[PATCH V3 0/4] record non-slab shrinkers for non-root memcgs when kmem is disabled

[PATCH V3 0/4] record non-slab shrinkers for non-root memcgs when kmem is disabled

[Haifeng Xu]

When registering new shrinkers, all memcgs need to expand shrinker info
if new allocated id exceeds shrinker_nr_max. But if kmem is disabled,
only non-slab shrinkers is useful in memcg slab shrink. So in this case,
it is enough to allocate non-slab shrinker info for non-root memcg. This
can save a bit of memory and reduce the holding time of shrinker lock.

With this optimization, the finish time of pod creation in our internal
test is reduced from 150 seconds to 69 seconds. We test it based on
stable kernel 6.6.102.

Changes since V2:
- read shrinker_nonslab_nr_max and shrinker_nr_max under after acquring
  the shrinker_mutex.

https://lore.kernel.org/all/20260310031250.289851-1-haifeng.xu@shopee.com/

Changes since V1:
- reuse shrinker_id() to retrieve the id of shrinker, this also fix the
  build error without CONFIG_MEMCG.

https://lore.kernel.org/all/20260306075757.198887-1-haifeng.xu@shopee.com/

Haifeng Xu (4):
  mm: shrinker: add one more parameter in shrinker_id()
  mm: shrinker: move shrinker_id() code block below memcg_kmem_online()
  mm: shrinker: optimize the allocation of shrinker_info when setting
    cgroup_memory_nokmem
  mm: shrinker: remove unnecessary check in shrink_slab_memcg()

 include/linux/memcontrol.h | 194 +++++++++++++++++++------------------
 include/linux/shrinker.h   |   3 +
 mm/huge_memory.c           |   4 +-
 mm/shrinker.c              | 134 +++++++++++++++++++++----
 4 files changed, 218 insertions(+), 117 deletions(-)

-- 
2.43.0

[PATCH V3 1/4] mm: shrinker: add one more parameter in shrinker_id()

[Haifeng Xu]

Add a parameter points to target memory cgroup in shrinker_id().
The following patch will use it to decide the id of shrinker.
No functional change here.

Signed-off-by: Haifeng Xu <haifeng.xu@shopee.com>
---
 include/linux/memcontrol.h |  4 ++--
 mm/huge_memory.c           |  4 ++--
 mm/shrinker.c              | 12 ++++++++----
 3 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 70b685a85bf4..a583dbc0adcc 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1634,7 +1634,7 @@ void free_shrinker_info(struct mem_cgroup *memcg);
 void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id);
 void reparent_shrinker_deferred(struct mem_cgroup *memcg);
 
-static inline int shrinker_id(struct shrinker *shrinker)
+static inline int shrinker_id(struct mem_cgroup *memcg, struct shrinker *shrinker)
 {
 	return shrinker->id;
 }
@@ -1670,7 +1670,7 @@ static inline void set_shrinker_bit(struct mem_cgroup *memcg,
 {
 }
 
-static inline int shrinker_id(struct shrinker *shrinker)
+static inline int shrinker_id(struct mem_cgroup *memcg, struct shrinker *shrinker)
 {
 	return -1;
 }
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 8e2746ea74ad..6050f8d71587 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -4353,7 +4353,7 @@ void deferred_split_folio(struct folio *folio, bool partially_mapped)
 		ds_queue->split_queue_len++;
 		if (memcg)
 			set_shrinker_bit(memcg, folio_nid(folio),
-					 shrinker_id(deferred_split_shrinker));
+					 shrinker_id(memcg, deferred_split_shrinker));
 	}
 	split_queue_unlock_irqrestore(ds_queue, flags);
 }
@@ -4509,7 +4509,7 @@ void reparent_deferred_split_queue(struct mem_cgroup *memcg)
 	ds_queue->split_queue_len = 0;
 
 	for_each_node(nid)
-		set_shrinker_bit(parent, nid, shrinker_id(deferred_split_shrinker));
+		set_shrinker_bit(parent, nid, shrinker_id(parent, deferred_split_shrinker));
 
