[PATCH 17/17] mm: list_lru: replace linear array with xarray

[Muchun Song <songmuchun@bytedance.com>]

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.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 include/linux/list_lru.h   |   6 +-
 include/linux/memcontrol.h |  10 ---
 mm/list_lru.c              | 159 ++++++++++++---------------------------------
 mm/memcontrol.c            |  71 ++------------------
 4 files changed, 49 insertions(+), 197 deletions(-)

diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h
index 9222d0295d30..b57556698de0 100644
--- a/include/linux/list_lru.h
+++ b/include/linux/list_lru.h
@@ -11,6 +11,7 @@
 #include <linux/list.h>
 #include <linux/nodemask.h>
 #include <linux/shrinker.h>
+#include <linux/xarray.h>
 
 struct mem_cgroup;
 
@@ -56,10 +57,8 @@ struct list_lru {
 #ifdef CONFIG_MEMCG_KMEM
 	struct list_head	list;
 	int			shrinker_id;
-	/* protects ->memcg_lrus->lrus[i] */
-	spinlock_t		lock;
 	/* for cgroup aware lrus points to per cgroup lists, otherwise NULL */
-	struct list_lru_memcg	__rcu *memcg_lrus;
+	struct xarray		*xa;
 #endif
 };
 
@@ -75,7 +74,6 @@ int __list_lru_init(struct list_lru *lru, bool memcg_aware,
 #define list_lru_init_memcg(lru, shrinker)		\
 	__list_lru_init((lru), true, NULL, shrinker)
 
-int memcg_update_all_list_lrus(int num_memcgs);
 void memcg_reparent_list_lrus(struct mem_cgroup *memcg, struct mem_cgroup *parent);
 
 /**
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 96a85cff248a..a0c77e8ec61a 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1649,8 +1649,6 @@ void obj_cgroup_uncharge(struct obj_cgroup *objcg, size_t size);
 extern struct static_key_false memcg_kmem_enabled_key;
 
 extern int memcg_nr_cache_ids;
-void memcg_get_cache_ids(void);
-void memcg_put_cache_ids(void);
 
 /*
  * Helper macro to loop through all memcg-specific caches. Callers must still
@@ -1725,14 +1723,6 @@ static inline int memcg_cache_id(struct mem_cgroup *memcg)
 	return -1;
 }
 
-static inline void memcg_get_cache_ids(void)
-{
-}
-
-static inline void memcg_put_cache_ids(void)
-{
-}
-
 static inline struct mem_cgroup *mem_cgroup_from_obj(void *p)
 {
        return NULL;
diff --git a/mm/list_lru.c b/mm/list_lru.c
index 6d7ae24a4a70..9878b08d44e4 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -20,7 +20,7 @@ static DEFINE_MUTEX(list_lrus_mutex);
 
 static inline bool list_lru_memcg_aware(struct list_lru *lru)
 {
-	return !!lru->memcg_lrus;
+	return !!lru->xa;
 }
 
 static void list_lru_register(struct list_lru *lru)
@@ -51,22 +51,12 @@ 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 *memcg_lrus;
-	struct list_lru_node *nlru = &lru->node[nid];
+	if (list_lru_memcg_aware(lru) && idx >= 0) {
+		struct list_lru_per_memcg *mlru = xa_load(lru->xa, idx);
 
-	/*
-	 * Either lock or RCU protects the array of per cgroup lists
-	 * from relocation (see memcg_update_list_lru).
-	 */
-	memcg_lrus = rcu_dereference_check(lru->memcg_lrus,
-					   lockdep_is_held(&nlru->lock));
-	if (memcg_lrus && idx >= 0) {
-		struct list_lru_per_memcg *mlru;
-
-		mlru = rcu_dereference_check(memcg_lrus->lrus[idx], true);
 		return mlru ? &mlru->nodes[nid] : NULL;
 	}
-	return &nlru->lru;
+	return &lru->node[nid].lru;
 }
 
