netdev - Re: [PATCH net-next 2/2] tcp: add net.ipv4.tcp_rtt

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAAVpQUBCCfzip0tgzu4Mc6MNiH6J-9aKk0dchC1Ox6NRarq_pw@mail.gmail.com>
Date: Mon, 17 Nov 2025 20:39:18 -0800
From: Kuniyuki Iwashima <kuniyu@...gle.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	Neal Cardwell <ncardwell@...gle.com>, netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH net-next 2/2] tcp: add net.ipv4.tcp_rtt_threshold sysctl

On Mon, Nov 17, 2025 at 5:28 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> This is a follow up of commit aa251c84636c ("tcp: fix too slow
> tcp_rcvbuf_grow() action") which brought again the issue that I tried
> to fix in commit 65c5287892e9 ("tcp: fix sk_rcvbuf overshoot")
>
> We also recently increased tcp_rmem[2] to 32 MB in commit 572be9bf9d0d
> ("tcp: increase tcp_rmem[2] to 32 MB")
>
> Idea of this patch is to not let tcp_rcvbuf_grow() grow sk->sk_rcvbuf
> too fast for small RTT flows. If sk->sk_rcvbuf is too big, this can
> force NIC driver to not recycle pages from the page pool, and also
> can cause cache evictions for DDIO enabled cpus/NIC, as receivers
> are usually slower than senders.
>
> Add net.ipv4.tcp_rtt_threshold sysctl, set by default to 1000 usec (1 ms)
> If RTT if smaller than the sysctl value, use the RTT/tcp_rtt_threshold
> ratio to control sk_rcvbuf inflation.
>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Reviewed-by: Kuniyuki Iwashima <kuniyu@...gle.com>