Re: mempolicies: fix policy_zone check

[Christoph Lameter <clameter@sgi.com>]

On Sat, 5 Aug 2006, Andi Kleen wrote:

> On Saturday 05 August 2006 01:54, Christoph Lameter wrote:
> 
> > So move the highest_zone() function from mm/page_alloc.c into
> > include/linux/gfp.h.  On the way we simplify the function and use the new
> > zone_type that was also introduced with the zone reduction patchset plus we
> > also specify the right type for the gfp flags parameter.
> 
> The function is a bit big to inline. Better keep it in page_alloc.c, but
> make it global.

Basically we have a maximum of 2 comparisons (no architecture 
supports 4 zones) in the function with a simple constant return.

Most modern processors can do that kind of thing inline without jumps and 
its just a few instructions (likely less than a function call). On most 
platforms that only support DMA and NORMAL we only have a single 
comparison.

Also having that function inline allows optimizations if the gfp flag is 
partially or fully known. If the compiler sees

gfp_zone(__GFP_HIGHMEM | blablabla) then it can substitute ZONE_HIGHMEM .
gfp_zone(GFP_USER) can be determined at compile time etc.

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