Date:	Wed, 7 May 2014 13:19:40 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Vladimir Davydov <vdavydov@...allels.com>
Cc:	akpm@...ux-foundation.org, hannes@...xchg.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH -mm 1/2] memcg: get rid of memcg_create_cache_name

On Wed 07-05-14 14:45:16, Vladimir Davydov wrote:
[...]
> From: Vladimir Davydov <vdavydov@...allels.com>
> Subject: [PATCH] memcg: get rid of memcg_create_cache_name
> 
> Instead of calling back to memcontrol.c from kmem_cache_create_memcg in
> order to just create the name of a per memcg cache, let's allocate it in
> place. We only need to pass the memcg name to kmem_cache_create_memcg
> for that - everything else can be done in slab_common.c.
> 
> Signed-off-by: Vladimir Davydov <vdavydov@...allels.com>

Acked-by: Michal Hocko <mhocko@...e.cz>

> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 6c59056f4bc6..7b639ab48aa8 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -501,8 +501,6 @@ void __memcg_kmem_uncharge_pages(struct page *page, int order);
>  
>  int memcg_cache_id(struct mem_cgroup *memcg);
>  
> -char *memcg_create_cache_name(struct mem_cgroup *memcg,
> -			      struct kmem_cache *root_cache);
>  int memcg_alloc_cache_params(struct mem_cgroup *memcg, struct kmem_cache *s,
>  			     struct kmem_cache *root_cache);
>  void memcg_free_cache_params(struct kmem_cache *s);
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index ecbec9ccb80d..86e5b26fbdab 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -117,7 +117,8 @@ struct kmem_cache *kmem_cache_create(const char *, size_t, size_t,
>  			void (*)(void *));
>  #ifdef CONFIG_MEMCG_KMEM
>  struct kmem_cache *kmem_cache_create_memcg(struct mem_cgroup *,
> -					   struct kmem_cache *);
> +					   struct kmem_cache *,
> +					   const char *);
>  #endif
>  void kmem_cache_destroy(struct kmem_cache *);
>  int kmem_cache_shrink(struct kmem_cache *);
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index f381239ab402..9ff3742f4154 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3101,29 +3101,6 @@ int memcg_update_cache_size(struct kmem_cache *s, int num_groups)
>  	return 0;
>  }
>  
> -char *memcg_create_cache_name(struct mem_cgroup *memcg,
> -			      struct kmem_cache *root_cache)
> -{
> -	static char *buf;
> -
> -	/*
> -	 * We need a mutex here to protect the shared buffer. Since this is
> -	 * expected to be called only on cache creation, we can employ the
> -	 * slab_mutex for that purpose.
> -	 */
> -	lockdep_assert_held(&slab_mutex);
> -
> -	if (!buf) {
> -		buf = kmalloc(NAME_MAX + 1, GFP_KERNEL);
> -		if (!buf)
> -			return NULL;
> -	}
> -
> -	cgroup_name(memcg->css.cgroup, buf, NAME_MAX + 1);
> -	return kasprintf(GFP_KERNEL, "%s(%d:%s)", root_cache->name,
> -			 memcg_cache_id(memcg), buf);
> -}
> -
>  int memcg_alloc_cache_params(struct mem_cgroup *memcg, struct kmem_cache *s,
>  			     struct kmem_cache *root_cache)
>  {
> @@ -3164,6 +3141,7 @@ void memcg_free_cache_params(struct kmem_cache *s)
>  static void memcg_kmem_create_cache(struct mem_cgroup *memcg,
>  				    struct kmem_cache *root_cache)
>  {
> +	static char *memcg_name_buf;	/* protected by memcg_slab_mutex */
>  	struct kmem_cache *cachep;
>  	int id;
>  
> @@ -3179,7 +3157,14 @@ static void memcg_kmem_create_cache(struct mem_cgroup *memcg,
>  	if (cache_from_memcg_idx(root_cache, id))
>  		return;
>  
> -	cachep = kmem_cache_create_memcg(memcg, root_cache);
> +	if (!memcg_name_buf) {
> +		memcg_name_buf = kmalloc(NAME_MAX + 1, GFP_KERNEL);
> +		if (!memcg_name_buf)
> +			return;
> +	}
> +
> +	cgroup_name(memcg->css.cgroup, memcg_name_buf, NAME_MAX + 1);
> +	cachep = kmem_cache_create_memcg(memcg, root_cache, memcg_name_buf);
>  	/*
>  	 * If we could not create a memcg cache, do not complain, because
>  	 * that's not critical at all as we can always proceed with the root
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 7e348cff814d..32175617cb75 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -264,13 +264,15 @@ EXPORT_SYMBOL(kmem_cache_create);
>   * kmem_cache_create_memcg - Create a cache for a memory cgroup.
>   * @memcg: The memory cgroup the new cache is for.
>   * @root_cache: The parent of the new cache.
> + * @memcg_name: The name of the memory cgroup (used for naming the new cache).
>   *
>   * This function attempts to create a kmem cache that will serve allocation
>   * requests going from @memcg to @root_cache. The new cache inherits properties
>   * from its parent.
>   */
>  struct kmem_cache *kmem_cache_create_memcg(struct mem_cgroup *memcg,
> -					   struct kmem_cache *root_cache)
> +					   struct kmem_cache *root_cache,
> +					   const char *memcg_name)
>  {
>  	struct kmem_cache *s = NULL;
>  	char *cache_name;
> @@ -280,7 +282,8 @@ struct kmem_cache *kmem_cache_create_memcg(struct mem_cgroup *memcg,
>  
>  	mutex_lock(&slab_mutex);
>  
> -	cache_name = memcg_create_cache_name(memcg, root_cache);
> +	cache_name = kasprintf(GFP_KERNEL, "%s(%d:%s)", root_cache->name,
> +			       memcg_cache_id(memcg), memcg_name);
>  	if (!cache_name)
>  		goto out_unlock;
>  

-- 
Michal Hocko
SUSE Labs
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