linux-kernel - Re: [PATCH v2 04/29] slub: always get the cache from its page in kfree

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Message-ID: <4FAD566C.3000804@parallels.com>
Date:	Fri, 11 May 2012 15:11:56 -0300
From:	Glauber Costa <glommer@...allels.com>
To:	Christoph Lameter <cl@...ux.com>
CC:	<linux-kernel@...r.kernel.org>, <cgroups@...r.kernel.org>,
	<linux-mm@...ck.org>, <kamezawa.hiroyu@...fujitsu.com>,
	Tejun Heo <tj@...nel.org>, Li Zefan <lizefan@...wei.com>,
	Greg Thelen <gthelen@...gle.com>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>, <devel@...nvz.org>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH v2 04/29] slub: always get the cache from its page in
 kfree

On 05/11/2012 03:06 PM, Christoph Lameter wrote:
> On Fri, 11 May 2012, Glauber Costa wrote:
>
>>> Adding a VM_BUG_ON may be useful to make sure that kmem_cache_free is
>>> always passed the correct slab cache.
>>
>> Well, problem is , it isn't always passed the "correct" slab cache.
>> At least not after this series, since we'll have child caches associated with
>> the main cache.
>>
>> So we'll pass, for instance, kmem_cache_free(dentry_cache...), but will in
>> fact free from the memcg copy of the dentry cache.
>
> Urg. But then please only do this for the MEMCG case and add a fat big
> warning in kmem_cache_free.

I can do that, of course.
Another option if you don't oppose, is to add another field in the 
kmem_cache structure (I tried to keep them at a minimum),
to record the parent cache we got created from.

Then, it gets trivial to do the following:

VM_BUG_ON(page->slab != s && page->slab != s->parent_cache);

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