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    SubjectRe: [PATCH 3/3] mlock: avoid dirtying pages and triggering writeback
    On Thu, 18 Nov 2010, Christoph Hellwig wrote:
    > 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.

    Whilst it's hard to argue against a request for testing, Dave's worries
    just sprang from a misunderstanding of all the talk about "avoiding ->
    page_mkwrite". There's nothing strange or risky about Michel's patch,
    it does not avoid ->page_mkwrite when there is a write: it just stops
    pretending that there was a write when locking down the shared area.


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      Last update: 2010-11-18 18:43    [W:0.021 / U:37.540 seconds]
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