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Subject[PATCH -mm v15 11/13] memcg: flush memcg items upon memcg destruction
Date
From: Glauber Costa <glommer@openvz.org>

When a memcg is destroyed, it won't be imediately released until all
objects are gone. This means that if a memcg is restarted with the very
same workload - a very common case, the objects already cached won't be
billed to the new memcg. This is mostly undesirable since a container
can exploit this by restarting itself every time it reaches its limit,
and then coming up again with a fresh new limit.

Since now we have targeted reclaim, I sustain that we should assume that
a memcg that is destroyed should be flushed away. It makes perfect sense
if we assume that a memcg that goes away most likely indicates an
isolated workload that is terminated.

Signed-off-by: Glauber Costa <glommer@openvz.org>
Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
mm/memcontrol.c | 28 ++++++++++++++++++++++++++++
1 file changed, 28 insertions(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 27f6d795090a..aed1456015cf 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6155,12 +6155,40 @@ static void memcg_destroy_kmem(struct mem_cgroup *memcg)
memcg_destroy_all_lrus(memcg);
}

+static void memcg_drop_slab(struct mem_cgroup *memcg)
+{
+ struct shrink_control shrink = {
+ .gfp_mask = GFP_KERNEL,
+ .target_mem_cgroup = memcg,
+ };
+ unsigned long nr_objects;
+
+ nodes_setall(shrink.nodes_to_scan);
+ do {
+ nr_objects = shrink_slab(&shrink, 1000, 1000);
+ } while (nr_objects > 10);
+}
+
static void kmem_cgroup_css_offline(struct mem_cgroup *memcg)
{
if (!memcg_kmem_is_active(memcg))
return;

/*
+ * When a memcg is destroyed, it won't be imediately released until all
+ * objects are gone. This means that if a memcg is restarted with the
+ * very same workload - a very common case, the objects already cached
+ * won't be billed to the new memcg. This is mostly undesirable since a
+ * container can exploit this by restarting itself every time it
+ * reaches its limit, and then coming up again with a fresh new limit.
+ *
+ * Therefore a memcg that is destroyed should be flushed away. It makes
+ * perfect sense if we assume that a memcg that goes away indicates an
+ * isolated workload that is terminated.
+ */
+ memcg_drop_slab(memcg);
+
+ /*
* kmem charges can outlive the cgroup. In the case of slab
* pages, for instance, a page contain objects from various
* processes. As we prevent from taking a reference for every
--
1.7.10.4


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