move page writeback acounting out of macros

page-writeback accounting is presently performed in the page-flags macros.
This is inconsistent and a bit ugly and makes it awkward to implement
per-backing_dev under-writeback page accounting.

So move this accounting down to the callsite(s).
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/page-flags.h

@@ -189,37 +189,15 @@ static inline void SetPageUptodate(struct page *page)
 #define __SetPagePrivate(page)  __set_bit(PG_private, &(page)->flags)
 #define __ClearPagePrivate(page) __clear_bit(PG_private, &(page)->flags)
 
+/*
+ * Only test-and-set exist for PG_writeback.  The unconditional operators are
+ * risky: they bypass page accounting.
+ */
 #define PageWriteback(page)	test_bit(PG_writeback, &(page)->flags)
-#define SetPageWriteback(page)						\
-	do {								\
-		if (!test_and_set_bit(PG_writeback,			\
-				&(page)->flags))			\
-			inc_zone_page_state(page, NR_WRITEBACK);	\
-	} while (0)
-#define TestSetPageWriteback(page)					\
-	({								\
-		int ret;						\
-		ret = test_and_set_bit(PG_writeback,			\
-					&(page)->flags);		\
-		if (!ret)						\
-			inc_zone_page_state(page, NR_WRITEBACK);	\
-		ret;							\
-	})
-#define ClearPageWriteback(page)					\
-	do {								\
-		if (test_and_clear_bit(PG_writeback,			\
-				&(page)->flags))			\
-			dec_zone_page_state(page, NR_WRITEBACK);	\
-	} while (0)
-#define TestClearPageWriteback(page)					\
-	({								\
-		int ret;						\
-		ret = test_and_clear_bit(PG_writeback,			\
-				&(page)->flags);			\
-		if (ret)						\
-			dec_zone_page_state(page, NR_WRITEBACK);	\
-		ret;							\
-	})
+#define TestSetPageWriteback(page) test_and_set_bit(PG_writeback,	\
+							&(page)->flags)
+#define TestClearPageWriteback(page) test_and_clear_bit(PG_writeback,	\
+							&(page)->flags)
 
 #define PageBuddy(page)		test_bit(PG_buddy, &(page)->flags)
 #define __SetPageBuddy(page)	__set_bit(PG_buddy, &(page)->flags)

mm/page-writeback.c

@@ -987,6 +987,8 @@ int test_clear_page_writeback(struct page *page)
 	} else {
 		ret = TestClearPageWriteback(page);
 	}
+	if (ret)
+		dec_zone_page_state(page, NR_WRITEBACK);
 	return ret;
 }
 
@@ -1012,6 +1014,8 @@ int test_set_page_writeback(struct page *page)
 	} else {
 		ret = TestSetPageWriteback(page);
 	}
+	if (!ret)
+		inc_zone_page_state(page, NR_WRITEBACK);
 	return ret;
 
 }