linux-kernel - Re: [patch 07/10] SLUB: Avoid referencing kmem_cache structure in __slab

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Message-Id: <20071030113848.930471e6.akpm@linux-foundation.org>
Date:	Tue, 30 Oct 2007 11:38:48 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Christoph Lameter <clameter@....com>
Cc:	matthew@....cx, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	penberg@...helsinki.fi
Subject: Re: [patch 07/10] SLUB: Avoid referencing kmem_cache structure in
 __slab_alloc

On Sat, 27 Oct 2007 20:32:03 -0700
Christoph Lameter <clameter@....com> wrote:

> There is the need to use the objects per slab in the first part of
> __slab_alloc() which is still pretty hot. Copy the number of objects
> per slab into the kmem_cache_cpu structure. That way we can get the
> value from a cache line that we already need to touch. This brings
> the kmem_cache_cpu structure up to 4 even words.
> 
> There is no increase in the size of kmem_cache_cpu since the size of object
> is rounded to the next word.
> 
> Signed-off-by: Christoph Lameter <clameter@....com>
> 
> ---
>  include/linux/slub_def.h |    1 +
>  mm/slub.c                |    3 ++-
>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> Index: linux-2.6/include/linux/slub_def.h
> ===================================================================
> --- linux-2.6.orig/include/linux/slub_def.h	2007-10-26 19:09:16.000000000 -0700
> +++ linux-2.6/include/linux/slub_def.h	2007-10-27 07:55:12.000000000 -0700
> @@ -17,6 +17,7 @@ struct kmem_cache_cpu {
>  	int node;
>  	unsigned int offset;
>  	unsigned int objsize;
> +	unsigned int objects;
>  };

mutter.  nr_objects would be a better name, but then one should rename
kmem_cache.objects too.

Better would be to comment the field.  Please devote extra care to commenting
data structures.
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