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

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Date:	Wed, 6 Apr 2016 10:33:19 +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 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]));

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