 unlock:
 	spin_unlock(&parent_ds_queue->split_queue_lock);
diff --git a/mm/shrinker.c b/mm/shrinker.c
index 7b61fc0ee78f..61dbb6afae52 100644
--- a/mm/shrinker.c
+++ b/mm/shrinker.c
@@ -255,11 +255,13 @@ static long xchg_nr_deferred_memcg(int nid, struct shrinker *shrinker,
 	struct shrinker_info *info;
 	struct shrinker_info_unit *unit;
 	long nr_deferred;
+	int id;
 
 	rcu_read_lock();
+	id = shrinker_id(memcg, shrinker);
 	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);
+	unit = info->unit[shrinker_id_to_index(id)];
+	nr_deferred = atomic_long_xchg(&unit->nr_deferred[shrinker_id_to_offset(id)], 0);
 	rcu_read_unlock();
 
 	return nr_deferred;
@@ -271,12 +273,14 @@ static long add_nr_deferred_memcg(long nr, int nid, struct shrinker *shrinker,
 	struct shrinker_info *info;
 	struct shrinker_info_unit *unit;
 	long nr_deferred;
+	int id;
 
 	rcu_read_lock();
+	id = shrinker_id(memcg, shrinker);
 	info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info);
-	unit = info->unit[shrinker_id_to_index(shrinker->id)];
+	unit = info->unit[shrinker_id_to_index(id)];
 	nr_deferred =
-		atomic_long_add_return(nr, &unit->nr_deferred[shrinker_id_to_offset(shrinker->id)]);
+		atomic_long_add_return(nr, &unit->nr_deferred[shrinker_id_to_offset(id)]);
 	rcu_read_unlock();
 
 	return nr_deferred;
-- 
2.43.0

[PATCH V3 2/4] mm: shrinker: move shrinker_id() code block below memcg_kmem_online()

[Haifeng Xu]

The following patch will use memcg_kmem_online() to decide the id
of shrinker, so move the code block down to reduce the diff noise
in the following patch.

No functional change here.

Signed-off-by: Haifeng Xu <haifeng.xu@shopee.com>
---
 include/linux/memcontrol.h | 188 ++++++++++++++++++-------------------
 1 file changed, 94 insertions(+), 94 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index a583dbc0adcc..ce7b5101bc02 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1582,100 +1582,6 @@ static inline void mem_cgroup_flush_foreign(struct bdi_writeback *wb)
 
 #endif	/* CONFIG_CGROUP_WRITEBACK */
 
-struct sock;
-#ifdef CONFIG_MEMCG
-extern struct static_key_false memcg_sockets_enabled_key;
-#define mem_cgroup_sockets_enabled static_branch_unlikely(&memcg_sockets_enabled_key)
-
-void mem_cgroup_sk_alloc(struct sock *sk);
-void mem_cgroup_sk_free(struct sock *sk);
-void mem_cgroup_sk_inherit(const struct sock *sk, struct sock *newsk);
-bool mem_cgroup_sk_charge(const struct sock *sk, unsigned int nr_pages,
-			  gfp_t gfp_mask);
-void mem_cgroup_sk_uncharge(const struct sock *sk, unsigned int nr_pages);
-
-#if BITS_PER_LONG < 64
-static inline void mem_cgroup_set_socket_pressure(struct mem_cgroup *memcg)
-{
-	u64 val = get_jiffies_64() + HZ;
-	unsigned long flags;
-
-	write_seqlock_irqsave(&memcg->socket_pressure_seqlock, flags);
-	memcg->socket_pressure = val;
-	write_sequnlock_irqrestore(&memcg->socket_pressure_seqlock, flags);
-}
-
-static inline u64 mem_cgroup_get_socket_pressure(struct mem_cgroup *memcg)
-{
-	unsigned int seq;
-	u64 val;
-
-	do {
-		seq = read_seqbegin(&memcg->socket_pressure_seqlock);
-		val = memcg->socket_pressure;
-	} while (read_seqretry(&memcg->socket_pressure_seqlock, seq));
-
-	return val;
-}
-#else
-static inline void mem_cgroup_set_socket_pressure(struct mem_cgroup *memcg)
-{
-	WRITE_ONCE(memcg->socket_pressure, jiffies + HZ);
-}
-
-static inline u64 mem_cgroup_get_socket_pressure(struct mem_cgroup *memcg)
-{
-	return READ_ONCE(memcg->socket_pressure);
-}
-#endif
-
-int alloc_shrinker_info(struct mem_cgroup *memcg);
-void free_shrinker_info(struct mem_cgroup *memcg);
-void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id);
-void reparent_shrinker_deferred(struct mem_cgroup *memcg);
-
-static inline int shrinker_id(struct mem_cgroup *memcg, struct shrinker *shrinker)
-{
-	return shrinker->id;
-}
-#else
-#define mem_cgroup_sockets_enabled 0
-
-static inline void mem_cgroup_sk_alloc(struct sock *sk)
-{
-}
-
-static inline void mem_cgroup_sk_free(struct sock *sk)
-{
-}
-
-static inline void mem_cgroup_sk_inherit(const struct sock *sk, struct sock *newsk)
-{
-}
-
-static inline bool mem_cgroup_sk_charge(const struct sock *sk,
-					unsigned int nr_pages,
-					gfp_t gfp_mask)
-{
-	return false;
-}
-
-static inline void mem_cgroup_sk_uncharge(const struct sock *sk,
-					  unsigned int nr_pages)
-{
-}
-
-static inline void set_shrinker_bit(struct mem_cgroup *memcg,
-				    int nid, int shrinker_id)
-{
-}
-
-static inline int shrinker_id(struct mem_cgroup *memcg, struct shrinker *shrinker)
-{
-	return -1;
-}
-#endif
-
 #ifdef CONFIG_MEMCG
 bool mem_cgroup_kmem_disabled(void);
 int __memcg_kmem_charge_page(struct page *page, gfp_t gfp, int order);
@@ -1844,6 +1750,100 @@ static inline bool memcg_is_dying(struct mem_cgroup *memcg)
 }
 #endif /* CONFIG_MEMCG */
 
