linux-kernel - Re: [PATCH] mm: fix account pmd page to the process

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Message-ID: <5763DC85.8080707@huawei.com>
Date:	Fri, 17 Jun 2016 19:18:29 +0800
From:	zhong jiang <zhongjiang@...wei.com>
To:	Michal Hocko <mhocko@...nel.org>
CC:	<akpm@...ux-foundation.org>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: fix account pmd page to the process

On 2016/6/16 23:42, Michal Hocko wrote:
> On Thu 16-06-16 19:36:11, zhongjiang wrote:
>> From: zhong jiang <zhongjiang@...wei.com>
>>
>> when a process acquire a pmd table shared by other process, we
>> increase the account to current process. otherwise, a race result
>> in other tasks have set the pud entry. so it no need to increase it.
>>
>> Signed-off-by: zhong jiang <zhongjiang@...wei.com>
>> ---
>>  mm/hugetlb.c | 5 ++---
>>  1 file changed, 2 insertions(+), 3 deletions(-)
>>
>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>> index 19d0d08..3b025c5 100644
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -4189,10 +4189,9 @@ pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud)
>>  	if (pud_none(*pud)) {
>>  		pud_populate(mm, pud,
>>  				(pmd_t *)((unsigned long)spte & PAGE_MASK));
>> -	} else {
>> +	} else 
>>  		put_page(virt_to_page(spte));
>> -		mm_inc_nr_pmds(mm);
>> -	}
> The code is quite puzzling but is this correct? Shouldn't we rather do
> mm_dec_nr_pmds(mm) in that path to undo the previous inc?
  Yes, you are right. I will modify it in V2.
 
  Thanks
  zhongjiang
>
>> +
>>  	spin_unlock(ptl);
>>  out:
>>  	pte = (pte_t *)pmd_alloc(mm, pud, addr);
>> -- 
>> 1.8.3.1