linux-kernel - Re: [PATCH v2] mm/hugetlb: remove redundant check in preparing and destroying gigantic page

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Date:   Tue, 2 Feb 2021 11:03:12 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     "Xu, Yanfei" <yanfei.xu@...driver.com>, akpm@...ux-foundation.org,
        David Hildenbrand <david@...hat.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm/hugetlb: remove redundant check in preparing and
 destroying gigantic page

On 2/2/21 4:19 AM, Xu, Yanfei wrote:
> I'm sorry for forgetting to add David.
> Now add David ：）
> 
> Thanks，
> Yanfei
> 
> On 2/2/21 7:20 PM, yanfei.xu@...driver.com wrote:
>> From: Yanfei Xu <yanfei.xu@...driver.com>
>>
>> Gigantic page is a compound page and its order is more than 1.
>> Thus it must be available for hpage_pincount. Let's remove the
>> redundant check for gigantic page.
>>
>> Signed-off-by: Yanfei Xu <yanfei.xu@...driver.com>
>> ---
>>   mm/hugetlb.c | 7 ++-----
>>   1 file changed, 2 insertions(+), 5 deletions(-)

I can not imagine a 'hugetlb gigantic page' being <= 1 order, so this change
makes sense.  Thanks,

Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>
-- 
Mike Kravetz

>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>> index a3e4fa2c5e94..dac5db569ccb 100644
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -1219,8 +1219,7 @@ static void destroy_compound_gigantic_page(struct page *page,
>>       struct page *p = page + 1;
>>         atomic_set(compound_mapcount_ptr(page), 0);
>> -    if (hpage_pincount_available(page))
>> -        atomic_set(compound_pincount_ptr(page), 0);
>> +    atomic_set(compound_pincount_ptr(page), 0);
>>         for (i = 1; i < nr_pages; i++, p = mem_map_next(p, page, i)) {
>>           clear_compound_head(p);
>> @@ -1501,9 +1500,7 @@ static void prep_compound_gigantic_page(struct page *page, unsigned int order)
>>           set_compound_head(p, page);
>>       }
>>       atomic_set(compound_mapcount_ptr(page), -1);
>> -
>> -    if (hpage_pincount_available(page))
>> -        atomic_set(compound_pincount_ptr(page), 0);
>> +    atomic_set(compound_pincount_ptr(page), 0);
>>   }
>>     /*
>>
>