See Figure for details of how page reads are satisfied.
Heavy boxes are decision points.
Note that we cannot avoid all server traffic even when reading unchanged files. The stateless nature of the NFS protocol requires us to confirm with the server that the file has not changed since we last read it. However, when reading large files, the majority of the disk traffic is due to many read RPCs, all of which are eliminated. All cached file data exists only in disk-based structures. Each remote file from which a page is cached has a corresponding local cache file.