| Message ID | 20201023184709.217614-1-arjunroy.kdev@gmail.com |
|---|---|
| State | New |
| Headers | show |
| Series | [net,v2] tcp: Prevent low rmem stalls with SO_RCVLOWAT. | expand |
On Fri, 23 Oct 2020 11:47:09 -0700 Arjun Roy wrote: > From: Arjun Roy <arjunroy@google.com> > > With SO_RCVLOWAT, under memory pressure, > it is possible to enter a state where: > > 1. We have not received enough bytes to satisfy SO_RCVLOWAT. > 2. We have not entered buffer pressure (see tcp_rmem_pressure()). > 3. But, we do not have enough buffer space to accept more packets. > > In this case, we advertise 0 rwnd (due to #3) but the application does > not drain the receive queue (no wakeup because of #1 and #2) so the > flow stalls. > > Modify the heuristic for SO_RCVLOWAT so that, if we are advertising > rwnd<=rcv_mss, force a wakeup to prevent a stall. > > Without this patch, setting tcp_rmem to 6143 and disabling TCP > autotune causes a stalled flow. With this patch, no stall occurs. This > is with RPC-style traffic with large messages. > > Fixes: 03f45c883c6f ("tcp: avoid extra wakeups for SO_RCVLOWAT users") > Signed-off-by: Arjun Roy <arjunroy@google.com> > Acked-by: Soheil Hassas Yeganeh <soheil@google.com> > Acked-by: Neal Cardwell <ncardwell@google.com> > Signed-off-by: Eric Dumazet <edumazet@google.com> Applied, thank you!
Hello: This patch was applied to netdev/net.git (refs/heads/master): On Fri, 23 Oct 2020 11:47:09 -0700 you wrote: > From: Arjun Roy <arjunroy@google.com> > > With SO_RCVLOWAT, under memory pressure, > it is possible to enter a state where: > > 1. We have not received enough bytes to satisfy SO_RCVLOWAT. > 2. We have not entered buffer pressure (see tcp_rmem_pressure()). > 3. But, we do not have enough buffer space to accept more packets. > > [...] Here is the summary with links: - [net,v2] tcp: Prevent low rmem stalls with SO_RCVLOWAT. https://git.kernel.org/netdev/net/c/435ccfa894e3 You are awesome, thank you! -- Deet-doot-dot, I am a bot. https://korg.docs.kernel.org/patchwork/pwbot.html
On Fri, Oct 23, 2020 at 7:13 PM Jakub Kicinski <kuba@kernel.org> wrote: > > On Fri, 23 Oct 2020 11:47:09 -0700 Arjun Roy wrote: > > From: Arjun Roy <arjunroy@google.com> > > > > With SO_RCVLOWAT, under memory pressure, > > it is possible to enter a state where: > > > > 1. We have not received enough bytes to satisfy SO_RCVLOWAT. > > 2. We have not entered buffer pressure (see tcp_rmem_pressure()). > > 3. But, we do not have enough buffer space to accept more packets. > > > > In this case, we advertise 0 rwnd (due to #3) but the application does > > not drain the receive queue (no wakeup because of #1 and #2) so the > > flow stalls. > > > > Modify the heuristic for SO_RCVLOWAT so that, if we are advertising > > rwnd<=rcv_mss, force a wakeup to prevent a stall. > > > > Without this patch, setting tcp_rmem to 6143 and disabling TCP > > autotune causes a stalled flow. With this patch, no stall occurs. This > > is with RPC-style traffic with large messages. > > > > Fixes: 03f45c883c6f ("tcp: avoid extra wakeups for SO_RCVLOWAT users") > > Signed-off-by: Arjun Roy <arjunroy@google.com> > > Acked-by: Soheil Hassas Yeganeh <soheil@google.com> > > Acked-by: Neal Cardwell <ncardwell@google.com> > > Signed-off-by: Eric Dumazet <edumazet@google.com> > > Applied, thank you! Ack, thanks for the quick review! -Arjun
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index bae4284bf542..b2bc3d7fe9e8 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -485,6 +485,8 @@ static inline bool tcp_stream_is_readable(const struct tcp_sock *tp, return true; if (tcp_rmem_pressure(sk)) return true; + if (tcp_receive_window(tp) <= inet_csk(sk)->icsk_ack.rcv_mss) + return true; } if (sk->sk_prot->stream_memory_read) return sk->sk_prot->stream_memory_read(sk); diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index fc445833b5e5..389d1b340248 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -4908,7 +4908,8 @@ void tcp_data_ready(struct sock *sk) int avail = tp->rcv_nxt - tp->copied_seq; if (avail < sk->sk_rcvlowat && !tcp_rmem_pressure(sk) && - !sock_flag(sk, SOCK_DONE)) + !sock_flag(sk, SOCK_DONE) && + tcp_receive_window(tp) > inet_csk(sk)->icsk_ack.rcv_mss) return; sk->sk_data_ready(sk);