linux-kernel - [PATCH v4 11/14] memcg: allow a memcg with kmem charges to be destructed.

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Date:	Mon,  8 Oct 2012 14:06:17 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	<linux-kernel@...r.kernel.org>
Cc:	<linux-mm@...ck.org>, Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Tejun Heo <tj@...nel.org>, <cgroups@...r.kernel.org>,
	<kamezawa.hiroyu@...fujitsu.com>, Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Greg Thelen <gthelen@...gle.com>, <devel@...nvz.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Glauber Costa <glommer@...allels.com>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: [PATCH v4 11/14] 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>
Reviewed-by: Michal Hocko <mhocko@...e.cz>
CC: Christoph Lameter <cl@...ux.com>
CC: Pekka Enberg <penberg@...helsinki.fi>
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 724a08b..2f92f89 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -546,6 +546,11 @@ static void disarm_kmem_keys(struct mem_cgroup *memcg)
 {
 	if (memcg_kmem_is_active(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)
@@ -3994,6 +3999,7 @@ 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);
 
@@ -4027,8 +4033,17 @@ 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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