linux-kernel - Re: [PATCH] mm, memcg: Report number of memcg caches in slabinfo

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Message-ID: <9e165eae-e354-04c4-6362-0f80fe819469@redhat.com>
Date:   Mon, 17 Jun 2019 10:50:23 -0400
From:   Waiman Long <longman@...hat.com>
To:     Michal Hocko <mhocko@...nel.org>
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@...ck.org,
        linux-kernel@...r.kernel.org, Roman Gushchin <guro@...com>,
        Johannes Weiner <hannes@...xchg.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        linux-api@...r.kernel.org
Subject: Re: [PATCH] mm, memcg: Report number of memcg caches in slabinfo

On 6/17/19 10:38 AM, Michal Hocko wrote:
> [Cc linux-api]
>
> On Mon 17-06-19 10:21:49, Waiman Long 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.
> How is a user going to use that information?  Btw. Don't we have an
> interface to display the number of (dead) cgroups?

The interface to report dead cgroups is for cgroup v2 (cgroup.stat)
only. I don't think there is a way to find that for cgroup v1. Also the
number of memcg kmem caches may not be the same as the number of
memcg's. It can range from 0 to above the number of memcg's.  So it is
an interesting number by itself.

>From the user perspective, if the numbers is way above the number of
memcg's, there is probably something wrong there.

Cheers,
Longman