linux-kernel - Re: [PATCH -mm 4/8] slub: never fail kmem_cache

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Date:	Fri, 30 May 2014 09:46:33 -0500 (CDT)
From:	Christoph Lameter <cl@...two.org>
To:	Vladimir Davydov <vdavydov@...allels.com>
cc:	akpm@...ux-foundation.org, hannes@...xchg.org, mhocko@...e.cz,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH -mm 4/8] slub: never fail kmem_cache_shrink

On Fri, 30 May 2014, Vladimir Davydov wrote:

> SLUB's kmem_cache_shrink not only removes empty slabs from the cache,
> but also sorts slabs by the number of objects in-use to cope with
> fragmentation. To achieve that, it tries to allocate a temporary array.
> If it fails, it will abort the whole procedure.

If we cannot allocate a kernel structure that is mostly less than a page
size then we have much more important things to worry about.

The maximum number of objects per slab is 512 on my system here.

> This is unacceptable for kmemcg, where we want to be sure that all empty
> slabs are removed from the cache on memcg offline, so let's just skip
> the de-fragmentation step if the allocation fails, but still get rid of
> empty slabs.

Lets just try the shrink and log the fact that it failed? Try again later?


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