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

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Date:	Mon, 09 Jul 2012 09:48:53 +0800
From:	Li Zhong <zhong@...ux.vnet.ibm.com>
To:	Glauber Costa <glommer@...allels.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 Fri, 2012-07-06 at 14:13 +0400, Glauber Costa wrote:
> 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

Thank you. I think it is better to have these things in the
slab_common.c. 

> 
> 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.

With slab_common, I think my slab/slob modifications are not needed any
more. After I understand the common patches, I will check whether the
aliasing problem in slub still exists, and if yes, try to send a patch
based on that. 

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