From ba9a72974fd85701aea843b276d9773809286e74 Mon Sep 17 00:00:00 2001 From: Filipe Brandenburger Date: Mon, 3 Mar 2014 15:38:25 -0800 Subject: memcg: reparent charges of children before processing parent commit 4fb1a86fb5e4209a7d4426d4e586c58e9edc74ac upstream. 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. [The version for 3.10.34 (or perhaps now 3.10.35) is this below. Yes, more differences, and the old mem_cgroup_reparent_charges line is intentionally left in for 3.10 whereas it was removed for 3.12+: that's because the css/cgroup iterator changed in between, it used not to supply the root of the subtree, but nowadays it does - Hugh] Fixes: e5fca243abae ("cgroup: use a dedicated workqueue for cgroup destruction") Signed-off-by: Filipe Brandenburger Signed-off-by: Hugh Dickins Reviewed-by: Tejun Heo Acked-by: Michal Hocko Cc: Johannes Weiner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- mm/memcontrol.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) (limited to 'mm') diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 6115b2bbd6e..f45e21ab9ce 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -6326,9 +6326,23 @@ static void mem_cgroup_invalidate_reclaim_iterators(struct mem_cgroup *memcg) static void mem_cgroup_css_offline(struct cgroup *cont) { struct mem_cgroup *memcg = mem_cgroup_from_cont(cont); + struct cgroup *iter; mem_cgroup_invalidate_reclaim_iterators(memcg); + + /* + * This requires that offlining is serialized. Right now that is + * guaranteed because css_killed_work_fn() holds the cgroup_mutex. + */ + rcu_read_lock(); + cgroup_for_each_descendant_post(iter, cont) { + rcu_read_unlock(); + mem_cgroup_reparent_charges(mem_cgroup_from_cont(iter)); + rcu_read_lock(); + } + rcu_read_unlock(); mem_cgroup_reparent_charges(memcg); + mem_cgroup_destroy_all_caches(memcg); } -- cgit v1.2.3