Re: [PATCH RFC mptcp-next] mptcp: support net.ipv4.tcp_rcvbuf_low_rtt

[Matthieu Baerts <matttbe@kernel.org>]

Hi Paolo,

On 27/11/2025 18:20, Paolo Abeni wrote:
> On 11/27/25 4:58 PM, Matthieu Baerts (NGI0) wrote:
>> This is a follow up of commit ecfea98b7d0d ("tcp: add
>> net.ipv4.tcp_rcvbuf_low_rtt"), but adapted to MPTCP.
>>
>> MPTCP has mptcp_rcvbuf_grow(), which is similar to tcp_rcvbuf_grow, but
>> adapted for the MPTCP-level socket.
>>
>> The idea here is similar to what has been done on TCP side: not let
>> mptcp_rcvbuf_grow() grow sk->sk_rcvbuf too fast for small RTT flows.
>> Quoting Eric: If sk->sk_rcvbuf is too big, this can force NIC driver to
>> not recycle pages from their page pool, and also can cause cache
>> evictions for DDIO enabled cpus/NIC, as receivers are usually slower
>> than senders.
>>
>> If RTT if smaller than the new net.ipv4.tcp_rcvbuf_low_rtt sysctl value,
>> use the RTT / tcp_rcvbuf_low_rtt ratio to control sk_rcvbuf inflation.
> 
> Instead of duplicating the TCP math, I suggest factoring it out in an
> helper and use it in both the TCP and MPTCP code.

Thank you for the review! Good idea!

I guess this patch can wait the next cycle, right? Or should I rush to
get this soon to stay in sync with TCP?

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.