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

To: Andi Kleen <ak@suse.de>
Subject: Re: [PATCH 3/4] Embed zone_id information within the zonelist->zones pointer
From: Andy Isaacson <adi@hexapodia.org>
Date: Tue, 14 Aug 2007 12:43:56 -0700
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>, Christoph Lameter <clameter@sgi.com>, Mel Gorman <mel@skynet.ie>, Lee.Schermerhorn@hp.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-mips@linux-mips.org
In-reply-to: <20070814202350.GT3406@bingen.suse.de>
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References: <Pine.LNX.4.64.0708131506030.28502@schroedinger.engr.sgi.com> <20070813230801.GH3406@bingen.suse.de> <Pine.LNX.4.64.0708131536340.29946@schroedinger.engr.sgi.com> <20070813234322.GJ3406@bingen.suse.de> <Pine.LNX.4.64.0708131553050.30626@schroedinger.engr.sgi.com> <20070814000041.GL3406@bingen.suse.de> <20070814002223.2d8d42c5@the-village.bc.nu> <20070814001441.GN3406@bingen.suse.de> <20070814191158.GB14093@hexapodia.org> <20070814202350.GT3406@bingen.suse.de>
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On Tue, Aug 14, 2007 at 10:23:51PM +0200, Andi Kleen wrote:
> > bcm43xx hardware does show up on low-end MIPS boxes (wrt54g anybody?)
> > that would be sorely hurt by excess copies.
> 
> Lowend boxes don't have more than 1GB of RAM. With <= 1GB you don't
> need to copy on bcm43xx.

OK, that makes sense and is reassuring, but note that some MIPS boxes
have only part of their physical memory below 1GB; IIRC the
BCM4704/BCM5836 supports up to 512MB of physical memory, with 256MB in
the first GB and the second 256MB located above the 1GB line.  (But it's
been a while since I've run such a machine, so I could be misremembering
the sizes and offsets.)

Yeah, if you stick a PCI chip with a 30-bit PCI DMA mask into a machine
with memory above 1GB, then copying has to happen.  Unless the memory
allocator can avoid returning memory in the un-dma-able region...

-andy

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