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

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Message-ID: <alpine.DEB.2.00.1002160849460.18275@router.home>
Date:	Tue, 16 Feb 2010 08:55:46 -0600 (CST)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Mel Gorman <mel@....ul.ie>
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, 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.

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.

> 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?

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