+struct sock;
+#ifdef CONFIG_MEMCG
+extern struct static_key_false memcg_sockets_enabled_key;
+#define mem_cgroup_sockets_enabled static_branch_unlikely(&memcg_sockets_enabled_key)
+
+void mem_cgroup_sk_alloc(struct sock *sk);
+void mem_cgroup_sk_free(struct sock *sk);
+void mem_cgroup_sk_inherit(const struct sock *sk, struct sock *newsk);
+bool mem_cgroup_sk_charge(const struct sock *sk, unsigned int nr_pages,
+			  gfp_t gfp_mask);
+void mem_cgroup_sk_uncharge(const struct sock *sk, unsigned int nr_pages);
+
+#if BITS_PER_LONG < 64
+static inline void mem_cgroup_set_socket_pressure(struct mem_cgroup *memcg)
+{
+	u64 val = get_jiffies_64() + HZ;
+	unsigned long flags;
+
+	write_seqlock_irqsave(&memcg->socket_pressure_seqlock, flags);
+	memcg->socket_pressure = val;
+	write_sequnlock_irqrestore(&memcg->socket_pressure_seqlock, flags);
+}
+
+static inline u64 mem_cgroup_get_socket_pressure(struct mem_cgroup *memcg)
+{
+	unsigned int seq;
+	u64 val;
+
+	do {
+		seq = read_seqbegin(&memcg->socket_pressure_seqlock);
+		val = memcg->socket_pressure;
+	} while (read_seqretry(&memcg->socket_pressure_seqlock, seq));
+
+	return val;
+}
+#else
+static inline void mem_cgroup_set_socket_pressure(struct mem_cgroup *memcg)
+{
+	WRITE_ONCE(memcg->socket_pressure, jiffies + HZ);
+}
+
+static inline u64 mem_cgroup_get_socket_pressure(struct mem_cgroup *memcg)
+{
+	return READ_ONCE(memcg->socket_pressure);
+}
+#endif
+
+int alloc_shrinker_info(struct mem_cgroup *memcg);
+void free_shrinker_info(struct mem_cgroup *memcg);
+void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id);
+void reparent_shrinker_deferred(struct mem_cgroup *memcg);
+
+static inline int shrinker_id(struct mem_cgroup *memcg, struct shrinker *shrinker)
+{
+	return shrinker->id;
+}
+#else
+#define mem_cgroup_sockets_enabled 0
+
+static inline void mem_cgroup_sk_alloc(struct sock *sk)
+{
+}
+
+static inline void mem_cgroup_sk_free(struct sock *sk)
+{
+}
+
+static inline void mem_cgroup_sk_inherit(const struct sock *sk, struct sock *newsk)
+{
+}
+
+static inline bool mem_cgroup_sk_charge(const struct sock *sk,
+					unsigned int nr_pages,
+					gfp_t gfp_mask)
+{
+	return false;
+}
+
+static inline void mem_cgroup_sk_uncharge(const struct sock *sk,
+					  unsigned int nr_pages)
+{
+}
+
+static inline void set_shrinker_bit(struct mem_cgroup *memcg,
+				    int nid, int shrinker_id)
+{
+}
+
+static inline int shrinker_id(struct mem_cgroup *memcg, struct shrinker *shrinker)
+{
+	return -1;
+}
+#endif
+
 #if defined(CONFIG_MEMCG) && defined(CONFIG_ZSWAP)
 bool obj_cgroup_may_zswap(struct obj_cgroup *objcg);
 void obj_cgroup_charge_zswap(struct obj_cgroup *objcg, size_t size);
-- 
2.43.0

