[PATCH 15/16] page-flags: look at head page if the flag is encoded in page->mapping

[Kirill A. Shutemov]

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@xxxxxxxxxxxxxxx>
---
 include/linux/page-flags.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index e3ccd95de660..6f5df65d1038 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -369,6 +369,7 @@ 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;
 }
 
@@ -381,6 +382,7 @@ 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);
 }
-- 
2.5.1

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