Re: [PATCH 6/6] memcg: disable memcg page stat accounting

[Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>]

On 03/12/2013 02:11 PM, Sha Zhengju wrote:
> Use jump label to patch the memcg page stat accounting code
> in or out when not used. when the first non-root memcg comes to
> life the code is patching in otherwise it is out.
> 
> Signed-off-by: Sha Zhengju <handai.szj-3b8fjiQLQpfQT0dZR+AlfA@public.gmane.org>
> ---
>  include/linux/memcontrol.h |   23 +++++++++++++++++++++++
>  mm/memcontrol.c            |   34 +++++++++++++++++++++++++++++++++-
>  2 files changed, 56 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index d6183f0..99dca91 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -42,6 +42,14 @@ struct mem_cgroup_reclaim_cookie {
>  };
>  
>  #ifdef CONFIG_MEMCG
> +
> +extern struct static_key memcg_in_use_key;
> +
> +static inline bool mem_cgroup_in_use(void)
> +{
> +	return static_key_false(&memcg_in_use_key);
> +}
> +

I believe the big advantage of the approach I've taken, including this
test in mem_cgroup_disabled(), is that we patch out a lot of things for
free.

We just need to be careful because some code expected that decision to
be permanent and now that status can change.

But I would still advocate for that.