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authorWang Sheng-Hui <shhuiw@gmail.com>2013-09-11 14:22:48 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2013-09-11 15:58:06 -0700
commitcf6fe945389e674130dc7564392930cf7fb9f5e8 (patch)
treeee75b30bb6fa6dcf8d4499a760095c221c59b00e /mm/page_alloc.c
parentfa0f281cf9de8e6877e6536f18a3fc77368df64d (diff)
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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/page_alloc.c')
-rw-r--r--mm/page_alloc.c11
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.