On Wed, Feb 06, 2019 at 10:50:00AM +0100, Jan Kara wrote: > MM/FS asks for lease to be revoked. The revoke handler agrees with the > other side on cancelling RDMA or whatever and drops the page pins. This takes a trip through userspace since the communication protocol is entirely managed in userspace. Most existing communication protocols don't have a 'cancel operation'. > Now I understand there can be HW / communication failures etc. in > which case the driver could either block waiting or make sure future > IO will fail and drop the pins. We can always rip things away from the userspace.. However.. > But under normal conditions there should be a way to revoke the > access. And if the HW/driver cannot support this, then don't let it > anywhere near DAX filesystem. I think the general observation is that people who want to do DAX & RDMA want it to actually work, without data corruption, random process kills or random communication failures. Really, few users would actually want to run in a system where revoke can be triggered. So.. how can the FS/MM side provide a guarantee to the user that revoke won't happen under a certain system design? Jason
