From 822cdd1152265d87fcfc974e06c3b68f762987fd Mon Sep 17 00:00:00 2001
From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Date: Fri, 15 Jan 2016 16:52:03 -0800
Subject: [PATCH] page-flags: look at head page if the flag is encoded in
 page->mapping
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PageAnon() and PageKsm() look at lower bits of page->mapping to check if
the page is Anon or KSM.  page->mapping can be overloaded in tail pages.

Let's always look at head page to avoid false-positives.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Christoph Lameter <cl@linux.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Steve Capper <steve.capper@linaro.org>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Jérôme Glisse <jglisse@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 include/linux/page-flags.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 818fa39538a9..190f1915a097 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -176,7 +176,7 @@ static inline int PageCompound(struct page *page)
 #define PF_NO_TAIL(page, enforce) ({					\
 		VM_BUG_ON_PGFLAGS(enforce && PageTail(page), page);	\
 		compound_head(page);})
-#define PF_NO_COMPOUND(page, enforce) ({					\
+#define PF_NO_COMPOUND(page, enforce) ({				\
 		VM_BUG_ON_PGFLAGS(enforce && PageCompound(page), page);	\
 		page;})
 
@@ -381,6 +381,7 @@ PAGEFLAG(Idle, idle, PF_ANY)
 
 static inline int PageAnon(struct page *page)
 {
+	page = compound_head(page);
 	return ((unsigned long)page->mapping & PAGE_MAPPING_ANON) != 0;
 }
 
@@ -393,6 +394,7 @@ static inline int PageAnon(struct page *page)
  */
 static inline int PageKsm(struct page *page)
 {
+	page = compound_head(page);
 	return ((unsigned long)page->mapping & PAGE_MAPPING_FLAGS) ==
 				(PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
 }
-- 
2.20.1