Merging upstream version 6.7.7.

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

1 files changed, 809 insertions, 0 deletions

diff --git a/mm/shrinker.c b/mm/shrinker.c
new file mode 100644
index 0000000000..dc5d2a6fcf
--- /dev/null
+++ b/mm/shrinker.c
@@ -0,0 +1,809 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/memcontrol.h>
+#include <linux/rwsem.h>
+#include <linux/shrinker.h>
+#include <linux/rculist.h>
+#include <trace/events/vmscan.h>
+
+#include "internal.h"
+
+LIST_HEAD(shrinker_list);
+DEFINE_MUTEX(shrinker_mutex);
+
+#ifdef CONFIG_MEMCG
+static int shrinker_nr_max;
+
+static inline int shrinker_unit_size(int nr_items)
+{
+	return (DIV_ROUND_UP(nr_items, SHRINKER_UNIT_BITS) * sizeof(struct shrinker_info_unit *));
+}
+
+static inline void shrinker_unit_free(struct shrinker_info *info, int start)
+{
+	struct shrinker_info_unit **unit;
+	int nr, i;
+
+	if (!info)
+		return;
+
+	unit = info->unit;
+	nr = DIV_ROUND_UP(info->map_nr_max, SHRINKER_UNIT_BITS);
+
+	for (i = start; i < nr; i++) {
+		if (!unit[i])
+			break;
+
+		kfree(unit[i]);
+		unit[i] = NULL;
+	}
+}
+
+static inline int shrinker_unit_alloc(struct shrinker_info *new,
+				       struct shrinker_info *old, int nid)
+{
+	struct shrinker_info_unit *unit;
+	int nr = DIV_ROUND_UP(new->map_nr_max, SHRINKER_UNIT_BITS);
+	int start = old ? DIV_ROUND_UP(old->map_nr_max, SHRINKER_UNIT_BITS) : 0;
+	int i;
+
+	for (i = start; i < nr; i++) {
+		unit = kzalloc_node(sizeof(*unit), GFP_KERNEL, nid);
+		if (!unit) {
+			shrinker_unit_free(new, start);
+			return -ENOMEM;
+		}
+
+		new->unit[i] = unit;
+	}
+
+	return 0;
+}
+
+void free_shrinker_info(struct mem_cgroup *memcg)
+{
+	struct mem_cgroup_per_node *pn;
+	struct shrinker_info *info;
+	int nid;
+
+	for_each_node(nid) {
+		pn = memcg->nodeinfo[nid];
+		info = rcu_dereference_protected(pn->shrinker_info, true);
+		shrinker_unit_free(info, 0);
+		kvfree(info);
+		rcu_assign_pointer(pn->shrinker_info, NULL);
+	}
+}
+
+int alloc_shrinker_info(struct mem_cgroup *memcg)
+{
+	struct shrinker_info *info;
+	int nid, ret = 0;
+	int array_size = 0;
+
+	mutex_lock(&shrinker_mutex);
+	array_size = shrinker_unit_size(shrinker_nr_max);
+	for_each_node(nid) {
+		info = kvzalloc_node(sizeof(*info) + array_size, GFP_KERNEL, nid);
+		if (!info)
+			goto err;
+		info->map_nr_max = shrinker_nr_max;
+		if (shrinker_unit_alloc(info, NULL, nid))
+			goto err;
+		rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_info, info);
+	}
+	mutex_unlock(&shrinker_mutex);
+
+	return ret;
+
+err:
+	mutex_unlock(&shrinker_mutex);
+	free_shrinker_info(memcg);
+	return -ENOMEM;
+}
+
+static struct shrinker_info *shrinker_info_protected(struct mem_cgroup *memcg,
+						     int nid)
+{
+	return rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_info,
+					 lockdep_is_held(&shrinker_mutex));
+}
+
+static int expand_one_shrinker_info(struct mem_cgroup *memcg, int new_size,
+				    int old_size, int new_nr_max)
+{
+	struct shrinker_info *new, *old;
+	struct mem_cgroup_per_node *pn;
+	int nid;
+
+	for_each_node(nid) {
+		pn = memcg->nodeinfo[nid];
+		old = shrinker_info_protected(memcg, nid);
+		/* Not yet online memcg */
+		if (!old)
+			return 0;
+
+		/* Already expanded this shrinker_info */
