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From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
To: Hillf Danton <hillf.zj@alibaba-inc.com>
CC: "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "'Kirill A. Shutemov'" <kirill.shutemov@linux.intel.com>,
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        "'Balbir Singh'" <bsingharora@gmail.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "'Naoya Horiguchi'" <nao.horiguchi@gmail.com>,
        "'Anshuman Khandual'" <khandual@linux.vnet.ibm.com>
Subject: Re: [PATCH v2 07/12] mm: thp: check pmd migration entry in common
 path
Thread-Topic: [PATCH v2 07/12] mm: thp: check pmd migration entry in common
 path
Thread-Index: AQHSOVF91G9mSKw0IEiSF7PKRh5xwqDRWmOAgAADwwCAAAHkAIAAAaEA
Date: Thu, 10 Nov 2016 09:34:10 +0000
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On Thu, Nov 10, 2016 at 05:28:20PM +0800, Hillf Danton wrote:
> On Thursday, November 10, 2016 5:22 PM Naoya Horiguchi wrote:
> > On Thu, Nov 10, 2016 at 05:08:07PM +0800, Hillf Danton wrote:
> > > On Tuesday, November 08, 2016 7:32 AM Naoya Horiguchi wrote:
> > > >
> > > > @@ -1013,6 +1027,9 @@ int do_huge_pmd_wp_page(struct fault_env *fe, pmd_t orig_pmd)
> > > >  	if (unlikely(!pmd_same(*fe->pmd, orig_pmd)))
> > > >  		goto out_unlock;
> > > >
> > > > +	if (unlikely(!pmd_present(orig_pmd)))
> > > > +		goto out_unlock;
> > > > +
> > >
> > > Can we encounter a migration entry after acquiring ptl ?
> > 
> > I think we can. thp migration code releases ptl after converting pmd into
> > migration entry, so other code can see it even within ptl.
> > 
> But we have a pmd_same check there, you see. 

You're right. So we can omit this pmd_present check.

Thanks,
Naoya Horiguchi