On Thu 23-08-12 20:30:34, Gavin Shan wrote:

On Thu, Aug 23, 2012 at 06:21:06PM +0800, Li Haifeng wrote:

[...]

quoted

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From d7cd78f9d71a5c9ddeed02724558096f0bb4508a Mon Sep 17 00:00:00 2001
From: Haifeng Li <redacted>
Date: Thu, 23 Aug 2012 16:27:19 +0800
Subject: [PATCH] Fixup the page of buddy_higher address's calculation

Some general questions:
Any word about the change? Is it really that obvious? Why do you think the
current state is incorrect? How did you find out?

And more specific below:

quoted

Signed-off-by: Haifeng Li <redacted>
---
 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 ddbc17d..5588f68 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c

@@ -579,7 +579,7 @@ static inline void __free_one_page(struct page *page,
                combined_idx = buddy_idx & page_idx;
                higher_page = page + (combined_idx - page_idx);
                buddy_idx = __find_buddy_index(combined_idx, order + 1);
-               higher_buddy = page + (buddy_idx - combined_idx);
+               higher_buddy = page + (buddy_idx - page_idx);

Haifeng, Not sure it would be better? At least, the expression
would be more explicitly meaningful than yours.

		    higher_buddy = higher_page + (buddy_idx - combined_idx);

Yes, indeed. It would be also good to mention that this is a regression
since 43506fad (mm/page_alloc.c: simplify calculation of combined index
of adjacent buddy lists). IIUC this basically disables the heuristic
because page_is_buddy will fail for order+1, right?

Maybe 2.6.38+ stable candidate, then.

Could you repost with the full changelog, please?

Thanks
-- 
Michal Hocko
SUSE Labs

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