Re: Question about __zone_watermark_ok: why there is a "+ 1" incomputing free_pages?

From: Mel Gorman
Date: Mon Dec 05 2011 - 12:06:51 EST


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@xxxxxxx>
> 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@xxxxxxxxx>
> Signed-off-by: Michal Hocko <mhocko@xxxxxxx>

Acked-by: Mel Gorman <mgorman@xxxxxxx>

--
Mel Gorman
SUSE Labs
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