linux-kernel - Re: [PATCH 1/8] memcg: export kmemcg cache id via cgroup fs

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Date:	Tue, 4 Feb 2014 15:40:33 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Vladimir Davydov <vdavydov@...allels.com>
Cc:	akpm@...ux-foundation.org, rientjes@...gle.com, penberg@...nel.org,
	cl@...ux.com, glommer@...il.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, devel@...nvz.org
Subject: Re: [PATCH 1/8] memcg: export kmemcg cache id via cgroup fs

On Sun 02-02-14 20:33:46, Vladimir Davydov wrote:
> Per-memcg kmem caches are named as follows:
> 
>   <global-cache-name>(<cgroup-kmem-id>:<cgroup-name>)
> 
> where <cgroup-kmem-id> is the unique id of the memcg the cache belongs
> to, <cgroup-name> is the relative name of the memcg on the cgroup fs.
> Cache names are exposed to userspace for debugging purposes (e.g. via
> sysfs in case of slub or via dmesg).

If this is only for debugging purposes then it shouldn't pollute regular
memcg cgroupfs namespace.

> Using relative names makes it impossible in general (in case the cgroup
> hierarchy is not flat) to find out which memcg a particular cache
> belongs to, because <cgroup-kmem-id> is not known to the user. Since
> using absolute cgroup names would be an overkill,

I do not consider it an overkill. We are using the full path when
dumping OOM information so I do not see any reason this should be any
different.

> let's fix this by
> exporting the id of kmem-active memcg via cgroup fs file
> "memory.kmem.id".
> 
> Signed-off-by: Vladimir Davydov <vdavydov@...allels.com>

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

> ---
>  mm/memcontrol.c |   12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 53385cd4e6f0..91d242707404 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3113,6 +3113,14 @@ int memcg_cache_id(struct mem_cgroup *memcg)
>  	return memcg ? memcg->kmemcg_id : -1;
>  }
>  
> +static s64 mem_cgroup_cache_id_read(struct cgroup_subsys_state *css,
> +				    struct cftype *cft)
> +{
> +	struct mem_cgroup *memcg = mem_cgroup_from_css(css);
> +
> +	return memcg_can_account_kmem(memcg) ? memcg_cache_id(memcg) : -1;
> +}
> +
>  static size_t memcg_caches_array_size(int num_groups)
>  {
>  	ssize_t size;
> @@ -6301,6 +6309,10 @@ static struct cftype mem_cgroup_files[] = {
>  #endif
>  #ifdef CONFIG_MEMCG_KMEM
>  	{
> +		.name = "kmem.id",
> +		.read_s64 = mem_cgroup_cache_id_read,
> +	},
> +	{
>  		.name = "kmem.limit_in_bytes",
>  		.private = MEMFILE_PRIVATE(_KMEM, RES_LIMIT),
>  		.write_string = mem_cgroup_write,
> -- 
> 1.7.10.4
> 

-- 
Michal Hocko
SUSE Labs
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