mm: list_lru: replace linear array with xarray

If we run 10k containers in the system, the size of the
list_lru_memcg->lrus can be ~96KB per list_lru.  When we decrease the
number containers, the size of the array will not be shrinked.  It is
not scalable.  The xarray is a good choice for this case.  We can save a
lot of memory when there are tens of thousands continers in the system.
If we use xarray, we also can remove the logic code of resizing array,
which can simplify the code.

[akpm@linux-foundation.org: remove unused local]

Link: https://lkml.kernel.org/r/20220228122126.37293-13-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Cc: Alex Shi <alexs@kernel.org>
Cc: Anna Schumaker <Anna.Schumaker@Netapp.com>
Cc: Chao Yu <chao@kernel.org>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Fam Zheng <fam.zheng@bytedance.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kari Argillander <kari.argillander@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Xiongchun Duan <duanxiongchun@bytedance.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 71 insertions, 209 deletions

diff --git a/mm/list_lru.c b/mm/list_lru.c
index 488dacd1f8ff..3fdae1688f82 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -52,21 +52,12 @@ static int lru_shrinker_id(struct list_lru *lru)
 static inline struct list_lru_one *
 list_lru_from_memcg_idx(struct list_lru *lru, int nid, int idx)
 {
-	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).
-	 */
-	mlrus = rcu_dereference_check(lru->mlrus, lockdep_is_held(&nlru->lock));
-	if (mlrus && idx >= 0) {
-		struct list_lru_per_memcg *mlru;
+	if (list_lru_memcg_aware(lru) && idx >= 0) {
+		struct list_lru_per_memcg *mlru = xa_load(&lru->xa, idx);
 
-		mlru = rcu_dereference_check(mlrus->mlru[idx], true);
 		return mlru ? &mlru->node[nid] : NULL;
 	}
-	return &nlru->lru;
+	return &lru->node[nid].lru;
 }
 
 static inline struct list_lru_one *
@@ -77,7 +68,7 @@ list_lru_from_kmem(struct list_lru *lru, int nid, void *ptr,
 	struct list_lru_one *l = &nlru->lru;
 	struct mem_cgroup *memcg = NULL;
 
-	if (!lru->mlrus)
+	if (!list_lru_memcg_aware(lru))
 		goto out;
 
 	memcg = mem_cgroup_from_obj(ptr);
@@ -309,16 +300,20 @@ unsigned long list_lru_walk_node(struct list_lru *lru, int nid,
 				 unsigned long *nr_to_walk)
 {
 	long isolated = 0;
-	int memcg_idx;
 
 	isolated += list_lru_walk_one(lru, nid, NULL, isolate, cb_arg,
 				      nr_to_walk);
+
+#ifdef CONFIG_MEMCG_KMEM
 	if (*nr_to_walk > 0 && list_lru_memcg_aware(lru)) {
-		for_each_memcg_cache_index(memcg_idx) {
+		struct list_lru_per_memcg *mlru;
+		unsigned long index;
+
+		xa_for_each(&lru->xa, index, mlru) {
 			struct list_lru_node *nlru = &lru->node[nid];
 
 			spin_lock(&nlru->lock);
-			isolated += __list_lru_walk_one(lru, nid, memcg_idx,
+			isolated += __list_lru_walk_one(lru, nid, index,
 							isolate, cb_arg,
 							nr_to_walk);
 			spin_unlock(&nlru->lock);
@@ -327,6 +322,8 @@ unsigned long list_lru_walk_node(struct list_lru *lru, int nid,
 				break;
 		}
 	}
+#endif
+
 	return isolated;
 }
 EXPORT_SYMBOL_GPL(list_lru_walk_node);
@@ -338,15 +335,6 @@ static void init_one_lru(struct list_lru_one *l)
 }
 
 #ifdef CONFIG_MEMCG_KMEM
-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(mlrus->mlru[i]);
-}
-
 static struct list_lru_per_memcg *memcg_init_list_lru_one(gfp_t gfp)
 {
 	int nid;
@@ -364,14 +352,7 @@ static struct list_lru_per_memcg *memcg_init_list_lru_one(gfp_t gfp)
 
 static void memcg_list_lru_free(struct list_lru *lru, int src_idx)
 {
-	struct list_lru_memcg *mlrus;
-	struct list_lru_per_memcg *mlru;
-
-	spin_lock_irq(&lru->lock);
-	mlrus = rcu_dereference_protected(lru->mlrus, true);
-	mlru = rcu_dereference_protected(mlrus->mlru[src_idx], true);
-	rcu_assign_pointer(mlrus->mlru[src_idx], NULL);
-	spin_unlock_irq(&lru->lock);
+	struct list_lru_per_memcg *mlru = xa_erase_irq(&lru->xa, src_idx);
 
