netdev - Re: [PATCH net-next 00/11] tcp: receive side improvements

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Message-ID: <CANn89iJp1N-1NBrqg4WsjYJgXNTHdgi8PQkezaFGCgFt-c0jDw@mail.gmail.com>
Date: Thu, 22 May 2025 07:11:31 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: Daniel Borkmann <daniel@...earbox.net>
Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Neal Cardwell <ncardwell@...gle.com>, 
	Simon Horman <horms@...nel.org>, Kuniyuki Iwashima <kuniyu@...zon.com>, Rick Jones <jonesrick@...gle.com>, 
	Wei Wang <weiwan@...gle.com>, netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH net-next 00/11] tcp: receive side improvements

On Thu, May 22, 2025 at 7:03 AM Daniel Borkmann <daniel@...earbox.net> wrote:
>
> Hi Eric,
>
> On 5/13/25 9:39 PM, Eric Dumazet wrote:
> > We have set tcp_rmem[2] to 15 MB for about 8 years at Google,
> > but had some issues for high speed flows on very small RTT.
>
> Are there plans to bump/modernize the rmem_default and rmem_max defaults,
> too? Looks like last time it was done back in commit eaa72dc4748 ("neigh:
> increase queue_len_bytes to match wmem_default"). Fwiw, we've experienced
> deployments where vxlan/geneve is being used for E/W to be affected to hit
> the distro default limits leading to UDP drops for TCP traffic. Would it
> make sense to move these e.g. to 4MB as well or do you have used another
> heuristic which worked well over the years?

Yes, I have a similar increase for send size, with tcp_notsent_lowat
set to avoid eating too much kernel memory for bulk senders.

Extract from Google server :

cat /proc/sys/net/ipv4/tcp_wmem
4096 262144 67108864
cat /proc/sys/net/ipv4/tcp_notsent_lowat
2097152