTIVATE_BASE + type, delta);
+
+	/*
+	 * Count the following two cases as stalls:
+	 * 1. For pages accessed through page tables, hotter pages pushed out
+	 *    hot pages which refaulted immediately.
+	 * 2. For pages accessed multiple times through file descriptors,
+	 *    they would have been protected by sort_folio().
+	 */
+	if (lru_gen_in_fault() || refs >= BIT(LRU_REFS_WIDTH) - 1) {
+		set_mask_bits(&folio->flags, 0, LRU_REFS_MASK | BIT(PG_workingset));
+		mod_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + type, delta);
+	}
+unlock:
+	rcu_read_unlock();
+}
+
+#else /* !CONFIG_LRU_GEN */
+
+static void *lru_gen_eviction(struct folio *folio)
+{
+	return NULL;
+}
+
+static bool lru_gen_test_recent(void *shadow, bool file, struct lruvec **lruvec,
+				unsigned long *token, bool *workingset)
+{
+	return false;
+}
+
+static void lru_gen_refault(struct folio *folio, void *shadow)
+{
+}
+
+#endif /* CONFIG_LRU_GEN */
+
+/**
+ * workingset_age_nonresident - age non-resident entries as LRU ages
+ * @lruvec: the lruvec that was aged
+ * @nr_pages: the number of pages to count
+ *
+ * As in-memory pages are aged, non-resident pages need to be aged as
+ * well, in order for the refault distances later on to be comparable
+ * to the in-memory dimensions. This function allows reclaim and LRU
+ * operations to drive the non-resident aging along in parallel.
+ */
+void workingset_age_nonresident(struct lruvec *lruvec, unsigned long nr_pages)
+{
+	/*
+	 * Reclaiming a cgroup means reclaiming all its children in a
+	 * round-robin fashion. That means that each cgroup has an LRU
+	 * order that is composed of the LRU orders of its child
+	 * cgroups; and every page has an LRU position not just in the
+	 * cgroup that owns it, but in all of that group's ancestors.
+	 *
+	 * So when the physical inactive list of a leaf cgroup ages,
+	 * the virtual inactive lists of all its parents, including
+	 * the root cgroup's, age as well.
+	 */
+	do {
+		atomic_long_add(nr_pages, &lruvec->nonresident_age);
+	} while ((lruvec = parent_lruvec(lruvec)));
+}
+
+/**
+ * workingset_eviction - note the eviction of a folio from memory
+ * @target_memcg: the cgroup that is causing the reclaim
+ * @folio: the folio being evicted
+ *
+ * Return: a shadow entry to be stored in @folio->mapping->i_pages in place
+ * of the evicted @folio so that a later refault can be detected.
+ */
+void *workingset_eviction(struct folio *folio, struct mem_cgroup *target_memcg)
+{
+	struct pglist_data *pgdat = folio_pgdat(folio);
+	unsigned long eviction;
+	struct lruvec *lruvec;
+	int memcgid;
+
+	/* Folio is fully exclusive and pins folio's memory cgroup pointer */
+	VM_BUG_ON_FOLIO(folio_test_lru(folio), folio);
+	VM_BUG_ON_FOLIO(folio_ref_count(folio), folio);
+	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
+
+	if (lru_gen_enabled())
+		return lru_gen_eviction(folio);
+
+	lruvec = mem_cgroup_lruvec(target_memcg, pgdat);
+	/* XXX: target_memcg can be NULL, go through lruvec */
+	memcgid = mem_cgroup_id(lruvec_memcg(lruvec));
+	eviction = atomic_long_read(&lruvec->nonresident_age);
+	eviction >>= bucket_order;
+	workingset_age_nonresident(lruvec, folio_nr_pages(folio));
+	return pack_shadow(memcgid, pgdat, eviction,
+				folio_test_workingset(folio));
+}
+
+/**
+ * workingset_test_recent - tests if the shadow entry is for a folio that was
+ * recently evicted. Also fills in @workingset with the value unpacked from
+ * shadow.
