(12/5/11 11:14 AM), Michal Hocko wrote:
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. --- 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> --- mm/page_alloc.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 9dd443d..8a2f1b6 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1457,7 +1457,7 @@ 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)
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