netdev - Re: [PATCH net-next 2/2] tcp: improve REUSEADDR/NOREUSEADDR cohabitation

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Date:	Thu, 21 May 2015 17:37:36 -0300
From:	Flavio Leitner <fbl@...hat.com>
To:	Eric Dumazet <edumazet@...gle.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Marcelo Ricardo Leitner <mleitner@...hat.com>
Subject: Re: [PATCH net-next 2/2] tcp: improve REUSEADDR/NOREUSEADDR
 cohabitation

On Wed, May 20, 2015 at 10:59:02AM -0700, Eric Dumazet wrote:
> inet_csk_get_port() randomization effort tends to spread
> sockets on all the available range (ip_local_port_range)
> 
> This is unfortunate because SO_REUSEADDR sockets have
> less requirements than non SO_REUSEADDR ones.
> 
> If an application uses SO_REUSEADDR hint, it is to try to
> allow source ports being shared.
> 
> So instead of picking a random port number in ip_local_port_range,
> lets try first in first half of the range.
> 
> This gives more chances to use upper half of the range for the
> sockets with strong requirements (not using SO_REUSEADDR)
> 
> Note this patch does not add a new sysctl, and only changes
> the way we try to pick port number.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Marcelo Ricardo Leitner <mleitner@...hat.com>
> Cc: Flavio Leitner <fbl@...hat.com>
> ---

The only downside I can see is that after the patch the applications
using the SO_REUSEADDR will reuse ports more often and that could
potentially trigger some bug.

Looks like a good change to me.

Acked-by: Flavio Leitner <fbl@...hat.com>

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