From: Michal Hocko <mhocko@suse.cz>
Date: Thu, 8 Dec 2011 04:41:50 +0000 (+1100)
Subject: mm: fix off-by-two in __zone_watermark_ok()
X-Git-Tag: next-20111209~3^2~139
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=d5219b0c21a77cdcfc381fdd9fbd4d8118f4bdcb;p=karo-tx-linux.git

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.

Reported-by: Wang Sheng-Hui <shhuiw@gmail.com>
Signed-off-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c52349a0adb0..af5467e3faa4 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1538,7 +1538,7 @@ static bool __zone_watermark_ok(struct zone *z, int order, unsigned long mark,
 	long min = mark;
 	int o;
 
-	free_pages -= (1 << order) + 1;
+	free_pages -= (1 << order) - 1;
 	if (alloc_flags & ALLOC_HIGH)
 		min -= min / 2;
 	if (alloc_flags & ALLOC_HARDER)