Messages in this thread | | | From | Menglong Dong <> | Date | Fri, 28 Jul 2023 10:37:55 +0800 | Subject | Re: [PATCH net-next 1/3] net: tcp: send zero-window ACK when no memory |
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On Fri, Jul 28, 2023 at 3:17 AM Eric Dumazet <edumazet@google.com> wrote: > > On Thu, Jul 27, 2023 at 2:51 PM <menglong8.dong@gmail.com> wrote: > > > > From: Menglong Dong <imagedong@tencent.com> > > > > For now, skb will be dropped when no memory, which makes client keep > > retrans util timeout and it's not friendly to the users. > > > > In this patch, we reply an ACK with zero-window in this case to update > > the snd_wnd of the sender to 0. Therefore, the sender won't timeout the > > connection and will probe the zero-window with the retransmits. > > > > Signed-off-by: Menglong Dong <imagedong@tencent.com> > > --- > > include/net/inet_connection_sock.h | 3 ++- > > net/ipv4/tcp_input.c | 4 ++-- > > net/ipv4/tcp_output.c | 14 +++++++++++--- > > 3 files changed, 15 insertions(+), 6 deletions(-) > > > > diff --git a/include/net/inet_connection_sock.h b/include/net/inet_connection_sock.h > > index c2b15f7e5516..be3c858a2ebb 100644 > > --- a/include/net/inet_connection_sock.h > > +++ b/include/net/inet_connection_sock.h > > @@ -164,7 +164,8 @@ enum inet_csk_ack_state_t { > > ICSK_ACK_TIMER = 2, > > ICSK_ACK_PUSHED = 4, > > ICSK_ACK_PUSHED2 = 8, > > - ICSK_ACK_NOW = 16 /* Send the next ACK immediately (once) */ > > + ICSK_ACK_NOW = 16, /* Send the next ACK immediately (once) */ > > + ICSK_ACK_NOMEM = 32, > > }; > > > > void inet_csk_init_xmit_timers(struct sock *sk, > > diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c > > index 3cd92035e090..03111af6115d 100644 > > --- a/net/ipv4/tcp_input.c > > +++ b/net/ipv4/tcp_input.c > > @@ -5061,7 +5061,8 @@ static void tcp_data_queue(struct sock *sk, struct sk_buff *skb) > > reason = SKB_DROP_REASON_PROTO_MEM; > > NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP); > > sk->sk_data_ready(sk); > > - goto drop; > > + inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOMEM; > > Also set ICSK_ACK_NOW ? > > We also need to make sure to send an immediate ACK WIN 0 in the case we queued > the skb in an empty receive queue and we were under pressure. > > We do not want to have a delayed ACK sending a normal RWIN, > then wait for another packet that we will probably drop. > > Look at the code : > > if (skb_queue_len(&sk->sk_receive_queue) == 0) > sk_forced_mem_schedule(sk, skb->truesize); > else if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) { > > and refactor it to make sure to set ICSK_ACK_NOMEM even on the first packet > that bypassed the rmem_schedule(). >
Ok, that makes sense.
> > > > + goto out_of_window; > > Why forcing quickack mode ? Please leave the "goto drop;" >
Hmm...because I want to make it send an immediate ACK. Obviously, a ICSK_ACK_NOW flag should be the better choice here.
> > } > > > > eaten = tcp_queue_rcv(sk, skb, &fragstolen); > > @@ -5102,7 +5103,6 @@ static void tcp_data_queue(struct sock *sk, struct sk_buff *skb) > > out_of_window: > > tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS); > > inet_csk_schedule_ack(sk); > > -drop: > > tcp_drop_reason(sk, skb, reason); > > return; > > } > >
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