linux-kernel - Re: [PATCH] mm-slab: allocate kmem_cache with __GFP

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Message-ID: <alpine.DEB.2.00.1107200950270.1472@router.home>
Date:	Wed, 20 Jul 2011 09:52:03 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
cc:	Mel Gorman <mgorman@...e.de>, Pekka Enberg <penberg@...nel.org>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Matt Mackall <mpm@...enic.com>
Subject: Re: [PATCH] mm-slab: allocate kmem_cache with __GFP_REPEAT

On Wed, 20 Jul 2011, Eric Dumazet wrote:

> > Slab's kmem_cache is configured with an array of NR_CPUS which is the
> > maximum nr of cpus supported. Some distros support 4096 cpus in order to
> > accomodate SGI machines. That array then will have the size of 4096 * 8 =
> > 32k
>
> We currently support a dynamic schem for the possible nodes :
>
> cache_cache.buffer_size = offsetof(struct kmem_cache, nodelists) +
> 	nr_node_ids * sizeof(struct kmem_list3 *);
>
> We could have a similar trick to make the real size both depends on
> nr_node_ids and nr_cpu_ids.
>
> (struct kmem_cache)->array would become a pointer.

We should be making it a per cpu pointer like slub then. I looked at what
it would take to do so a couple of month ago but it was quite invasive.

The other solution is to use slub instead.

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