mm: correct the comment about the value for buddy _mapcount
Subsystems (2)
PATCH 1/1 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 <[email protected]>
--- mm/page_alloc.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-)
mm/page_alloc.c +7 -4
@@ -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.
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