> > > > > > > Remove logic to create child bio in the async flush function which > > > > causes child bio to get executed after parent bio 'pmem_make_request' > > > > completes. This resulted in wrong ordering of REQ_PREFLUSH with the > > > > data write request. > > > > > > > > Instead we are performing flush from the parent bio to maintain the > > > > correct order. Also, returning from function 'pmem_make_request' if > > > > REQ_PREFLUSH returns an error. > > > > > > > > Reported-by: Jeff Moyer <jmoyer@xxxxxxxxxx> > > > > Signed-off-by: Pankaj Gupta <pagupta@xxxxxxxxxx> > > > > > > There's a slight change in behavior for the error path in the > > > virtio_pmem driver. Previously, all errors from virtio_pmem_flush were > > > converted to -EIO. Now, they are reported as-is. I think this is > > > actually an improvement. > > > > > > I'll also note that the current behavior can result in data corruption, > > > so this should be tagged for stable. > > > > I added that and was about to push this out, but what about the fact > > that now the guest will synchronously wait for flushing to occur. The > > goal of the child bio was to allow that to be an I/O wait with > > overlapping I/O, or at least not blocking the submission thread. Does > > the block layer synchronously wait for PREFLUSH requests? If not I > > think a synchronous wait is going to be a significant performance > > regression. Are there any numbers to accompany this change? > > Why not just swap the parent child relationship in the PREFLUSH case? I we are already inside parent bio "make_request" function and we create child bio. How we exactly will swap the parent/child relationship for PREFLUSH case? Child bio is queued after parent bio completes. Thanks, Pankaj > >
