On Thu 27-07-17 14:04:27, Roman Gushchin wrote:
> A removed memory cgroup with a defined memory.low and some belonging
> pagecache has very low chances to be freed.
>
> If a cgroup has been removed, there is likely no memory pressure inside
> the cgroup, and the pagecache is protected from the external pressure
> by the defined low limit. The cgroup will be freed only after
> the reclaim of all belonging pages. And it will not happen until
> there are any reclaimable memory in the system. That means,
> there is a good chance, that a cold pagecache will reside
> in the memory for an undefined amount of time, wasting
> system resources.
>
> This problem was fixed earlier by commit fa06235b8eb0
> ("cgroup: reset css on destruction"), but it's not a best way
> to do it, as we can't really reset all limits/counters during
> cgroup offlining.
>
> Signed-off-by: Roman Gushchin <guro@xxxxxx>
> Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
> Cc: Tejun Heo <tj@xxxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Cc: kernel-team@xxxxxx
> Cc: cgroups@xxxxxxxxxxxxxxx
> Cc: linux-mm@xxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
my ack for this patch still holds.
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> mm/memcontrol.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index d61133e6af99..7b24210596ea 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4300,6 +4300,8 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
> }
> spin_unlock(&memcg->event_list_lock);
>
> + memcg->low = 0;
> +
> memcg_offline_kmem(memcg);
> wb_memcg_offline(memcg);
>
> --
> 2.13.3
--
Michal Hocko
SUSE Labs
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