netdev - Re: [PATCH net-next v3] tcp: enable mid stream window clamp

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Message-ID: <CANn89iL+nob7ipXSmbyv0PrWfvq6hRtQJnTG=L6cvbdAx-C+4w@mail.gmail.com>
Date:   Thu, 26 Aug 2021 12:32:15 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Yuchung Cheng <ycheng@...gle.com>
Cc:     Neil Spring <ntspring@...com>, David Miller <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        Neal Cardwell <ncardwell@...gle.com>
Subject: Re: [PATCH net-next v3] tcp: enable mid stream window clamp

On Thu, Aug 26, 2021 at 12:11 PM Yuchung Cheng <ycheng@...gle.com> wrote:
>
> On Wed, Aug 25, 2021 at 2:02 PM Neil Spring <ntspring@...com> wrote:
> >
> > The TCP_WINDOW_CLAMP socket option is defined in tcp(7) to "Bound the size
> > of the advertised window to this value."  Window clamping is distributed
> > across two variables, window_clamp ("Maximal window to advertise" in
> > tcp.h) and rcv_ssthresh ("Current window clamp").
> >
> > This patch updates the function where the window clamp is set to also
> > reduce the current window clamp, rcv_sshthresh, if needed.  With this,
> > setting the TCP_WINDOW_CLAMP option has the documented effect of limiting
> > the window.
> This patch looks like a bug-fix so it should be applied to net not net-next?

It seems TCP_WINDOW_CLAMP never worked in this context, not sure
if any application was expecting it to work.

Note that if we target net tree, we would like a Fixes: tag.

I will give my SOB a bit later in the day, I have to run some errands.

Thanks.