netdev - Re: Re: [EXT] Re: tcp: socket stuck with zero receive window after SACK

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Message-ID: <CADVnQy=x9D7ad8LGpBTj0CUeEXCpqLiiGsbdoy8se_epUckdzA@mail.gmail.com>
Date: Mon, 9 Jun 2025 13:47:18 -0400
From: Neal Cardwell <ncardwell@...gle.com>
To: Simon Campion <simon.campion@...pl.com>
Cc: netdev@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>, 
	Yuchung Cheng <ycheng@...gle.com>, Kevin Yang <yyd@...gle.com>, Jon Maloy <jmaloy@...hat.com>
Subject: Re: Re: [EXT] Re: tcp: socket stuck with zero receive window after SACK

On Tue, Jun 3, 2025 at 3:27 AM Simon Campion <simon.campion@...pl.com> wrote:
>
> > I agree it will take a while to gather more confidence that the issue
> > is gone for your workload with net.ipv4.tcp_shrink_window=0.
>
> To confirm, it's been over a week since we set
> net.ipv4.tcp_shrink_window=0, and so far we haven't seen an issue with
> TCP connections being stuck with a zero window and an empty recv-q.
> So, it looks like the problem is either entirely gone or occurs much
> less frequently with net.ipv4.tcp_shrink_window=0.
>
> We also attempted to reproduce the issue with a program that sends
> data over a TCP connection but leaves out the first N bytes.
> Unfortunately, we haven't been able to reproduce the issue so far,
> even with net.ipv4.tcp_shrink_window=1 and with a system under memory
> pressure.

Thanks for the detailed update! Those are very useful data points.

best regards,
neal