[PATCH V3 3/4] mm: shrinker: optimize the allocation of shrinker_info when setting cgroup_memory_nokmem

[Haifeng Xu]

When kmem is disabled, memcg slab shrink only call non-slab shrinkers,
so just allocates shrinker info for non-slab shrinkers to non-root memcgs.

Therefore, if memcg_kmem_online is true, all things keep same as before.
Otherwise, root memcg allocates id from shrinker_idr to identify each
shrinker and non-root memcgs use nonslab_id to identify non-slab shrinkers.
The size of shrinkers_info in non-root memcgs can be very low because the
number of shrinkers marked as SHRINKER_NONSLAB | SHRINKER_MEMCG_AWARE is
few. Also, the time spending in expand_shrinker_info() can reduce a lot.

When setting shrinker bit or updating nr_deferred, use nonslab_id for
non-root memcgs if the shrinker is marked as SHRINKER_NONSLAB.

Signed-off-by: Haifeng Xu <haifeng.xu@shopee.com>
---
 include/linux/memcontrol.h |   8 ++-
 include/linux/shrinker.h   |   3 +
 mm/shrinker.c              | 117 +++++++++++++++++++++++++++++++++----
 3 files changed, 115 insertions(+), 13 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index ce7b5101bc02..3edd6211aed2 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1804,7 +1804,13 @@ void reparent_shrinker_deferred(struct mem_cgroup *memcg);
 
 static inline int shrinker_id(struct mem_cgroup *memcg, struct shrinker *shrinker)
 {
-	return shrinker->id;
+	int id = shrinker->id;
+
+	if (!memcg_kmem_online() && (shrinker->flags & SHRINKER_NONSLAB) &&
+	    memcg != root_mem_cgroup)
+		id = shrinker->nonslab_id;
+
+	return id;
 }
 #else
 #define mem_cgroup_sockets_enabled 0
diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
index 1a00be90d93a..df53008ed8b5 100644
--- a/include/linux/shrinker.h
+++ b/include/linux/shrinker.h
@@ -107,6 +107,9 @@ struct shrinker {
 #ifdef CONFIG_MEMCG
 	/* ID in shrinker_idr */
 	int id;
+
+	/* ID in shrinker_nonslab_idr */
+	int nonslab_id;
 #endif
 #ifdef CONFIG_SHRINKER_DEBUG
 	int debugfs_id;
diff --git a/mm/shrinker.c b/mm/shrinker.c
index 61dbb6afae52..3137518bc746 100644
--- a/mm/shrinker.c
+++ b/mm/shrinker.c
@@ -12,6 +12,7 @@ DEFINE_MUTEX(shrinker_mutex);
 