 	/*
 	 * The __list_lru_walk_one() can walk the list of this node.
@@ -383,78 +364,27 @@ static void memcg_list_lru_free(struct list_lru *lru, int src_idx)
 		kvfree_rcu(mlru, rcu);
 }
 
-static int memcg_init_list_lru(struct list_lru *lru, bool memcg_aware)
+static inline void memcg_init_list_lru(struct list_lru *lru, bool memcg_aware)
 {
-	struct list_lru_memcg *mlrus;
-	int size = memcg_nr_cache_ids;
-
+	if (memcg_aware)
+		xa_init_flags(&lru->xa, XA_FLAGS_LOCK_IRQ);
 	lru->memcg_aware = memcg_aware;
-	if (!memcg_aware)
-		return 0;
-
-	spin_lock_init(&lru->lock);
-
-	mlrus = kvzalloc(struct_size(mlrus, mlru, size), GFP_KERNEL);
-	if (!mlrus)
-		return -ENOMEM;
-
-	RCU_INIT_POINTER(lru->mlrus, mlrus);
-
-	return 0;
 }
 
 static void memcg_destroy_list_lru(struct list_lru *lru)
 {
-	struct list_lru_memcg *mlrus;
+	XA_STATE(xas, &lru->xa, 0);
+	struct list_lru_per_memcg *mlru;
 
 	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().
-	 */
-	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(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(lru->mlrus,
-					lockdep_is_held(&list_lrus_mutex));
-	new = kvmalloc(struct_size(new, mlru, new_size), GFP_KERNEL);
-	if (!new)
-		return -ENOMEM;
-
-	spin_lock_irq(&lru->lock);
-	memcpy(&new->mlru, &old->mlru, flex_array_size(new, mlru, old_size));
-	memset(&new->mlru[old_size], 0, flex_array_size(new, mlru, new_size - old_size));
-	rcu_assign_pointer(lru->mlrus, new);
-	spin_unlock_irq(&lru->lock);
-
-	kvfree_rcu(old, rcu);
-	return 0;
-}
-
-int memcg_update_all_list_lrus(int new_size)
-{
-	int ret = 0;
-	struct list_lru *lru;
-	int old_size = memcg_nr_cache_ids;
-
-	mutex_lock(&list_lrus_mutex);
-	list_for_each_entry(lru, &memcg_list_lrus, list) {
-		ret = memcg_update_list_lru(lru, old_size, new_size);
-		if (ret)
-			break;
+	xas_lock_irq(&xas);
+	xas_for_each(&xas, mlru, ULONG_MAX) {
+		kfree(mlru);
+		xas_store(&xas, NULL);
 	}
-	mutex_unlock(&list_lrus_mutex);
-	return ret;
+	xas_unlock_irq(&xas);
 }
 
 static void memcg_reparent_list_lru_node(struct list_lru *lru, int nid,
@@ -521,7 +451,7 @@ void memcg_reparent_list_lrus(struct mem_cgroup *memcg, struct mem_cgroup *paren
 		struct mem_cgroup *child;
 
 		child = mem_cgroup_from_css(css);
-		child->kmemcg_id = parent->kmemcg_id;
+		WRITE_ONCE(child->kmemcg_id, parent->kmemcg_id);
 	}
 	rcu_read_unlock();
 
@@ -531,21 +461,12 @@ void memcg_reparent_list_lrus(struct mem_cgroup *memcg, struct mem_cgroup *paren
 	mutex_unlock(&list_lrus_mutex);
 }
 
-static bool memcg_list_lru_allocated(struct mem_cgroup *memcg,
-				     struct list_lru *lru)
+static inline bool memcg_list_lru_allocated(struct mem_cgroup *memcg,
+					    struct list_lru *lru)
 {
-	bool allocated;
-	int idx;
-
-	idx = memcg->kmemcg_id;
-	if (unlikely(idx < 0))
-		return true;
+	int idx = memcg->kmemcg_id;
 
-	rcu_read_lock();
-	allocated = !!rcu_access_pointer(rcu_dereference(lru->mlrus)->mlru[idx]);
-	rcu_read_unlock();
-
-	return allocated;
+	return idx < 0 || xa_load(&lru->xa, idx);
 }
 
 int memcg_list_lru_alloc(struct mem_cgroup *memcg, struct list_lru *lru,
@@ -553,11 +474,11 @@ int memcg_list_lru_alloc(struct mem_cgroup *memcg, struct list_lru *lru,
 {
 	int i;
 	unsigned long flags;
-	struct list_lru_memcg *mlrus;
 	struct list_lru_memcg_table {
 		struct list_lru_per_memcg *mlru;
 		struct mem_cgroup *memcg;
 	} *table;
+	XA_STATE(xas, &lru->xa, 0);
 
 	if (!list_lru_memcg_aware(lru) || memcg_list_lru_allocated(memcg, lru))
 		return 0;
@@ -586,27 +507,48 @@ int memcg_list_lru_alloc(struct mem_cgroup *memcg, struct list_lru *lru,
 		}
 	}
 
