[PATCH v3 70/76] mm: list_lru: allocate list_lru_one only when needed

From: Muchun Song
Date: Tue Sep 14 2021 - 03:45:49 EST

In our server, we found a suspected memory leak problem. The kmalloc-32
consumes more than 6GB of memory. Other kmem_caches consume less than
2GB memory.

After our in-depth analysis, the memory consumption of kmalloc-32 slab
cache is the cause of list_lru_one allocation.

crash> p memcg_nr_cache_ids
memcg_nr_cache_ids = $2 = 24574

memcg_nr_cache_ids is very large and memory consumption of each list_lru
can be calculated with the following formula.

num_numa_node * memcg_nr_cache_ids * 32 (kmalloc-32)

There are 4 numa nodes in our system, so each list_lru consumes ~3MB.

crash> list super_blocks | wc -l
952

Every mount will register 2 list lrus, one is for inode, another is for
dentry. There are 952 super_blocks. So the total memory is 952 * 2 * 3
MB (~5.6GB). But the number of memory cgroup is less than 500. So I
guess more than 12286 containers have been deployed on this machine (I
do not know why there are so many containers, it may be a user's bug or
the user really want to do that). And memcg_nr_cache_ids has not been
reduced to a suitable value. This can waste a lot of memory.

Now the infrastructure for dynamic list_lru_one allocation is ready, so
remove statically allocated memory code to save memory.

Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
---
include/linux/list_lru.h | 8 +--
mm/list_lru.c | 125 +++++++++++++++++++++++++++--------------------
mm/memcontrol.c | 7 ++-
3 files changed, 81 insertions(+), 59 deletions(-)

diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h
index 50a3144016b4..62f407831b8c 100644
--- a/include/linux/list_lru.h
+++ b/include/linux/list_lru.h
@@ -32,14 +32,15 @@ struct list_lru_one {
};

struct list_lru_per_memcg {
+ struct rcu_head rcu;
/* array of per cgroup per node lists, indexed by node id */
- struct list_lru_one nodes[0];
+ struct list_lru_one nodes[];
};

struct list_lru_memcg {
struct rcu_head rcu;
/* array of per cgroup lists, indexed by memcg_cache_id */
- struct list_lru_per_memcg *lrus[];
+ struct list_lru_per_memcg __rcu *lrus[];
};

struct list_lru_node {
@@ -76,7 +77,8 @@ int __list_lru_init(struct list_lru *lru, bool memcg_aware,
__list_lru_init((lru), true, NULL, shrinker)

int memcg_update_all_list_lrus(int num_memcgs);
-void memcg_drain_all_list_lrus(int src_idx, struct mem_cgroup *dst_memcg);
+void memcg_drain_all_list_lrus(struct mem_cgroup *src_memcg,
+ struct mem_cgroup *dst_memcg);

/**
* list_lru_add: add an element to the lru list's tail
diff --git a/mm/list_lru.c b/mm/list_lru.c
index eea29eb4cf48..48651c29a9d1 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -60,8 +60,12 @@ list_lru_from_memcg_idx(struct list_lru *lru, int nid, int idx)
*/
memcg_lrus = rcu_dereference_check(lru->memcg_lrus,
lockdep_is_held(&nlru->lock));
- if (memcg_lrus && idx >= 0)
- return &memcg_lrus->lrus[idx]->nodes[nid];
+ 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;
}

@@ -184,11 +188,12 @@ unsigned long list_lru_count_one(struct list_lru *lru,
int nid, struct mem_cgroup *memcg)
{
struct list_lru_one *l;
- long count;
+ long count = 0;

rcu_read_lock();
l = list_lru_from_memcg_idx(lru, nid, memcg_cache_id(memcg));
- count = READ_ONCE(l->nr_items);
+ if (l)
+ count = READ_ONCE(l->nr_items);
rcu_read_unlock();

if (unlikely(count < 0))
@@ -217,8 +222,11 @@ __list_lru_walk_one(struct list_lru *lru, int nid, int memcg_idx,
struct list_head *item, *n;
unsigned long isolated = 0;

