Re: [PATCH 04/19] Convert gfp_zone() to use a table of precalculated values

[Christoph Lameter <cl@linux-foundation.org>]

On Tue, 24 Feb 2009, Mel Gorman wrote:

>  static inline enum zone_type gfp_zone(gfp_t flags)
>  {
> -#ifdef CONFIG_ZONE_DMA
> -	if (flags & __GFP_DMA)
> -		return ZONE_DMA;
> -#endif
> -#ifdef CONFIG_ZONE_DMA32
> -	if (flags & __GFP_DMA32)
> -		return ZONE_DMA32;
> -#endif
> -	if ((flags & (__GFP_HIGHMEM | __GFP_MOVABLE)) ==
> -			(__GFP_HIGHMEM | __GFP_MOVABLE))
> -		return ZONE_MOVABLE;
> -#ifdef CONFIG_HIGHMEM
> -	if (flags & __GFP_HIGHMEM)
> -		return ZONE_HIGHMEM;
> -#endif
> -	return ZONE_NORMAL;
> +	return gfp_zone_table[flags & GFP_ZONEMASK];
>  }

Aassume

GFP_DMA		= 0x01
GFP_DMA32	= 0x02
GFP_MOVABLE	= 0x04
GFP_HIGHMEM	= 0x08

ZONE_NORMAL	= 0
ZONE_DMA	= 1
ZONE_DMA32	= 2
ZONE_MOVABLE	= 3
ZONE_HIGHMEM	= 4

then we could implement gfp_zone simply as:

static inline enum zone_type gfp_zone(gfp_t flags)
{
	return ffs(flags & 0xf);
}

However, this would return ZONE_MOVABLE if only GFP_MOVABLE would be
set but not GFP_HIGHMEM.

If we could make sure that GFP_MOVABLE always includes GFP_HIGHMEM then
this would not be a problem.

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