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

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Message-Id: <1394607486-31493-1-git-send-email-jungsoo.son@lge.com>
Date:	Wed, 12 Mar 2014 15:58:06 +0900
From:	Jungsoo Son <jungsoo.son@....com>
To:	akpm@...ux-foundation.org
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Jungsoo Son <jungsoo.son@....com>,
	Minchan Kim <minchan@...nel.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: [PATCH] page owners: correct page->order when to free page

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@....com>
Cc: Minchan Kim <minchan@...nel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
---
 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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