On Mon, Jul 14, 2025 at 08:28:22AM -0400, Jeff Layton wrote: > On Mon, 2025-07-14 at 14:23 +1000, NeilBrown wrote: > > On Mon, 14 Jul 2025, Mike Snitzer wrote: > > > From: Mike Snitzer <snitzer@xxxxxxxxxxxxxxx> > > > > > > This knob influences the LOCALIO handshake so that it happens > > > synchronously upon NFS client creation.. which reduces the window of > > > opportunity for a bunch of IO to flood page cache and send out over to > > > NFSD before LOCALIO handshake negotiates that the client and server > > > are local. The knob is: > > > echo N > /sys/module/nfs/parameters/localio_async_probe > > > > I understand why you are adding this but .... yuck. Tuning knobs are > > best avoided. > > > > Maybe we could still do the probe async, but in mount wait for 200ms, > > or for the probe to get a reply. That should make everyone happy. > > > > NeilBrown > > > > Agreed. I'd prefer to not need a tuning knob for this. Doing a short > wait in the mount for localio negotiation would be a lot more > reasonable. OK. > That said, why is the LOCALIO negotiation taking so long? Shouldn't > that be basically instantaneous during the mount? Do we really have > applications that are hammering reads and writes just after the mount > returns but before the localio negotiation completes? Yes, buffered IO in particular brings the hammer via a storm of page cache IO that takes a while to be complete before LOCALIO ever gets an opportunity to service NFS client IO. Mike
