linux-kernel - Re: [PATCH] memcg: don't initialize kmem-cache destroying work for root caches

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Message-ID: <51A56C60.9030306@parallels.com>
Date:	Wed, 29 May 2013 08:18:00 +0530
From:	Glauber Costa <glommer@...allels.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Andrey Vagin <avagin@...nvz.org>, <linux-kernel@...r.kernel.org>,
	<linux-mm@...ck.org>, <cgroups@...r.kernel.org>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Balbir Singh <bsingharora@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH] memcg: don't initialize kmem-cache destroying work for
 root caches

On 05/29/2013 04:23 AM, Andrew Morton wrote:
> On Tue, 14 May 2013 16:38:38 +0400 Andrey Vagin <avagin@...nvz.org> wrote:
> 
>> struct memcg_cache_params has a union. Different parts of this union are
>> used for root and non-root caches. A part with destroying work is used only
>> for non-root caches.
> 
> That union is a bit dangerous.  Perhaps it would be better to do
> something like
> 
> --- a/include/linux/slab.h~a
> +++ a/include/linux/slab.h
> @@ -337,15 +337,17 @@ static __always_inline int kmalloc_size(
>  struct memcg_cache_params {
>  	bool is_root_cache;
>  	union {
> -		struct kmem_cache *memcg_caches[0];
> -		struct {
> +		struct memcg_root_cache {
> +			struct kmem_cache *caches[0];
> +		} memcg_root_cache;
> +		struct memcg_child_cache {
>  			struct mem_cgroup *memcg;
>  			struct list_head list;
>  			struct kmem_cache *root_cache;
>  			bool dead;
>  			atomic_t nr_pages;
>  			struct work_struct destroy;
> -		};
> +		} memcg_child_cache;
>  	};
>  };
> 
> And then adopt the convention of selecting either memcg_root_cache or
> memcg_child_cache at the highest level then passing the more strongly
> typed pointer to callees.
> 

Since it is already creating problems, yes, I agree.

I will try to cook up something soon.

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