+		if (new_nr_max <= old->map_nr_max)
+			continue;
+
+		new = kvzalloc_node(sizeof(*new) + new_size, GFP_KERNEL, nid);
+		if (!new)
+			return -ENOMEM;
+
+		new->map_nr_max = new_nr_max;
+
+		memcpy(new->unit, old->unit, old_size);
+		if (shrinker_unit_alloc(new, old, nid)) {
+			kvfree(new);
+			return -ENOMEM;
+		}
+
+		rcu_assign_pointer(pn->shrinker_info, new);
+		kvfree_rcu(old, rcu);
+	}
+
+	return 0;
+}
+
+static int expand_shrinker_info(int new_id)
+{
+	int ret = 0;
+	int new_nr_max = round_up(new_id + 1, SHRINKER_UNIT_BITS);
+	int new_size, old_size = 0;
+	struct mem_cgroup *memcg;
+
+	if (!root_mem_cgroup)
+		goto out;
+
+	lockdep_assert_held(&shrinker_mutex);
+
+	new_size = shrinker_unit_size(new_nr_max);
+	old_size = shrinker_unit_size(shrinker_nr_max);
+
+	memcg = mem_cgroup_iter(NULL, NULL, NULL);
+	do {
+		ret = expand_one_shrinker_info(memcg, new_size, old_size,
+					       new_nr_max);
+		if (ret) {
+			mem_cgroup_iter_break(NULL, memcg);
+			goto out;
+		}
+	} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
+out:
+	if (!ret)
+		shrinker_nr_max = new_nr_max;
+
+	return ret;
+}
+
+static inline int shrinker_id_to_index(int shrinker_id)
+{
+	return shrinker_id / SHRINKER_UNIT_BITS;
+}
+
+static inline int shrinker_id_to_offset(int shrinker_id)
+{
+	return shrinker_id % SHRINKER_UNIT_BITS;
+}
+
+static inline int calc_shrinker_id(int index, int offset)
+{
+	return index * SHRINKER_UNIT_BITS + offset;
+}
+
+void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
+{
+	if (shrinker_id >= 0 && memcg && !mem_cgroup_is_root(memcg)) {
+		struct shrinker_info *info;
+		struct shrinker_info_unit *unit;
+
+		rcu_read_lock();
+		info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info);
+		unit = info->unit[shrinker_id_to_index(shrinker_id)];
+		if (!WARN_ON_ONCE(shrinker_id >= info->map_nr_max)) {
+			/* Pairs with smp mb in shrink_slab() */
+			smp_mb__before_atomic();
+			set_bit(shrinker_id_to_offset(shrinker_id), unit->map);
+		}
+		rcu_read_unlock();
+	}
+}
+
+static DEFINE_IDR(shrinker_idr);
+
+static int shrinker_memcg_alloc(struct shrinker *shrinker)
+{
+	int id, ret = -ENOMEM;
+
+	if (mem_cgroup_disabled())
+		return -ENOSYS;
+
+	mutex_lock(&shrinker_mutex);
+	id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);
+	if (id < 0)
+		goto unlock;
+
+	if (id >= shrinker_nr_max) {
+		if (expand_shrinker_info(id)) {
+			idr_remove(&shrinker_idr, id);
+			goto unlock;
+		}
+	}
+	shrinker->id = id;
+	ret = 0;
+unlock:
+	mutex_unlock(&shrinker_mutex);
+	return ret;
+}
+
+static void shrinker_memcg_remove(struct shrinker *shrinker)
+{
+	int id = shrinker->id;
+
+	BUG_ON(id < 0);
+
+	lockdep_assert_held(&shrinker_mutex);
+
+	idr_remove(&shrinker_idr, id);
+}
+
+static long xchg_nr_deferred_memcg(int nid, struct shrinker *shrinker,
+				   struct mem_cgroup *memcg)
+{
+	struct shrinker_info *info;
+	struct shrinker_info_unit *unit;
+	long nr_deferred;
+
+	rcu_read_lock();
+	info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info);
+	unit = info->unit[shrinker_id_to_index(shrinker->id)];
+	nr_deferred = atomic_long_xchg(&unit->nr_deferred[shrinker_id_to_offset(shrinker->id)], 0);
+	rcu_read_unlock();
+
+	return nr_deferred;
+}
+
+static long add_nr_deferred_memcg(long nr, int nid, struct shrinker *shrinker,
