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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>