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authorFilipe Brandenburger <filbranden@google.com>2014-03-03 15:38:25 -0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-03-23 21:38:20 -0700
commitba9a72974fd85701aea843b276d9773809286e74 (patch)
treedad34d0c0f0e91e9b0cdfc682aec3fe18aff68b4 /mm
parentf1352fb2a38e6d57c9ec7f96c5449db616e04ef2 (diff)
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 <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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/memcontrol.c14
1 files changed, 14 insertions, 0 deletions
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);
}