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

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Message-ID: <1311170893.2338.29.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC>
Date:	Wed, 20 Jul 2011 16:08:13 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Christoph Lameter <cl@...ux.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

Le mercredi 20 juillet 2011 à 08:56 -0500, Christoph Lameter a écrit :
> On Wed, 20 Jul 2011, Mel Gorman wrote:
> 
> > > The changelog isn't that convincing, really. This is
> > > kmem_cache_create() so I'm surprised we'd ever get NULL here in
> > > practice. Does this fix some problem you're seeing? If this is
> > > really an issue, I'd blame the page allocator as GFP_KERNEL should
> > > just work.
> > >
> >
> > Besides, is allocating from cache_cache really a
> > PAGE_ALLOC_COSTLY_ORDER allocation? On my laptop at least, it's an
> > order-2 allocation which is supporting up to 512 CPUs and 512 nodes.
> 
> 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.



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