 #ifdef CONFIG_MEMCG
 static int shrinker_nr_max;
+static int shrinker_nonslab_nr_max;
 
 static inline int shrinker_unit_size(int nr_items)
 {
@@ -78,15 +79,26 @@ int alloc_shrinker_info(struct mem_cgroup *memcg)
 {
 	int nid, ret = 0;
 	int array_size = 0;
+	int alloc_nr_max;
 
 	mutex_lock(&shrinker_mutex);
-	array_size = shrinker_unit_size(shrinker_nr_max);
+
+	if (memcg_kmem_online()) {
+		alloc_nr_max = shrinker_nr_max;
+	} else {
+		if (memcg == root_mem_cgroup)
+			alloc_nr_max = shrinker_nr_max;
+		else
+			alloc_nr_max = shrinker_nonslab_nr_max;
+	}
+
+	array_size = shrinker_unit_size(alloc_nr_max);
 	for_each_node(nid) {
 		struct shrinker_info *info = kvzalloc_node(sizeof(*info) + array_size,
 							   GFP_KERNEL, nid);
 		if (!info)
 			goto err;
-		info->map_nr_max = shrinker_nr_max;
+		info->map_nr_max = alloc_nr_max;
 		if (shrinker_unit_alloc(info, NULL, nid)) {
 			kvfree(info);
 			goto err;
@@ -147,33 +159,47 @@ static int expand_one_shrinker_info(struct mem_cgroup *memcg, int new_size,
 	return 0;
 }
 
-static int expand_shrinker_info(int new_id)
+static int expand_shrinker_info(int new_id, bool full, bool root)
 {
 	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;
+	struct mem_cgroup *start = NULL;
+	int old_nr_max = shrinker_nr_max;
 
 	if (!root_mem_cgroup)
 		goto out;
 
 	lockdep_assert_held(&shrinker_mutex);
 
+	if (!full && !root) {
+		start = root_mem_cgroup;
+		old_nr_max = shrinker_nonslab_nr_max;
+	}
+
 	new_size = shrinker_unit_size(new_nr_max);
-	old_size = shrinker_unit_size(shrinker_nr_max);
+	old_size = shrinker_unit_size(old_nr_max);
+
+	memcg = mem_cgroup_iter(NULL, start, NULL);
+	if (!memcg)
+		goto out;
 
-	memcg = mem_cgroup_iter(NULL, NULL, NULL);
 	do {
 		ret = expand_one_shrinker_info(memcg, new_size, old_size,
 					       new_nr_max);
-		if (ret) {
+		if (ret || (root && memcg == root_mem_cgroup)) {
 			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;
+	if (!ret) {
+		if (!full && !root)
+			shrinker_nonslab_nr_max = new_nr_max;
+		else
+			shrinker_nr_max = new_nr_max;
+	}
 
 	return ret;
 }
@@ -212,25 +238,58 @@ void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
 }
 
 static DEFINE_IDR(shrinker_idr);
+static DEFINE_IDR(shrinker_nonslab_idr);
 
 static int shrinker_memcg_alloc(struct shrinker *shrinker)
 {
 	int id, ret = -ENOMEM;
+	bool kmem_online;
 
 	if (mem_cgroup_disabled())
 		return -ENOSYS;
 
+	kmem_online = memcg_kmem_online();
 	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)) {
+		/* If memcg_kmem_online() returns true, expand shrinker
+		 * info for all memcgs, otherwise, expand shrinker info
+		 * for root memcg only
+		 */
+		if (expand_shrinker_info(id, kmem_online, !kmem_online)) {
 			idr_remove(&shrinker_idr, id);
 			goto unlock;
 		}
 	}
+
+	shrinker->nonslab_id = -1;
+	/*
+	 * If cgroup_memory_nokmem is set, record shrinkers with SHRINKER_NONSLAB
+	 * because memcg slab shrink only call non-slab shrinkers.
+	 */
+	if (!kmem_online && shrinker->flags & SHRINKER_NONSLAB) {
+		int nonslab_id;
+
+		nonslab_id = idr_alloc(&shrinker_nonslab_idr, shrinker, 0, 0, GFP_KERNEL);
+		if (nonslab_id < 0) {
+			idr_remove(&shrinker_idr, id);
+			goto unlock;
+		}
+
+		if (nonslab_id >= shrinker_nonslab_nr_max) {
+			/* expand shrinker info for non-root memcgs */
+			if (expand_shrinker_info(nonslab_id, false, false)) {
+				idr_remove(&shrinker_idr, id);
+				idr_remove(&shrinker_nonslab_idr, nonslab_id);
+				goto unlock;
+			}
+		}
+		shrinker->nonslab_id = nonslab_id;
+	}
+
 	shrinker->id = id;
 	ret = 0;
 unlock:
@@ -247,6 +306,12 @@ static void shrinker_memcg_remove(struct shrinker *shrinker)
 	lockdep_assert_held(&shrinker_mutex);
 
