Re: [PATCH v10 30/35] memcg: scan cache objects hierarchically

[Andrew Morton <akpm@linux-foundation.org>]

On Mon,  3 Jun 2013 23:29:59 +0400 Glauber Costa <glommer@openvz.org> wrote:

> When reaching shrink_slab, we should descent in children memcg searching

"descend into child memcgs"

> for objects that could be shrunk. This is true even if the memcg does

"can be"

> not have kmem limits on, since the kmem res_counter will also be billed
> against the user res_counter of the parent.
> 
> It is possible that we will free objects and not free any pages, that
> will just harm the child groups without helping the parent group at all.
> But at this point, we basically are prepared to pay the price.
> 
> ...
>
>  #ifdef CONFIG_MEMCG_KMEM
> +bool memcg_kmem_should_reclaim(struct mem_cgroup *memcg)
> +{
> +	struct mem_cgroup *iter;
> +
> +	for_each_mem_cgroup_tree(iter, memcg) {
> +		if (memcg_kmem_is_active(iter)) {
> +			mem_cgroup_iter_break(memcg, iter);
> +			return true;
> +		}
> +	}
> +	return false;
> +}

Locking requirements for this function?  Perhaps the
for_each_mem_cgroup_tree() definition site would be an appropriate
place to document this.

>  static inline bool memcg_can_account_kmem(struct mem_cgroup *memcg)
>  {
>  	return !mem_cgroup_disabled() && !mem_cgroup_is_root(memcg) &&
>
> ...
>

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