On Wed, Jun 12, 2019 at 08:23:20PM -0700, Matthew Wilcox wrote: > On Thu, Jun 13, 2019 at 10:25:55AM +1000, Dave Chinner wrote: > > On Wed, Jun 12, 2019 at 05:37:53AM -0700, Matthew Wilcox wrote: > > > That's rather different from the normal meaning of 'exclusive' in the > > > context of locks, which is "only one user can have access to this at > > > a time". > > > > Layout leases are not locks, they are a user access policy object. > > It is the process/fd which holds the lease and it's the process/fd > > that is granted exclusive access. This is exactly the same semantic > > as O_EXCL provides for granting exclusive access to a block device > > via open(), yes? > > This isn't my understanding of how RDMA wants this to work, so we should > probably clear that up before we get too far down deciding what name to > give it. > > For the RDMA usage case, it is entirely possible that both process A > and process B which don't know about each other want to perform RDMA to > file F. So there will be two layout leases active on this file at the > same time. It's fine for IOs to simultaneously be active to both leases. > But if the filesystem wants to move blocks around, it has to break > both leases. > > If Process C tries to do a write to file F without a lease, there's no > problem, unless a side-effect of the write would be to change the block > mapping, in which case either the leases must break first, or the write > must be denied. > > Jason, please correct me if I've misunderstood the RDMA needs here. Yes, I think you've captured it Based on Dave's remarks how frequently a filesystem needs to break the lease will determine if it is usuable to be combined with RDMA or not... Jason