+				  struct mem_cgroup *memcg)
+{
+	struct shrinker_info *info;
+	struct shrinker_info_unit *unit;
+	long nr_deferred;
+
+	rcu_read_lock();
+	info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info);
+	unit = info->unit[shrinker_id_to_index(shrinker->id)];
+	nr_deferred =
+		atomic_long_add_return(nr, &unit->nr_deferred[shrinker_id_to_offset(shrinker->id)]);
+	rcu_read_unlock();
+
+	return nr_deferred;
+}
+
+void reparent_shrinker_deferred(struct mem_cgroup *memcg)
+{
+	int nid, index, offset;
+	long nr;
+	struct mem_cgroup *parent;
+	struct shrinker_info *child_info, *parent_info;
+	struct shrinker_info_unit *child_unit, *parent_unit;
+
+	parent = parent_mem_cgroup(memcg);
+	if (!parent)
+		parent = root_mem_cgroup;
+
+	/* Prevent from concurrent shrinker_info expand */
+	mutex_lock(&shrinker_mutex);
+	for_each_node(nid) {
+		child_info = shrinker_info_protected(memcg, nid);
+		parent_info = shrinker_info_protected(parent, nid);
+		for (index = 0; index < shrinker_id_to_index(child_info->map_nr_max); index++) {
+			child_unit = child_info->unit[index];
+			parent_unit = parent_info->unit[index];
+			for (offset = 0; offset < SHRINKER_UNIT_BITS; offset++) {
+				nr = atomic_long_read(&child_unit->nr_deferred[offset]);
+				atomic_long_add(nr, &parent_unit->nr_deferred[offset]);
+			}
+		}
+	}
+	mutex_unlock(&shrinker_mutex);
+}
+#else
+static int shrinker_memcg_alloc(struct shrinker *shrinker)
+{
+	return -ENOSYS;
+}
+
+static void shrinker_memcg_remove(struct shrinker *shrinker)
+{
+}
+
+static long xchg_nr_deferred_memcg(int nid, struct shrinker *shrinker,
+				   struct mem_cgroup *memcg)
+{
+	return 0;
+}
+
+static long add_nr_deferred_memcg(long nr, int nid, struct shrinker *shrinker,
+				  struct mem_cgroup *memcg)
+{
+	return 0;
+}
+#endif /* CONFIG_MEMCG */
+
+static long xchg_nr_deferred(struct shrinker *shrinker,
+			     struct shrink_control *sc)
+{
+	int nid = sc->nid;
+
+	if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
+		nid = 0;
+
+	if (sc->memcg &&
+	    (shrinker->flags & SHRINKER_MEMCG_AWARE))
+		return xchg_nr_deferred_memcg(nid, shrinker,
+					      sc->memcg);
+
+	return atomic_long_xchg(&shrinker->nr_deferred[nid], 0);
+}
+
+
+static long add_nr_deferred(long nr, struct shrinker *shrinker,
+			    struct shrink_control *sc)
+{
+	int nid = sc->nid;
+
+	if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
+		nid = 0;
+
+	if (sc->memcg &&
+	    (shrinker->flags & SHRINKER_MEMCG_AWARE))
+		return add_nr_deferred_memcg(nr, nid, shrinker,
+					     sc->memcg);
+
+	return atomic_long_add_return(nr, &shrinker->nr_deferred[nid]);
+}
+
+#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;
+	long batch_size = shrinker->batch ? shrinker->batch
+					  : SHRINK_BATCH;
+	long scanned = 0, next_deferred;
+
+	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 = xchg_nr_deferred(shrinker, shrinkctl);
+
+	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 = nr >> priority;
+	total_scan += delta;
+	total_scan = min(total_scan, (2 * freeable));
+
+	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();
+	}
+
+	/*
+	 * The deferred work is increased by any new work (delta) that wasn't
+	 * done, decreased by old deferred work that was done now.
