Re: [PATCH v3 4/6] memcg: move charges to root cgroup if use_hierarchy=0.

[Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

On Fri, May 11, 2012 at 06:49:22PM +0900, KAMEZAWA Hiroyuki wrote:
> @@ -3351,9 +3339,8 @@ int mem_cgroup_move_hugetlb_parent(int idx, struct cgroup *cgroup,
>  	struct page_cgroup *pc;
>  	int csize,  ret = 0;
>  	struct res_counter *fail_res;
> -	struct cgroup *pcgrp = cgroup->parent;
> -	struct mem_cgroup *parent = mem_cgroup_from_cont(pcgrp);
>  	struct mem_cgroup *memcg  = mem_cgroup_from_cont(cgroup);
> +	struct mem_cgroup *parent = parent_mem_cgroup(memcg);
>  	struct res_counter *counter;
>  
>  	if (!get_page_unless_zero(page))
> @@ -3366,13 +3353,11 @@ int mem_cgroup_move_hugetlb_parent(int idx, struct cgroup *cgroup,
>  
>  	csize = PAGE_SIZE << compound_order(page);
>  	/* If parent->use_hierarchy == 0, we need to charge parent */
> -	if (!parent->use_hierarchy) {
> -		ret = res_counter_charge(&parent->hugepage[idx],
> -					 csize, &fail_res);
> -		if (ret) {
> -			ret = -EBUSY;
> -			goto err_out;
> -		}
> +	if (!parent) {
> +		parent = root_mem_cgroup;
> +		/* root has no limit */
> +		res_counter_charge_nofail(&parent->hugepage[idx],
> +				 csize, &fail_res);
>  	}
>  	counter = &memcg->hugepage[idx];
>  	res_counter_uncharge_until(counter, counter->parent, csize);

This function can simply return 0 now, so no point in having int
return.  Make it return void?

Also, follow-up patches to cleanup -ENOMEM failure handling in the
callers would be nice.

Thanks.

-- 
tejun