Re: [PATCH 08/25] Calculate the preferred zone for allocation onlyonce

[Pekka Enberg]

Hi Mel,

On Mon, 2009-04-20 at 23:19 +0100, Mel Gorman wrote:
> get_page_from_freelist() can be called multiple times for an
> allocation.
> Part of this calculates the preferred_zone which is the first usable
> zone in the zonelist. This patch calculates preferred_zone once.
> 
> Signed-off-by: Mel Gorman <mel@xxxxxxxxx>

Reviewed-by: Pekka Enberg <penberg@xxxxxxxxxxxxxx>

> @@ -1772,11 +1774,20 @@ __alloc_pages_nodemask(gfp_t gfp_mask,
> unsigned int order,
>  	if (unlikely(!zonelist->_zonerefs->zone))
>  		return NULL;
>  
> +	/* The preferred zone is used for statistics later */
> +	(void)first_zones_zonelist(zonelist, high_zoneidx, nodemask,
> +							&preferred_zone);
> +	if (!preferred_zone)
> +		return NULL;

You might want to add an explanation to the changelog why this change is
safe. It looked like a functional change at first glance and it was
pretty difficult to convince myself that __alloc_pages_slowpath() will
always return NULL when there's no preferred zone because of the other
cleanups in this patch series.

> +
> +	/* First allocation attempt */
>  	page = get_page_from_freelist(gfp_mask|__GFP_HARDWALL, nodemask, order,
> -			zonelist, high_zoneidx, ALLOC_WMARK_LOW|ALLOC_CPUSET);
> +			zonelist, high_zoneidx, ALLOC_WMARK_LOW|ALLOC_CPUSET,
> +			preferred_zone);
>  	if (unlikely(!page))
>  		page = __alloc_pages_slowpath(gfp_mask, order,
> -				zonelist, high_zoneidx, nodemask);
> +				zonelist, high_zoneidx, nodemask,
> +				preferred_zone);
>  
>  	return page;
>  }

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