linux-kernel - Re: [RFC PATCH 2/2] mm: drain memcg stocks on css offlining

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Message-ID: <20180815072900.GM32645@dhcp22.suse.cz>
Date:   Wed, 15 Aug 2018 09:29:00 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Roman Gushchin <guro@...com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-team@...com, Johannes Weiner <hannes@...xchg.org>,
        Konstantin Khlebnikov <koct9i@...il.com>,
        Tejun Heo <tj@...nel.org>
Subject: Re: [RFC PATCH 2/2] mm: drain memcg stocks on css offlining

On Tue 14-08-18 17:36:20, Roman Gushchin wrote:
> Memcg charge is batched using per-cpu stocks, so an offline memcg
> can be pinned by a cached charge up to a moment, when a process
> belonging to some other cgroup will charge some memory on the same
> cpu. In other words, cached charges can prevent a memory cgroup
> from being reclaimed for some time, without any clear need.
> 
> Let's optimize it by explicit draining of all stocks on css offlining.
> As draining is performed asynchronously, and is skipped if any
> parallel draining is happening, it's cheap.

Yes this makes sense.

> Signed-off-by: Roman Gushchin <guro@...com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Michal Hocko <mhocko@...nel.org>
> Cc: Konstantin Khlebnikov <koct9i@...il.com>
> Cc: Tejun Heo <tj@...nel.org>

Acked-by: Michal Hocko <mhocko@...e.com>

> ---
>  mm/memcontrol.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 4e3c1315b1de..cfb64b5b9957 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4575,6 +4575,8 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
>  	memcg_offline_kmem(memcg);
>  	wb_memcg_offline(memcg);
>  
> +	drain_all_stock(memcg);
> +
>  	mem_cgroup_id_put(memcg);
>  }
>  
> -- 
> 2.14.4

-- 
Michal Hocko
SUSE Labs