linux-kernel - Re: [RFC PROPOSAL] memcg: per-memcg user space reclaim interface

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Date:   Wed, 12 Aug 2020 13:47:39 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Michal Koutný <mkoutny@...e.com>
Cc:     Michal Hocko <mhocko@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Roman Gushchin <guro@...com>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        David Rientjes <rientjes@...gle.com>,
        Greg Thelen <gthelen@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Cgroups <cgroups@...r.kernel.org>
Subject: Re: [RFC PROPOSAL] memcg: per-memcg user space reclaim interface

Hi Michal,

On Tue, Aug 11, 2020 at 10:36 AM Michal Koutný <mkoutny@...e.com> wrote:
>
> Hi Shakeel.
>
> On Tue, Jul 07, 2020 at 10:02:50AM -0700, Shakeel Butt <shakeelb@...gle.com> wrote:
> > > Well, I was talkingg about memory.low. It is not meant only to protect
> > > from the global reclaim. It can be used for balancing memory reclaim
> > > from _any_ external memory pressure source. So it is somehow related to
> > > the usecase you have mentioned.
> > >
> >
> > For the uswapd use-case, I am not concerned about the external memory
> > pressure source but the application hitting its own memory.high limit
> > and getting throttled.
> FTR, you can transform own memory.high into "external" pressure with a
> hierarchy such as
>
>   limit-group                   memory.high=N+margin memory.low=0
>   `- latency-sensitive-group    memory.low=N
>   `- regular-group              memory.low=0
>
> Would that ensure the latency targets?
>

My concern was not "whom to reclaim from" but it was "If I use
memory.high for reclaim, processes running in that memcg can hit
memory.high and get throttled". However Roman has reduced the window
where that can happen. Anyways I will send the next version after this
merge window closes.

Shakeel