[PATCH] page owners: correct page->order when to free page

[Jungsoo Son]

When I use PAGE_OWNER in mmotm tree, I found a problem that mismatches
the number of allocated pages. When I investigate, the problem is that
set_page_order is called for only a head page if freed page is merged to
a higher order page in the buddy allocator so tail pages of the higher
order page couldn't be reset to page->order = -1.

It means when we do 'cat /proc/page-owner', it could show wrong
information.

So page->order should be set to -1 for all the tail pages as well as the
first page before buddy allocator merges them.

This patch is for clearing page->order of all the tail pages in
free_pages_prepare() when to free page.

Signed-off-by: Jungsoo Son <jungsoo.son@xxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
---
 mm/page_alloc.c |    7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index dfbc967..9b946f0 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -741,6 +741,13 @@ static bool free_pages_prepare(struct page *page, unsigned int order)
 	if (bad)
 		return false;
 
+#ifdef CONFIG_PAGE_OWNER
+	for (i = 0; i < (1 << order); i++) {
+		struct page *p = (page + i);
+		p->order = -1;
+	}
+#endif
+
 	if (!PageHighMem(page)) {
 		debug_check_no_locks_freed(page_address(page),
 					   PAGE_SIZE << order);
-- 
1.7.9.5

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