linux-kernel - Re: [PATCH v3 4/6] memcg: move charges to root cgroup if use

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Message-ID: <20120514201438.GI2366@google.com>
Date:	Mon, 14 May 2012 13:14:38 -0700
From:	Tejun Heo <tj@...nel.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Han Ying <yinghan@...gle.com>,
	Glauber Costa <glommer@...allels.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hiroyuki Kamezawa <kamezawa.hiroyuki@...il.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 4/6] memcg: move charges to root cgroup if
 use_hierarchy=0.

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
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