Since slab objects and kmem pages are charged to object cgroup instead
of memory cgroup, memcg_reparent_objcgs() will reparent this cgroup and
all its descendants to its parent cgroup. This already makes further
list_lru_add()'s add elements to the parent's list. So it is unnecessary
to change kmemcg_id of an offline cgroup to its parent's id. It just
wastes CPU cycles. Just to remove those redundant code.
Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
---
mm/memcontrol.c | 19 ++++---------------
1 file changed, 4 insertions(+), 15 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 6538595994d2..e26f87cd7e4c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3645,8 +3645,7 @@ static int memcg_online_kmem(struct mem_cgroup *memcg)
static void memcg_offline_kmem(struct mem_cgroup *memcg)
{
- struct cgroup_subsys_state *css;
- struct mem_cgroup *parent, *child;
+ struct mem_cgroup *parent;
int kmemcg_id;
if (memcg->kmem_state != KMEM_ONLINE)
@@ -3664,21 +3663,11 @@ static void memcg_offline_kmem(struct mem_cgroup *memcg)
BUG_ON(kmemcg_id < 0);
/*
- * 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. The
- * ordering is imposed by list_lru_node->lock taken by
+ * After we have finished memcg_reparent_objcgs(), all list_lrus
+ * corresponding to this cgroup are guaranteed to remain empty.
+ * The ordering is imposed by list_lru_node->lock taken by
* memcg_drain_all_list_lrus().
*/
- rcu_read_lock(); /* can be called from css_free w/o cgroup_mutex */
- css_for_each_descendant_pre(css, &memcg->css) {
- child = mem_cgroup_from_css(css);
- BUG_ON(child->kmemcg_id != kmemcg_id);
- child->kmemcg_id = parent->kmemcg_id;
- }
- rcu_read_unlock();
-
memcg_drain_all_list_lrus(kmemcg_id, parent);
memcg_free_cache_id(kmemcg_id);
--
2.11.0
