linux-kernel - Re: [PATCH V4 1/1] rcu: introduce kfree

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Message-ID: <4D802746.3020509@cn.fujitsu.com>
Date:	Wed, 16 Mar 2011 10:58:14 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	paulmck@...ux.vnet.ibm.com, Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Manfred Spraul <manfred@...orfullife.com>
Subject: Re: [PATCH V4 1/1] rcu: introduce kfree_rcu()

On 03/15/2011 09:07 PM, Arnd Bergmann wrote:
> On Tuesday 15 March 2011, Paul E. McKenney wrote:
>> And it makes use of statically allocated structures a bit clunky.
> 
> How do statically allocated structures relate to this? I would
> expect that you never call kfree_rcu on them, so it shouldn't
> matter.
> 
>> Yet another approach is to use the low-order bit of the rcu_head pointer,
>> given that the rcu_head structure does have to be aligned.  If this bit
>> is set, then the function pointer could be interpreted as an offset.
>> This approach might also allow a slab_free_rcu() to be constructed, given
>> that the full 32 bits of the function pointer would be available.
>> For example, if the upper 16 bits are zero, the low-order 16 bits are
>> the offset.  If the upper 16 bits are 0x1, then the low-order 16 bits
>> might be an index that selects the desired slab cache.
> 
> This solution sounds like a clear improvement over the patch that Lai
> Jiangshan posted, without any downsides.
> 

This solution is good, but it changes too much code, I think we will switch to
this solution until my posted solution can't work under some real bad situation
happened.
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