SUNRPC: Add a server side per-connection limit

Allow the user to limit the number of requests serviced through a single
connection, to help prevent faster clients from starving slower clients.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

Documentation/kernel-parameters.txt

@@ -3832,6 +3832,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			using these two parameters to set the minimum and
 			maximum port values.
 
+	sunrpc.svc_rpc_per_connection_limit=
+			[NFS,SUNRPC]
+			Limit the number of requests that the server will
+			process in parallel from a single connection.
+			The default value is 0 (no limit).
+
 	sunrpc.pool_mode=
 			[NFS]
 			Control how the NFS server code allocates CPUs to