Re: [PATCH -mm] slab: use cgroup ino for naming per memcg caches

From: Andrew Morton <akpm@linux-foundation.org>
To: Vladimir Davydov <vdavydov@parallels.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>,
	Michal Hocko <mhocko@suse.cz>, Christoph Lameter <cl@linux.com>,
	Pekka Enberg <penberg@kernel.org>,
	David Rientjes <rientjes@google.com>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>, <linux-mm@kvack.org>,
	<cgroups@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH -mm] slab: use cgroup ino for naming per memcg caches
Date: Tue, 7 Apr 2015 13:38:19 -0700	[thread overview]
Message-ID: <20150407133819.993be7a53a3aa16311aba1f5@linux-foundation.org> (raw)
In-Reply-To: <1428414798-12932-1-git-send-email-vdavydov@parallels.com>

On Tue, 7 Apr 2015 16:53:18 +0300 Vladimir Davydov <vdavydov@parallels.com> wrote:

> The name of a per memcg kmem cache consists of three parts: the global
> kmem cache name, the cgroup name, and the css id. The latter is used to
> guarantee cache name uniqueness.
> 
> Since css ids are opaque to the userspace, in general it is impossible
> to find a cache's owner cgroup given its name: there might be several
> same-named cgroups with different parents so that their caches' names
> will only differ by css id. Looking up the owner cgroup by a cache name,
> however, could be useful for debugging. For instance, the cache name is
> dumped to dmesg on a slab allocation failure. Another example is
> /sys/kernel/slab, which exports some extra info/tunables for SLUB caches

/proc/sys/kernel/slab?

> referring to them by name.
> 
> This patch substitutes the css id with cgroup inode number, which, just
> like css id, is reserved until css free, so that the cache names are
> still guaranteed to be unique, but, in contrast to css id, it can be
> easily obtained from userspace.
> 
> ...
>
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -478,7 +478,7 @@ void memcg_create_kmem_cache(struct mem_cgroup *memcg,
>  			     struct kmem_cache *root_cache)
>  {
>  	static char memcg_name_buf[NAME_MAX + 1]; /* protected by slab_mutex */
> -	struct cgroup_subsys_state *css = mem_cgroup_css(memcg);
> +	struct cgroup *cgroup;
>  	struct memcg_cache_array *arr;
>  	struct kmem_cache *s = NULL;
>  	char *cache_name;
> @@ -508,9 +508,10 @@ void memcg_create_kmem_cache(struct mem_cgroup *memcg,
>  	if (arr->entries[idx])
>  		goto out_unlock;
>  
> -	cgroup_name(css->cgroup, memcg_name_buf, sizeof(memcg_name_buf));
> -	cache_name = kasprintf(GFP_KERNEL, "%s(%d:%s)", root_cache->name,
> -			       css->id, memcg_name_buf);
> +	cgroup = mem_cgroup_css(memcg)->cgroup;
> +	cgroup_name(cgroup, memcg_name_buf, sizeof(memcg_name_buf));
> +	cache_name = kasprintf(GFP_KERNEL, "%s(%lu:%s)", root_cache->name,
> +			(unsigned long)cgroup_ino(cgroup), memcg_name_buf);
>  	if (!cache_name)
>  		goto out_unlock;

Is this interface documented anywhere?