- l = list_lru_from_memcg_idx(lru, nid, memcg_idx);
restart:
+ l = list_lru_from_memcg_idx(lru, nid, memcg_idx);
+ if (!l)
+ goto out;
+
list_for_each_safe(item, n, &l->list) {
enum lru_status ret;

@@ -262,6 +270,7 @@ __list_lru_walk_one(struct list_lru *lru, int nid, int memcg_idx,
BUG();
}
}
+out:
return isolated;
}

@@ -354,20 +363,26 @@ static struct list_lru_per_memcg *memcg_list_lru_alloc(gfp_t gfp)
return lru;
}

-static int memcg_init_list_lru_range(struct list_lru_memcg *memcg_lrus,
- int begin, int end)
+static void memcg_list_lru_free(struct list_lru *lru, int src_idx)
{
- int i;
+ struct list_lru_memcg *memcg_lrus;
+ struct list_lru_per_memcg *mlru;

- for (i = begin; i < end; i++) {
- memcg_lrus->lrus[i] = memcg_list_lru_alloc(GFP_KERNEL);
- if (!memcg_lrus->lrus[i])
- goto fail;
- }
- return 0;
-fail:
- memcg_destroy_list_lru_range(memcg_lrus, begin, i);
- return -ENOMEM;
+ 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);
+
+ /*
+ * The __list_lru_walk_one() can walk the list of this node.
+ * We need kvfree_rcu() here. And the walking of the list
+ * is under lru->node[nid]->lock, which can serve as a RCU
+ * read-side critical section.
+ */
+ if (mlru)
+ kvfree_rcu(mlru, rcu);
}

static int memcg_init_list_lru(struct list_lru *lru, bool memcg_aware)
@@ -381,15 +396,11 @@ static int memcg_init_list_lru(struct list_lru *lru, bool memcg_aware)

spin_lock_init(&lru->lock);

- memcg_lrus = kvmalloc(sizeof(*memcg_lrus) +
+ memcg_lrus = kvzalloc(sizeof(*memcg_lrus) +
size * sizeof(memcg_lrus->lrus[0]), GFP_KERNEL);
if (!memcg_lrus)
return -ENOMEM;

- if (memcg_init_list_lru_range(memcg_lrus, 0, size)) {
- kvfree(memcg_lrus);
- return -ENOMEM;
- }
RCU_INIT_POINTER(lru->memcg_lrus, memcg_lrus);

return 0;
@@ -423,13 +434,9 @@ static int memcg_update_list_lru(struct list_lru *lru, int old_size, int new_siz
if (!new)
return -ENOMEM;

- if (memcg_init_list_lru_range(new, old_size, new_size)) {
- kvfree(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);

@@ -437,20 +444,6 @@ static int memcg_update_list_lru(struct list_lru *lru, int old_size, int new_siz
return 0;
}

-static void memcg_cancel_update_list_lru(struct list_lru *lru,
- int old_size, int new_size)
-{
- struct list_lru_memcg *memcg_lrus;
-
- memcg_lrus = rcu_dereference_protected(lru->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_range(memcg_lrus, old_size, new_size);
-}
-
int memcg_update_all_list_lrus(int new_size)
{
int ret = 0;
@@ -461,15 +454,10 @@ int memcg_update_all_list_lrus(int new_size)
list_for_each_entry(lru, &memcg_list_lrus, list) {
ret = memcg_update_list_lru(lru, old_size, new_size);
if (ret)
- goto fail;
+ break;
}
-out:
mutex_unlock(&list_lrus_mutex);
return ret;
-fail:
- list_for_each_entry_continue_reverse(lru, &memcg_list_lrus, list)
- memcg_cancel_update_list_lru(lru, old_size, new_size);
- goto out;
}

static void memcg_drain_list_lru_node(struct list_lru *lru, int nid,
@@ -486,6 +474,8 @@ static void memcg_drain_list_lru_node(struct list_lru *lru, int nid,
spin_lock_irq(&nlru->lock);

src = list_lru_from_memcg_idx(lru, nid, src_idx);
+ if (!src)
+ goto out;
dst = list_lru_from_memcg_idx(lru, nid, dst_idx);

list_splice_init(&src->list, &dst->list);
@@ -495,7 +485,7 @@ static void memcg_drain_list_lru_node(struct list_lru *lru, int nid,
set_shrinker_bit(dst_memcg, nid, lru_shrinker_id(lru));
src->nr_items = 0;
}
-
+out:
spin_unlock_irq(&nlru->lock);
}

