This patchset is an update to a patchset that I posted just over a year ago [1]. That version had client and server patches. This one is just the server-side patches. NFSv4.1 adds a GET_DIR_DELEGATION operation, to allow clients to request a delegation on a directory. If the client holds a directory delegation, then it knows that nothing will change the dentries in it until it has been recalled. In 2023, Rick Macklem gave a talk at the NFS Bakeathon on his implementation of directory delegations for FreeBSD [2], and showed that it can greatly improve LOOKUP-heavy workloads. There is also some earlier work by CITI [3] that showed similar results. The SMB protocol also has a similar sort of construct, and they have also seen large performance improvements on certain workloads. This version also starts with support for trivial directory delegations.
