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

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Date:	Thu, 16 Jun 2016 17:43:24 +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,
	"Kirill A. Shutemov" <kirill@...temov.name>
Subject: Re: [PATCH] mm: fix account pmd page to the process

[It seems that this patch has been sent several times and this
particular copy didn't add Kirill who has added this code CC him now]

On Thu 16-06-16 17:42:14, 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?
> 
> > +
> >  	spin_unlock(ptl);
> >  out:
> >  	pte = (pte_t *)pmd_alloc(mm, pud, addr);
> > -- 
> > 1.8.3.1
> 
> -- 
> Michal Hocko
> SUSE Labs

-- 
Michal Hocko
SUSE Labs