mm: return boolean from page_has_private()

Make page_has_private() return a true boolean value and remove the double
negations from the two callsites using it for arithmetic.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Christoph Lameter <cl@linux-foundation.org>
Reviewed-by: Christoph Lameter <cl@linux-foundation.org>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 172119c..f5b5f02 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -286,7 +286,7 @@
 
 static inline int is_page_cache_freeable(struct page *page)
 {
-	return page_count(page) - !!page_has_private(page) == 2;
+	return page_count(page) - page_has_private(page) == 2;
 }
 
 static int may_write_to_queue(struct backing_dev_info *bdi)