SUNRPC: Change TCP socket space reservation

The current server rpc tcp code attempts to predict how much writeable
socket space will be available to a given RPC call before accepting it
for processing.  On a 40GigE network, we've found this throttles
individual clients long before the network or disk is saturated.  The
server may handle more clients easily, but the bandwidth of individual
clients is still artificially limited.

Instead of trying (and failing) to predict how much writeable socket space
will be available to the RPC call, just fall back to the simple model of
deferring processing until the socket is uncongested.

This may increase the risk of fast clients starving slower clients; in
such cases, the previous patch allows setting a hard per-connection
limit.
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

net/sunrpc/svcsock.c

@@ -432,42 +432,10 @@ static void svc_write_space(struct sock *sk)
 static int svc_tcp_has_wspace(struct svc_xprt *xprt)
 {
 	struct svc_sock *svsk = container_of(xprt, struct svc_sock, sk_xprt);
-	struct svc_serv *serv = svsk->sk_xprt.xpt_server;
-	int required;
 
 	if (test_bit(XPT_LISTENER, &xprt->xpt_flags))
 		return 1;
-	required = atomic_read(&xprt->xpt_reserved) + serv->sv_max_mesg;
-	if (sk_stream_wspace(svsk->sk_sk) >= required ||
-	    (sk_stream_min_wspace(svsk->sk_sk) == 0 &&
-	     atomic_read(&xprt->xpt_reserved) == 0))
-		return 1;
-	set_bit(SOCK_NOSPACE, &svsk->sk_sock->flags);
-	return 0;
-}
-
-static void svc_tcp_write_space(struct sock *sk)
-{
-	struct svc_sock *svsk = (struct svc_sock *)(sk->sk_user_data);
-	struct socket *sock = sk->sk_socket;
-
-	if (!svsk)
-		return;
-
-	if (!sk_stream_is_writeable(sk) || !sock)
-		return;
-	if (svc_tcp_has_wspace(&svsk->sk_xprt)) {
-		clear_bit(SOCK_NOSPACE, &sock->flags);
-		svc_write_space(sk);
-	}
-}
-
-static void svc_tcp_adjust_wspace(struct svc_xprt *xprt)
-{
-	struct svc_sock *svsk = container_of(xprt, struct svc_sock, sk_xprt);
-
-	if (svc_tcp_has_wspace(xprt))
-		clear_bit(SOCK_NOSPACE, &svsk->sk_sock->flags);
+	return !test_bit(SOCK_NOSPACE, &svsk->sk_sock->flags);
 }
 
 /*
@@ -1272,7 +1240,6 @@ static struct svc_xprt_ops svc_tcp_ops = {
 	.xpo_has_wspace = svc_tcp_has_wspace,
 	.xpo_accept = svc_tcp_accept,
 	.xpo_secure_port = svc_sock_secure_port,
-	.xpo_adjust_wspace = svc_tcp_adjust_wspace,
 };
 
 static struct svc_xprt_class svc_tcp_class = {
@@ -1313,7 +1280,7 @@ static void svc_tcp_init(struct svc_sock *svsk, struct svc_serv *serv)
 		dprintk("setting up TCP socket for reading\n");
 		sk->sk_state_change = svc_tcp_state_change;
 		sk->sk_data_ready = svc_data_ready;
-		sk->sk_write_space = svc_tcp_write_space;
+		sk->sk_write_space = svc_write_space;
 
 		svsk->sk_reclen = 0;
 		svsk->sk_tcplen = 0;
@@ -1383,14 +1350,8 @@ static struct svc_sock *svc_setup_socket(struct svc_serv *serv,
 	/* Initialize the socket */
 	if (sock->type == SOCK_DGRAM)
 		svc_udp_init(svsk, serv);
-	else {
-		/* initialise setting must have enough space to
-		 * receive and respond to one request.
-		 */
-		svc_sock_setbufsize(svsk->sk_sock, 4 * serv->sv_max_mesg,
-					4 * serv->sv_max_mesg);
+	else
 		svc_tcp_init(svsk, serv);
-	}
 
 	dprintk("svc: svc_setup_socket created %p (inet %p)\n",
 				svsk, svsk->sk_sk);