netdev - Re: PROBLEM: Linux kernel 2.6.31 IPv4 TCP fails to open huge amount of outgoing connections (unable to bind ... )

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Message-ID: <20100421001448.GA31724@ioremap.net>
Date:	Wed, 21 Apr 2010 04:14:48 +0400
From:	Evgeniy Polyakov <zbr@...emap.net>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Gaspar Chilingarov <gasparch@...il.com>,
	netdev <netdev@...r.kernel.org>
Subject: Re: PROBLEM: Linux kernel 2.6.31 IPv4 TCP fails to open huge amount of outgoing connections (unable to bind ... )

Hi.

On Wed, Apr 21, 2010 at 01:42:25AM +0200, Eric Dumazet (eric.dumazet@...il.com) wrote:
> If you want to check source, its in file net/ipv4/inet_connection_sock.c
> 
> function inet_csk_get_port()
> 
> you can remove the 
> 
> if (atomic_read(&hashinfo->bsockets) > (high - low) + 1) { 
> 	spin_unlock(&head->lock); 
> 	snum = smallest_rover; 
> 	goto have_snum;
> }
> 
> It will solve your problem (but bind() will probably be slow)

Netcat uses SO_REUSEADDR, so its the code path which generates an error,
but this part actually returns a port number not en error. I suppose
what happend is 'attempts' check faired and thus system failed to find
a small enough bucket which does not conflict. To test this we can
remove 'smallest_size = tb->num_owners;' assignment, but bind() can be
damn slow in this case indeed.

-- 
	Evgeniy Polyakov
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