linux-kernel - Re: [PATCH powerpc 2/2] kfree the cache name of pgtable cache if SLUB is used

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Date:	Fri, 6 Jul 2012 14:13:13 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	Li Zhong <zhong@...ux.vnet.ibm.com>
CC:	Christoph Lameter <cl@...ux.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>,
	"Benjamin Herrenschmidt" <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	linux-mm <linux-mm@...ck.org>,
	PowerPC email list <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH powerpc 2/2] kfree the cache name  of pgtable cache if
 SLUB is used

On 07/05/2012 01:29 PM, Li Zhong wrote:
> On Thu, 2012-07-05 at 12:23 +0400, Glauber Costa wrote:
>> On 07/05/2012 05:41 AM, Li Zhong wrote:
>>> On Wed, 2012-07-04 at 16:40 +0400, Glauber Costa wrote:
>>>> On 07/04/2012 01:00 PM, Li Zhong wrote:
>>>>> On Tue, 2012-07-03 at 15:36 -0500, Christoph Lameter wrote:
>>>>>>> Looking through the emails it seems that there is an issue with alias
>>>>>>> strings. 
>>>>> To be more precise, there seems no big issue currently. I just wanted to
>>>>> make following usage of kmem_cache_create (SLUB) possible:
>>>>>
>>>>> 	name = some string kmalloced
>>>>> 	kmem_cache_create(name, ...)
>>>>> 	kfree(name);
>>>>
>>>> Out of curiosity: Why?
>>>> This is not (currently) possible with the other allocators (may change
>>>> with christoph's unification patches), so you would be making your code
>>>> slub-dependent.
>>>>
>>>
>>> For slub itself, I think it's not good that: in some cases, the name
>>> string could be kfreed ( if it was kmalloced ) immediately after calling
>>> the cache create; in some other case, the name string needs to be kept
>>> valid until some init calls finished. 
>>>
>>> I agree with you that it would make the code slub-dependent, so I'm now
>>> working on the consistency of the other allocators regarding this name
>>> string duplicating thing. 
>>
>> If you really need to kfree the string, or even if it is easier for you
>> this way, it can be done. As a matter of fact, this is the case for me.
>> Just that your patch is not enough. Christoph has a patch that makes
>> this behavior consistent over all allocators.
> 
> Sorry, I didn't know that. Seems I don't need to continue the half-done
> work in slab. If possible, would you please give me a link of the patch?
> Thank you. 
> 

Sorry for the delay. In case you haven't found it out yourself yet:

http://www.spinics.net/lists/linux-mm/msg36149.html

Please not this posted patch as is has a bug.

I do believe that your take on the aliasing code adds value to it. But
as I've already said once, might have to dig a bit deeper in that to get
to end of the rabbit hole.


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