 static inline struct list_lru_one *
@@ -310,16 +300,18 @@ 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);
 	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);
@@ -339,15 +331,6 @@ 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 *memcg_lrus,
-					 int begin, int end)
-{
-	int i;
-
-	for (i = begin; i < end; i++)
-		kfree(memcg_lrus->lrus[i]);
-}
-
 static struct list_lru_per_memcg *list_lru_per_memcg_alloc(gfp_t gfp)
 {
 	int nid;
@@ -365,79 +348,35 @@ static struct list_lru_per_memcg *list_lru_per_memcg_alloc(gfp_t gfp)
 
 static int memcg_init_list_lru(struct list_lru *lru, bool memcg_aware)
 {
-	struct list_lru_memcg *memcg_lrus;
-	int size = memcg_nr_cache_ids;
-
 	if (!memcg_aware) {
-		lru->memcg_lrus = NULL;
+		lru->xa = NULL;
 		return 0;
 	}
 
-	spin_lock_init(&lru->lock);
-
-	memcg_lrus = kvzalloc(sizeof(*memcg_lrus) +
-			      size * sizeof(memcg_lrus->lrus[0]), GFP_KERNEL);
-	if (!memcg_lrus)
+	lru->xa = kmalloc(sizeof(*lru->xa), GFP_KERNEL);
+	if (!lru->xa)
 		return -ENOMEM;
-
-	RCU_INIT_POINTER(lru->memcg_lrus, memcg_lrus);
+	xa_init_flags(lru->xa, XA_FLAGS_LOCK_IRQ);
 
 	return 0;
 }
 
 static void memcg_destroy_list_lru(struct list_lru *lru)
 {
-	struct list_lru_memcg *memcg_lrus;
+	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().
-	 */
-	memcg_lrus = rcu_dereference_protected(lru->memcg_lrus, true);
-	memcg_destroy_list_lru_range(memcg_lrus, 0, memcg_nr_cache_ids);
-	kvfree(memcg_lrus);
-}
-
-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->memcg_lrus,
-					lockdep_is_held(&list_lrus_mutex));
-	new = kvmalloc(sizeof(*new) + new_size * sizeof(new->lrus[0]), GFP_KERNEL);
-	if (!new)
-		return -ENOMEM;
-
-	spin_lock_irq(&lru->lock);
-	memcpy(&new->lrus, &old->lrus, old_size * sizeof(new->lrus[0]));
-	memset(&new->lrus[old_size], 0, (new_size - old_size) * sizeof(new->lrus[0]));
-	rcu_assign_pointer(lru->memcg_lrus, 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, &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);
+
+	kfree(lru->xa);
 }
 
 static void memcg_reparent_list_lru_node(struct list_lru *lru, int nid,
@@ -471,15 +410,7 @@ static void memcg_reparent_list_lru_node(struct list_lru *lru, int nid,
 
 static void list_lru_per_memcg_free(struct list_lru *lru, int src_idx)
 {
-	struct list_lru_memcg *memcg_lrus;
-	struct list_lru_per_memcg *mlru;
-
-	spin_lock_irq(&lru->lock);
-	memcg_lrus = rcu_dereference_protected(lru->memcg_lrus, true);
-	mlru = rcu_dereference_protected(memcg_lrus->lrus[src_idx], true);
-	if (mlru)
-		rcu_assign_pointer(memcg_lrus->lrus[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.
@@ -529,28 +460,18 @@ void memcg_reparent_list_lrus(struct mem_cgroup *memcg, struct mem_cgroup *paren
 static bool list_lru_per_memcg_allocated(struct list_lru *lru,
 					 struct mem_cgroup *memcg)
 {
-	struct list_lru_memcg *memcg_lrus;
 	int idx = memcg_cache_id(memcg);
 
