diff mbox series

[062/262] mm: memcontrol: remove kmemcg_id reparenting

Message ID 20211105203753.q3Y-GvB-j%akpm@linux-foundation.org (mailing list archive)
State New
Headers show
Series [001/262] scripts/spelling.txt: add more spellings to spelling.txt | expand

Commit Message

Andrew Morton Nov. 5, 2021, 8:37 p.m. UTC 
From: Muchun Song <songmuchun@bytedance.com>
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@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Roman 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: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memcontrol.c |   19 ++++---------------
 1 file changed, 4 insertions(+), 15 deletions(-)
diff mbox series

Patch

--- 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);