+ * @shadow: the shadow entry to be tested.
+ * @file: whether the corresponding folio is from the file lru.
+ * @workingset: where the workingset value unpacked from shadow should
+ * be stored.
+ *
+ * Return: true if the shadow is for a recently evicted folio; false otherwise.
+ */
+bool workingset_test_recent(void *shadow, bool file, bool *workingset)
+{
+	struct mem_cgroup *eviction_memcg;
+	struct lruvec *eviction_lruvec;
+	unsigned long refault_distance;
+	unsigned long workingset_size;
+	unsigned long refault;
+	int memcgid;
+	struct pglist_data *pgdat;
+	unsigned long eviction;
+
+	if (lru_gen_enabled())
+		return lru_gen_test_recent(shadow, file, &eviction_lruvec, &eviction, workingset);
+
+	unpack_shadow(shadow, &memcgid, &pgdat, &eviction, workingset);
+	eviction <<= bucket_order;
+
+	/*
+	 * Look up the memcg associated with the stored ID. It might
+	 * have been deleted since the folio's eviction.
+	 *
+	 * Note that in rare events the ID could have been recycled
+	 * for a new cgroup that refaults a shared folio. This is
+	 * impossible to tell from the available data. However, this
+	 * should be a rare and limited disturbance, and activations
+	 * are always speculative anyway. Ultimately, it's the aging
+	 * algorithm's job to shake out the minimum access frequency
+	 * for the active cache.
+	 *
+	 * XXX: On !CONFIG_MEMCG, this will always return NULL; it
+	 * would be better if the root_mem_cgroup existed in all
+	 * configurations instead.
+	 */
+	eviction_memcg = mem_cgroup_from_id(memcgid);
+	if (!mem_cgroup_disabled() && !eviction_memcg)
+		return false;
+
+	eviction_lruvec = mem_cgroup_lruvec(eviction_memcg, pgdat);
+	refault = atomic_long_read(&eviction_lruvec->nonresident_age);
+
+	/*
+	 * Calculate the refault distance
+	 *
+	 * The unsigned subtraction here gives an accurate distance
+	 * across nonresident_age overflows in most cases. There is a
+	 * special case: usually, shadow entries have a short lifetime
+	 * and are either refaulted or reclaimed along with the inode
+	 * before they get too old.  But it is not impossible for the
+	 * nonresident_age to lap a shadow entry in the field, which
+	 * can then result in a false small refault distance, leading
+	 * to a false activation should this old entry actually
+	 * refault again.  However, earlier kernels used to deactivate
+	 * unconditionally with *every* reclaim invocation for the
+	 * longest time, so the occasional inappropriate activation
+	 * leading to pressure on the active list is not a problem.
+	 */
+	refault_distance = (refault - eviction) & EVICTION_MASK;
+
+	/*
+	 * Compare the distance to the existing workingset size. We
+	 * don't activate pages that couldn't stay resident even if
+	 * all the memory was available to the workingset. Whether
+	 * workingset competition needs to consider anon or not depends
+	 * on having free swap space.
+	 */
+	workingset_size = lruvec_page_state(eviction_lruvec, NR_ACTIVE_FILE);
+	if (!file) {
+		workingset_size += lruvec_page_state(eviction_lruvec,
+						     NR_INACTIVE_FILE);
+	}
+	if (mem_cgroup_get_nr_swap_pages(eviction_memcg) > 0) {
+		workingset_size += lruvec_page_state(eviction_lruvec,
+						     NR_ACTIVE_ANON);
+		if (file) {
+			workingset_size += lruvec_page_state(eviction_lruvec,
+						     NR_INACTIVE_ANON);
+		}
+	}
+
+	return refault_distance <= workingset_size;
+}
+
+/**
+ * workingset_refault - Evaluate the refault of a previously evicted folio.
+ * @folio: The freshly allocated replacement folio.
