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

[Kirill A. Shutemov]

PageAnon() and PageKsm() look on 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 on 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 55a69c40e4ae..07fa2781df23 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -385,6 +385,7 @@ PAGEFLAG_FALSE(HWPoison)
 
 static inline int PageAnon(struct page *page)
 {
+	page = compound_head(page);
 	return ((unsigned long)page->mapping & PAGE_MAPPING_ANON) != 0;
 }
 
@@ -397,6 +398,7 @@ 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);
 }
-- 
2.1.4

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