NFSD With Linux 6.6 Brings A Thrilling New Feature

Chuck Lever III of Oracle has submitted the NFSD changes for Linux 6.6 for this NFS server of which he is particularly thrilled about one of the new features this cycle.

The headline feature of NFSD in Linux 6.6 is adding NFSv4 write delegation support. Chuck explained:

"I'm thrilled to announce that the Linux in-kernel NFS server now offers NFSv4 write delegations. A write delegation enables a client to cache data and metadata for a single file more aggressively, reducing network round trips and server workload. Many thanks to Dai Ngo for contributing this facility, and to Jeff Layton and Neil Brown for reviewing and testing it."

Oracle documentation on NFSv4 write delegation explains:

"NFS version 4 provides both client support and server support for delegation. Delegation is a technique by which the server delegates the management of a file to a client. For example, the server could grant either a read delegation or a write delegation to a client. Read delegations can be granted to multiple clients at the same time, because these read delegations do not conflict with each other. A write delegation can be granted to only one client, because a write delegation conflicts with any file access by any other client. While holding a write delegation, the client would not send various operations to the server because the client is guaranteed exclusive access to a file. Similarly, the client would not send various operations to the server while holding a read delegation. The reason is that the server guarantees that no client can open the file in write mode. The effect of delegation is to greatly reduce the interactions between the server and the client for delegated files. Therefore, network traffic is reduced, and performance on the client and the server is improved. Note, however, that the degree of performance improvement depends on the kind of file interaction used by an application and the amount of network and server congestion."

Other NFSD work for Linux 6.6 includes dropping the DES and triple-DES-based Kerberos encryption types in the kernel's SunRPC implementation, improvements to the NFS server UDP and TCP socket transports, and beginning to overhaul the SunRPC thread scheduler.

More details on the NFSD changes for Linux 6.6 via this pull request.