netdev - Re: [PATCH 4/5 (resend)] net: Make ifindex generation per-net namespace (v2)

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Date:	Tue, 07 Aug 2012 15:13:12 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Pavel Emelyanov <xemul@...allels.com>
Cc:	David Miller <davem@...emloft.net>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: [PATCH 4/5 (resend)] net: Make ifindex generation per-net
 namespace (v2)

On Tue, 2012-08-07 at 16:37 +0400, Pavel Emelyanov wrote:
> >> @@ -62,6 +62,7 @@ struct net {
> >>  	struct sock 		*rtnl;			/* rtnetlink socket */
> >>  	struct sock		*genl_sock;
> >>  
> >> +	int			ifindex;
> > 
> > could you place ifindex right after dev_base_seq : avoid two holes
> > and use the same cache line, dirtied in
> > list_netdevice()/unlist_netdevice()
> 
> Sure! Here it is:
> 
> From: Pavel Emelyanov <xemul@...allels.com>
> Subject: [PATCH 4/5] net: Make ifindex generation per-net namespace
> 
> Strictly speaking this is only _really_ required for checkpoint-restore to
> make loopback device always have the same index.
> 
> This change appears to be safe wrt "ifindex should be unique per-system"
> concept, as all the ifindex usage is either already made per net namespace
> of is explicitly limited with init_net only.
> 
> There are two cool side effects of this. The first one -- ifindices of
> devices in container are always small, regardless of how many containers
> we've started (and re-started) so far. The second one is -- we can speed
> up the loopback ifidex access as shown in the next patch.
> 
> v2: Place ifindex right after dev_base_seq : avoid two holes and use the
>     same cache line, dirtied in list_netdevice()/unlist_netdevice()
> 
> Signed-off-by: Pavel Emelyanov <xemul@...allels.com>
> ---
Acked-by: Eric Dumazet <edumazet@...gle.com>


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