| From | Luis Henriques <> | Subject | [PATCH 3.11 109/144] memcg: reparent charges of children before processing parent | Date | Tue, 1 Apr 2014 12:15:13 +0100 |
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3.11.10.7 -stable review patch. If anyone has any objections, please let me know.
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From: Filipe Brandenburger <filbranden@google.com>
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.
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> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> [ Hugh: 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. ] [ luis: backported to 3.11: used Hugh's backport to 3.10 ] Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- mm/memcontrol.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index bb13089..4e4b328 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -6346,11 +6346,25 @@ 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; kmem_cgroup_css_offline(memcg); 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); vmpressure_cleanup(&memcg->vmpressure); } -- 1.9.1
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