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Date: Thu, 14 Oct 2010 13:18:33 +0800
From: =?utf-8?Q?Am=C3=A9rico?= Wang <xiyou.wangcong@gmail.com>
To: gaoqiang <834555262@qq.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: dear list
Message-ID: <20101014051833.GA5167@cr0.nay.redhat.com>
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On Thu, Sep 02, 2010 at 02:51:48PM +0800, gaoqiang wrote:
>I'm a newbie and got some question when learning the linux kernel
>
>about a macro:
>
>page_to_pfn(pg)
>
>I traced its definition,and finally got that:
>
>#define __page_to_pfn(page) ((unsigned long)((page) - mem_map) +
>ARCH_PFN_OFFSET)
>
>
>why hot ((unsigned long)((page)-mem_map + ARCH_PFN_OFFSET)/sizeof
>(struct page)
>

Sorry for the really long delay.

That is because both 'page' and 'mem_map' have type 'struct page *'.