+ * @shadow: Shadow entry of the evicted folio.
+ *
+ * Calculates and evaluates the refault distance of the previously
+ * evicted folio in the context of the node and the memcg whose memory
+ * pressure caused the eviction.
+ */
+void workingset_refault(struct folio *folio, void *shadow)
+{
+	bool file = folio_is_file_lru(folio);
+	struct pglist_data *pgdat;
+	struct mem_cgroup *memcg;
+	struct lruvec *lruvec;
+	bool workingset;
+	long nr;
+
+	if (lru_gen_enabled()) {
+		lru_gen_refault(folio, shadow);
+		return;
+	}
+
+	/* Flush stats (and potentially sleep) before holding RCU read lock */
+	mem_cgroup_flush_stats_ratelimited();
+
+	rcu_read_lock();
+
+	/*
+	 * The activation decision for this folio is made at the level
+	 * where the eviction occurred, as that is where the LRU order
+	 * during folio reclaim is being determined.
+	 *
+	 * However, the cgroup that will own the folio is the one that
+	 * is actually experiencing the refault event.
+	 */
+	nr = folio_nr_pages(folio);
+	memcg = folio_memcg(folio);
+	pgdat = folio_pgdat(folio);
+	lruvec = mem_cgroup_lruvec(memcg, pgdat);
+
+	mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + file, nr);
+
+	if (!workingset_test_recent(shadow, file, &workingset))
+		goto out;
+
+	folio_set_active(folio);
+	workingset_age_nonresident(lruvec, nr);
+	mod_lruvec_state(lruvec, WORKINGSET_ACTIVATE_BASE + file, nr);
+
+	/* Folio was active prior to eviction */
+	if (workingset) {
+		folio_set_workingset(folio);
+		/*
+		 * XXX: Move to folio_add_lru() when it supports new vs
+		 * putback
+		 */
+		lru_note_cost_refault(folio);
+		mod_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + file, nr);
+	}
+out:
+	rcu_read_unlock();
+}
+
+/**
+ * workingset_activation - note a page activation
+ * @folio: Folio that is being activated.
+ */
+void workingset_activation(struct folio *folio)
+{
+	struct mem_cgroup *memcg;
+
+	rcu_read_lock();
+	/*
+	 * Filter non-memcg pages here, e.g. unmap can call
+	 * mark_page_accessed() on VDSO pages.
+	 *
+	 * XXX: See workingset_refault() - this should return
+	 * root_mem_cgroup even for !CONFIG_MEMCG.
+	 */
+	memcg = folio_memcg_rcu(folio);
+	if (!mem_cgroup_disabled() && !memcg)
+		goto out;
+	workingset_age_nonresident(folio_lruvec(folio), folio_nr_pages(folio));
+out:
+	rcu_read_unlock();
+}
+
+/*
+ * Shadow entries reflect the share of the working set that does not
+ * fit into memory, so their number depends on the access pattern of
+ * the workload.  In most cases, they will refault or get reclaimed
+ * along with the inode, but a (malicious) workload that streams
+ * through files with a total size several times that of available
+ * memory, while preventing the inodes from being reclaimed, can
+ * create excessive amounts of shadow nodes.  To keep a lid on this,
+ * track shadow nodes and reclaim them when they grow way past the
+ * point where they would still be useful.
+ */
+
+struct list_lru shadow_nodes;
+
+void workingset_update_node(struct xa_node *node)
+{
+	struct address_space *mapping;
+
+	/*
+	 * Track non-empty nodes that contain only shadow entries;
+	 * unlink those that contain pages or are being freed.
+	 *
+	 * Avoid acquiring the list_lru lock when the nodes are
+	 * already where they should be. The list_empty() test is safe
+	 * as node->private_list is protected by the i_pages lock.
