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

Glauber Costa
2012-10-08T10:07:57Z

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@parallels.com>
Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
CC: Christoph Lameter <cl@linux.com>
CC: Pekka Enberg <penberg@cs.helsinki.fi>
CC: Johannes Weiner <hannes@cmpxchg.org>
CC: Suleiman Souhlal <suleiman@google.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