netdev - Re: [PATCH 1/2] net: vlan: 802.1ad S-VLAN support

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Date:	Sat, 12 Nov 2011 17:06:40 +0100
From:	Michał Mirosław <mirqus@...il.com>
To:	David Lamparter <equinox@...c24.net>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	kaber@...sh.net
Subject: Re: [PATCH 1/2] net: vlan: 802.1ad S-VLAN support

2011/11/12 David Lamparter <equinox@...c24.net>:
> On Fri, Nov 11, 2011 at 08:22:35PM -0500, David Miller wrote:
>> > @@ -87,7 +97,8 @@ struct vlan_group {
>> >                                         */
>> >     unsigned int            nr_vlans;
>> >     struct hlist_node       hlist;  /* linked list */
>> > -   struct net_device **vlan_devices_arrays[VLAN_GROUP_ARRAY_SPLIT_PARTS];
>> > +   struct net_device **vlan_devices_arrays[VLAN_N_PROTOCOL]
>> > +                                           [VLAN_GROUP_ARRAY_SPLIT_PARTS];
>> >     struct rcu_head         rcu;
>> >  };
>>
>> This is a terrible waste of memory.  You're now using 5 times as much space,
>> the vast majority of which will be entirely unused.
>
> VLAN_GROUP_ARRAY_SPLIT_PARTS is 8; so the memory consumption of this was
> previously 8 * ptr = 64 bytes and is now 5 * 8 * ptr = 320 bytes. I thought
> those extra 256 bytes per VLAN-carrying master device are worth the
> simplicity, especially since this saves me impacts on 802.1Q C-VLAN
> lookup performance elsewhere.

I misread this as a table of all VLANs. It doesn't look that terrible
now compared to old scheme. In the case when you have only a handful
of VLANs configured you waste a 4kB per VLAN (but that's how it is
done already).

Best Regards,
Michał Mirosław
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