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

[Christoph Hellwig]

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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