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

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Message-ID: <681ed4dc-e8a5-afcf-98b6-c17544c6094d@redhat.com>
Date:   Tue, 18 Jun 2019 15:27:24 -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 6/18/19 2:32 PM, Michal Hocko wrote:
> On Tue 18-06-19 12:59:24, Waiman Long wrote:
>> On 6/18/19 8:37 AM, Michal Hocko wrote:
> [...]
>>> Is this useful enough to put into slabinfo? Doesn't this sound more like
>>> a debugfs kinda a thing?
>> I guess it is probably more on the debug side of things. I add it to
>> slabinfo as the data is readily available. It will be much more work if
>> we need to export the data via debugfs.
>>
>> We are seeing the kmem_cache slab growing continuously overtime when
>> running a container-based workloads. Roman's kmem_cache reparenting
>> patch will hopefully solve a major part of the problem, but we still
>> need a way to confirm that by looking at how many memcg kmem_caches are
>> associated with each root kmem_cache.
> I am not disputing usefulness. Dead memcgs are showing up as a problem
> for a longer time and having a more debugging information is definitely
> useful. I am just not really sure that /proc/slabinfo is the proper
> vehicle for that information. It might be just easier to stick it there
> but that is not the best justification for adding something we will have
> to maintain for ever. Not to mention that the number of dead memcgs
> might not be enough to debug further when we can easily end up needing
> to provide more in something less "carved in stone" kinda interface like
> debugfs.
>
Fair enough.

I will rework the patch and expose the information via debugfs then.

Cheers,
Longman