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

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Message-ID: <20160616154214.GA12284@dhcp22.suse.cz>
Date:	Thu, 16 Jun 2016 17:42:15 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	zhongjiang <zhongjiang@...wei.com>
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 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?

> +
>  	spin_unlock(ptl);
>  out:
>  	pte = (pte_t *)pmd_alloc(mm, pud, addr);
> -- 
> 1.8.3.1

-- 
Michal Hocko
SUSE Labs