On Mon, Jan 16, 2017 at 5:50 PM, Darrick J. Wong <darrick.wong@xxxxxxxxxx> wrote: > On Mon, Jan 16, 2017 at 03:00:41PM -0500, Jeff Moyer wrote: >> "Darrick J. Wong" <darrick.wong@xxxxxxxxxx> writes: >> >> >> - Whenever you mount a filesystem with DAX, it spits out a message that says >> >> "DAX enabled. Warning: EXPERIMENTAL, use at your own risk". What criteria >> >> needs to be met for DAX to no longer be considered experimental? >> > >> > For XFS I'd like to get reflink working with it, for starters. >> >> What do you mean by this, exactly? When Dave outlined the requirements >> for PMEM_IMMUTABLE, it was very clear that metadata updates would not be >> possible. And would you really cosider this a barrier to marking dax >> fully supported? I wouldn't. > > For PMEM_IMMUTABLE files, yes, reflink cannot be supported. > > I'm talking about supporting reflink for DAX files that are /not/ > PMEM_IMMUTABLE, where user programs can mmap pmem directly but write > activity still must use fsync/msync to ensure that everything's on disk. > > I wouldn't consider it a barrier in general (since ext4 also prints > EXPERIMENTAL warnings for DAX), merely one for XFS. I don't even think > it's that big of a hurdle -- afaict XFS ought to be able to achieve this > by modifying iomap_begin to allocate new pmem blocks, memcpy the > contents, and update the memory mappings. I think. > >> > We probably need a bunch more verification work to show that file IO >> > doesn't adopt any bad quirks having turned on the per-inode DAX flag. >> >> Can you be more specific? We have ltp and xfstests. If you have some >> mkfs/mount options that you think should be tested, speak up. Beyond >> that, if it passes ./check -g auto and ltp, are we good? > > That's probably good -- I simply wanted to know if we'd at least gotten > to the point that someone had run both suites with and without DAX and > not seen any major regressions between the two. Yes, xfstests is part the dax development flow. The hard part has been maintaining a blacklist of tests that fail in both the DAX and non-DAX cases, or false negatives due to DAX disabling delayed allocation -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>