linux-kernel - Re: [PATCH] memcg: add support to generate the total count of children from root

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Message-ID: <CANfR36hBxRsHV+JZfT6_RZRXBvCu0p=4xUOSxzco-BvrTEP37w@mail.gmail.com>
Date:   Tue, 24 Nov 2020 13:36:00 +0000
From:   Aaron Tomlin <atomlin@...hat.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>, hannes@...xchg.org,
        vdavydov.dev@...il.com, Andrew Morton <akpm@...ux-foundation.org>,
        cgroups@...r.kernel.org, linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH] memcg: add support to generate the total count of
 children from root

On Tue, 24 Nov 2020 at 11:26, Michal Hocko <mhocko@...e.com> wrote:
>
> On Tue 24-11-20 10:58:36, Aaron Tomlin wrote:
> > Each memory-controlled cgroup is assigned a unique ID and the total
> > number of memory cgroups is limited to MEM_CGROUP_ID_MAX.
> >
> > This patch provides the ability to determine the number of
> > memory cgroups from the root memory cgroup, only.
> > A value of 1 (i.e. self count) is returned if there are no children.
> > For example, the number of memory cgroups can be established by
> > reading the /sys/fs/cgroup/memory/memory.total_cnt file.
>

Hi Michal,

> Could you add some explanation why is this information useful for
> userspace? Who is going to use it and why a simple scripting on top of
> cgroupfs is insufficient.

Thank you for your feedback.

Indeed, one can use a command/script to manually calculate this.
Having said that, one that creates a significant number of
memory-controlled cgroups may prefer a quick, simple and reliable method
to generate the aforementioned data, for management purposes only.
As such, I thought this patch might be particularly useful.

Kind regards,
-- 
Aaron Tomlin