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Date:   Thu, 6 Aug 2020 21:16:03 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Michal =?ISO-8859-1?Q?Koutn=FD?= <mkoutny@suse.com>
Cc:     Roman Gushchin <guro@fb.com>, Dennis Zhou <dennis@kernel.org>,
        Tejun Heo <tj@kernel.org>, Christoph Lameter <cl@linux.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Shakeel Butt <shakeelb@google.com>, linux-mm@kvack.org,
        kernel-team@fb.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 4/5] mm: memcg: charge memcg percpu memory to the
 parent cgroup
Message-Id: <20200806211603.195727c03995c3a25ffc6d76@linux-foundation.org>
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        <20200623184515.4132564-5-guro@fb.com>
        <20200729171039.GA22229@blackbody.suse.cz>
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On Wed, 29 Jul 2020 19:10:39 +0200 Michal Koutn=FD <mkoutny@suse.com> wrote:

> Hello.
>=20
> On Tue, Jun 23, 2020 at 11:45:14AM -0700, Roman Gushchin <guro@fb.com> wr=
ote:
> > Because the size of memory cgroup internal structures can dramatically
> > exceed the size of object or page which is pinning it in the memory, it=
's
> > not a good idea to simple ignore it.  It actually breaks the isolation
> > between cgroups.
> No doubt about accounting the memory if it's significant amount.
>=20
> > Let's account the consumed percpu memory to the parent cgroup.
> Why did you choose charging to the parent of the created cgroup?
>=20
> Should the charge go the cgroup _that is creating_ the new memcg?
>=20
> One reason is that there are the throttling mechanisms for memory limits
> and those are better exercised when the actor and its memory artefact
> are the same cgroup, aren't they?
>=20
> The second reason is based on the example Dlegation Containment
> (Documentation/admin-guide/cgroup-v2.rst)
>=20
> > For an example, let's assume cgroups C0 and C1 have been delegated to
> > user U0 who created C00, C01 under C0 and C10 under C1 as follows and
> > all processes under C0 and C1 belong to U0::
> >=20
> >   ~~~~~~~~~~~~~ - C0 - C00
> >   ~ cgroup    ~      \ C01
> >   ~ hierarchy ~
> >   ~~~~~~~~~~~~~ - C1 - C10
>=20
> Thanks to permissions a task running in C0 creating a cgroup in C1 would
> deplete C1's supply victimizing tasks inside C1.

These week-old issues appear to be significant.  Roman?  Or someone
else?