On Mon, Aug 7, 2023 at 3:47 PM <[email protected]> wrote:
>
> From: Menglong Dong <[email protected]>
>
> 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 <[email protected]>
> ---
> v2:
> - send 0 rwin ACK for the receive queue empty case when necessary
> - send the ACK immediately by using the ICSK_ACK_NOW flag
> ---
> include/net/inet_connection_sock.h | 3 ++-
> net/ipv4/tcp_input.c | 14 +++++++++++---
> net/ipv4/tcp_output.c | 14 +++++++++++---
> 3 files changed, 24 insertions(+), 7 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 8e96ebe373d7..aae485d0a3b6 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -5059,12 +5059,20 @@ static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
>
> /* Ok. In sequence. In window. */
> queue_and_out:
> - 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)) {
> + if (skb_queue_len(&sk->sk_receive_queue) == 0) {
> + if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) {
> + sk_forced_mem_schedule(sk, skb->truesize);
I think we want sk->sk_data_ready() here, to let applications drain the queue,
regardless of sk->sk_rcvlowat value.
> + inet_csk(sk)->icsk_ack.pending |=
> + (ICSK_ACK_NOMEM | ICSK_ACK_NOW);
> + inet_csk_schedule_ack(sk);
> + }
> + } else if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) {
> reason = SKB_DROP_REASON_PROTO_MEM;
> NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);
> sk->sk_data_ready(sk);
We also want to keep this sk->sk_data_ready(sk) call.
> + inet_csk(sk)->icsk_ack.pending |=
> + (ICSK_ACK_NOMEM | ICSK_ACK_NOW);
> + inet_csk_schedule_ack(sk);
> goto drop;
> }
This would suggest a different code refactoring, to avoid code duplication.
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 57c8af1859c16eba5e952a23ea959b628006f9c1..dde6c44f2c1e33dcf60c23b49cd99f270874ca96
100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5050,13 +5050,17 @@ static void tcp_data_queue(struct sock *sk,
struct sk_buff *skb)
/* Ok. In sequence. In window. */
queue_and_out:
- 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)) {
- reason = SKB_DROP_REASON_PROTO_MEM;
- NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);
+ if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) {
+ /* TODO: maybe ratelimit these WIN 0 ACK ? */
+ inet_csk(sk)->icsk_ack.pending |=
CSK_ACK_NOMEM | ICSK_ACK_NOW;
+ inet_csk_schedule_ack(sk);
sk->sk_data_ready(sk);
- goto drop;
+ if (skb_queue_len(&sk->sk_receive_queue)) {
+ reason = SKB_DROP_REASON_PROTO_MEM;
+ NET_INC_STATS(sock_net(sk),
LINUX_MIB_TCPRCVQDROP);
+ goto drop;
+ }
+ sk_forced_mem_schedule(sk, skb->truesize);
}
eaten = tcp_queue_rcv(sk, skb, &fragstolen);
On Mon, Aug 7, 2023 at 10:05 PM Eric Dumazet <[email protected]> wrote:
>
> On Mon, Aug 7, 2023 at 3:47 PM <[email protected]> wrote:
> >
> > From: Menglong Dong <[email protected]>
> >
> > 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 <[email protected]>
> > ---
> > v2:
> > - send 0 rwin ACK for the receive queue empty case when necessary
> > - send the ACK immediately by using the ICSK_ACK_NOW flag
> > ---
> > include/net/inet_connection_sock.h | 3 ++-
> > net/ipv4/tcp_input.c | 14 +++++++++++---
> > net/ipv4/tcp_output.c | 14 +++++++++++---
> > 3 files changed, 24 insertions(+), 7 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 8e96ebe373d7..aae485d0a3b6 100644
> > --- a/net/ipv4/tcp_input.c
> > +++ b/net/ipv4/tcp_input.c
> > @@ -5059,12 +5059,20 @@ static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
> >
> > /* Ok. In sequence. In window. */
> > queue_and_out:
> > - 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)) {
> > + if (skb_queue_len(&sk->sk_receive_queue) == 0) {
> > + if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) {
> > + sk_forced_mem_schedule(sk, skb->truesize);
>
> I think we want sk->sk_data_ready() here, to let applications drain the queue,
> regardless of sk->sk_rcvlowat value.
>
>
> > + inet_csk(sk)->icsk_ack.pending |=
> > + (ICSK_ACK_NOMEM | ICSK_ACK_NOW);
> > + inet_csk_schedule_ack(sk);
> > + }
> > + } else if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) {
> > reason = SKB_DROP_REASON_PROTO_MEM;
> > NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);
> > sk->sk_data_ready(sk);
>
> We also want to keep this sk->sk_data_ready(sk) call.
>
> > + inet_csk(sk)->icsk_ack.pending |=
> > + (ICSK_ACK_NOMEM | ICSK_ACK_NOW);
> > + inet_csk_schedule_ack(sk);
> > goto drop;
> > }
>
> This would suggest a different code refactoring, to avoid code duplication.
>
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index 57c8af1859c16eba5e952a23ea959b628006f9c1..dde6c44f2c1e33dcf60c23b49cd99f270874ca96
> 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -5050,13 +5050,17 @@ static void tcp_data_queue(struct sock *sk,
> struct sk_buff *skb)
>
> /* Ok. In sequence. In window. */
> queue_and_out:
> - 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)) {
> - reason = SKB_DROP_REASON_PROTO_MEM;
> - NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);
> + if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) {
> + /* TODO: maybe ratelimit these WIN 0 ACK ? */
> + inet_csk(sk)->icsk_ack.pending |=
> CSK_ACK_NOMEM | ICSK_ACK_NOW;
> + inet_csk_schedule_ack(sk);
> sk->sk_data_ready(sk);
> - goto drop;
> + if (skb_queue_len(&sk->sk_receive_queue)) {
> + reason = SKB_DROP_REASON_PROTO_MEM;
> + NET_INC_STATS(sock_net(sk),
> LINUX_MIB_TCPRCVQDROP);
> + goto drop;
> + }
> + sk_forced_mem_schedule(sk, skb->truesize);
> }
>
> eaten = tcp_queue_rcv(sk, skb, &fragstolen);
Looks much better, thank you!