From:   Muchun Song <songmuchun@bytedance.com>
To:     willy@infradead.org, akpm@linux-foundation.org, hannes@cmpxchg.org,
        mhocko@kernel.org, vdavydov.dev@gmail.com, shakeelb@google.com,
        guro@fb.com, shy828301@gmail.com, alexs@kernel.org,
        richard.weiyang@gmail.com, david@fromorbit.com,
        trond.myklebust@hammerspace.com, anna.schumaker@netapp.com,
        jaegeuk@kernel.org, chao@kernel.org, kari.argillander@gmail.com
Cc:     linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, linux-nfs@vger.kernel.org,
        zhengqi.arch@bytedance.com, duanxiongchun@bytedance.com,
        fam.zheng@bytedance.com, smuchun@gmail.com,
        Muchun Song <songmuchun@bytedance.com>
Subject: [PATCH v5 01/16] mm: list_lru: optimize memory consumption of arrays of per cgroup lists
Date:   Mon, 20 Dec 2021 16:56:34 +0800
Message-Id: <20211220085649.8196-2-songmuchun@bytedance.com>
In-Reply-To: <20211220085649.8196-1-songmuchun@bytedance.com>
References: <20211220085649.8196-1-songmuchun@bytedance.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

The list_lru uses an array (list_lru_memcg->lru) to store pointers
which point to the list_lru_one. And the array is per memcg per node.
Therefore, the size of the arrays will be 10K * number_of_node * 8 (
a pointer size on 64 bits system) when we run 10k containers in the
system. The memory consumption of the arrays becomes significant. The
more numa node, the more memory it consumes.

I have done a simple test, which creates 10K memcg and mount point
each in a two-node system. The memory consumption of the list_lru
will be 24464MB. After converting the array from per memcg per node
to per memcg, the memory consumption is going to be 21957MB. It is
reduces by 2.5GB. In our AMD servers with 8 numa nodes in those
sysuem, the memory consumption could be more significant. The savings
come from the list_lru_one heads, that it also simplifies the
alloc/dealloc path.

The new scheme looks like the following.

  +----------+   mlrus   +----------------+   mlru   +----------------------+
  | list_lru +---------->| list_lru_memcg +--------->|  list_lru_per_memcg  |
  +----------+           +----------------+          +----------------------+
                                                     |  list_lru_per_memcg  |
                                                     +----------------------+
                                                     |          ...         |
                          +--------------+   node    +----------------------+
                          | list_lru_one |<----------+  list_lru_per_memcg  |
                          +--------------+           +----------------------+
                          | list_lru_one |
                          +--------------+
                          |      ...     |
                          +--------------+
                          | list_lru_one |
                          +--------------+

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
---
 include/linux/list_lru.h |  17 ++--
 mm/list_lru.c            | 206 +++++++++++++++++------------------------------
 2 files changed, 86 insertions(+), 137 deletions(-)

diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h
index 1b5fceb565df..729a27b6ff53 100644
--- a/include/linux/list_lru.h
+++ b/include/linux/list_lru.h
@@ -31,10 +31,15 @@ struct list_lru_one {
 	long			nr_items;
 };
 
+struct list_lru_per_memcg {
+	/* array of per cgroup per node lists, indexed by node id */
+	struct list_lru_one	node[0];
+};
+
 struct list_lru_memcg {
-	struct rcu_head		rcu;
+	struct rcu_head			rcu;
 	/* array of per cgroup lists, indexed by memcg_cache_id */
-	struct list_lru_one	*lru[];
+	struct list_lru_per_memcg	*mlru[];
 };
 
 struct list_lru_node {
@@ -42,11 +47,7 @@ struct list_lru_node {
 	spinlock_t		lock;
 	/* global list, used for the root cgroup in cgroup aware lrus */
 	struct list_lru_one	lru;
-#ifdef CONFIG_MEMCG_KMEM
-	/* for cgroup aware lrus points to per cgroup lists, otherwise NULL */
-	struct list_lru_memcg	__rcu *memcg_lrus;
-#endif
-	long nr_items;
+	long			nr_items;
 } ____cacheline_aligned_in_smp;
 
