From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [PATCH v2 nf-next] netfilter: conntrack: remove the central
 spinlock
Date: Wed, 22 May 2013 14:34:49 -0700
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Cc: Pablo Neira Ayuso <pablo@netfilter.org>,
	netfilter-devel@vger.kernel.org, netdev <netdev@vger.kernel.org>,
	Tom Herbert <therbert@google.com>,
	Patrick McHardy <kaber@trash.net>
To: Joe Perches <joe@perches.com>
Return-path: <netfilter-devel-owner@vger.kernel.org>
In-Reply-To: <1369257171.2143.120.camel@joe-AO722>
Sender: netfilter-devel-owner@vger.kernel.org
List-Id: netdev.vger.kernel.org

On Wed, 2013-05-22 at 14:12 -0700, Joe Perches wrote:
> On Wed, 2013-05-22 at 13:48 -0700, Eric Dumazet wrote:
> > On Wed, 2013-05-22 at 13:38 -0700, Joe Perches wrote:
> > 
> > > u16 for cpu is hardly used at all.
> > 
> > Its used in network tree.
> > 
> > The day it has to change, don't worry, I think we'll be able to handle
> > it.
> > 
> > For the meantime, I do not want to add 4 more bytes to conntrack
> > structure, its already bloated enough.
> 
> I wrote "nice" already, no worries.
> 
> btw: netdevice.h could possibly convert xmit_lock_owner
> to u16 as well for that same 4 byte savings if the -1
> test was converted too.
> ---
>  include/linux/netdevice.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 60584b1..c38cd29 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -528,7 +528,7 @@ struct netdev_queue {
>   * write mostly part
>   */
>  	spinlock_t		_xmit_lock ____cacheline_aligned_in_smp;
> -	int			xmit_lock_owner;
> +	u16			xmit_lock_owner;
>  	/*

Typical machines have less than 10 structures like this one, there is no
gain trying to save some bytes, and more gain trying to get correct
alignments ;)

While conntracking can easily consume more than 10.000.000 conntracks on
a machine.