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Subject: Re: [PATCH 03/10] mm: Add support for a filesystem to control swap
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From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Christoph Hellwig <hch@infradead.org>
Cc: Mel Gorman <mgorman@suse.de>, Linux-MM <linux-mm@kvack.org>,
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        Neil Brown <neilb@suse.de>
Date: Mon, 12 Sep 2011 11:04:45 +0200
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On Fri, 2011-09-09 at 09:36 -0400, Christoph Hellwig wrote:
> The equivalent of ->direct_IO should be used for both reads and writes.

So the difference between DIO and swapIO is that swapIO needs the block
map pinned in memory.. So at the very least you'll need those
swap_{activate,deactivate} aops. The read/write-page thingies could
indeed be shared with DIO.