linux-kernel - Re: [PATCH -mm 7/8] slub: make dead caches discard free slabs immediately

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Message-ID: <alpine.DEB.2.10.1405300955120.11943@gentwo.org>
Date:	Fri, 30 May 2014 09:57:10 -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 7/8] slub: make dead caches discard free slabs
 immediately

On Fri, 30 May 2014, Vladimir Davydov wrote:

> (3) is a bit more difficult, because slabs are added to per-cpu partial
> lists lock-less. Fortunately, we only have to handle the __slab_free
> case, because, as there shouldn't be any allocation requests dispatched
> to a dead memcg cache, get_partial_node() should never be called. In
> __slab_free we use cmpxchg to modify kmem_cache_cpu->partial (see
> put_cpu_partial) so that setting ->partial to a special value, which
> will make put_cpu_partial bail out, will do the trick.
>
> Note, this shouldn't affect performance, because keeping empty slabs on
> per node lists as well as using per cpu partials are only worthwhile if
> the cache is used for allocations, which isn't the case for dead caches.

This all sounds pretty good to me but we still have some pretty extensive
modifications that I would rather avoid.

In put_cpu_partial you can simply check that the memcg is dead right? This
would avoid all the other modifications I would think and will not require
a special value for the per cpu partial pointer.
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