On Fri, Jun 19, 2020 at 09:56:33PM -0400, J. Bruce Fields wrote: > On Sat, Jun 20, 2020 at 11:49:57AM +1000, Dave Chinner wrote: > > On Fri, Jun 19, 2020 at 06:28:43PM -0400, J. Bruce Fields wrote: > > > On Sat, Jun 20, 2020 at 08:10:44AM +1000, Dave Chinner wrote: > > > > On Fri, Jun 19, 2020 at 04:40:33PM -0400, J. Bruce Fields wrote: > > > > > On Fri, Jun 19, 2020 at 12:44:55PM +1000, Dave Chinner wrote: > > > > > > On Thu, Jun 18, 2020 at 10:20:05PM -0400, J. Bruce Fields wrote: > > > > > > > My memory was that after Jeff Layton's i_version patches, there wasn't > > > > > > > really a significant performance hit any more, so the ability to turn it > > > > > > > off is no longer useful. > > > > > > > > > > > > Yes, I completely agree with you here. However, with some > > > > > > filesystems allowing it to be turned off, we can't just wave our > > > > > > hands and force enable the option. Those filesystems - if the > > > > > > maintainers chose to always enable iversion - will have to go > > > > > > through a mount option deprecation period before permanently > > > > > > enabling it. > > > > > > > > > > I don't understand why. > > > > > > > > > > The filesystem can continue to let people set iversion or noiversion as > > > > > they like, while under the covers behaving as if iversion is always set. > > > > > I can't see how that would break any application. (Or even how an > > > > > application would be able to detect that the filesystem was doing this.) > > > > > > > > It doesn't break functionality, but it affects performance. > > > > > > I thought you just agreed above that any performance hit was not > > > "significant". > > > > Yes, but that's just /my opinion/. > > > > However, other people have different opinions on this matter (and we > > know that from the people who considered XFS v4 -> v5 going slower > > because iversion a major regression), and so we must acknowledge > > those opinions even if we don't agree with them. > > Do you have any of those reports handy? Were there numbers? e.g. RH BZ #1355813 when v5 format was enabled by default in RHEL7. Numbers were 40-47% performance degradation for in-cache writes caused by the original IVERSION implementation using iozone. There were others I recall, all realted to similar high-IOP small random writes workloads typical of databases.... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx
