linux-kernel - Re: [PATCH] mm: hugetlb: bail out unmapping after serving reference page

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Message-Id: <20120321140019.9ca39a31.akpm@linux-foundation.org>
Date:	Wed, 21 Mar 2012 14:00:19 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Hillf Danton <dhillf@...il.com>, Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Michal Hocko <mhocko@...e.cz>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH] mm: hugetlb: bail out unmapping after serving reference
 page

On Thu, 23 Feb 2012 12:12:38 -0800
Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Thu, 23 Feb 2012 21:05:41 +0800
> Hillf Danton <dhillf@...il.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@...il.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?
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