linux-kernel - Re: [PATCH mm v2] memcg: notify about global mem_cgroup

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Message-ID: <20220628090819.GB30543@blackbody.suse.cz>
Date:   Tue, 28 Jun 2022 11:08:19 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Roman Gushchin <roman.gushchin@...ux.dev>
Cc:     Vasily Averin <vvs@...nvz.org>,
        Muchun Song <songmuchun@...edance.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Michal Hocko <mhocko@...e.com>, kernel@...nvz.org,
        LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Cgroups <cgroups@...r.kernel.org>
Subject: Re: [PATCH mm v2] memcg: notify about global mem_cgroup_id space
 depletion

On Mon, Jun 27, 2022 at 06:11:27PM -0700, Roman Gushchin <roman.gushchin@...ux.dev> wrote:
> I think a better approach will be to add a cgroup event (displayed via
> cgroup.events) about reaching the maximum limit of cgroups. E.g.
> cgroups.events::max_nr_reached.

This sounds like a good generalization.

> Then you can set cgroup.max.descendants to some value below memcg_id
> space size. It's more work, but IMO it's a better way to communicate
> this event. As a bonus, you can easily get an idea which cgroup
> depletes the limit.

Just mind there's a difference between events: what cgroup's limit was
hit and what cgroup was affected by the limit [1] (the former is more
useful for the calibration if I understand the situation).

Michal

[1] https://lore.kernel.org/all/20200205134426.10570-2-mkoutny@suse.com/