linux-kernel - Re: [PATCH 3/4] Embed zone_id information within the zonelist->zones pointer

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Message-ID: <Pine.LNX.4.64.0708131550100.30626@schroedinger.engr.sgi.com>
Date:	Mon, 13 Aug 2007 15:52:54 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Andi Kleen <ak@...e.de>
cc:	Mel Gorman <mel@...net.ie>, Lee.Schermerhorn@...com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 3/4] Embed zone_id information within the zonelist->zones
 pointer

On Tue, 14 Aug 2007, Andi Kleen wrote:

> > I am not sure what you mean by that. Ia64 ZONE_DMA == x86_84 ZONE_DMA32?
> 
> Hmm, when I wrote GFP_DMA32 it was a #define GFP_DMA32 GFP_DMA 
> on ia64 so that drivers not need to ifdef.  Someone nasty
> seems to have removed that too. I guess it would be best
> to readd.

What would be the point?

> But then it wouldn't make sense to have GFP_DMA on ia64 and GFP_DMA32
> on x86. Since driver writers are more likely to test on x86
> I would recommend ia64 having compatible semantics. It'll
> save everybody trouble long term. This means it wouldn't 
> help on IA64 machines that don't have a DMA zone -- they
> would still need to validate drivers especially -- but at least
> the others.

There are no compatible semantics. ZONE_DMA may mean something different 
for each arch depending on its need. An arch may not have a need for a 4GB 
boundary (such as s390).

> Also from my driver review driver authors often seem to have
> trouble understanding what GFP_DMA really does. With GFP_DMA32 it 
> is clearer that it applies to a address range and is not
> some synonym for pci_map_*

GFP_DMA32 is clear because there are no other arches to muddy up the 
waters.

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