NFSD: Convert the filecache to use rhashtable

BugLink: https://bugs.launchpad.net/bugs/2065435

[ Upstream commit ce502f8 ]

Enable the filecache hash table to start small, then grow with the
workload. Smaller server deployments benefit because there should
be lower memory utilization. Larger server deployments should see
improved scaling with the number of open files.

Suggested-by: Jeff Layton <[email protected]>
Suggested-by: Dave Chinner <[email protected]>
Reviewed-by: Jeff Layton <[email protected]>
Signed-off-by: Chuck Lever <[email protected]>
Signed-off-by: Manuel Diewald <[email protected]>
Signed-off-by: Roxana Nicolescu <[email protected]>

Author: chucklever