linux-kernel - [PATCH v6 11/29] memcg: allow a memcg with kmem charges to be destructed.

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Message-Id: <1351771665-11076-12-git-send-email-glommer@parallels.com>
Date:	Thu,  1 Nov 2012 16:07:27 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	<linux-mm@...ck.org>
Cc:	<linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	<kamezawa.hiroyu@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Tejun Heo <tj@...nel.org>, Michal Hocko <mhocko@...e.cz>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Glauber Costa <glommer@...allels.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Suleiman Souhlal <suleiman@...gle.com>
Subject: [PATCH v6 11/29] 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>
CC: Tejun Heo <tj@...nel.org>
---
 mm/memcontrol.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 403f5a7..61a382a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -545,6 +545,11 @@ 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)
@@ -3995,6 +4000,7 @@ 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);
 
@@ -4028,8 +4034,17 @@ 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;
-- 
1.7.11.7

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