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Date: Thu, 17 Apr 2014 08:28:20 +0800
Message-ID: <CAA_GA1d1uKtqAxhgzx-pwkymvndmJb4PpMLQZHcetvgf16vBeg@mail.gmail.com>
Subject: Re: [PATCH] thp: close race between split and zap huge pages
From: Bob Liu <lliubbo@gmail.com>
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To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Andrea Arcangeli <aarcange@redhat.com>, Andrew Morton <akpm@linux-foundation.org>, Rik van Riel <riel@redhat.com>, Mel Gorman <mgorman@suse.de>, Michel Lespinasse <walken@google.com>, Sasha Levin <sasha.levin@oracle.com>, Dave Jones <davej@redhat.com>, Vlastimil Babka <vbabka@suse.cz>, Linux-MM <linux-mm@kvack.org>, Linux-Kernel <linux-kernel@vger.kernel.org>

On Wed, Apr 16, 2014 at 4:42 PM, Kirill A. Shutemov
<kirill@shutemov.name> wrote:
> 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.

Oh, yes. That's right.

BTW, it looks like this bug was introduced by the same reason.
https://lkml.org/lkml/2014/4/16/403

-- 
Regards,
--Bob

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