+	 *
+	 * And it is capped to two times of the freeable items.
+	 */
+	next_deferred = max_t(long, (nr + delta - scanned), 0);
+	next_deferred = min(next_deferred, (2 * freeable));
+
+	/*
+	 * move the unused scan count back into the shrinker in a
+	 * manner that handles concurrent updates.
+	 */
+	new_nr = add_nr_deferred(next_deferred, shrinker, shrinkctl);
+
+	trace_mm_shrink_slab_end(shrinker, shrinkctl->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 shrinker_info *info;
+	unsigned long ret, freed = 0;
+	int offset, index = 0;
+
+	if (!mem_cgroup_online(memcg))
+		return 0;
+
+	/*
+	 * lockless algorithm of memcg shrink.
+	 *
+	 * The shrinker_info may be freed asynchronously via RCU in the
+	 * expand_one_shrinker_info(), so the rcu_read_lock() needs to be used
+	 * to ensure the existence of the shrinker_info.
+	 *
+	 * The shrinker_info_unit is never freed unless its corresponding memcg
+	 * is destroyed. Here we already hold the refcount of memcg, so the
+	 * memcg will not be destroyed, and of course shrinker_info_unit will
+	 * not be freed.
+	 *
+	 * So in the memcg shrink:
+	 *  step 1: use rcu_read_lock() to guarantee existence of the
+	 *          shrinker_info.
+	 *  step 2: after getting shrinker_info_unit we can safely release the
+	 *          RCU lock.
+	 *  step 3: traverse the bitmap and calculate shrinker_id
+	 *  step 4: use rcu_read_lock() to guarantee existence of the shrinker.
+	 *  step 5: use shrinker_id to find the shrinker, then use
+	 *          shrinker_try_get() to guarantee existence of the shrinker,
+	 *          then we can release the RCU lock to do do_shrink_slab() that
+	 *          may sleep.
+	 *  step 6: do shrinker_put() paired with step 5 to put the refcount,
+	 *          if the refcount reaches 0, then wake up the waiter in
+	 *          shrinker_free() by calling complete().
+	 *          Note: here is different from the global shrink, we don't
+	 *                need to acquire the RCU lock to guarantee existence of
+	 *                the shrinker, because we don't need to use this
+	 *                shrinker to traverse the next shrinker in the bitmap.
+	 *  step 7: we have already exited the read-side of rcu critical section
+	 *          before calling do_shrink_slab(), the shrinker_info may be
+	 *          released in expand_one_shrinker_info(), so go back to step 1
+	 *          to reacquire the shrinker_info.
