Messages in this thread | | | Date | Thu, 18 Nov 2010 09:41:22 -0800 (PST) | From | Hugh Dickins <> | Subject | Re: [PATCH 3/3] mlock: avoid dirtying pages and triggering writeback |
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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.
Hugh
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