netdev - Re: [PATCH net-next] net: tcp: support to probe tcp receiver OOM

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Message-ID: <CANn89iKHfAWj_e6aqWiNQJfe2LOeaX3-Grx3w0LpxoKH9i86Cg@mail.gmail.com>
Date: Mon, 26 Jun 2023 15:26:57 +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, corbet@....net, dsahern@...nel.org, kuniyu@...zon.com, 
	morleyd@...gle.com, imagedong@...cent.com, mfreemon@...udflare.com, 
	mubashirq@...gle.com, netdev@...r.kernel.org, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] net: tcp: support to probe tcp receiver OOM

On Mon, Jun 26, 2023 at 12:01 PM <menglong8.dong@...il.com> wrote:
>
> From: Menglong Dong <imagedong@...cent.com>
>
> For now, skb will be dropped directly if rmem schedule fails, which means
> tcp_try_rmem_schedule() returns an error. This can happen on following
> cases:
>
> 1. The total memory allocated for TCP protocol is up to tcp_mem[2], and
>    the receive queue of the tcp socket is not empty.
> 2. The receive buffer of the tcp socket is full, which can happen on small
>    packet cases.
>
> If the user hangs and doesn't take away the packet in the receive queue
> with recv() or read() for a long time, the sender will keep
> retransmitting until timeout, and the tcp connection will break.
>
> In order to handle such case, we introduce the tcp protocol OOM detection
> in following steps, as Neal Cardwell suggested:

net-next is closed.

I think I suggested something much simpler, and not intrusive like your patch.
(Your patch adds code in the fast path, and yet another sysctl)

If we can not queue an incoming packet because we are under memory stress,
simply send an ACK with WIN 0