tcp: simplify tcp_current_mss

There's very little need for most of the callsites to get
tp->xmit_goal_size updated. That will cost us divide as is,
so slice the function in two. Also, the only users of the
tp->xmit_goal_size are directly behind tcp_current_mss(),
so there's no need to store that variable into tcp_sock
at all! The drop of xmit_goal_size currently leaves 16-bit
hole and some reorganization would again be necessary to
change that (but I'm aiming to fill that hole with u16
xmit_goal_size_segs to cache the results of the remaining
divide to get that tso on regression).

Bring xmit_goal_size parts into tcp.c
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Cc: Evgeniy Polyakov <zbr@ioremap.net>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/tcp.h

@@ -248,7 +248,6 @@ struct tcp_sock {
 	/* inet_connection_sock has to be the first member of tcp_sock */
 	struct inet_connection_sock	inet_conn;
 	u16	tcp_header_len;	/* Bytes of tcp header to send		*/
-	u16	xmit_size_goal;	/* Goal for segmenting output packets	*/
 
 /*
  *	Header prediction flags

include/net/tcp.h

@@ -481,7 +481,16 @@ static inline void tcp_clear_xmit_timers(struct sock *sk)
 }
 
 extern unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu);
-extern unsigned int tcp_current_mss(struct sock *sk, int large);
+extern unsigned int tcp_current_mss(struct sock *sk);
+
+/* Bound MSS / TSO packet size with the half of the window */
+static inline int tcp_bound_to_half_wnd(struct tcp_sock *tp, int pktsize)
+{
+	if (tp->max_window && pktsize > (tp->max_window >> 1))
+		return max(tp->max_window >> 1, 68U - tp->tcp_header_len);
+	else
+		return pktsize;
+}
 
 /* tcp.c */
 extern void tcp_get_info(struct sock *, struct tcp_info *);
@@ -822,7 +831,7 @@ static inline void tcp_push_pending_frames(struct sock *sk)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 
-	__tcp_push_pending_frames(sk, tcp_current_mss(sk, 1), tp->nonagle);
+	__tcp_push_pending_frames(sk, tcp_current_mss(sk), tp->nonagle);
 }
 
 static inline void tcp_init_wl(struct tcp_sock *tp, u32 seq)

net/ipv4/tcp.c

@@ -661,6 +661,37 @@ struct sk_buff *sk_stream_alloc_skb(struct sock *sk, int size, gfp_t gfp)
 	return NULL;
 }
 
+static unsigned int tcp_xmit_size_goal(struct sock *sk, u32 mss_now,
+				       int large_allowed)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	u32 xmit_size_goal;
+
+	xmit_size_goal = mss_now;
+
+	if (large_allowed && sk_can_gso(sk)) {
+		xmit_size_goal = ((sk->sk_gso_max_size - 1) -
+				  inet_csk(sk)->icsk_af_ops->net_header_len -
+				  inet_csk(sk)->icsk_ext_hdr_len -
+				  tp->tcp_header_len);
+
+		xmit_size_goal = tcp_bound_to_half_wnd(tp, xmit_size_goal);
+		xmit_size_goal -= (xmit_size_goal % mss_now);
+	}
+
+	return xmit_size_goal;
+}
+
+static int tcp_send_mss(struct sock *sk, int *size_goal, int flags)
+{
+	int mss_now;
+
+	mss_now = tcp_current_mss(sk);
+	*size_goal = tcp_xmit_size_goal(sk, mss_now, !(flags & MSG_OOB));
+
+	return mss_now;
+}
+
 static ssize_t do_tcp_sendpages(struct sock *sk, struct page **pages, int poffset,
 			 size_t psize, int flags)
 {
@@ -677,8 +708,7 @@ static ssize_t do_tcp_sendpages(struct sock *sk, struct page **pages, int poffse
 
 	clear_bit(SOCK_ASYNC_NOSPACE, &sk->sk_socket->flags);
 
-	mss_now = tcp_current_mss(sk, !(flags&MSG_OOB));
-	size_goal = tp->xmit_size_goal;
+	mss_now = tcp_send_mss(sk, &size_goal, flags);
 	copied = 0;
 
 	err = -EPIPE;
@@ -761,8 +791,7 @@ static ssize_t do_tcp_sendpages(struct sock *sk, struct page **pages, int poffse
 		if ((err = sk_stream_wait_memory(sk, &timeo)) != 0)
 			goto do_error;
 
-		mss_now = tcp_current_mss(sk, !(flags&MSG_OOB));
-		size_goal = tp->xmit_size_goal;
+		mss_now = tcp_send_mss(sk, &size_goal, flags);
 	}
 
 out:
@@ -844,8 +873,7 @@ int tcp_sendmsg(struct kiocb *iocb, struct socket *sock, struct msghdr *msg,
 	/* This should be in poll */
 	clear_bit(SOCK_ASYNC_NOSPACE, &sk->sk_socket->flags);
 
-	mss_now = tcp_current_mss(sk, !(flags&MSG_OOB));
-	size_goal = tp->xmit_size_goal;
+	mss_now = tcp_send_mss(sk, &size_goal, flags);
 
 	/* Ok commence sending. */
 	iovlen = msg->msg_iovlen;
@@ -1007,8 +1035,7 @@ int tcp_sendmsg(struct kiocb *iocb, struct socket *sock, struct msghdr *msg,
 			if ((err = sk_stream_wait_memory(sk, &timeo)) != 0)
 				goto do_error;
 