@@ -506,11 +496,37 @@ static void memcg_drain_list_lru(struct list_lru *lru,

for_each_node(i)
memcg_drain_list_lru_node(lru, i, src_idx, dst_memcg);
+
+ memcg_list_lru_free(lru, src_idx);
}

-void memcg_drain_all_list_lrus(int src_idx, struct mem_cgroup *dst_memcg)
+void memcg_drain_all_list_lrus(struct mem_cgroup *src_memcg,
+ struct mem_cgroup *dst_memcg)
{
+ struct cgroup_subsys_state *css;
struct list_lru *lru;
+ int src_idx = src_memcg->kmemcg_id;
+
+ /*
+ * Change kmemcg_id of this cgroup and all its descendants to the
+ * parent's id, and then move all entries from this cgroup's list_lrus
+ * to ones of the parent.
+ *
+ * After we have finished, all list_lrus corresponding to this cgroup
+ * are guaranteed to remain empty. So we can safely free this cgroup's
+ * list lrus which is freed in memcg_list_lru_free().
+ * Changing ->kmemcg_id to the parent can prevent list_lru_memcg_alloc()
+ * from allocating list lrus for this cgroup after calling
+ * memcg_list_lru_free().
+ */
+ rcu_read_lock();
+ css_for_each_descendant_pre(css, &src_memcg->css) {
+ struct mem_cgroup *memcg;
+
+ memcg = mem_cgroup_from_css(css);
+ memcg->kmemcg_id = dst_memcg->kmemcg_id;
+ }
+ rcu_read_unlock();

mutex_lock(&list_lrus_mutex);
list_for_each_entry(lru, &memcg_list_lrus, list)
@@ -529,7 +545,7 @@ static bool memcg_list_lru_skip_alloc(struct list_lru *lru,

rcu_read_lock();
memcg_lrus = rcu_dereference(lru->memcg_lrus);
- if (memcg_lrus->lrus[idx]) {
+ if (rcu_access_pointer(memcg_lrus->lrus[idx])) {
rcu_read_unlock();
return true;
}
@@ -544,7 +560,7 @@ int list_lru_memcg_alloc(struct list_lru *lru, struct mem_cgroup *memcg, gfp_t g
struct list_lru_memcg *memcg_lrus;
int i;

- struct list_lru_memcg {
+ struct list_lru_memcg_table {
struct list_lru_per_memcg *mlru;
struct mem_cgroup *memcg;
} *table;
@@ -588,11 +604,12 @@ int list_lru_memcg_alloc(struct list_lru *lru, struct mem_cgroup *memcg, gfp_t g
memcg_lrus = rcu_dereference_protected(lru->memcg_lrus, true);
while (i--) {
int index = memcg_cache_id(table[i].memcg);
+ struct list_lru_per_memcg *mlru = table[i].mlru;

- if (memcg_lrus->lrus[index])
- kfree(table[i].mlru);
+ if (index < 0 || rcu_dereference_protected(memcg_lrus->lrus[index], true))
+ kfree(mlru);
else
- memcg_lrus->lrus[index] = table[i].mlru;
+ rcu_assign_pointer(memcg_lrus->lrus[index], mlru);
}
spin_unlock_irqrestore(&lru->lock, flags);

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 0e8c8d8465e5..2045cd8b1d7f 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3635,10 +3635,13 @@ static void memcg_offline_kmem(struct mem_cgroup *memcg)

memcg_reparent_objcgs(memcg, parent);

+ /*
+ * memcg_drain_all_list_lrus() can change memcg->kmemcg_id.
+ * Cache it to @kmemcg_id.
+ */
kmemcg_id = memcg->kmemcg_id;

- /* memcg_reparent_objcgs() must be called before this. */
- memcg_drain_all_list_lrus(kmemcg_id, parent);
+ memcg_drain_all_list_lrus(memcg, parent);

memcg_free_cache_id(kmemcg_id);
}
--
2.11.0