-	if (unlikely(idx < 0))
+	if (unlikely(idx < 0) || xa_load(lru->xa, idx))
 		return true;
-
-	rcu_read_lock();
-	memcg_lrus = rcu_dereference(lru->memcg_lrus);
-	if (rcu_access_pointer(memcg_lrus->lrus[idx])) {
-		rcu_read_unlock();
-		return true;
-	}
-	rcu_read_unlock();
-
 	return false;
 }
 
 int list_lru_memcg_alloc(struct list_lru *lru, struct mem_cgroup *memcg, gfp_t gfp)
 {
+	XA_STATE(xas, lru->xa, 0);
 	unsigned long flags;
-	struct list_lru_memcg *memcg_lrus;
-	int i;
+	int i, ret = 0;
 
 	struct list_lru_memcg {
 		struct list_lru_per_memcg *mlru;
@@ -592,22 +513,31 @@ int list_lru_memcg_alloc(struct list_lru *lru, struct mem_cgroup *memcg, gfp_t g
 		}
 	}
 
-	spin_lock_irqsave(&lru->lock, flags);
-	memcg_lrus = rcu_dereference_protected(lru->memcg_lrus, true);
+	xas_lock_irqsave(&xas, flags);
 	while (i--) {
 		int idx = memcg_cache_id(table[i].memcg);
 		struct list_lru_per_memcg *mlru = table[i].mlru;
 
-		if (idx < 0 || rcu_dereference_protected(memcg_lrus->lrus[idx], true))
+		xas_set(&xas, idx);
+retry:
+		if (unlikely(ret || idx < 0 || xas_load(&xas))) {
 			kfree(mlru);
-		else
-			rcu_assign_pointer(memcg_lrus->lrus[idx], mlru);
+		} else {
+			ret = xa_err(xas_store(&xas, mlru));
+			if (ret) {
+				xas_unlock_irqrestore(&xas, flags);
+				if (xas_nomem(&xas, gfp))
+					ret = 0;
+				xas_lock_irqsave(&xas, flags);
+				goto retry;
+			}
+		}
 	}
-	spin_unlock_irqrestore(&lru->lock, flags);
+	xas_unlock_irqrestore(&xas, flags);
 
 	kfree(table);
 
-	return 0;
+	return ret;
 }
 #else
 static int memcg_init_list_lru(struct list_lru *lru, bool memcg_aware)
@@ -632,7 +562,6 @@ 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)
@@ -655,7 +584,6 @@ int __list_lru_init(struct list_lru *lru, bool memcg_aware,
 
 	list_lru_register(lru);
 out:
-	memcg_put_cache_ids();
 	return err;
 }
 EXPORT_SYMBOL_GPL(__list_lru_init);
@@ -666,8 +594,6 @@ 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);
@@ -677,6 +603,5 @@ 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 02a65ff3b77a..b30832266bf7 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -352,28 +352,9 @@ 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
@@ -2832,49 +2813,6 @@ __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);
-}
-
 /*
  * obj_cgroup_uncharge_pages: uncharge a number of kernel pages from a objcg
  * @objcg: object cgroup to uncharge
@@ -3451,13 +3389,14 @@ static int memcg_online_kmem(struct mem_cgroup *memcg)
 
 	BUG_ON(memcg->kmemcg_id >= 0);
 
-	memcg_id = memcg_alloc_cache_id();
+	memcg_id = ida_simple_get(&memcg_cache_ida, 0, MEMCG_CACHES_MAX_SIZE,
+				  GFP_KERNEL);
 	if (memcg_id < 0)
 		return memcg_id;
 
 	objcg = obj_cgroup_alloc();
 	if (!objcg) {
-		memcg_free_cache_id(memcg_id);
+		ida_simple_remove(&memcg_cache_ida, memcg_id);
 		return -ENOMEM;
 	}
 	objcg->memcg = memcg;
@@ -3494,7 +3433,7 @@ static void memcg_offline_kmem(struct mem_cgroup *memcg)
 	/* memcg_reparent_objcgs() must be called before this. */
 	memcg_reparent_list_lrus(memcg, parent);
 
-	memcg_free_cache_id(kmemcg_id);
+	ida_simple_remove(&memcg_cache_ida, kmemcg_id);
 }
 #else
 static int memcg_online_kmem(struct mem_cgroup *memcg)
-- 
2.11.0