netdev - Re: [PATCH net] net: increase SOMAXCONN to 4096

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Message-Id: <20191031.140213.1989291310066375753.davem@davemloft.net>
Date:   Thu, 31 Oct 2019 14:02:13 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com,
        ncardwell@...gle.com, ycheng@...gle.com, w@....eu, ycao009@....edu
Subject: Re: [PATCH net] net: increase SOMAXCONN to 4096

From: Eric Dumazet <edumazet@...gle.com>
Date: Wed, 30 Oct 2019 09:36:20 -0700

> SOMAXCONN is /proc/sys/net/core/somaxconn default value.
> 
> It has been defined as 128 more than 20 years ago.
> 
> Since it caps the listen() backlog values, the very small value has
> caused numerous problems over the years, and many people had
> to raise it on their hosts after beeing hit by problems.
> 
> Google has been using 1024 for at least 15 years, and we increased
> this to 4096 after TCP listener rework has been completed, more than
> 4 years ago. We got no complain of this change breaking any
> legacy application.
> 
> Many applications indeed setup a TCP listener with listen(fd, -1);
> meaning they let the system select the backlog.
> 
> Raising SOMAXCONN lowers chance of the port being unavailable under
> even small SYNFLOOD attack, and reduces possibilities of side channel
> vulnerabilities.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied.