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

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Date:	Wed, 6 Apr 2016 11:09:42 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Nikolay Borisov <kernel@...p.com>
Cc:	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	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 Wed 06-04-16 10:33:19, Nikolay Borisov wrote:
> 
> 
> On 04/06/2016 10:26 AM, Nikolay Borisov wrote:
> > 
> > 
> > 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]));
> 
> Oops, that should be:
> 
> round_down(nr_pages, 1 << huge_page_order(&hstates[idx]));

round_down is a bit nicer.

Anyway
Acked-by: Michal Hocko <mhocko@...e.com>

-- 
Michal Hocko
SUSE Labs