Hi, On 2021-01-07 09:52:01 +1100, Dave Chinner wrote: > On Tue, Dec 29, 2020 at 10:28:19PM -0800, Andres Freund wrote: > > Which brings me to $subject: > > > > Would it make sense to add a variant of FALLOC_FL_ZERO_RANGE that > > doesn't convert extents into unwritten extents, but instead uses > > blkdev_issue_zeroout() if supported? Mostly interested in xfs/ext4 > > myself, but ... > > We have explicit requests from users (think initialising large VM > images) that FALLOC_FL_ZERO_RANGE must never fall back to writing > zeroes manually. That behaviour makes a lot of sense for quite a few use cases - I wasn't trying to make it sound like it should not be available. Nor that FALLOC_FL_ZERO_RANGE should behave differently. > IOWs, while you might want FALLOC_FL_ZERO_RANGE to explicitly write > zeros, we have users who explicitly don't want it to do this. Right - which is why I was asking for a variant of FALLOC_FL_ZERO_RANGE (jokingly named FALLOC_FL_ZERO_RANGE_BUT_REALLY in the subject), rather than changing the behaviour. > Perhaps we should add want FALLOC_FL_CONVERT_RANGE, which tells the > filesystem to convert an unwritten range of zeros to a written range > by manually writing zeros. i.e. you do FALLOC_FL_ZERO_RANGE to zero > the range and fill holes using metadata manipulation, followed by > FALLOC_FL_WRITE_RANGE to then convert the "metadata zeros" to real > written zeros. Yep, something like that would do the trick. Perhaps FALLOC_FL_MATERIALIZE_RANGE? Greetings, Andres Freund
