linux-kernel - Re: [PATCH] mm, memcg: Add a memcg

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Message-ID: <CALvZod6T31z2P+wdUz3LVYO3dTSbOc89cKDn=8LKpN+ZovL8jw@mail.gmail.com>
Date:   Wed, 19 Jun 2019 08:35:47 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Waiman Long <longman@...hat.com>
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...nel.org>, Roman Gushchin <guro@...com>,
        Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>
Subject: Re: [PATCH] mm, memcg: Add a memcg_slabinfo debugfs file

On Wed, Jun 19, 2019 at 8:30 AM Waiman Long <longman@...hat.com> wrote:
>
> On 6/19/19 11:18 AM, Shakeel Butt wrote:
> > On Wed, Jun 19, 2019 at 7:46 AM Waiman Long <longman@...hat.com> wrote:
> >> There are concerns about memory leaks from extensive use of memory
> >> cgroups as each memory cgroup creates its own set of kmem caches. There
> >> is a possiblity that the memcg kmem caches may remain even after the
> >> memory cgroup removal. Therefore, it will be useful to show how many
> >> memcg caches are present for each of the kmem caches.
> >>
> >> This patch introduces a new <debugfs>/memcg_slabinfo file which is
> >> somewhat similar to /proc/slabinfo in format, but lists only slabs that
> >> are in memcg kmem caches. Information available in /proc/slabinfo are
> >> not repeated in memcg_slabinfo.
> >>
> > At Google, we have an interface /proc/slabinfo_full which shows each
> > kmem cache (root and memcg) on a separate line i.e. no accumulation.
> > This interface has helped us a lot for debugging zombies and memory
> > leaks. The name of the memcg kmem caches include the memcg name, css
> > id and "dead" for offlined memcgs. I think these extra information is
> > much more useful for debugging. What do you think?
> >
> > Shakeel
>
> Yes, I think that can be a good idea. My only concern is that it can be
> very verbose. Will work on a v2 patch.
>

Yes, it is very verbose but it is only for debugging and normal users
should not be (continuously) reading that interface.

Shakeel