linux-kernel - Re: [PATCH] mm: memcontrol: asynchronous reclaim for memory.high

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Message-ID: <20200227095859.GA3771@dhcp22.suse.cz>
Date:   Thu, 27 Feb 2020 10:58:59 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Yang Shi <yang.shi@...ux.alibaba.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>, Roman Gushchin <guro@...com>,
        Linux MM <linux-mm@...ck.org>,
        Cgroups <cgroups@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH] mm: memcontrol: asynchronous reclaim for memory.high

On Wed 26-02-20 16:12:23, Yang Shi wrote:
[...]
> Actually I'm wondering if we really need account CPU cycles used by
> background reclaimer or not. For our usecase (this may be not general), the
> purpose of background reclaimer is to avoid latency sensitive workloads get
> into direct relcaim (avoid the stall from direct relcaim). In fact it just
> "steal" CPU cycles from lower priority or best-effort workloads to guarantee
> latency sensitive workloads behave well. If the "stolen" CPU cycles are
> accounted, it means the latency sensitive workloads would get throttled from
> somewhere else later, i.e. by CPU share.

I believe we need to because that work is not for free and so you are
essentially stealing those CPUs cycles from everybody else outside of
your throttled cgroup.
-- 
Michal Hocko
SUSE Labs