Commit 64268868 authored by Muchun Song's avatar Muchun Song Committed by Linus Torvalds
Browse files

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 remove the redundant code.

Link: https://lkml.kernel.org/r/20211025125102.56533-1-songmuchun@bytedance.com


Signed-off-by: default avatarMuchun Song <songmuchun@bytedance.com>
Acked-by: default avatarRoman Gushchin <guro@fb.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Shakeel Butt <shakeelb@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 41d17431

mm/memcontrol.c

+4 −15
Original line number Diff line number Diff line
@@ -3650,8 +3650,7 @@ 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)
@@ -3669,21 +3668,11 @@ 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);