[Devel] Re: [PATCH v8 1/9] Basic kernel memory functionality for the Memory Controller

[KAMEZAWA Hiroyuki]

On Mon,  5 Dec 2011 19:34:55 -0200
Glauber Costa <glommer at parallels.com> wrote:

> This patch lays down the foundation for the kernel memory component
> of the Memory Controller.
> 
> As of today, I am only laying down the following files:
> 
>  * memory.independent_kmem_limit
>  * memory.kmem.limit_in_bytes (currently ignored)
>  * memory.kmem.usage_in_bytes (always zero)
> 
> Signed-off-by: Glauber Costa <glommer at parallels.com>
> Reviewed-by: Kirill A. Shutemov <kirill at shutemov.name>
> CC: Paul Menage <paul at paulmenage.org>
> CC: Greg Thelen <gthelen at google.com>

As I wrote, please CC Johannes and  Michal Hocko for memcg related parts.

A few questions.
==
> +	val = !!val;
> +
> +	if (parent && parent->use_hierarchy &&
> +	   (val != parent->kmem_independent_accounting))
> +		return -EINVAL;
==
Hm, why you check val != parent->kmem_independent_accounting ?

	if (parent && parent->use_hierarchy)
		return -EINVAL;
?

BTW, you didn't check this cgroup has children or not.
I think

	if (this_cgroup->use_hierarchy &&
             !list_empty(this_cgroup->childlen))
		return -EINVAL;


==
> +	/*
> +	 * TODO: We need to handle the case in which we are doing
> +	 * independent kmem accounting as authorized by our parent,
> +	 * but then our parent changes its parameter.
> +	 */
> +	cgroup_lock();
> +	memcg->kmem_independent_accounting = val;
> +	cgroup_unlock();

Do we need cgroup_lock() here ?

Thanks,
-Kame