linux-kernel - Re: [RFC] how should we deal with dead memcgs' kmem caches?

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Date:	Mon, 21 Apr 2014 21:56:14 +0400
From:	Vladimir Davydov <vdavydov@...allels.com>
To:	Christoph Lameter <cl@...ux.com>
CC:	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pekka Enberg <penberg@...nel.org>,
	Glauber Costa <glommer@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	<devel@...nvz.org>
Subject: Re: [RFC] how should we deal with dead memcgs' kmem caches?

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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