+	 */
+	mapping = container_of(node->array, struct address_space, i_pages);
+	lockdep_assert_held(&mapping->i_pages.xa_lock);
+
+	if (node->count && node->count == node->nr_values) {
+		if (list_empty(&node->private_list)) {
+			list_lru_add(&shadow_nodes, &node->private_list);
+			__inc_lruvec_kmem_state(node, WORKINGSET_NODES);
+		}
+	} else {
+		if (!list_empty(&node->private_list)) {
+			list_lru_del(&shadow_nodes, &node->private_list);
+			__dec_lruvec_kmem_state(node, WORKINGSET_NODES);
+		}
+	}
+}
+
+static unsigned long count_shadow_nodes(struct shrinker *shrinker,
+					struct shrink_control *sc)
+{
+	unsigned long max_nodes;
+	unsigned long nodes;
+	unsigned long pages;
+
+	nodes = list_lru_shrink_count(&shadow_nodes, sc);
+	if (!nodes)
+		return SHRINK_EMPTY;
+
+	/*
+	 * Approximate a reasonable limit for the nodes
+	 * containing shadow entries. We don't need to keep more
+	 * shadow entries than possible pages on the active list,
+	 * since refault distances bigger than that are dismissed.
+	 *
+	 * The size of the active list converges toward 100% of
+	 * overall page cache as memory grows, with only a tiny
+	 * inactive list. Assume the total cache size for that.
+	 *
+	 * Nodes might be sparsely populated, with only one shadow
+	 * entry in the extreme case. Obviously, we cannot keep one
+	 * node for every eligible shadow entry, so compromise on a
+	 * worst-case density of 1/8th. Below that, not all eligible
+	 * refaults can be detected anymore.
+	 *
+	 * On 64-bit with 7 xa_nodes per page and 64 slots
+	 * each, this will reclaim shadow entries when they consume
+	 * ~1.8% of available memory:
+	 *
+	 * PAGE_SIZE / xa_nodes / node_entries * 8 / PAGE_SIZE
+	 */
+#ifdef CONFIG_MEMCG
+	if (sc->memcg) {
+		struct lruvec *lruvec;
+		int i;
+
+		mem_cgroup_flush_stats();
+		lruvec = mem_cgroup_lruvec(sc->memcg, NODE_DATA(sc->nid));
+		for (pages = 0, i = 0; i < NR_LRU_LISTS; i++)
+			pages += lruvec_page_state_local(lruvec,
+							 NR_LRU_BASE + i);
+		pages += lruvec_page_state_local(
+			lruvec, NR_SLAB_RECLAIMABLE_B) >> PAGE_SHIFT;
+		pages += lruvec_page_state_local(
+			lruvec, NR_SLAB_UNRECLAIMABLE_B) >> PAGE_SHIFT;
+	} else
+#endif
+		pages = node_present_pages(sc->nid);
+
+	max_nodes = pages >> (XA_CHUNK_SHIFT - 3);
+
+	if (nodes <= max_nodes)
+		return 0;
+	return nodes - max_nodes;
+}
+
+static enum lru_status shadow_lru_isolate(struct list_head *item,
+					  struct list_lru_one *lru,
+					  spinlock_t *lru_lock,
+					  void *arg) __must_hold(lru_lock)
+{
+	struct xa_node *node = container_of(item, struct xa_node, private_list);
+	struct address_space *mapping;
+	int ret;
+
+	/*
+	 * Page cache insertions and deletions synchronously maintain
+	 * the shadow node LRU under the i_pages lock and the
+	 * lru_lock.  Because the page cache tree is emptied before
+	 * the inode can be destroyed, holding the lru_lock pins any
+	 * address_space that has nodes on the LRU.
+	 *
+	 * We can then safely transition to the i_pages lock to
+	 * pin only the address_space of the particular node we want
+	 * to reclaim, take the node off-LRU, and drop the lru_lock.
