linux-kernel - [PATCH v3 11/13] memcg: allow a memcg with kmem charges to be destructed.

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Date:	Tue, 18 Sep 2012 18:04:08 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	<linux-kernel@...r.kernel.org>
Cc:	<cgroups@...r.kernel.org>, <kamezawa.hiroyu@...fujitsu.com>,
	<devel@...nvz.org>, Tejun Heo <tj@...nel.org>,
	<linux-mm@...ck.org>, Suleiman Souhlal <suleiman@...gle.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mel Gorman <mgorman@...e.de>,
	David Rientjes <rientjes@...gle.com>,
	Glauber Costa <glommer@...allels.com>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>
Subject: [PATCH v3 11/13] memcg: allow a memcg with kmem charges to be destructed.

Because the ultimate goal of the kmem tracking in memcg is to track slab
pages as well, we can't guarantee that we'll always be able to point a
page to a particular process, and migrate the charges along with it -
since in the common case, a page will contain data belonging to multiple
processes.

Because of that, when we destroy a memcg, we only make sure the
destruction will succeed by discounting the kmem charges from the user
charges when we try to empty the cgroup.

Signed-off-by: Glauber Costa <glommer@...allels.com>
Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC: Christoph Lameter <cl@...ux.com>
CC: Pekka Enberg <penberg@...helsinki.fi>
CC: Michal Hocko <mhocko@...e.cz>
CC: Johannes Weiner <hannes@...xchg.org>
CC: Suleiman Souhlal <suleiman@...gle.com>
---
 mm/memcontrol.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index aada601..b05ecac 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -631,6 +631,11 @@ static void disarm_kmem_keys(struct mem_cgroup *memcg)
 {
 	if (memcg_kmem_is_accounted(memcg))
 		static_key_slow_dec(&memcg_kmem_enabled_key);
+	/*
+	 * This check can't live in kmem destruction function,
+	 * since the charges will outlive the cgroup
+	 */
+	WARN_ON(res_counter_read_u64(&memcg->kmem, RES_USAGE) != 0);
 }
 #else
 static void disarm_kmem_keys(struct mem_cgroup *memcg)
@@ -3933,6 +3938,7 @@ static int mem_cgroup_force_empty(struct mem_cgroup *memcg, bool free_all)
 	int node, zid, shrink;
 	int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
 	struct cgroup *cgrp = memcg->css.cgroup;
+	u64 usage;
 
 	css_get(&memcg->css);
 
@@ -3966,8 +3972,17 @@ move_account:
 		mem_cgroup_end_move(memcg);
 		memcg_oom_recover(memcg);
 		cond_resched();
+		/*
+		 * Kernel memory may not necessarily be trackable to a specific
+		 * process. So they are not migrated, and therefore we can't
+		 * expect their value to drop to 0 here.
+		 *
+		 * having res filled up with kmem only is enough
+		 */
+		usage = res_counter_read_u64(&memcg->res, RES_USAGE) -
+			res_counter_read_u64(&memcg->kmem, RES_USAGE);
 	/* "ret" should also be checked to ensure all lists are empty. */
-	} while (res_counter_read_u64(&memcg->res, RES_USAGE) > 0 || ret);
+	} while (usage > 0 || ret);
 out:
 	css_put(&memcg->css);
 	return ret;
-- 
1.7.11.4

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