-	spin_lock_irqsave(&lru->lock, flags);
-	mlrus = rcu_dereference_protected(lru->mlrus, true);
+	xas_lock_irqsave(&xas, flags);
 	while (i--) {
-		int index = table[i].memcg->kmemcg_id;
+		int index = READ_ONCE(table[i].memcg->kmemcg_id);
 		struct list_lru_per_memcg *mlru = table[i].mlru;
 
-		if (index < 0 || rcu_dereference_protected(mlrus->mlru[index], true))
+		xas_set(&xas, index);
+retry:
+		if (unlikely(index < 0 || xas_error(&xas) || xas_load(&xas))) {
 			kfree(mlru);
-		else
-			rcu_assign_pointer(mlrus->mlru[index], mlru);
+		} else {
+			xas_store(&xas, mlru);
+			if (xas_error(&xas) == -ENOMEM) {
+				xas_unlock_irqrestore(&xas, flags);
+				if (xas_nomem(&xas, gfp))
+					xas_set_err(&xas, 0);
+				xas_lock_irqsave(&xas, flags);
+				/*
+				 * The xas lock has been released, this memcg
+				 * can be reparented before us. So reload
+				 * memcg id. More details see the comments
+				 * in memcg_reparent_list_lrus().
+				 */
+				index = READ_ONCE(table[i].memcg->kmemcg_id);
+				if (index < 0)
+					xas_set_err(&xas, 0);
+				else if (!xas_error(&xas) && index != xas.xa_index)
+					xas_set(&xas, index);
+				goto retry;
+			}
+		}
 	}
-	spin_unlock_irqrestore(&lru->lock, flags);
-
+	/* xas_nomem() is used to free memory instead of memory allocation. */
+	if (xas.xa_alloc)
+		xas_nomem(&xas, gfp);
+	xas_unlock_irqrestore(&xas, flags);
 	kfree(table);
 
-	return 0;
+	return xas_error(&xas);
 }
 #else
-static int memcg_init_list_lru(struct list_lru *lru, bool memcg_aware)
+static inline void memcg_init_list_lru(struct list_lru *lru, bool memcg_aware)
 {
-	return 0;
 }
 
 static void memcg_destroy_list_lru(struct list_lru *lru)
@@ -618,7 +560,6 @@ int __list_lru_init(struct list_lru *lru, bool memcg_aware,
 		    struct lock_class_key *key, struct shrinker *shrinker)
 {
 	int i;
-	int err = -ENOMEM;
 
 #ifdef CONFIG_MEMCG_KMEM
 	if (shrinker)
@@ -626,11 +567,10 @@ int __list_lru_init(struct list_lru *lru, bool memcg_aware,
 	else
 		lru->shrinker_id = -1;
 #endif
-	memcg_get_cache_ids();
 
 	lru->node = kcalloc(nr_node_ids, sizeof(*lru->node), GFP_KERNEL);
 	if (!lru->node)
-		goto out;
+		return -ENOMEM;
 
 	for_each_node(i) {
 		spin_lock_init(&lru->node[i].lock);
@@ -639,18 +579,10 @@ int __list_lru_init(struct list_lru *lru, bool memcg_aware,
 		init_one_lru(&lru->node[i].lru);
 	}
 
-	err = memcg_init_list_lru(lru, memcg_aware);
-	if (err) {
-		kfree(lru->node);
-		/* Do this so a list_lru_destroy() doesn't crash: */
-		lru->node = NULL;
-		goto out;
-	}
-
+	memcg_init_list_lru(lru, memcg_aware);
 	list_lru_register(lru);
-out:
-	memcg_put_cache_ids();
-	return err;
+
+	return 0;
 }
 EXPORT_SYMBOL_GPL(__list_lru_init);
 
@@ -660,8 +592,6 @@ void list_lru_destroy(struct list_lru *lru)
 	if (!lru->node)
 		return;
 
