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Message-ID: <53555BBE.2020804@parallels.com>
Date: Mon, 21 Apr 2014 21:56:14 +0400
From: Vladimir Davydov <vdavydov@parallels.com>
MIME-Version: 1.0
Subject: Re: [RFC] how should we deal with dead memcgs' kmem caches?
References: <5353A3E3.4020302@parallels.com> <alpine.DEB.2.10.1404211128450.28094@gentwo.org>
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To: Christoph Lameter <cl@linux.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>, Michal Hocko <mhocko@suse.cz>, Andrew Morton <akpm@linux-foundation.org>, Pekka Enberg <penberg@kernel.org>, Glauber Costa <glommer@gmail.com>, LKML <linux-kernel@vger.kernel.org>, Linux Memory Management List <linux-mm@kvack.org>, devel@openvz.org

21.04.2014 20:29, Christoph Lameter:
> On Sun, 20 Apr 2014, Vladimir Davydov wrote:
> 
>> * Way #1 - prevent dead kmem caches from caching slabs on free *
>>
>> We can modify sl[au]b implementation so that it won't cache any objects
>> on free if the kmem cache belongs to a dead memcg. Then it'd be enough
>> to drain per-cpu pools of all dead kmem caches on css offline - no new
>> slabs will be added there on further frees, and the last object will go
>> away along with the last slab.
> 
> You can call kmem_cache_shrink() to force slab allocators to drop cached
> objects after a free.

Yes, but the question is when and how often should we do that? Calling
it after each kfree would be an overkill, because there may be plenty of
objects in a dead cache. Calling it periodically or on vmpressure is the
first thing that springs to mind - that's covered by "way #2".

Thanks.

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