Re: [PATCH 2/6] memcg, slab: kmem_cache_create_memcg(): free memcgparams on error

From: Michal Hocko
Date: Thu Dec 19 2013 - 04:21:14 EST


On Thu 19-12-13 13:01:28, Vladimir Davydov wrote:
> 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()

yes I am all for cleaning up this mess. I am still trying to wrap my
head around what is each of this function responsible for.
Absolute lack of documentation is not helping at all...

>
> ?
>
> Thanks.

--
Michal Hocko
SUSE Labs
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