From mboxrd@z Thu Jan  1 00:00:00 1970
From: Michal Hocko <mhocko@kernel.org>
Subject: Re: [PATCH] mm, memcg: Report number of memcg caches in slabinfo
Date: Tue, 18 Jun 2019 14:37:50 +0200
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To: Waiman Long <longman@redhat.com>
Cc: Christoph Lameter <cl@linux.com>, Pekka Enberg <penberg@kernel.org>, David Rientjes <rientjes@google.com>, Joonsoo Kim <iamjoonsoo.kim@lge.com>, Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Roman Gushchin <guro@fb.com>, Johannes Weiner <hannes@cmpxchg.org>, Shakeel Butt <shakeelb@google.com>, Vladimir Davydov <vdavydov.dev@gmail.com>, linux-api@vger.kernel.org
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On Mon 17-06-19 10:50:23, Waiman Long wrote:
> 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.

Doesn't debug_legacy_files provide the information for both cgroups
APIs?

> 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.

Is this useful enough to put into slabinfo? Doesn't this sound more like
a debugfs kinda a thing?

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

-- 
Michal Hocko
SUSE Labs