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

[Glauber Costa <glommer@parallels.com>]

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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