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

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Message-ID: <20201126110220.k4o6s32er5jy2mdk@ava.usersys.com>
Date:   Thu, 26 Nov 2020 11:02:20 +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 2020-11-24 13:47 +0000, Aaron Tomlin wrote:
> On Tue, 24 Nov 2020 at 13:36, Michal Hocko <mhocko@...e.com> wrote:
> > This like any other user visible interface would be a much easier sell
> > if there was a clear usecase to justify it. I do not see anything
> > controversial about exporting such a value but my general take is that
> > we are only adding new interface when existing ones are insufficient. A
> > performance might be a very good reason but that would really require to
> > come with some real life numbers.

Michal,

> Fair enough and understood.
> 
> At this stage, I unfortunately do not have such supporting data. This was only
> useful in an isolated situation. Having said this, I thought that the
> aforementioned interface would be helpful to others, in particular, given the
> known limitation.

Furthermore, I can see that this is already provided via /proc/cgroups
(see proc_cgroupstats_show()). As such, another possibility:
the proposed interface could reliably produce the difference between the
maximum permitted memory-controlled cgroup count and the used count
(i.e. the remaining memory cgroup count, from root); albeit, I doubt that
this would be particularly useful to others i.e., the use-case would be
rather limited.


Kind regards,

-- 
Aaron Tomlin