Re: [PATCH 1/3] net: introduce a list of device addresses dev_addr_list (v3)

Jiri Pirko
2009-04-18T07:45:32Z

Sat, Apr 18, 2009 at 09:35:32AM CEST, dada1@cosmosbay.com wrote:
>Jiri Pirko a écrit :
>> Fri, Apr 17, 2009 at 05:33:15PM CEST, shemminger@vyatta.com wrote:
>>
>> <snip>
>>
>>>> +struct netdev_hw_addr {
>>>> + struct list_head list;
>>>> + unsigned char addr[MAX_ADDR_LEN];
>>>> + int refcount;
>>>> + struct rcu_head rcu_head;
>>>> +};
>>> Minor nit, the ordering of elements cause holes that might not be
>>> needed.
>>
>> Agree that ordering might be done better. Will do.
>>> Space saving? is rcu_head needed or would using synchronize_net
>>> make code cleaner and save space.
>>>
>>
>> Well I originaly had this done by synchronize_rcu(). Eric argued that it might
>> cause especially __hw_addr_del_multiple_ii() to run long and suggested to use
>> call_rcu() instead. I plan to switch this to kfree_rcu() (or whatever it's
>> called) once it hits the tree.
>>
>
>Yes, and dont forget we wont save space, as we allocate a full
>cache line to hold a 'struct netdev_hw_addr', since we dont want this
>critical and read_mostly object polluted by a hot spot elsewhere in kernel...
>
>Considering this, letting 'rcu_head' at the end of structure, even if we
>have an eventual hole on 64 bit arches is not really a problem, and IMHO
>the best thing to do, as rcu_head is only used at dismantle time.

I will order the struct better, there are archs with small cache line size where
it makes sense.

>
>And yes, maybe kfree_rcu() will makes its way in kernel, eventually :)
>
>Thank you
>
>