On Tue 18-09-12 18:04:08, 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 <glom...@parallels.com>
> Acked-by: Kamezawa Hiroyuki <kamezawa.hir...@jp.fujitsu.com>
> CC: Christoph Lameter <c...@linux.com>
> CC: Pekka Enberg <penb...@cs.helsinki.fi>
> CC: Michal Hocko <mho...@suse.cz>
> CC: Johannes Weiner <han...@cmpxchg.org>
> CC: Suleiman Souhlal <sulei...@google.com>
Looks good.
Reviewed-by: Michal Hocko <mho...@suse.cz>
> ---
> 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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--
Michal Hocko
SUSE Labs
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