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From: Andi Kleen <ak@suse.de>
To: Christoph Lameter <clameter@sgi.com>
Subject: Re: [RFC 4/8] page allocator: Optional ZONE_DMA
Date: Sat, 8 Jul 2006 02:23:01 +0200
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Cc: linux-kernel@vger.kernel.org, Nick Piggin <nickpiggin@yahoo.com.au>,
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On Saturday 08 July 2006 02:05, Christoph Lameter wrote:
> Make ZONE_DMA optional in the page allocator

Hmm, we should rename you the "ifdef warrior"

> - ifdef all code for ZONE_DMA and related definition
> 
> - Without ZONE_DMA, ZONE_HIGHMEM and ZONE_DMA32 we fall back
>   to an empty GFP_ZONEMASK and a ZONES_SHIFT of zero (since there
>   is only one zone....).
> 
> - We need to fix the use of ZONE_DMA in the memory policy layer.
>   ZONE_DMA is used there as the first zone so use 0 instead.


Is the barely better code really worth all the ugliness from the ifdefs? I have doubts.

I think your idea of saving some cache lines by not having the unused
zones in the fallback lists etc. is a good one, but your current implementation
with its ifdef maze is extremly ugly. Surely this can be a done less
intrusively?

-Andi