thp: clear page compound

split_huge_page must transform a compound page to a regular page and needs
ClearPageCompound.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Christoph Lameter <cl@linux-foundation.org>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/page-flags.h

@@ -347,7 +347,7 @@ static inline void set_page_writeback(struct page *page)
  * tests can be used in performance sensitive paths. PageCompound is
  * generally not used in hot code paths.
  */
-__PAGEFLAG(Head, head)
+__PAGEFLAG(Head, head) CLEARPAGEFLAG(Head, head)
 __PAGEFLAG(Tail, tail)
 
 static inline int PageCompound(struct page *page)
@@ -355,6 +355,13 @@ static inline int PageCompound(struct page *page)
 	return page->flags & ((1L << PG_head) | (1L << PG_tail));
 
 }
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+static inline void ClearPageCompound(struct page *page)
+{
+	BUG_ON(!PageHead(page));
+	ClearPageHead(page);
+}
+#endif
 #else
 /*
  * Reduce page flag use as much as possible by overlapping
@@ -392,6 +399,14 @@ static inline void __ClearPageTail(struct page *page)
 	page->flags &= ~PG_head_tail_mask;
 }
 
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+static inline void ClearPageCompound(struct page *page)
+{
+	BUG_ON((page->flags & PG_head_tail_mask) != (1 << PG_compound));
+	clear_bit(PG_compound, &page->flags);
+}
+#endif
+
 #endif /* !PAGEFLAGS_EXTENDED */
 
 #ifdef CONFIG_MMU