NFS directory delegations allow for an efficiency win by knowing if nobody else modified the directory on the NFS server then there are some re-validation shortcuts than can be subsequently taken by the NFS client. This work was pursued by Oracle to allow for better NFS efficiency when knowing a particular directory hasn't changed from underneath the client. For Linux 6.19 the directory delegation is hooked up for ACCESS, CREATE, UNLINK, and RENAME operations.
The directory_delegations module parameter is added to the NFS module for disabling the directory delegation feature if desired for debugging / testing / performance evaluation purposes.
Besides this basic directory delegation support, the NFS client merge brings code clean-ups to the SunRPC back channel code and various bug fixes throughout.
Merged last week meanwhile was the NFSD server changes for Linux 6.19 that add an option to disable I/O caching for that Linux 6.18 feature is now extended to include using direct I/O. The intent there is on further reducing the memory footprint consumed by NFS clients when accessing large data sets. Plus NFSD saw various minor optimizations and other code improvements.