linux-kernel - Re: [PATCH v4 net-next 3/3] ipv4/udp: Add 4-tuple hash for connected socket

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Message-ID: <9c636d54-4276-4e28-abd3-0860bc738640@redhat.com>
Date: Mon, 14 Oct 2024 12:19:46 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Philo Lu <lulie@...ux.alibaba.com>, netdev@...r.kernel.org
Cc: willemdebruijn.kernel@...il.com, davem@...emloft.net,
 edumazet@...gle.com, kuba@...nel.org, dsahern@...nel.org,
 antony.antony@...unet.com, steffen.klassert@...unet.com,
 linux-kernel@...r.kernel.org, dust.li@...ux.alibaba.com,
 jakub@...udflare.com, fred.cc@...baba-inc.com,
 yubing.qiuyubing@...baba-inc.com
Subject: Re: [PATCH v4 net-next 3/3] ipv4/udp: Add 4-tuple hash for connected
 socket

On 10/12/24 03:29, Philo Lu wrote:
> Currently, the udp_table has two hash table, the port hash and portaddr
> hash. Usually for UDP servers, all sockets have the same local port and
> addr, so they are all on the same hash slot within a reuseport group.
> 
> In some applications, UDP servers use connect() to manage clients. In
> particular, when firstly receiving from an unseen 4 tuple, a new socket
> is created and connect()ed to the remote addr:port, and then the fd is
> used exclusively by the client.

How do you handle the following somewhat racing scenario? a 2nd packet 
beloning to the same 4-tulpe lands into the unconnected socket receive 
queue just after the 1st one, before the connected socket is created. 
The server process such packet after the connected socket creation.

How many connected sockets is your system serving concurrently? Possibly 
it would make sense to allocate a larger hash table for the connected 
UDP sockets, using separate/different min/max/scale values WRT to the 
unconnected tables.

Cheers,

Paolo