netdev - Re: [PATCH net-next v4 0/4] net: tcp: support probing OOM

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Date: Fri, 11 Aug 2023 09:39:15 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: menglong8.dong@...il.com
Cc: ncardwell@...gle.com, davem@...emloft.net, kuba@...nel.org, 
	pabeni@...hat.com, dsahern@...nel.org, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, flyingpeng@...cent.com, 
	Menglong Dong <imagedong@...cent.com>
Subject: Re: [PATCH net-next v4 0/4] net: tcp: support probing OOM

On Fri, Aug 11, 2023 at 5:01 AM <menglong8.dong@...il.com> wrote:
>
> From: Menglong Dong <imagedong@...cent.com>
>
> In this series, we make some small changes to make the tcp retransmission
> become zero-window probes if the receiver drops the skb because of memory
> pressure.
>
> In the 1st patch, we reply a zero-window ACK if the skb is dropped
> because out of memory, instead of dropping the skb silently.
>
> In the 2nd patch, we allow a zero-window ACK to update the window.
>
> In the 3rd patch, fix unexcepted socket die when snd_wnd is 0 in
> tcp_retransmit_timer().
>
> In the 4th patch, we refactor the debug message in tcp_retransmit_timer()
> to make it more correct.
>
> After these changes, the tcp can probe the OOM of the receiver forever.
>
> Changes since v3:
> - make the timeout "2 * TCP_RTO_MAX" in the 3rd patch
> - tp->retrans_stamp is not based on jiffies and can't be compared with
>   icsk->icsk_timeout in the 3rd patch. Fix it.
> - introduce the 4th patch
>
> Changes since v2:
> - refactor the code to avoid code duplication in the 1st patch
> - use after() instead of max() in tcp_rtx_probe0_timed_out()
>
> Changes since v1:
> - send 0 rwin ACK for the receive queue empty case when necessary in the
>   1st patch
> - send the ACK immediately by using the ICSK_ACK_NOW flag in the 1st
>   patch
> - consider the case of the connection restart from idle, as Neal comment,
>   in the 3rd patch

SGTM, thanks.

Reviewed-by: Eric Dumazet <edumazet@...gle.com>