Re: [PATCH net-next v2] net/smc: Reduce overflow of smc clcsock listen queue

From: "D. Wythe" <alibuda@linux.alibaba.com>
To: Karsten Graul <kgraul@linux.ibm.com>
Cc: dust.li@linux.alibaba.com, kuba@kernel.org, davem@davemloft.net,
	netdev@vger.kernel.org, linux-s390@vger.kernel.org,
	linux-rdma@vger.kernel.org
Subject: Re: [PATCH net-next v2] net/smc: Reduce overflow of smc clcsock listen queue
Date: Wed, 5 Jan 2022 23:06:12 +0800	[thread overview]
Message-ID: <20220105150612.GA75522@e02h04389.eu6sqa> (raw)
In-Reply-To: <b98aefce-e425-9501-aacc-8e5a4a12953e@linux.ibm.com>

LGTM. Fallback makes the restrictions on SMC dangling
connections more meaningful to me, compared to dropping them.

Overall, i see there are two scenario.

1. Drop the overflow connections limited by userspace application
accept.

2. Fallback the overflow connections limited by the heavy process of
current SMC handshake. ( We can also control its behavior through
sysctl.)

I'll follow those advise to improve my patch, more advise will be highly
appreciated.

Thanks all. 

On Wed, Jan 05, 2022 at 02:17:41PM +0100, Karsten Graul wrote:
> On 05/01/2022 09:57, dust.li wrote:
> > On Wed, Jan 05, 2022 at 12:40:49PM +0800, D. Wythe wrote:
> > I'm thinking maybe we can actively fall back to TCP in this case ? Not
> > sure if this is a good idea.
> 
> I think its a good decision to switch new connections to use the TCP fallback when the
> current queue of connections waiting for a SMC handshake is too large.
> With this the application is able to accept all incoming connections and they are not
> dropped. The only thing that is be different compared to TCP is that the order of the
> accepted connections is changed, connections that came in later might reach the user space 
> application earlier than connections that still run the SMC hand shake processing. 
> But I think that is semantically okay.