-	memcg_get_cache_ids();
-
 	list_lru_unregister(lru);
 
 	memcg_destroy_list_lru(lru);
@@ -671,6 +601,5 @@ void list_lru_destroy(struct list_lru *lru)
 #ifdef CONFIG_MEMCG_KMEM
 	lru->shrinker_id = -1;
 #endif
-	memcg_put_cache_ids();
 }
 EXPORT_SYMBOL_GPL(list_lru_destroy);
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c36b0a0dbc19..68eb62d10c48 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -351,42 +351,17 @@ static void memcg_reparent_objcgs(struct mem_cgroup *memcg,
  * This will be used as a shrinker list's index.
  * The main reason for not using cgroup id for this:
  *  this works better in sparse environments, where we have a lot of memcgs,
- *  but only a few kmem-limited. Or also, if we have, for instance, 200
- *  memcgs, and none but the 200th is kmem-limited, we'd have to have a
- *  200 entry array for that.
- *
- * The current size of the caches array is stored in memcg_nr_cache_ids. It
- * will double each time we have to increase it.
+ *  but only a few kmem-limited.
  */
 static DEFINE_IDA(memcg_cache_ida);
-int memcg_nr_cache_ids;
-
-/* Protects memcg_nr_cache_ids */
-static DECLARE_RWSEM(memcg_cache_ids_sem);
-
-void memcg_get_cache_ids(void)
-{
-	down_read(&memcg_cache_ids_sem);
-}
-
-void memcg_put_cache_ids(void)
-{
-	up_read(&memcg_cache_ids_sem);
-}
 
 /*
- * MIN_SIZE is different than 1, because we would like to avoid going through
- * the alloc/free process all the time. In a small machine, 4 kmem-limited
- * cgroups is a reasonable guess. In the future, it could be a parameter or
- * tunable, but that is strictly not necessary.
- *
  * MAX_SIZE should be as large as the number of cgrp_ids. Ideally, we could get
  * this constant directly from cgroup, but it is understandable that this is
  * better kept as an internal representation in cgroup.c. In any case, the
  * cgrp_id space is not getting any smaller, and we don't have to necessarily
  * increase ours as well if it increases.
  */
-#define MEMCG_CACHES_MIN_SIZE 4
 #define MEMCG_CACHES_MAX_SIZE MEM_CGROUP_ID_MAX
 
 /*
@@ -2944,49 +2919,6 @@ __always_inline struct obj_cgroup *get_obj_cgroup_from_current(void)
 	return objcg;
 }
 
-static int memcg_alloc_cache_id(void)
-{
-	int id, size;
-	int err;
-
-	id = ida_simple_get(&memcg_cache_ida,
-			    0, MEMCG_CACHES_MAX_SIZE, GFP_KERNEL);
-	if (id < 0)
-		return id;
-
-	if (id < memcg_nr_cache_ids)
-		return id;
-
-	/*
-	 * There's no space for the new id in memcg_caches arrays,
-	 * so we have to grow them.
-	 */
-	down_write(&memcg_cache_ids_sem);
-
-	size = 2 * (id + 1);
-	if (size < MEMCG_CACHES_MIN_SIZE)
-		size = MEMCG_CACHES_MIN_SIZE;
-	else if (size > MEMCG_CACHES_MAX_SIZE)
-		size = MEMCG_CACHES_MAX_SIZE;
-
-	err = memcg_update_all_list_lrus(size);
-	if (!err)
-		memcg_nr_cache_ids = size;
-
-	up_write(&memcg_cache_ids_sem);
-
-	if (err) {
-		ida_simple_remove(&memcg_cache_ida, id);
-		return err;
-	}
-	return id;
-}
-
-static void memcg_free_cache_id(int id)
-{
-	ida_simple_remove(&memcg_cache_ida, id);
-}
-
 static void memcg_account_kmem(struct mem_cgroup *memcg, int nr_pages)
 {
 	mod_memcg_state(memcg, MEMCG_KMEM, nr_pages);
@@ -3673,13 +3605,14 @@ static int memcg_online_kmem(struct mem_cgroup *memcg)
 	if (unlikely(mem_cgroup_is_root(memcg)))
 		return 0;
 
-	memcg_id = memcg_alloc_cache_id();
+	memcg_id = ida_alloc_max(&memcg_cache_ida, MEMCG_CACHES_MAX_SIZE - 1,
+				 GFP_KERNEL);
 	if (memcg_id < 0)
 		return memcg_id;
 
 	objcg = obj_cgroup_alloc();
 	if (!objcg) {
-		memcg_free_cache_id(memcg_id);
+		ida_free(&memcg_cache_ida, memcg_id);
 		return -ENOMEM;
 	}
 	objcg->memcg = memcg;
@@ -3723,7 +3656,7 @@ static void memcg_offline_kmem(struct mem_cgroup *memcg)
 	 */
 	memcg_reparent_list_lrus(memcg, parent);
 
-	memcg_free_cache_id(kmemcg_id);
+	ida_free(&memcg_cache_ida, kmemcg_id);
 }
 #else
 static int memcg_online_kmem(struct mem_cgroup *memcg)