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    SubjectRe: [PATCH v3 11/13] memcg: allow a memcg with kmem charges to be destructed.
    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 <glommer@parallels.com>
    > Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    > CC: Christoph Lameter <cl@linux.com>
    > CC: Pekka Enberg <penberg@cs.helsinki.fi>
    > CC: Michal Hocko <mhocko@suse.cz>
    > CC: Johannes Weiner <hannes@cmpxchg.org>
    > CC: Suleiman Souhlal <suleiman@google.com>

    Looks good.
    Reviewed-by: Michal Hocko <mhocko@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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