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

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Message-ID: <20070814194356.GL21492@hexapodia.org>
Date:	Tue, 14 Aug 2007 12:43:56 -0700
From:	Andy Isaacson <adi@...apodia.org>
To:	Andi Kleen <ak@...e.de>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Christoph Lameter <clameter@....com>,
	Mel Gorman <mel@...net.ie>, Lee.Schermerhorn@...com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-mips@...ux-mips.org
Subject: Re: [PATCH 3/4] Embed zone_id information within the zonelist->zones pointer

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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