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Date: Mon, 5 Dec 2011 17:14:43 +0100
From: Michal Hocko <mhocko@suse.cz>
Subject: Re: Question about __zone_watermark_ok: why there is a "+ 1" in
 computing free_pages?
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To: Wang Sheng-Hui <shhuiw@gmail.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Mel Gorman <mgorman@suse.de>, Andrew Morton <akpm@linux-foundation.org>

On Fri 25-11-11 09:21:35, Wang Sheng-Hui wrote:
> In line 1459, we have "free_pages -= (1 << order) + 1;".
> Suppose allocating one 0-order page, here we'll get
>     free_pages -= 1 + 1
> I wonder why there is a "+ 1"?

Good spot. Check the patch bellow.
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