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Date: Tue, 4 Jul 2006 08:10:54 -0700 (PDT)
From: Christoph Lameter <clameter@sgi.com>
To: Christoph Hellwig <hch@infradead.org>
cc: linux-kernel@vger.kernel.org, akpm@osdl.org,
       Hugh Dickins <hugh@veritas.com>, Con Kolivas <kernel@kolivas.org>,
       Marcelo Tosatti <marcelo@kvack.org>,
       Nick Piggin <nickpiggin@yahoo.com.au>, Andi Kleen <ak@suse.de>
Subject: Re: [RFC 0/8] Reduce MAX_NR_ZONES and remove useless zones.
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On Tue, 4 Jul 2006, Christoph Hellwig wrote:

> On Mon, Jul 03, 2006 at 04:26:57PM -0700, Christoph Lameter wrote:
> > > Which btw is utterly wrong.  It should have a 4GB ZONE_DMA32 and everything
> > > else in ZONE_NORMAL.
> > 
> > So we want to change the definition of ZONE_DMA to refer to the first 16MB 
> > only? ZONE_DMA32 is always a 4GB border?
> 
> The definition of ZONE_DMA32 is to be te 32bit border.  I think we should
> implement it wherever possible but at least on all architectures that
> maybe have non-iommu implementations.  ZONE_DMA should be an arch-specific
> low memory zone.

I guess then we should drop ZONE_DMA (its a misnoner anyways since it 
seems to indicate that DMA is only possible in this zone). Instead use

ZONE_ISA_DMA		-> ISA DMA Area (16 MB boundary)
ZONE_32BIT_DMA		-> 32bit DMA area (well 900 MB on x86_64 but somewhere in that area)
			only used for 64 bit platforms with 32 bit devices.
<and maybe define new ones in the future?>

Some arches seem to make ZONE_DMA their default zone instead of 
ZONE_NORMAL if DMA is possible to all of memory. I think in that case we 
should have no ZONE_DMA at all.