+ mm-memcontrol-remove-kmemcg_id-reparenting.patch added to -mm tree

The patch titled
     Subject: mm: memcontrol: remove kmemcg_id reparenting
has been added to the -mm tree.  Its filename is
     mm-memcontrol-remove-kmemcg_id-reparenting.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-memcontrol-remove-kmemcg_id-reparenting.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-memcontrol-remove-kmemcg_id-reparenting.patch

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------------------------------------------------------
From: Muchun Song <redacted>
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 <redacted>
Acked-by: Roman Gushchin <redacted>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Shakeel Butt <redacted>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 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);

_

Patches currently in -mm which might be from songmuchun@bytedance.com are

mm-list_lru-remove-holding-lru-lock.patch
mm-list_lru-fix-the-return-value-of-list_lru_count_one.patch
mm-memcontrol-remove-kmemcg_id-reparenting.patch
mm-memcontrol-remove-the-kmem-states.patch