linux-kernel - Re: [RFC][PATCH 5/6] teach smaps_pte

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Date:	Tue, 01 Feb 2011 07:02:30 -0800
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Michael J Wolf <mjwolf@...ibm.com>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [RFC][PATCH 5/6] teach smaps_pte_range() about THP pmds

On Tue, 2011-02-01 at 11:11 +0100, Johannes Weiner wrote:
> On Mon, Jan 31, 2011 at 04:34:03PM -0800, Dave Hansen wrote:
> > +	if (pmd_trans_huge(*pmd)) {
> > +		if (pmd_trans_splitting(*pmd)) {
> > +			spin_unlock(&walk->mm->page_table_lock);
> > +			wait_split_huge_page(vma->anon_vma, pmd);
> > +			spin_lock(&walk->mm->page_table_lock);
> > +			goto normal_ptes;
> > +		}
> > +		smaps_pte_entry(*(pte_t *)pmd, addr, HPAGE_SIZE, walk);
> > +		return 0;
> > +	}
> > +normal_ptes:
> >  	split_huge_page_pmd(walk->mm, pmd);
> 
> This line can go away now...?

I did this because I was unsure what keeps khugepaged away from the
newly-split ptes between the wait_split_huge_page() and the
reacquisition of the mm->page_table_lock.  mmap_sem, perhaps?

Looking at follow_page() and some of the other wait_split_huge_page(),
it looks like this is unnecessary.  

-- Dave

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