NFSv4.x: Add kernel parameter to control the callback server

Add support for the kernel parameter nfs.callback_nr_threads to set
the number of threads that will be assigned to the callback channel.

Add support for the kernel parameter nfs.nfs.max_session_cb_slots
to set the maximum size of the callback channel slot table.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

Documentation/kernel-parameters.txt

@@ -2420,6 +2420,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 	nfsrootdebug	[NFS] enable nfsroot debugging messages.
 			See Documentation/filesystems/nfs/nfsroot.txt.
 
+	nfs.callback_nr_threads=
+			[NFSv4] set the total number of threads that the
+			NFS client will assign to service NFSv4 callback
+			requests.
+
 	nfs.callback_tcpport=
 			[NFS] set the TCP port on which the NFSv4 callback
 			channel should listen.
@@ -2443,6 +2448,13 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			of returning the full 64-bit number.
 			The default is to return 64-bit inode numbers.
 
+	nfs.max_session_cb_slots=
+			[NFSv4.1] Sets the maximum number of session
+			slots the client will assign to the callback
+			channel. This determines the maximum number of
+			callbacks the client will process in parallel for
+			a particular server.
+
 	nfs.max_session_slots=
 			[NFSv4.1] Sets the maximum number of session slots
 			the client will attempt to negotiate with the server.