 struct list_lru {
@@ -55,6 +56,8 @@ struct list_lru {
 	struct list_head	list;
 	int			shrinker_id;
 	bool			memcg_aware;
+	/* for cgroup aware lrus points to per cgroup lists, otherwise NULL */
+	struct list_lru_memcg	__rcu *mlrus;
 #endif
 };
 
diff --git a/mm/list_lru.c b/mm/list_lru.c
index 0cd5e89ca063..7d1356241aa8 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -49,35 +49,37 @@ static int lru_shrinker_id(struct list_lru *lru)
 }
 
 static inline struct list_lru_one *
-list_lru_from_memcg_idx(struct list_lru_node *nlru, int idx)
+list_lru_from_memcg_idx(struct list_lru *lru, int nid, int idx)
 {
-	struct list_lru_memcg *memcg_lrus;
+	struct list_lru_memcg *mlrus;
+	struct list_lru_node *nlru = &lru->node[nid];
+
 	/*
 	 * Either lock or RCU protects the array of per cgroup lists
-	 * from relocation (see memcg_update_list_lru_node).
+	 * from relocation (see memcg_update_list_lru).
 	 */
-	memcg_lrus = rcu_dereference_check(nlru->memcg_lrus,
-					   lockdep_is_held(&nlru->lock));
-	if (memcg_lrus && idx >= 0)
-		return memcg_lrus->lru[idx];
+	mlrus = rcu_dereference_check(lru->mlrus, lockdep_is_held(&nlru->lock));
+	if (mlrus && idx >= 0)
+		return &mlrus->mlru[idx]->node[nid];
 	return &nlru->lru;
 }
 
 static inline struct list_lru_one *
-list_lru_from_kmem(struct list_lru_node *nlru, void *ptr,
+list_lru_from_kmem(struct list_lru *lru, int nid, void *ptr,
 		   struct mem_cgroup **memcg_ptr)
 {
+	struct list_lru_node *nlru = &lru->node[nid];
 	struct list_lru_one *l = &nlru->lru;
 	struct mem_cgroup *memcg = NULL;
 
-	if (!nlru->memcg_lrus)
+	if (!lru->mlrus)
 		goto out;
 
 	memcg = mem_cgroup_from_obj(ptr);
 	if (!memcg)
 		goto out;
 
-	l = list_lru_from_memcg_idx(nlru, memcg_cache_id(memcg));
+	l = list_lru_from_memcg_idx(lru, nid, memcg_cache_id(memcg));
 out:
 	if (memcg_ptr)
 		*memcg_ptr = memcg;
@@ -103,18 +105,18 @@ static inline bool list_lru_memcg_aware(struct list_lru *lru)
 }
 
 static inline struct list_lru_one *
-list_lru_from_memcg_idx(struct list_lru_node *nlru, int idx)
+list_lru_from_memcg_idx(struct list_lru *lru, int nid, int idx)
 {
-	return &nlru->lru;
+	return &lru->node[nid].lru;
 }
 
 static inline struct list_lru_one *
-list_lru_from_kmem(struct list_lru_node *nlru, void *ptr,
+list_lru_from_kmem(struct list_lru *lru, int nid, void *ptr,
 		   struct mem_cgroup **memcg_ptr)
 {
 	if (memcg_ptr)
 		*memcg_ptr = NULL;
-	return &nlru->lru;
+	return &lru->node[nid].lru;
 }
 #endif /* CONFIG_MEMCG_KMEM */
 
