netdev - Re: [PATCH net-next 1/2] tcp: do not set a zero size receive buffer

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Message-ID: <20250721083000.5f545b8a@kernel.org>
Date: Mon, 21 Jul 2025 08:30:00 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Paolo Abeni <pabeni@...hat.com>
Cc: Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org, Neal
 Cardwell <ncardwell@...gle.com>, Kuniyuki Iwashima <kuniyu@...gle.com>,
 "David S. Miller" <davem@...emloft.net>, David Ahern <dsahern@...nel.org>,
 Simon Horman <horms@...nel.org>, Matthieu Baerts <matttbe@...nel.org>
Subject: Re: [PATCH net-next 1/2] tcp: do not set a zero size receive buffer

On Mon, 21 Jul 2025 08:27:28 -0700 Jakub Kicinski wrote:
> > With just the 0 rmem check in tcp_prune_queue(), such function will
> > still invoke tcp_clamp_window() that will shrink the receive buffer to
> > 110592.
> > tcp_collapse() can't make enough room and the incoming packet will be
> > dropped. I think we should instead accept such packet.
> > 
> > Side note: the above data are taken from an actual reproduction of the issue
> > 
> > Please LMK if the above clarifies a bit my doubt or if a full pktdrill
> > is needed.  
> 
> Not the first time we stumble on packetdrills for scaling ratio.
> Solving it is probably outside the scope of this discussion but 
> I wonder what would be the best way to do it. My go to is to
> integrate packetdrill with netdevsim and have an option for netdevsim
> to inflate truesize on demand. But perhaps there's a clever way we can
> force something like tap to give us the ratio we desire. Other ideas?

FWIW didn't see Eric's reply before hitting send..