linux-kernel - Re: [PATCH 3/3] mlock: avoid dirtying pages and triggering writeback

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Date:	Thu, 18 Nov 2010 08:37:02 -0500
From:	Christoph Hellwig <hch@...radead.org>
To:	Dave Chinner <david@...morbit.com>
Cc:	Michel Lespinasse <walken@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Nick Piggin <npiggin@...nel.dk>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Kosaki Motohiro <kosaki.motohiro@...fujitsu.com>,
	Theodore Tso <tytso@...gle.com>,
	Michael Rubin <mrubin@...gle.com>,
	Suleiman Souhlal <suleiman@...gle.com>
Subject: Re: [PATCH 3/3] mlock: avoid dirtying pages and triggering writeback

On Thu, Nov 18, 2010 at 10:11:43AM +1100, Dave Chinner wrote:
> Hence I think that avoiding ->page_mkwrite callouts is likely to
> break some filesystems in subtle, undetected ways.  IMO, regardless
> of what is done, it would be really good to start by writing a new
> regression test to exercise and encode the expected the mlock
> behaviour so we can detect regressions later on....

I think it would help if we could drink a bit of the test driven design
coolaid here. Michel, can you write some testcases where pages on a
shared mapping are mlocked, then dirtied and then munlocked, and then
written out using msync/fsync.  Anything that fails this test on
btrfs/ext4/gfs/xfs/etc obviously doesn't work.

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