@@ -127,7 +129,7 @@ bool list_lru_add(struct list_lru *lru, struct list_head *item)
 
 	spin_lock(&nlru->lock);
 	if (list_empty(item)) {
-		l = list_lru_from_kmem(nlru, item, &memcg);
+		l = list_lru_from_kmem(lru, nid, item, &memcg);
 		list_add_tail(item, &l->list);
 		/* Set shrinker bit if the first element was added */
 		if (!l->nr_items++)
@@ -150,7 +152,7 @@ bool list_lru_del(struct list_lru *lru, struct list_head *item)
 
 	spin_lock(&nlru->lock);
 	if (!list_empty(item)) {
-		l = list_lru_from_kmem(nlru, item, NULL);
+		l = list_lru_from_kmem(lru, nid, item, NULL);
 		list_del_init(item);
 		l->nr_items--;
 		nlru->nr_items--;
@@ -180,12 +182,11 @@ EXPORT_SYMBOL_GPL(list_lru_isolate_move);
 unsigned long list_lru_count_one(struct list_lru *lru,
 				 int nid, struct mem_cgroup *memcg)
 {
-	struct list_lru_node *nlru = &lru->node[nid];
 	struct list_lru_one *l;
 	long count;
 
 	rcu_read_lock();
-	l = list_lru_from_memcg_idx(nlru, memcg_cache_id(memcg));
+	l = list_lru_from_memcg_idx(lru, nid, memcg_cache_id(memcg));
 	count = READ_ONCE(l->nr_items);
 	rcu_read_unlock();
 
@@ -206,16 +207,16 @@ unsigned long list_lru_count_node(struct list_lru *lru, int nid)
 EXPORT_SYMBOL_GPL(list_lru_count_node);
 
 static unsigned long
-__list_lru_walk_one(struct list_lru_node *nlru, int memcg_idx,
+__list_lru_walk_one(struct list_lru *lru, int nid, int memcg_idx,
 		    list_lru_walk_cb isolate, void *cb_arg,
 		    unsigned long *nr_to_walk)
 {
-
+	struct list_lru_node *nlru = &lru->node[nid];
 	struct list_lru_one *l;
 	struct list_head *item, *n;
 	unsigned long isolated = 0;
 
-	l = list_lru_from_memcg_idx(nlru, memcg_idx);
+	l = list_lru_from_memcg_idx(lru, nid, memcg_idx);
 restart:
 	list_for_each_safe(item, n, &l->list) {
 		enum lru_status ret;
@@ -272,8 +273,8 @@ list_lru_walk_one(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
 	unsigned long ret;
 
 	spin_lock(&nlru->lock);
-	ret = __list_lru_walk_one(nlru, memcg_cache_id(memcg), isolate, cb_arg,
-				  nr_to_walk);
+	ret = __list_lru_walk_one(lru, nid, memcg_cache_id(memcg), isolate,
+				  cb_arg, nr_to_walk);
 	spin_unlock(&nlru->lock);
 	return ret;
 }
@@ -288,8 +289,8 @@ list_lru_walk_one_irq(struct list_lru *lru, int nid, struct mem_cgroup *memcg,
 	unsigned long ret;
 
 	spin_lock_irq(&nlru->lock);
-	ret = __list_lru_walk_one(nlru, memcg_cache_id(memcg), isolate, cb_arg,
-				  nr_to_walk);
+	ret = __list_lru_walk_one(lru, nid, memcg_cache_id(memcg), isolate,
+				  cb_arg, nr_to_walk);
 	spin_unlock_irq(&nlru->lock);
 	return ret;
 }
@@ -308,7 +309,7 @@ unsigned long list_lru_walk_node(struct list_lru *lru, int nid,
 			struct list_lru_node *nlru = &lru->node[nid];
 
 			spin_lock(&nlru->lock);
-			isolated += __list_lru_walk_one(nlru, memcg_idx,
+			isolated += __list_lru_walk_one(lru, nid, memcg_idx,
 							isolate, cb_arg,
 							nr_to_walk);
 			spin_unlock(&nlru->lock);
@@ -328,166 +329,111 @@ static void init_one_lru(struct list_lru_one *l)
 }
 
 #ifdef CONFIG_MEMCG_KMEM
-static void __memcg_destroy_list_lru_node(struct list_lru_memcg *memcg_lrus,
-					  int begin, int end)
+static void memcg_destroy_list_lru_range(struct list_lru_memcg *mlrus,
+					 int begin, int end)
 {
 	int i;
 
 	for (i = begin; i < end; i++)
-		kfree(memcg_lrus->lru[i]);
+		kfree(mlrus->mlru[i]);
 }
 
