On Tue, Jan 12, 2021 at 10:01:35AM +0200, Avi Kivity wrote: > On 1/12/21 3:07 AM, Dave Chinner wrote: > > Hi folks, > > > > This is the XFS implementation on the sub-block DIO optimisations > > for written extents that I've mentioned on #xfs and a couple of > > times now on the XFS mailing list. > > > > It takes the approach of using the IOMAP_NOWAIT non-blocking > > IO submission infrastructure to optimistically dispatch sub-block > > DIO without exclusive locking. If the extent mapping callback > > decides that it can't do the unaligned IO without extent > > manipulation, sub-block zeroing, blocking or splitting the IO into > > multiple parts, it aborts the IO with -EAGAIN. This allows the high > > level filesystem code to then take exclusive locks and resubmit the > > IO once it has guaranteed no other IO is in progress on the inode > > (the current implementation). > > > Can you expand on the no-splitting requirement? Does it involve only > splitting by XFS (IO spans >1 extents) or lower layers (RAID)? XFS only. > The reason I'm concerned is that it's the constraint that the application > has least control over. I guess I could use RWF_NOWAIT to avoid blocking my > main thread (but last time I tried I'd get occasional EIOs that frightened > me off that). Spurious EIO from RWF_NOWAIT is a bug that needs to be fixed. DO you have any details? Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx
