On Mon, Jun 25, 2012 at 06:15:27PM +0400, Glauber Costa wrote:
> 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>
> CC: Christoph Lameter <cl@linux.com>
> CC: Pekka Enberg <penberg@cs.helsinki.fi>
> CC: Michal Hocko <mhocko@suse.cz>
> CC: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> CC: Johannes Weiner <hannes@cmpxchg.org>
> CC: Suleiman Souhlal <suleiman@google.com>
> ---
> mm/memcontrol.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index a6a440b..bb9b6fe 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -598,6 +598,11 @@ static void disarm_kmem_keys(struct mem_cgroup *memcg)
> {
> if (test_bit(KMEM_ACCOUNTED_THIS, &memcg->kmem_accounted))
> static_key_slow_dec(&mem_cgroup_kmem_enabled_key);
> + /*
> + * This check can't live in kmem destruction function,
> + * since the charges will outlive the cgroup
> + */
> + BUG_ON(res_counter_read_u64(&memcg->kmem, RES_USAGE) != 0);
WARN_ON() please. Misaccounted kernel usually is better than dead
kernel.
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