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Date: Wed, 21 Mar 2012 14:00:19 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Hillf Danton <dhillf@gmail.com>, Linux-MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>, Michal Hocko <mhocko@suse.cz>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        Hugh Dickins <hughd@google.com>
Subject: Re: [PATCH] mm: hugetlb: bail out unmapping after serving reference
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On Thu, 23 Feb 2012 12:12:38 -0800
Andrew Morton <akpm@linux-foundation.org> wrote:

> On Thu, 23 Feb 2012 21:05:41 +0800
> Hillf Danton <dhillf@gmail.com> wrote:
> 
> > and a follow-up cleanup also attached.
> 
> Please, never put more than one patches in an email - it is rather a
> pain to manually unpick everything.
> 
> > When unmapping given VM range, a couple of code duplicate, such as pte_page()
> > and huge_pte_none(), so a cleanup needed to compact them together.
> > 
> > Signed-off-by: Hillf Danton <dhillf@gmail.com>
> > ---
> > 
> > --- a/mm/hugetlb.c	Thu Feb 23 20:13:06 2012
> > +++ b/mm/hugetlb.c	Thu Feb 23 20:30:16 2012
> > @@ -2245,16 +2245,23 @@ void __unmap_hugepage_range(struct vm_ar
> >  		if (huge_pmd_unshare(mm, &address, ptep))
> >  			continue;
> > 
> > +		pte = huge_ptep_get(ptep);
> > +		if (huge_pte_none(pte))
> > +			continue;
> > +
> > +		/*
> > +		 * HWPoisoned hugepage is already unmapped and dropped reference
> > +		 */
> > +		if (unlikely(is_hugetlb_entry_hwpoisoned(pte)))
> > +			continue;
> > +
> > +		page = pte_page(pte);
> >  		/*
> >  		 * If a reference page is supplied, it is because a specific
> >  		 * page is being unmapped, not a range. Ensure the page we
> >  		 * are about to unmap is the actual page of interest.
> >  		 */
> >  		if (ref_page) {
> > -			pte = huge_ptep_get(ptep);
> > -			if (huge_pte_none(pte))
> > -				continue;
> > -			page = pte_page(pte);
> >  			if (page != ref_page)
> >  				continue;
> > 
> > @@ -2267,16 +2274,6 @@ void __unmap_hugepage_range(struct vm_ar
> >  		}
> > 
> >  		pte = huge_ptep_get_and_clear(mm, address, ptep);
> > -		if (huge_pte_none(pte))
> > -			continue;
> > -
> > -		/*
> > -		 * HWPoisoned hugepage is already unmapped and dropped reference
> > -		 */
> > -		if (unlikely(is_hugetlb_entry_hwpoisoned(pte)))
> > -			continue;
> > -
> > -		page = pte_page(pte);
> >  		if (pte_dirty(pte))
> >  			set_page_dirty(page);
> >  		list_add(&page->lru, &page_list);
> 
> This changes behaviour when ref_page refers to a hwpoisoned page.

Respond, please?