linux-kernel - Re: [this_cpu_xx V8 03/16] Use this

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Message-ID: <4B2DEA33.7000800@cs.helsinki.fi>
Date:	Sun, 20 Dec 2009 11:11:15 +0200
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Christoph Lameter <cl@...ux-foundation.org>
CC:	Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org,
	Mel Gorman <mel@....ul.ie>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Subject: Re: [this_cpu_xx V8 03/16] Use this_cpu operations in slub

Christoph Lameter wrote:
> Using per cpu allocations removes the needs for the per cpu arrays in the
> kmem_cache struct. These could get quite big if we have to support systems
> with thousands of cpus. The use of this_cpu_xx operations results in:
> 
> 1. The size of kmem_cache for SMP configuration shrinks since we will only
>    need 1 pointer instead of NR_CPUS. The same pointer can be used by all
>    processors. Reduces cache footprint of the allocator.
> 
> 2. We can dynamically size kmem_cache according to the actual nodes in the
>    system meaning less memory overhead for configurations that may potentially
>    support up to 1k NUMA nodes / 4k cpus.
> 
> 3. We can remove the diddle widdle with allocating and releasing of
>    kmem_cache_cpu structures when bringing up and shutting down cpus. The cpu
>    alloc logic will do it all for us. Removes some portions of the cpu hotplug
>    functionality.
> 
> 4. Fastpath performance increases since per cpu pointer lookups and
>    address calculations are avoided.
> 
> V7-V8
> - Convert missed get_cpu_slab() under CONFIG_SLUB_STATS
> 
> Cc: Pekka Enberg <penberg@...helsinki.fi>
> Signed-off-by: Christoph Lameter <cl@...ux-foundation.org>

Patches 3-6 applied.
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