 	idr_remove(&shrinker_idr, id);
+
+	if (shrinker->flags & SHRINKER_NONSLAB) {
+		id = shrinker->nonslab_id;
+		if (id >= 0)
+			idr_remove(&shrinker_nonslab_idr, id);
+	}
 }
 
 static long xchg_nr_deferred_memcg(int nid, struct shrinker *shrinker,
@@ -305,10 +370,33 @@ void reparent_shrinker_deferred(struct mem_cgroup *memcg)
 		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]);
+
+				/*
+				 * If memcg_kmem_online() is false, the non-root memcgs use
+				 * nonslab_id but root memory cgroup use id. When reparenting
+				 * shrinker info to it, must convert the nonslab_id to id.
+				 */
+				if (!memcg_kmem_online() &&  parent == root_mem_cgroup) {
+					int id, p_index, p_off;
+					struct shrinker *shrinker;
+
+					id = calc_shrinker_id(index, offset);
+					shrinker = idr_find(&shrinker_nonslab_idr, id);
+					if (shrinker) {
+						id = shrinker->id;
+						p_index = shrinker_id_to_index(id);
+						p_off = shrinker_id_to_offset(id);
+
+						parent_unit = parent_info->unit[p_index];
+						atomic_long_add(nr,
+								&parent_unit->nr_deferred[p_off]);
+					}
+				} else {
+					parent_unit = parent_info->unit[index];
+					atomic_long_add(nr, &parent_unit->nr_deferred[offset]);
+				}
 			}
 		}
 	}
@@ -538,7 +626,12 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 			int shrinker_id = calc_shrinker_id(index, offset);
 
 			rcu_read_lock();
-			shrinker = idr_find(&shrinker_idr, shrinker_id);
+
+			if (memcg_kmem_online())
+				shrinker = idr_find(&shrinker_idr, shrinker_id);
+			else
+				shrinker = idr_find(&shrinker_nonslab_idr, shrinker_id);
+
 			if (unlikely(!shrinker || !shrinker_try_get(shrinker))) {
 				clear_bit(offset, unit->map);
 				rcu_read_unlock();
-- 
2.43.0

Re: [PATCH V3 3/4] mm: shrinker: optimize the allocation of shrinker_info when setting cgroup_memory_nokmem

[Andrew Morton]

On Wed, 11 Mar 2026 11:02:34 +0800 Haifeng Xu <haifeng.xu@shopee.com> wrote:

> When kmem is disabled, memcg slab shrink only call non-slab shrinkers,
> so just allocates shrinker info for non-slab shrinkers to non-root memcgs.

What happens if memcg kmem is enabled later on?

Re: [PATCH V3 3/4] mm: shrinker: optimize the allocation of shrinker_info when setting cgroup_memory_nokmem

[Haifeng Xu]

On 2026/3/12 05:19, Andrew Morton wrote:
> On Wed, 11 Mar 2026 11:02:34 +0800 Haifeng Xu <haifeng.xu@shopee.com> wrote:
> 
>> When kmem is disabled, memcg slab shrink only call non-slab shrinkers,
>> so just allocates shrinker info for non-slab shrinkers to non-root memcgs.
> 
> What happens if memcg kmem is enabled later on?

cgroup_memory_nokmem is a boot parameter. If memcg kmem is enabled, all things
keep same as before, root and non-root memcgs allocate id from shrinker_idr.

[PATCH V3 4/4] mm: shrinker: remove unnecessary check in shrink_slab_memcg()

[Haifeng Xu]

If memcg_kmem_online() is false, only non-slab shrinkers are recorded
in the map, so remove the check.

Signed-off-by: Haifeng Xu <haifeng.xu@shopee.com>
---
 mm/shrinker.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/mm/shrinker.c b/mm/shrinker.c
index 3137518bc746..98307a9bd00e 100644
--- a/mm/shrinker.c
+++ b/mm/shrinker.c
@@ -639,11 +639,6 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 			}
 			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);
-- 
2.43.0