-			mss_now = tcp_current_mss(sk, !(flags&MSG_OOB));
-			size_goal = tp->xmit_size_goal;
+			mss_now = tcp_send_mss(sk, &size_goal, flags);
 		}
 	}
 

net/ipv4/tcp_input.c

@@ -2864,7 +2864,7 @@ void tcp_simple_retransmit(struct sock *sk)
 	const struct inet_connection_sock *icsk = inet_csk(sk);
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct sk_buff *skb;
-	unsigned int mss = tcp_current_mss(sk, 0);
+	unsigned int mss = tcp_current_mss(sk);
 	u32 prior_lost = tp->lost_out;
 
 	tcp_for_write_queue(skb, sk) {

net/ipv4/tcp_output.c

@@ -921,7 +921,7 @@ int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
 	 * factor and mss.
 	 */
 	if (tcp_skb_pcount(skb) > 1)
-		tcp_set_skb_tso_segs(sk, skb, tcp_current_mss(sk, 1));
+		tcp_set_skb_tso_segs(sk, skb, tcp_current_mss(sk));
 
 	return 0;
 }
@@ -982,15 +982,6 @@ void tcp_mtup_init(struct sock *sk)
 	icsk->icsk_mtup.probe_size = 0;
 }
 
-/* Bound MSS / TSO packet size with the half of the window */
-static int tcp_bound_to_half_wnd(struct tcp_sock *tp, int pktsize)
-{
-	if (tp->max_window && pktsize > (tp->max_window >> 1))
-		return max(tp->max_window >> 1, 68U - tp->tcp_header_len);
-	else
-		return pktsize;
-}
-
 /* This function synchronize snd mss to current pmtu/exthdr set.
 
    tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
@@ -1037,22 +1028,17 @@ unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
 /* Compute the current effective MSS, taking SACKs and IP options,
  * and even PMTU discovery events into account.
  */
-unsigned int tcp_current_mss(struct sock *sk, int large_allowed)
+unsigned int tcp_current_mss(struct sock *sk)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct dst_entry *dst = __sk_dst_get(sk);
 	u32 mss_now;
-	u16 xmit_size_goal;
-	int doing_tso = 0;
 	unsigned header_len;
 	struct tcp_out_options opts;
 	struct tcp_md5sig_key *md5;
 
 	mss_now = tp->mss_cache;
 
-	if (large_allowed && sk_can_gso(sk))
-		doing_tso = 1;
-
 	if (dst) {
 		u32 mtu = dst_mtu(dst);
 		if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
@@ -1070,19 +1056,6 @@ unsigned int tcp_current_mss(struct sock *sk, int large_allowed)
 		mss_now -= delta;
 	}
 
-	xmit_size_goal = mss_now;
-
-	if (doing_tso) {
-		xmit_size_goal = ((sk->sk_gso_max_size - 1) -
-				  inet_csk(sk)->icsk_af_ops->net_header_len -
-				  inet_csk(sk)->icsk_ext_hdr_len -
-				  tp->tcp_header_len);
-
-		xmit_size_goal = tcp_bound_to_half_wnd(tp, xmit_size_goal);
-		xmit_size_goal -= (xmit_size_goal % mss_now);
-	}
-	tp->xmit_size_goal = xmit_size_goal;
-
 	return mss_now;
 }
 
@@ -1264,7 +1237,7 @@ int tcp_may_send_now(struct sock *sk)
 	struct sk_buff *skb = tcp_send_head(sk);
 
 	return (skb &&
-		tcp_snd_test(sk, skb, tcp_current_mss(sk, 1),
+		tcp_snd_test(sk, skb, tcp_current_mss(sk),
 			     (tcp_skb_is_last(sk, skb) ?
 			      tp->nonagle : TCP_NAGLE_PUSH)));
 }
@@ -1421,7 +1394,7 @@ static int tcp_mtu_probe(struct sock *sk)
 		return -1;
 
 	/* Very simple search strategy: just double the MSS. */
-	mss_now = tcp_current_mss(sk, 0);
+	mss_now = tcp_current_mss(sk);
 	probe_size = 2 * tp->mss_cache;
 	size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
 	if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high)) {
@@ -1903,7 +1876,7 @@ int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
 	if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
 		return -EHOSTUNREACH; /* Routing failure or similar. */
 
-	cur_mss = tcp_current_mss(sk, 0);
+	cur_mss = tcp_current_mss(sk);
 
 	/* If receiver has shrunk his window, and skb is out of
 	 * new window, do not retransmit it. The exception is the
@@ -2111,7 +2084,7 @@ void tcp_send_fin(struct sock *sk)
 	 * unsent frames.  But be careful about outgoing SACKS
 	 * and IP options.
 	 */
-	mss_now = tcp_current_mss(sk, 1);
+	mss_now = tcp_current_mss(sk);
 
 	if (tcp_send_head(sk) != NULL) {
 		TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_FIN;
@@ -2523,7 +2496,7 @@ int tcp_write_wakeup(struct sock *sk)
 	if ((skb = tcp_send_head(sk)) != NULL &&
 	    before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) {
 		int err;
-		unsigned int mss = tcp_current_mss(sk, 0);
+		unsigned int mss = tcp_current_mss(sk);
 		unsigned int seg_size = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
 
 		if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq))