page-flags: look at head page if the flag is encoded in page->mapping

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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 55a69c40e4aed14593b91a0896a63b2269b86a79..07fa2781df23e7601830daa1e95392bfdaca5399 100644 (file)
--- 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);
 }