linux-kernel - Re: [PATCH 2/2] hugetlbfs: add swap entry check in follow_hugetlb

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Date:	Fri, 29 Mar 2013 13:23:38 -0400
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Hugh Dickins <hughd@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	stable@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] hugetlbfs: add swap entry check in
 follow_hugetlb_page()

Hi,

On Fri, Mar 29, 2013 at 02:57:30PM +0100, Michal Hocko wrote:
> On Thu 28-03-13 11:42:38, Naoya Horiguchi wrote:
> [...]
> > @@ -2968,7 +2968,8 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
> >  		 * first, for the page indexing below to work.
> >  		 */
> >  		pte = huge_pte_offset(mm, vaddr & huge_page_mask(h));
> > -		absent = !pte || huge_pte_none(huge_ptep_get(pte));
> > +		absent = !pte || huge_pte_none(huge_ptep_get(pte)) ||
> > +			is_swap_pte(huge_ptep_get(pte));
> 
> is_swap_pte doesn't seem right. Shouldn't you use is_hugetlb_entry_hwpoisoned
> instead?

I tested only hwpoisoned hugepage, but the same can happen for hugepages
under migration. So I intended to filter out all types of swap entries.
The local variable 'absent' seems to mean whether data on the address
is immediately available, so swap type entry isn't included in it.

Thanks,
Naoya
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