Return-Path: <linux-kernel-owner+w=401wt.eu-S1756026AbZDRHg0@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1756026AbZDRHg0 (ORCPT <rfc822;w@1wt.eu>);
	Sat, 18 Apr 2009 03:36:26 -0400
Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753791AbZDRHgP
	(ORCPT <rfc822;linux-kernel-outgoing>);
	Sat, 18 Apr 2009 03:36:15 -0400
Received: from gw1.cosmosbay.com ([212.99.114.194]:33127 "EHLO
	gw1.cosmosbay.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1752103AbZDRHgO convert rfc822-to-8bit (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Sat, 18 Apr 2009 03:36:14 -0400
Message-ID: <49E982C4.8020407@cosmosbay.com>
Date: Sat, 18 Apr 2009 09:35:32 +0200
From: Eric Dumazet <dada1@cosmosbay.com>
User-Agent: Thunderbird 2.0.0.21 (Windows/20090302)
MIME-Version: 1.0
To: Jiri Pirko <jpirko@redhat.com>
CC: Stephen Hemminger <shemminger@vyatta.com>, linux-kernel@vger.kernel.org,
       netdev@vger.kernel.org, jgarzik@pobox.com, davem@davemloft.net,
       bridge@lists.linux-foundation.org, fubar@us.ibm.com,
       bonding-devel@lists.sourceforge.net, kaber@trash.net,
       mschmidt@redhat.com, ivecera@redhat.com
Subject: Re: [PATCH 1/3] net: introduce a list of device addresses	dev_addr_list
 (v3)
References: <20090313183303.GF3436@psychotron.englab.brq.redhat.com> <20090415081720.GA21342@psychotron.englab.brq.redhat.com> <20090415081819.GB21342@psychotron.englab.brq.redhat.com> <20090415180215.GA22540@psychotron.englab.brq.redhat.com> <20090417115723.GE9556@psychotron.englab.brq.redhat.com> <20090417083315.2f089755@nehalam> <20090418070151.GA3370@psychotron.englab.brq.redhat.com>
In-Reply-To: <20090418070151.GA3370@psychotron.englab.brq.redhat.com>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 8BIT
X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-1.6 (gw1.cosmosbay.com [0.0.0.0]); Sat, 18 Apr 2009 09:35:33 +0200 (CEST)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 1543
Lines: 43

Jiri Pirko a ?crit :
> 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.

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

Thank you


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/