+	 */
+again:
+	rcu_read_lock();
+	info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info);
+	if (unlikely(!info))
+		goto unlock;
+
+	if (index < shrinker_id_to_index(info->map_nr_max)) {
+		struct shrinker_info_unit *unit;
+
+		unit = info->unit[index];
+
+		rcu_read_unlock();
+
+		for_each_set_bit(offset, unit->map, SHRINKER_UNIT_BITS) {
+			struct shrink_control sc = {
+				.gfp_mask = gfp_mask,
+				.nid = nid,
+				.memcg = memcg,
+			};
+			struct shrinker *shrinker;
+			int shrinker_id = calc_shrinker_id(index, offset);
+
+			rcu_read_lock();
+			shrinker = idr_find(&shrinker_idr, shrinker_id);
+			if (unlikely(!shrinker || !shrinker_try_get(shrinker))) {
+				clear_bit(offset, unit->map);
+				rcu_read_unlock();
+				continue;
+			}
+			rcu_read_unlock();
+
+			/* Call non-slab shrinkers even though kmem is disabled */
+			if (!memcg_kmem_online() &&
+			    !(shrinker->flags & SHRINKER_NONSLAB))
+				continue;
+
+			ret = do_shrink_slab(&sc, shrinker, priority);
+			if (ret == SHRINK_EMPTY) {
+				clear_bit(offset, unit->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
+				 * 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
+					set_shrinker_bit(memcg, nid, shrinker_id);
+			}
+			freed += ret;
+			shrinker_put(shrinker);
+		}
+
+		index++;
+		goto again;
+	}
+unlock:
+	rcu_read_unlock();
+	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.
+ */
+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);
+
+	/*
+	 * lockless algorithm of global shrink.
+	 *
+	 * In the unregistration setp, the shrinker will be freed asynchronously
+	 * via RCU after its refcount reaches 0. So both rcu_read_lock() and
+	 * shrinker_try_get() can be used to ensure the existence of the shrinker.
+	 *
+	 * So in the global shrink:
+	 *  step 1: use rcu_read_lock() to guarantee existence of the shrinker
+	 *          and the validity of the shrinker_list walk.
+	 *  step 2: use shrinker_try_get() to try get the refcount, if successful,
+	 *          then the existence of the shrinker can also be guaranteed,
+	 *          so we can release the RCU lock to do do_shrink_slab() that
+	 *          may sleep.
+	 *  step 3: *MUST* to reacquire the RCU lock before calling shrinker_put(),
+	 *          which ensures that neither this shrinker nor the next shrinker
+	 *          will be freed in the next traversal operation.
+	 *  step 4: do shrinker_put() paired with step 2 to put the refcount,
+	 *          if the refcount reaches 0, then wake up the waiter in
+	 *          shrinker_free() by calling complete().
+	 */
+	rcu_read_lock();
+	list_for_each_entry_rcu(shrinker, &shrinker_list, list) {
+		struct shrink_control sc = {
+			.gfp_mask = gfp_mask,
+			.nid = nid,
+			.memcg = memcg,
+		};
+
+		if (!shrinker_try_get(shrinker))
+			continue;
+
+		rcu_read_unlock();
+
+		ret = do_shrink_slab(&sc, shrinker, priority);
+		if (ret == SHRINK_EMPTY)
+			ret = 0;
+		freed += ret;
+
+		rcu_read_lock();
+		shrinker_put(shrinker);
+	}
+
+	rcu_read_unlock();
+	cond_resched();
+	return freed;
+}
+
+struct shrinker *shrinker_alloc(unsigned int flags, const char *fmt, ...)
