diff options
| author | Wang Sheng-Hui <shhuiw@gmail.com> | 2013-09-11 14:22:48 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2013-09-11 15:58:06 -0700 |
| commit | cf6fe945389e674130dc7564392930cf7fb9f5e8 (patch) | |
| tree | ee75b30bb6fa6dcf8d4499a760095c221c59b00e /mm | |
| parent | fa0f281cf9de8e6877e6536f18a3fc77368df64d (diff) | |
mm: correct the comment about the value for buddy _mapcount
Set _mapcount PAGE_BUDDY_MAPCOUNT_VALUE to make the page buddy. Not the
magic number -2.
Signed-off-by: Wang Sheng-Hui <shhuiw@gmail.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
| -rw-r--r-- | mm/page_alloc.c | 11 |
1 files changed, 7 insertions, 4 deletions
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index ff2782576e39..0ee638f76ebe 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -489,8 +489,10 @@ __find_buddy_index(unsigned long page_idx, unsigned int order) * (c) a page and its buddy have the same order && * (d) a page and its buddy are in the same zone. * - * For recording whether a page is in the buddy system, we set ->_mapcount -2. - * Setting, clearing, and testing _mapcount -2 is serialized by zone->lock. + * For recording whether a page is in the buddy system, we set ->_mapcount + * PAGE_BUDDY_MAPCOUNT_VALUE. + * Setting, clearing, and testing _mapcount PAGE_BUDDY_MAPCOUNT_VALUE is + * serialized by zone->lock. * * For recording page's order, we use page_private(page). */ @@ -528,8 +530,9 @@ static inline int page_is_buddy(struct page *page, struct page *buddy, * as necessary, plus some accounting needed to play nicely with other * parts of the VM system. * At each level, we keep a list of pages, which are heads of continuous - * free pages of length of (1 << order) and marked with _mapcount -2. Page's - * order is recorded in page_private(page) field. + * free pages of length of (1 << order) and marked with _mapcount + * PAGE_BUDDY_MAPCOUNT_VALUE. Page's order is recorded in page_private(page) + * field. * So when we are allocating or freeing one, we can derive the state of the * other. That is, if we allocate a small block, and both were * free, the remainder of the region must be split into blocks. |