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

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Date:	Wed, 6 Apr 2016 10:26:47 +0300
From:	Nikolay Borisov <kernel@...p.com>
To:	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Michal Hocko <mhocko@...e.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] mm, hugetlb_cgroup: round limit_in_bytes down to hugepage
 size



On 04/06/2016 04:25 AM, David Rientjes wrote:
> The page_counter rounds limits down to page size values.  This makes
> sense, except in the case of hugetlb_cgroup where it's not possible to
> charge partial hugepages.
> 
> Round the hugetlb_cgroup limit down to hugepage size.
> 
> Signed-off-by: David Rientjes <rientjes@...gle.com>
> ---
>  mm/hugetlb_cgroup.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
> --- a/mm/hugetlb_cgroup.c
> +++ b/mm/hugetlb_cgroup.c
> @@ -288,6 +288,7 @@ static ssize_t hugetlb_cgroup_write(struct kernfs_open_file *of,
>  
>  	switch (MEMFILE_ATTR(of_cft(of)->private)) {
>  	case RES_LIMIT:
> +		nr_pages &= ~((1 << huge_page_order(&hstates[idx])) - 1);

Why not:

nr_pages = round_down(nr_pages, huge_page_order(&hstates[idx]));


>  		mutex_lock(&hugetlb_limit_mutex);
>  		ret = page_counter_limit(&h_cg->hugepage[idx], nr_pages);
>  		mutex_unlock(&hugetlb_limit_mutex);
>