From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Date: Wed, 26 Sep 2012 01:32:55 +0000 (+1000)
Subject: pagemap: fix wrong KPF_THP on slab pages
X-Git-Tag: next-20120926~2^2~406
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=ae9a556165646942828021ec72492f6cc6684aa8;p=karo-tx-linux.git

pagemap: fix wrong KPF_THP on slab pages

KPF_THP can be set on non-huge compound pages like slab pages, because
PageTransCompound only sees PG_head and PG_tail. Obviously this is a bug
and breaks user space applications which look for thp via /proc/kpageflags.
Currently thp is constructed only on anonymous pages, so this patch makes
KPF_THP be set when both of PageAnon and PageTransCompound are true.

Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Andi Kleen <andi.kleen@intel.com>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/fs/proc/page.c b/fs/proc/page.c
index 7fcd0d60a968..f7cd2f6c0a58 100644
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -115,7 +115,12 @@ u64 stable_page_flags(struct page *page)
 		u |= 1 << KPF_COMPOUND_TAIL;
 	if (PageHuge(page))
 		u |= 1 << KPF_HUGE;
-	else if (PageTransCompound(page))
+	/*
+	 * Since THP is relevant only for anonymous pages so far, we check it
+	 * explicitly with PageAnon. Otherwise thp is confounded with non-huge
+	 * compound pages like slab pages.
+	 */
+	else if (PageTransCompound(page) && PageAnon(page))
 		u |= 1 << KPF_THP;
 
 	/*