linux-kernel - Re: [PATCH mm v5 0/9] memcg: accounting for objects allocated by mkdir, cgroup

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Date:   Fri, 24 Jun 2022 15:59:51 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Vasily Averin <vvs@...nvz.org>, kernel@...nvz.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Michal Koutný <mkoutny@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Muchun Song <songmuchun@...edance.com>,
        Cgroups <cgroups@...r.kernel.org>
Subject: Re: [PATCH mm v5 0/9] memcg: accounting for objects allocated by
 mkdir, cgroup

On Thu 23-06-22 09:55:33, Shakeel Butt wrote:
> On Thu, Jun 23, 2022 at 9:07 AM Michal Hocko <mhocko@...e.com> wrote:
> >
> > On Thu 23-06-22 18:03:31, Vasily Averin wrote:
> > > Dear Michal,
> > > do you still have any concerns about this patch set?
> >
> > Yes, I do not think we have concluded this to be really necessary. IIRC
> > Roman would like to see lingering cgroups addressed in not-so-distant
> > future (http://lkml.kernel.org/r/Ypd2DW7id4M3KJJW@carbon) and we already
> > have a limit for the number of cgroups in the tree. So why should we
> > chase after allocations that correspond the cgroups and somehow try to
> > cap their number via the memory consumption. This looks like something
> > that will get out of sync eventually and it also doesn't seem like the
> > best control to me (comparing to an explicit limit to prevent runaways).
> > --
> 
> Let me give a counter argument to that. On a system running multiple
> workloads, how can the admin come up with a sensible limit for the
> number of cgroups?

How is that any easier through memory consumption? Something that might
change between kernel versions? Is it even possible to prevent from id
depletion by the memory consumption? Any medium sized memcg can easily
consume all the ids AFAICS.
-- 
Michal Hocko
SUSE Labs