Set _mapcount PAGE_BUDDY_MAPCOUNT_VALUE to make the page buddy. Not the magic number -2. Signed-off-by: Wang Sheng-Hui <shhuiw@xxxxxxxxx> --- mm/page_alloc.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index b100255..345f57b 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -488,8 +488,10 @@ __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). */ @@ -527,8 +529,9 @@ 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. -- 1.7.10.4 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>