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Date: Thu, 25 Apr 2013 19:28:34 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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Subject: Re: mm: BUG in do_huge_pmd_wp_page
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To: Simon Jeons <simon.jeons@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>, Sasha Levin <sasha.levin@oracle.com>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Andrew Morton <akpm@linux-foundation.org>, David Rientjes <rientjes@google.com>, Andrea Arcangeli <aarcange@redhat.com>, Mel Gorman <mgorman@suse.de>, Dave Jones <davej@redhat.com>, linux-mm <linux-mm@kvack.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>

On 04/24/2013 04:40 PM, Simon Jeons wrote:
> 
> I see in memblock_trim_memory(): start = round_up(orig_start, align);
> here align is PAGE_SIZE, so the dump of zone ranges in my machine is [ 
>   0.000000]  DMA      [mem 0x00001000-0x00ffffff]. Why PFN 0 is not
> used? just for align?
> 

PFN 0 contains the real-mode interrupt vector table and BIOS data area,
so we just reserve it.  Avoids issues with zero being special, too.

	-hpa


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