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

>> @@ -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@parallels.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@parallels.com>
---
 include/net/net_namespace.h |    1 +
 net/core/dev.c              |    4 ++--
 2 files changed, 3 insertions(+), 2 deletions(-)

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@parallels.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@parallels.com>
> ---
Acked-by: Eric Dumazet <edumazet@google.com>


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