xprtrdma: Avoid calls to ro_unmap_safe()

Micro-optimization: Most of the time, calls to ro_unmap_safe are
expensive no-ops. Call only when there is work to do.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

net/sunrpc/xprtrdma/transport.c

@@ -621,6 +621,7 @@ xprt_rdma_free(struct rpc_task *task)
 
 	dprintk("RPC:       %s: called on 0x%p\n", __func__, req->rl_reply);
 
+	if (unlikely(!list_empty(&req->rl_registered)))
 		ia->ri_ops->ro_unmap_safe(r_xprt, req, !RPC_IS_ASYNC(task));
 	rpcrdma_unmap_sges(ia, req);
 	rpcrdma_buffer_put(req);
@@ -657,6 +658,7 @@ xprt_rdma_send_request(struct rpc_task *task)
 	int rc = 0;
 
 	/* On retransmit, remove any previously registered chunks */
+	if (unlikely(!list_empty(&req->rl_registered)))
 		r_xprt->rx_ia.ri_ops->ro_unmap_safe(r_xprt, req, false);
 
 	rc = rpcrdma_marshal_req(rqst);