linux-kernel - Re: [PATCH 2/6] memcg, slab: kmem_cache_create

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Date:	Thu, 19 Dec 2013 13:01:28 +0400
From:	Vladimir Davydov <vdavydov@...allels.com>
To:	Michal Hocko <mhocko@...e.cz>
CC:	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	<cgroups@...r.kernel.org>, <devel@...nvz.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Glauber Costa <glommer@...il.com>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/6] memcg, slab: kmem_cache_create_memcg(): free memcg
 params on error

On 12/19/2013 12:48 PM, Michal Hocko wrote:
> On Thu 19-12-13 10:32:29, Vladimir Davydov wrote:
>> On 12/18/2013 09:06 PM, Michal Hocko wrote:
>>> On Wed 18-12-13 17:16:53, Vladimir Davydov wrote:
>>>> Plus, rename memcg_register_cache() to memcg_init_cache_params(),
>>>> because it actually does not register the cache anywhere, but simply
>>>> initialize kmem_cache::memcg_params.
>>> I've almost missed this is a memory leak fix.
>> Yeah, the comment is poor, sorry about that. Will fix it.
>>
>>> I do not mind renaming and the name but wouldn't
>>> memcg_alloc_cache_params suit better?
>> As you wish. I don't have a strong preference for memcg_init_cache_params.
> I really hate naming... but it seems that alloc is a better fit. _init_
> would expect an already allocated object.
>
> Btw. memcg_free_cache_params is called only once which sounds
> suspicious. The regular destroy path should use it as well?
> [...]

The usual destroy path uses memcg_release_cache(), which does the trick.
Plus, it actually "unregisters" the cache. BTW, I forgot to substitute
kfree(s->memcg_params) with the new memcg_free_cache_params() there.
Although it currently does not break anything, better to fix it in case
new memcg_free_cache_params() will have to do something else.

And you're right about the naming is not good.

Currently we have:

  on create:
    memcg_register_cache()
    memcg_cache_list_add()
  on destroy:
    memcg_release_cache()

After this patch we would have:

  on create:
    memcg_alloc_cache_params()
    memcg_register_cache()
  on destroy:
    memcg_release_cache()

Still not perfect: "alloc" does not have corresponding "free", while
"register" does not have corresponding "unregister", everything is done
by "release".

What do you think about splitting memcg_release_cache() into two functions:

    memcg_unregister_cache()
    memcg_free_cache_params()

?

Thanks.
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