+	 */
+
+	mapping = container_of(node->array, struct address_space, i_pages);
+
+	/* Coming from the list, invert the lock order */
+	if (!xa_trylock(&mapping->i_pages)) {
+		spin_unlock_irq(lru_lock);
+		ret = LRU_RETRY;
+		goto out;
+	}
+
+	/* For page cache we need to hold i_lock */
+	if (mapping->host != NULL) {
+		if (!spin_trylock(&mapping->host->i_lock)) {
+			xa_unlock(&mapping->i_pages);
+			spin_unlock_irq(lru_lock);
+			ret = LRU_RETRY;
+			goto out;
+		}
+	}
+
+	list_lru_isolate(lru, item);
+	__dec_lruvec_kmem_state(node, WORKINGSET_NODES);
+
+	spin_unlock(lru_lock);
+
+	/*
+	 * The nodes should only contain one or more shadow entries,
+	 * no pages, so we expect to be able to remove them all and
+	 * delete and free the empty node afterwards.
+	 */
+	if (WARN_ON_ONCE(!node->nr_values))
+		goto out_invalid;
+	if (WARN_ON_ONCE(node->count != node->nr_values))
+		goto out_invalid;
+	xa_delete_node(node, workingset_update_node);
+	__inc_lruvec_kmem_state(node, WORKINGSET_NODERECLAIM);
+
+out_invalid:
+	xa_unlock_irq(&mapping->i_pages);
+	if (mapping->host != NULL) {
+		if (mapping_shrinkable(mapping))
+			inode_add_lru(mapping->host);
+		spin_unlock(&mapping->host->i_lock);
+	}
+	ret = LRU_REMOVED_RETRY;
+out:
+	cond_resched();
+	spin_lock_irq(lru_lock);
+	return ret;
+}
+
+static unsigned long scan_shadow_nodes(struct shrinker *shrinker,
+				       struct shrink_control *sc)
+{
+	/* list_lru lock nests inside the IRQ-safe i_pages lock */
+	return list_lru_shrink_walk_irq(&shadow_nodes, sc, shadow_lru_isolate,
+					NULL);
+}
+
+static struct shrinker workingset_shadow_shrinker = {
+	.count_objects = count_shadow_nodes,
+	.scan_objects = scan_shadow_nodes,
+	.seeks = 0, /* ->count reports only fully expendable nodes */
+	.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE,
+};
+
+/*
+ * Our list_lru->lock is IRQ-safe as it nests inside the IRQ-safe
+ * i_pages lock.
+ */
+static struct lock_class_key shadow_nodes_key;
+
+static int __init workingset_init(void)
+{
+	unsigned int timestamp_bits;
+	unsigned int max_order;
+	int ret;
+
+	BUILD_BUG_ON(BITS_PER_LONG < EVICTION_SHIFT);
+	/*
+	 * Calculate the eviction bucket size to cover the longest
+	 * actionable refault distance, which is currently half of
+	 * memory (totalram_pages/2). However, memory hotplug may add
+	 * some more pages at runtime, so keep working with up to
+	 * double the initial memory by using totalram_pages as-is.
+	 */
+	timestamp_bits = BITS_PER_LONG - EVICTION_SHIFT;
+	max_order = fls_long(totalram_pages() - 1);
+	if (max_order > timestamp_bits)
+		bucket_order = max_order - timestamp_bits;
+	pr_info("workingset: timestamp_bits=%d max_order=%d bucket_order=%u\n",
+	       timestamp_bits, max_order, bucket_order);
+
+	ret = prealloc_shrinker(&workingset_shadow_shrinker, "mm-shadow");
+	if (ret)
+		goto err;
+	ret = __list_lru_init(&shadow_nodes, true, &shadow_nodes_key,
+			      &workingset_shadow_shrinker);
+	if (ret)
+		goto err_list_lru;
+	register_shrinker_prepared(&workingset_shadow_shrinker);
+	return 0;
+err_list_lru:
+	free_prealloced_shrinker(&workingset_shadow_shrinker);
+err:
+	return ret;
+}
+module_init(workingset_init);