@@ -3654,8 +3654,7 @@ 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)
@@ -3672,22 +3671,7 @@ static void memcg_offline_kmem(struct mem_cgroup *memcg)
kmemcg_id = memcg->kmemcg_id;
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
- * 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_reparent_objcgs() must be called before this. */
memcg_drain_all_list_lrus(kmemcg_id, parent);
memcg_free_cache_id(kmemcg_id);
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 the parent cgroup. This already makes further list_lru_add()'s add elements to the parent's list. So we do not need to change kmemcg_id of an offline cgroup to its parent's id. It is just waste CPU cycles. Just remove those redundant code. Signed-off-by: Muchun Song <songmuchun@bytedance.com> --- mm/memcontrol.c | 20 ++------------------ 1 file changed, 2 insertions(+), 18 deletions(-)