-static int __memcg_init_list_lru_node(struct list_lru_memcg *memcg_lrus,
-				      int begin, int end)
+static int memcg_init_list_lru_range(struct list_lru_memcg *mlrus,
+				     int begin, int end)
 {
 	int i;
 
 	for (i = begin; i < end; i++) {
-		struct list_lru_one *l;
+		int nid;
+		struct list_lru_per_memcg *mlru;
 
-		l = kmalloc(sizeof(struct list_lru_one), GFP_KERNEL);
-		if (!l)
+		mlru = kmalloc(struct_size(mlru, node, nr_node_ids), GFP_KERNEL);
+		if (!mlru)
 			goto fail;
 
-		init_one_lru(l);
-		memcg_lrus->lru[i] = l;
+		for_each_node(nid)
+			init_one_lru(&mlru->node[nid]);
+		mlrus->mlru[i] = mlru;
 	}
 	return 0;
 fail:
-	__memcg_destroy_list_lru_node(memcg_lrus, begin, i);
+	memcg_destroy_list_lru_range(mlrus, begin, i);
 	return -ENOMEM;
 }
 
-static int memcg_init_list_lru_node(struct list_lru_node *nlru)
+static int memcg_init_list_lru(struct list_lru *lru, bool memcg_aware)
 {
-	struct list_lru_memcg *memcg_lrus;
+	struct list_lru_memcg *mlrus;
 	int size = memcg_nr_cache_ids;
 
-	memcg_lrus = kvmalloc(struct_size(memcg_lrus, lru, size), GFP_KERNEL);
-	if (!memcg_lrus)
+	lru->memcg_aware = memcg_aware;
+	if (!memcg_aware)
+		return 0;
+
+	mlrus = kvmalloc(struct_size(mlrus, mlru, size), GFP_KERNEL);
+	if (!mlrus)
 		return -ENOMEM;
 
-	if (__memcg_init_list_lru_node(memcg_lrus, 0, size)) {
-		kvfree(memcg_lrus);
+	if (memcg_init_list_lru_range(mlrus, 0, size)) {
+		kvfree(mlrus);
 		return -ENOMEM;
 	}
-	RCU_INIT_POINTER(nlru->memcg_lrus, memcg_lrus);
+	RCU_INIT_POINTER(lru->mlrus, mlrus);
 
 	return 0;
 }
 
-static void memcg_destroy_list_lru_node(struct list_lru_node *nlru)
+static void memcg_destroy_list_lru(struct list_lru *lru)
 {
-	struct list_lru_memcg *memcg_lrus;
+	struct list_lru_memcg *mlrus;
+
+	if (!list_lru_memcg_aware(lru))
+		return;
+
 	/*
 	 * This is called when shrinker has already been unregistered,
 	 * and nobody can use it. So, there is no need to use kvfree_rcu().
 	 */
-	memcg_lrus = rcu_dereference_protected(nlru->memcg_lrus, true);
-	__memcg_destroy_list_lru_node(memcg_lrus, 0, memcg_nr_cache_ids);
-	kvfree(memcg_lrus);
+	mlrus = rcu_dereference_protected(lru->mlrus, true);
+	memcg_destroy_list_lru_range(mlrus, 0, memcg_nr_cache_ids);
+	kvfree(mlrus);
 }
 
-static int memcg_update_list_lru_node(struct list_lru_node *nlru,
-				      int old_size, int new_size)
+static int memcg_update_list_lru(struct list_lru *lru, int old_size, int new_size)
 {
 	struct list_lru_memcg *old, *new;
 
 	BUG_ON(old_size > new_size);
 
-	old = rcu_dereference_protected(nlru->memcg_lrus,
+	old = rcu_dereference_protected(lru->mlrus,
 					lockdep_is_held(&list_lrus_mutex));
-	new = kvmalloc(struct_size(new, lru, new_size), GFP_KERNEL);
+	new = kvmalloc(struct_size(new, mlru, new_size), GFP_KERNEL);
 	if (!new)
 		return -ENOMEM;
 
