linux-kernel - Re: [PATCH 05/12] Memory compaction core

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Message-ID: <20100216145943.GA997@csn.ul.ie>
Date:	Tue, 16 Feb 2010 14:59:44 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Adam Litke <agl@...ibm.com>, Avi Kivity <avi@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 05/12] Memory compaction core

On Tue, Feb 16, 2010 at 08:55:46AM -0600, Christoph Lameter wrote:
> On Tue, 16 Feb 2010, Mel Gorman wrote:
> 
> > Because how do I tell in advance that the data I am migrating from DMA can
> > be safely relocated to the NORMAL zone? We don't save GFP flags. Granted,
> > for DMA, that will not matter as pages that must be in DMA will also not by
> > migratable. However, buffer pages should not get relocated to HIGHMEM for
> > example which is more likely to happen. It could be special cased but
> > I'm not aware of ZONE_DMA-related pressure problems that would make this
> > worthwhile and if so, it should be handled as a separate patch series.
> 
> Oh there are numerous ZONE_DMA pressure issues if you have ancient /
> screwed up hardware that can only operate on DMA or DMA32 memory.
> 

I've never ran into the issue. I was under the impression that the only
device that might care these days are floopy disks.

> Moving page cache pages out of the DMA zone would be good. A
> write request will cause the page to bounce back to the DMA zone if the
> device requires the page there.
> 
> But I also think that the patchset should be as simple as possible so that
> it can be merged soon.
> 

Agreed.

> > Ah, it was 2009 when I last kicked this around heavily :) I'll update
> > it.
> 
> But it was authored in 2009. May be important if patent or other
> copyright claims arise. 2009-2010?
> 

2007-2010 in that case because 2007 was when I first prototyped this.

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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