linux-kernel - Re: Question about __zone_watermark_ok: why there is a "+ 1" in computing free

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Message-ID: <20111205170646.GC5070@suse.de>
Date:	Mon, 5 Dec 2011 17:06:46 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Wang Sheng-Hui <shhuiw@...il.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: Question about __zone_watermark_ok: why there is a "+ 1" in
 computing free_pages?

On Mon, Dec 05, 2011 at 05:14:43PM +0100, Michal Hocko wrote:
> From 38a1cf351b111e8791d2db538c8b0b912f5df8b8 Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@...e.cz>
> Date: Mon, 5 Dec 2011 17:04:23 +0100
> Subject: [PATCH] mm: fix off-by-two in __zone_watermark_ok
> 
> 88f5acf8 [mm: page allocator: adjust the per-cpu counter threshold when
> memory is low] changed the form how free_pages is calculated but it
> forgot that we used to do free_pages - ((1 << order) - 1) so we ended up
> with off-by-two when calculating free_pages.
> 
> Spotted-by: Wang Sheng-Hui <shhuiw@...il.com>
> Signed-off-by: Michal Hocko <mhocko@...e.cz>

Acked-by: Mel Gorman <mgorman@...e.de>

-- 
Mel Gorman
SUSE Labs
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