-	if (__memcg_init_list_lru_node(new, old_size, new_size)) {
+	if (memcg_init_list_lru_range(new, old_size, new_size)) {
 		kvfree(new);
 		return -ENOMEM;
 	}
 
-	memcpy(&new->lru, &old->lru, flex_array_size(new, lru, old_size));
-	rcu_assign_pointer(nlru->memcg_lrus, new);
+	memcpy(&new->mlru, &old->mlru, flex_array_size(new, mlru, old_size));
+	rcu_assign_pointer(lru->mlrus, new);
 	kvfree_rcu(old, rcu);
 	return 0;
 }
 
-static void memcg_cancel_update_list_lru_node(struct list_lru_node *nlru,
-					      int old_size, int new_size)
-{
-	struct list_lru_memcg *memcg_lrus;
-
-	memcg_lrus = rcu_dereference_protected(nlru->memcg_lrus,
-					       lockdep_is_held(&list_lrus_mutex));
-	/* do not bother shrinking the array back to the old size, because we
-	 * cannot handle allocation failures here */
-	__memcg_destroy_list_lru_node(memcg_lrus, old_size, new_size);
-}
-
-static int memcg_init_list_lru(struct list_lru *lru, bool memcg_aware)
-{
-	int i;
-
-	lru->memcg_aware = memcg_aware;
-
-	if (!memcg_aware)
-		return 0;
-
-	for_each_node(i) {
-		if (memcg_init_list_lru_node(&lru->node[i]))
-			goto fail;
-	}
-	return 0;
-fail:
-	for (i = i - 1; i >= 0; i--) {
-		if (!lru->node[i].memcg_lrus)
-			continue;
-		memcg_destroy_list_lru_node(&lru->node[i]);
-	}
-	return -ENOMEM;
-}
-
-static void memcg_destroy_list_lru(struct list_lru *lru)
-{
-	int i;
-
-	if (!list_lru_memcg_aware(lru))
-		return;
-
-	for_each_node(i)
-		memcg_destroy_list_lru_node(&lru->node[i]);
-}
-
-static int memcg_update_list_lru(struct list_lru *lru,
-				 int old_size, int new_size)
-{
-	int i;
-
-	for_each_node(i) {
-		if (memcg_update_list_lru_node(&lru->node[i],
-					       old_size, new_size))
-			goto fail;
-	}
-	return 0;
-fail:
-	for (i = i - 1; i >= 0; i--) {
-		if (!lru->node[i].memcg_lrus)
-			continue;
-
-		memcg_cancel_update_list_lru_node(&lru->node[i],
-						  old_size, new_size);
-	}
-	return -ENOMEM;
-}
-
 static void memcg_cancel_update_list_lru(struct list_lru *lru,
 					 int old_size, int new_size)
 {
-	int i;
+	struct list_lru_memcg *mlrus;
 
-	for_each_node(i)
-		memcg_cancel_update_list_lru_node(&lru->node[i],
-						  old_size, new_size);
+	mlrus = rcu_dereference_protected(lru->mlrus,
+					  lockdep_is_held(&list_lrus_mutex));
+	/*
+	 * Do not bother shrinking the array back to the old size, because we
+	 * cannot handle allocation failures here.
+	 */
+	memcg_destroy_list_lru_range(mlrus, old_size, new_size);
 }
 
 int memcg_update_all_list_lrus(int new_size)
@@ -524,8 +470,8 @@ static void memcg_drain_list_lru_node(struct list_lru *lru, int nid,
 	 */
 	spin_lock_irq(&nlru->lock);
 
-	src = list_lru_from_memcg_idx(nlru, src_idx);
-	dst = list_lru_from_memcg_idx(nlru, dst_idx);
+	src = list_lru_from_memcg_idx(lru, nid, src_idx);
+	dst = list_lru_from_memcg_idx(lru, nid, dst_idx);
 
 	list_splice_init(&src->list, &dst->list);
 
-- 
2.11.0