linux-kernel - Re: Fixup the page of buddy_higher address's calculation

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Message-ID: <CAFNq8R6uiNhBR8BJD2B=ehFFk=aY0Be1DLRRbiXWKQP4LHPC=Q@mail.gmail.com>
Date:	Fri, 24 Aug 2012 17:08:36 +0800
From:	Li Haifeng <omycle@...il.com>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Gavin Shan <shangw@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	Minchan Kim <minchan.kim@...il.com>,
	Johannes Weiner <jweiner@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: Fixup the page of buddy_higher address's calculation

2012/8/24 Michal Hocko <mhocko@...e.cz>:
> On Fri 24-08-12 10:08:20, Li Haifeng wrote:
> [...]
>> 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.
>
> Sorry for insisting but could you add an information about when this has
> been introduced (I have mentioned the commit in the other email) and the
> effect of the bug so that we can consider whether this is worth
> backporting to stable trees.
>
>> Signed-off-by: Haifeng Li <omycle@...il.com>
>> Signed-off-by: Gavin Shan <shangw@...ux.vnet.ibm.com>
>
> Other than that
> Reviewed-by: Michal Hocko <mhocko@...e.cz>
>
>> ---
>>  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
>
> --
> Michal Hocko
> SUSE Labs

I am sorry Michal. I misinterpreted what you mean.

And the post blow is OK?
------------------------------------------>
Subject: [PATCH] Fix the page address of higher page's buddy calculation

The heuristic method for buddy has been introduced since
43506fad(mm/page_alloc.c: simplify calculation of combined index
of adjacent buddy lists). But the page address of higher page's
buddy was wrongly calculated, which will lead page_is_buddy to
fail for ever. IOW, the heuristic method would be disabled with the wrong
page address of higher page's buddy.

Calculating 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 <omycle@...il.com>
Signed-off-by: Gavin Shan <shangw@...ux.vnet.ibm.com>
Reviewed-by: Michal Hocko <mhocko@...e.cz>
---
 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..0754a3c 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 = 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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