On Tue, 25 Feb 2014, Lukáš Czerner wrote: > Date: Tue, 25 Feb 2014 22:01:06 +0100 (CET) > From: Lukáš Czerner <lczerner@xxxxxxxxxx> > To: Dave Chinner <david@xxxxxxxxxxxxx> > Cc: linux-ext4@xxxxxxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx > Subject: Re: [PATCH 6/6] ext4/242: Add ext4 specific test for fallocate zero > range > > On Wed, 26 Feb 2014, Dave Chinner wrote: > > > Date: Wed, 26 Feb 2014 07:53:49 +1100 > > From: Dave Chinner <david@xxxxxxxxxxxxx> > > To: Lukas Czerner <lczerner@xxxxxxxxxx> > > Cc: linux-ext4@xxxxxxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx > > Subject: Re: [PATCH 6/6] ext4/242: Add ext4 specific test for fallocate zero > > range > > > > On Tue, Feb 25, 2014 at 08:15:28PM +0100, Lukas Czerner wrote: > > > This is copy of xfs/242. However it's better to make it file system > > > specific because the range can be zeroes either directly by writing > > > zeroes, or converting to unwritten extent, so the actual result might > > > differ from file system to file system. > > > > You could say the same thing about preallocation using unwritten > > extents. Yet, funnily enough, we have generic tests for them because > > all filesystems currently use unwritten extents for preallocation > > and behave identically.... > > > > This test is no different - all filesystems currently use unwritten > > extents, and so this test should be generic because all existing > > filesystems *should* behave the same. > > > > When we get a filesystem that zeros rather uses unwritten extents, > > we can add a new *generic* test that tests for zeroed data extents > > rather than unwritten extents. All that we will need is a method of > > checking what behaviour the filesystem has and adding that to a > > _requires directive to ensure the correct generic fallocate tests > > are run... > > Currently xfs/242 fails on xfs for me and it does behave differently > than ext4. Also I had to change to 242.out a bit because ext4 was > a little different. It seems to me that it was expected that when > the extent is small enough it would be overwritten by zeroes rather > than converted to unwritten, but I have not looked into > implementation. > > Btw this kind of optimization is actually something I've been > thinking of as well for ext4. Rather than going though the hassle of > changing extents around it might be worth in some situation to zero > out. But that's an optimization I have not implemented yet. Oops, I am taking it back. It's just too late and apparently I've overlooked something. -Lukas > > -Lukas > > > > > > Cheers, > > > > Dave. > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html >
