diff options
authorFilipe Brandenburger <filbranden@google.com>2014-03-03 15:38:25 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2014-03-04 07:55:48 -0800
commit4fb1a86fb5e4209a7d4426d4e586c58e9edc74ac (patch)
parentce48225fe3b1b0d1fc9fceb96ac3d8a879e45114 (diff)
memcg: reparent charges of children before processing parent
Sometimes the cleanup after memcg hierarchy testing gets stuck in mem_cgroup_reparent_charges(), unable to bring non-kmem usage down to 0. There may turn out to be several causes, but a major cause is this: the workitem to offline parent can get run before workitem to offline child; parent's mem_cgroup_reparent_charges() circles around waiting for the child's pages to be reparented to its lrus, but it's holding cgroup_mutex which prevents the child from reaching its mem_cgroup_reparent_charges(). Further testing showed that an ordered workqueue for cgroup_destroy_wq is not always good enough: percpu_ref_kill_and_confirm's call_rcu_sched stage on the way can mess up the order before reaching the workqueue. Instead, when offlining a memcg, call mem_cgroup_reparent_charges() on all its children (and grandchildren, in the correct order) to have their charges reparented first. Fixes: e5fca243abae ("cgroup: use a dedicated workqueue for cgroup destruction") Signed-off-by: Filipe Brandenburger <filbranden@google.com> Signed-off-by: Hugh Dickins <hughd@google.com> Reviewed-by: Tejun Heo <tj@kernel.org> Acked-by: Michal Hocko <mhocko@suse.cz> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: <stable@vger.kernel.org> [v3.10+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 files changed, 9 insertions, 1 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9d17310be470..5b6b0039f725 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6595,6 +6595,7 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
struct mem_cgroup *memcg = mem_cgroup_from_css(css);
struct mem_cgroup_event *event, *tmp;
+ struct cgroup_subsys_state *iter;
* Unregister events and notify userspace.
@@ -6611,7 +6612,14 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
- mem_cgroup_reparent_charges(memcg);
+ /*
+ * This requires that offlining is serialized. Right now that is
+ * guaranteed because css_killed_work_fn() holds the cgroup_mutex.
+ */
+ css_for_each_descendant_post(iter, css)
+ mem_cgroup_reparent_charges(mem_cgroup_from_css(iter));