linux-kernel - Re: [patch v2] mm, hugetlb_cgroup: round limit_in

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Message-ID: <20160407125145.GD32755@dhcp22.suse.cz>
Date:	Thu, 7 Apr 2016 14:51:45 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Nikolay Borisov <kernel@...p.com>,
	Johannes Weiner <hannes@...xchg.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [patch v2] mm, hugetlb_cgroup: round limit_in_bytes down to
 hugepage size

On Wed 06-04-16 15:10:23, David Rientjes wrote:
[...]
> +static void hugetlb_cgroup_init(struct hugetlb_cgroup *h_cgroup,
> +				struct hugetlb_cgroup *parent_h_cgroup)
> +{
> +	int idx;
> +
> +	for (idx = 0; idx < HUGE_MAX_HSTATE; idx++) {
> +		struct page_counter *counter = &h_cgroup->hugepage[idx];
> +		struct page_counter *parent = NULL;
> +		unsigned long limit;
> +		int ret;
> +
> +		if (parent_h_cgroup)
> +			parent = &parent_h_cgroup->hugepage[idx];
> +		page_counter_init(counter, parent);
> +
> +		limit = round_down(PAGE_COUNTER_MAX,
> +				   1 << huge_page_order(&hstates[idx]));
> +		ret = page_counter_limit(counter, limit);
> +		VM_BUG_ON(ret);
> +	}
> +}

I fail to see the point for this. Why would want to round down
PAGE_COUNTER_MAX? It will never make a real difference. Or am I missing
something?
-- 
Michal Hocko
SUSE Labs