linux-kernel - Re: [PATCH 3/6] change alloc function in alloc_slab

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Message-ID: <20100413155253.GD25756@csn.ul.ie>
Date:	Tue, 13 Apr 2010 16:52:53 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Bob Liu <lliubbo@...il.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: [PATCH 3/6] change alloc function in alloc_slab_page

On Wed, Apr 14, 2010 at 12:25:00AM +0900, Minchan Kim wrote:
> alloc_slab_page never calls alloc_pages_node with -1.

Are you certain? What about

__kmalloc
  -> slab_alloc (passed -1 as a node from __kmalloc)
    -> __slab_alloc
      -> new_slab
        -> allocate_slab
          -> alloc_slab_page

> It means node's validity check is unnecessary.
> So we can use alloc_pages_exact_node instead of alloc_pages_node.
> It could avoid comparison and branch as 6484eb3e2a81807722 tried.
> 
> Cc: Christoph Lameter <cl@...ux-foundation.org>
> Signed-off-by: Minchan Kim <minchan.kim@...il.com>
> ---
>  mm/slub.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index b364844..9984165 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1084,7 +1084,7 @@ static inline struct page *alloc_slab_page(gfp_t flags, int node,
>  	if (node == -1)
>  		return alloc_pages(flags, order);
>  	else
> -		return alloc_pages_node(node, flags, order);
> +		return alloc_pages_exact_node(node, flags, order);
>  }
>  
>  static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
> -- 
> 1.7.0.5
> 

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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