linux-kernel - Re: [PATCH] thp: close race between split and zap huge pages

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Message-ID: <20140416084236.GA23247@node.dhcp.inet.fi>
Date:	Wed, 16 Apr 2014 11:42:36 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Bob Liu <lliubbo@...il.com>
Cc:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Michel Lespinasse <walken@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Dave Jones <davej@...hat.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Linux-MM <linux-mm@...ck.org>,
	Linux-Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] thp: close race between split and zap huge pages

On Wed, Apr 16, 2014 at 07:52:29AM +0800, Bob Liu wrote:
> >         *ptl = pmd_lock(mm, pmd);
> > -       if (pmd_none(*pmd))
> > +       if (!pmd_present(*pmd))
> >                 goto unlock;
> 
> But I didn't get the idea why pmd_none() was removed?

!pmd_present(*pmd) is weaker check then pmd_none(*pmd). I mean if
pmd_none(*pmd) is true then pmd_present(*pmd) is always false.
Correct me if I'm wrong.

-- 
 Kirill A. Shutemov
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