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". > IOWs, it can make certain workloads go a lot slower in some > circumstances. And that can result in unexectedly breaking SLAs or > slow down a complex, finely tuned data center wide workload to the > point it no longer meets requirements. Such changes in behaviour are > considered a regression, especially if they result from a change that > just ignores the mount option that turned off that specific feature. I get that, but, what's the threshhold here for a significant risk of regression? The "noiversion" behavior is kinda painful for NFS. --b.
