> Am 30.07.2016 um 15:20 schrieb Nguyễn Thái Ngọc Duy <pclouds@xxxxxxxxx>: > > Let's start with the commit message of [1] from freebsd.git [2] > > Sync timestamp changes for inodes of special files to disk as late > as possible (when the inode is reclaimed). Temporarily only do > this if option UFS_LAZYMOD configured and softupdates aren't > enabled. UFS_LAZYMOD is intentionally left out of > /sys/conf/options. > > This is mainly to avoid almost useless disk i/o on battery powered > machines. It's silly to write to disk (on the next sync or when > the inode becomes inactive) just because someone hit a key or > something wrote to the screen or /dev/null. > > PR: 5577 [3] > > The short version of that, in the context of t7063, is that when a > directory is updated, its mtime may be updated later, not > immediately. This can be shown with a simple command sequence > > date; sleep 1; touch abc; rm abc; sleep 10; ls -lTd . > > One would expect that the date shown in `ls` would be one second from > `date`, but it's 10 seconds later. If we put another `ls -lTd .` in > front of `sleep 10`, then the date of the last `ls` comes as > expected. The first `ls` somehow forces mtime to be updated. > > t7063 is really sensitive to directory mtime. When mtime is too "new", > git code suspects racy timestamps and will not trigger the shortcut in > untracked cache, in t7063.26 (or t7063.25 before this patch) and > eventually be detected in t7063.28 > > We have two options thanks to this special FreeBSD feature: > > 1) Stop supporting untracked cache on FreeBSD. Skip t7063 entirely > when running on FreeBSD > > 2) Work around this problem (using the same 'ls' trick) and continue > to support untracked cache on FreeBSD > > I initially wanted to go with 1) because I didn't know the exact > nature of this feature and feared that it would make untracked cache > work unreliably, using the cached version when it should not. > > Since the behavior of this thing is clearer now. The picture is not > that bad. If this indeed happens often, untracked cache would assume > racy condition more often and _fall back_ to non-untracked cache code > paths. Which means it may be less effective, but it will not show > wrong things. > > This patch goes with option 2. > > PS. For those who want to look further in FreeBSD source code, this > flag is now called IN_LAZYMOD. I can see it's effective in ext2 and > ufs. zfs is questionable. > > [1] 660e6408e6df99a20dacb070c5e7f9739efdf96d > [2] git://github.com/freebsd/freebsd.git > [3] https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=5577 > > Reported-by: Eric Wong <e@xxxxxxxxx> > Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@xxxxxxxxx> > --- > This is only of those commits that commit messages are more important > than the patch itself. One of the good notes about directory mtime, > if we start to use it in more places in git. > > t/t7063-status-untracked-cache.sh | 4 ++++ > t/test-lib.sh | 6 ++++++ > 2 files changed, 10 insertions(+) > > diff --git a/t/t7063-status-untracked-cache.sh b/t/t7063-status-untracked-cache.sh > index a971884..08fc586 100755 > --- a/t/t7063-status-untracked-cache.sh > +++ b/t/t7063-status-untracked-cache.sh > @@ -419,6 +419,10 @@ test_expect_success 'create/modify files, some of which are gitignored' ' > rm base > ' > > +test_expect_success FREEBSD 'Work around lazy mtime update' ' > + ls -ld . >/dev/null > +' > + the term FREEBSD may be too generic to point out a single feature in an OS distributution. Following your investigations, it may even be possible that other systems adapt this "feature"? How about LAZY_DIR_MTIME_UPDATE (or similar) -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html