+{
+	struct shrinker *shrinker;
+	unsigned int size;
+	va_list ap;
+	int err;
+
+	shrinker = kzalloc(sizeof(struct shrinker), GFP_KERNEL);
+	if (!shrinker)
+		return NULL;
+
+	va_start(ap, fmt);
+	err = shrinker_debugfs_name_alloc(shrinker, fmt, ap);
+	va_end(ap);
+	if (err)
+		goto err_name;
+
+	shrinker->flags = flags | SHRINKER_ALLOCATED;
+	shrinker->seeks = DEFAULT_SEEKS;
+
+	if (flags & SHRINKER_MEMCG_AWARE) {
+		err = shrinker_memcg_alloc(shrinker);
+		if (err == -ENOSYS) {
+			/* Memcg is not supported, fallback to non-memcg-aware shrinker. */
+			shrinker->flags &= ~SHRINKER_MEMCG_AWARE;
+			goto non_memcg;
+		}
+
+		if (err)
+			goto err_flags;
+
+		return shrinker;
+	}
+
+non_memcg:
+	/*
+	 * The nr_deferred is available on per memcg level for memcg aware
+	 * shrinkers, so only allocate nr_deferred in the following cases:
+	 *  - non-memcg-aware shrinkers
+	 *  - !CONFIG_MEMCG
+	 *  - memcg is disabled by kernel command line
+	 */
+	size = sizeof(*shrinker->nr_deferred);
+	if (flags & SHRINKER_NUMA_AWARE)
+		size *= nr_node_ids;
+
+	shrinker->nr_deferred = kzalloc(size, GFP_KERNEL);
+	if (!shrinker->nr_deferred)
+		goto err_flags;
+
+	return shrinker;
+
+err_flags:
+	shrinker_debugfs_name_free(shrinker);
+err_name:
+	kfree(shrinker);
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(shrinker_alloc);
+
+void shrinker_register(struct shrinker *shrinker)
+{
+	if (unlikely(!(shrinker->flags & SHRINKER_ALLOCATED))) {
+		pr_warn("Must use shrinker_alloc() to dynamically allocate the shrinker");
+		return;
+	}
+
+	mutex_lock(&shrinker_mutex);
+	list_add_tail_rcu(&shrinker->list, &shrinker_list);
+	shrinker->flags |= SHRINKER_REGISTERED;
+	shrinker_debugfs_add(shrinker);
+	mutex_unlock(&shrinker_mutex);
+
+	init_completion(&shrinker->done);
+	/*
+	 * Now the shrinker is fully set up, take the first reference to it to
+	 * indicate that lookup operations are now allowed to use it via
+	 * shrinker_try_get().
+	 */
+	refcount_set(&shrinker->refcount, 1);
+}
+EXPORT_SYMBOL_GPL(shrinker_register);
+
+static void shrinker_free_rcu_cb(struct rcu_head *head)
+{
+	struct shrinker *shrinker = container_of(head, struct shrinker, rcu);
+
+	kfree(shrinker->nr_deferred);
+	kfree(shrinker);
+}
+
+void shrinker_free(struct shrinker *shrinker)
+{
+	struct dentry *debugfs_entry = NULL;
+	int debugfs_id;
+
+	if (!shrinker)
+		return;
+
+	if (shrinker->flags & SHRINKER_REGISTERED) {
+		/* drop the initial refcount */
+		shrinker_put(shrinker);
+		/*
+		 * Wait for all lookups of the shrinker to complete, after that,
+		 * no shrinker is running or will run again, then we can safely
+		 * free it asynchronously via RCU and safely free the structure
+		 * where the shrinker is located, such as super_block etc.
+		 */
+		wait_for_completion(&shrinker->done);
+	}
+
+	mutex_lock(&shrinker_mutex);
+	if (shrinker->flags & SHRINKER_REGISTERED) {
+		/*
+		 * Now we can safely remove it from the shrinker_list and then
+		 * free it.
+		 */
+		list_del_rcu(&shrinker->list);
+		debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id);
+		shrinker->flags &= ~SHRINKER_REGISTERED;
+	}
+
+	shrinker_debugfs_name_free(shrinker);
+
+	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
+		shrinker_memcg_remove(shrinker);
+	mutex_unlock(&shrinker_mutex);
+
+	if (debugfs_entry)
+		shrinker_debugfs_remove(debugfs_entry, debugfs_id);
+
+	call_rcu(&shrinker->rcu, shrinker_free_rcu_cb);
+}
+EXPORT_SYMBOL_GPL(shrinker_free);