netdev - Re: [PATCH 1/3] net: introduce a list of device addresses dev_addr

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Message-ID: <49E982C4.8020407@cosmosbay.com>
Date:	Sat, 18 Apr 2009 09:35:32 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Jiri Pirko <jpirko@...hat.com>
CC:	Stephen Hemminger <shemminger@...tta.com>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	jgarzik@...ox.com, davem@...emloft.net,
	bridge@...ts.linux-foundation.org, fubar@...ibm.com,
	bonding-devel@...ts.sourceforge.net, kaber@...sh.net,
	mschmidt@...hat.com, ivecera@...hat.com
Subject: Re: [PATCH 1/3] net: introduce a list of device addresses	dev_addr_list
 (v3)

Jiri Pirko a écrit :
> Fri, Apr 17, 2009 at 05:33:15PM CEST, shemminger@...tta.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.

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

Thank you


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