From: Muchun Song <songmuchun@xxxxxxxxxxxxx> Subject: mm: memcontrol: remove kmemcg_id reparenting 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. Link: https://lkml.kernel.org/r/20211025125102.56533-1-songmuchun@xxxxxxxxxxxxx Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx> Acked-by: Roman Gushchin <guro@xxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxxxx> Cc: Shakeel Butt <shakeelb@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/memcontrol.c | 19 ++++--------------- 1 file changed, 4 insertions(+), 15 deletions(-) --- a/mm/memcontrol.c~mm-memcontrol-remove-kmemcg_id-reparenting +++ a/mm/memcontrol.c @@ -3650,8 +3650,7 @@ static int memcg_online_kmem(struct mem_ 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) @@ -3669,21 +3668,11 @@ static void memcg_offline_kmem(struct me 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); _
