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

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Message-ID: <CAA_GA1d1uKtqAxhgzx-pwkymvndmJb4PpMLQZHcetvgf16vBeg@mail.gmail.com>
Date:	Thu, 17 Apr 2014 08:28:20 +0800
From:	Bob Liu <lliubbo@...il.com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
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 4:42 PM, Kirill A. Shutemov
<kirill@...temov.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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