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tcp: fix delayed acks behavior for SO_RCVLOWAT 

We should not delay acks if there are not enough bytes
in receive queue to satisfy SO_RCVLOWAT.

Since [E]POLLIN event is not going to be generated, there is little
hope for a delayed ack to be useful.

In fact, delaying ACK prevents sender from completing
the transfer.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2018-04-16 10:33:36 -07:00 committed by David S. Miller
parent d1361840f8
commit 796f82eafc
1 changed files with 5 additions and 2 deletions
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7
net/ipv4/tcp_input.c
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@ -5026,9 +5026,12 @@ static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
/* More than one full frame received... */ /* More than one full frame received... */
if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss && if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss &&
/* ... and right edge of window advances far enough. /* ... and right edge of window advances far enough.
* (tcp_recvmsg() will send ACK otherwise). Or... * (tcp_recvmsg() will send ACK otherwise).
* If application uses SO_RCVLOWAT, we want send ack now if
* we have not received enough bytes to satisfy the condition.
*/ */
__tcp_select_window(sk) >= tp->rcv_wnd) || (tp->rcv_nxt - tp->copied_seq < sk->sk_rcvlowat ||
__tcp_select_window(sk) >= tp->rcv_wnd)) ||
/* We ACK each frame or... */ /* We ACK each frame or... */
tcp_in_quickack_mode(sk) || tcp_in_quickack_mode(sk) ||
/* We have out of order data. */ /* We have out of order data. */