2012/8/23 Michal Hocko [off-list ref]:

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

quoted

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

[...]

quoted

quoted

quoted

quoted

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);

Thanks Gavin. Yes, it's more meaningful. :)

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?

OK.

Thanks
--
Michal Hocko
SUSE Labs

Also sorry for the confusing title. Repost it.
------------------------------------------------------>
Subject: [PATCH] Fix the page address of higher page's buddy calculation

Calculate the page address of higher page's buddy should be based
higher_page with the offset between index of higher page and
index of higher page's buddy.

Signed-off-by: Haifeng Li <redacted>
Signed-off-by: Gavin Shan <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 cdef1d4..642cd62 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c

@@ -536,7 +536,7 @@ 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 = higher_page + (buddy_idx - combined_idx);
                if (page_is_buddy(higher_page, higher_buddy, order + 1)) {
                        list_add_tail(&page->lru,
                                &zone->free_area[order].free_list[migratetype]);
--

1.7.5.4

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