linux-kernel - Re: [PATCH 4/6] change alloc function in vmemmap_alloc

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Date:	Tue, 13 Apr 2010 16:59:37 +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 4/6] change alloc function in vmemmap_alloc_block

On Wed, Apr 14, 2010 at 12:25:01AM +0900, Minchan Kim wrote:
> if node_state is N_HIGH_MEMORY, node doesn't have -1.

Also, if node_state is called with -1, a negative index is being checked in
a bitmap and that would be pretty broken in itself. I can't see a problem
with this patch.

Reviewed-by: Mel Gorman <mel@....ul.ie>

> 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/sparse-vmemmap.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
> index 392b9bb..7710ebc 100644
> --- a/mm/sparse-vmemmap.c
> +++ b/mm/sparse-vmemmap.c
> @@ -53,7 +53,7 @@ void * __meminit vmemmap_alloc_block(unsigned long size, int node)
>  		struct page *page;
>  
>  		if (node_state(node, N_HIGH_MEMORY))
> -			page = alloc_pages_node(node,
> +			page = alloc_pages_exact_node(node,
>  				GFP_KERNEL | __GFP_ZERO, get_order(size));
>  		else
>  			page = alloc_pages(GFP_KERNEL | __GFP_ZERO,
> -- 
> 1.7.0.5
> 

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