SLUB: Do our own flags based on PG_active and PG_error

The atomicity when handling flags in SLUB is not necessary since both flags
used by SLUB are not updated in a racy way. Flag updates are either done
during slab creation or destruction or under slab_lock. Some of these flags
do not have the non atomic variants that we need. So define our own.

Signed-off-by: Christoph Lameter <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

mm/slub.c

···
  * 			the fast path and disables lockless freelists.
  */
 
+#define FROZEN (1 << PG_active)
+
+#ifdef CONFIG_SLUB_DEBUG
+#define SLABDEBUG (1 << PG_error)
+#else
+#define SLABDEBUG 0
+#endif
+
 static inline int SlabFrozen(struct page *page)
 {
-	return PageActive(page);
+	return page->flags & FROZEN;
 }
 
 static inline void SetSlabFrozen(struct page *page)
 {
-	SetPageActive(page);
+	page->flags |= FROZEN;
 }
 
 static inline void ClearSlabFrozen(struct page *page)
 {
-	ClearPageActive(page);
+	page->flags &= ~FROZEN;
 }
 
 static inline int SlabDebug(struct page *page)
 {
-#ifdef CONFIG_SLUB_DEBUG
-	return PageError(page);
-#else
-	return 0;
-#endif
+	return page->flags & SLABDEBUG;
 }
 
 static inline void SetSlabDebug(struct page *page)
 {
-#ifdef CONFIG_SLUB_DEBUG
-	SetPageError(page);
-#endif
+	page->flags |= SLABDEBUG;
 }
 
 static inline void ClearSlabDebug(struct page *page)
 {
-#ifdef CONFIG_SLUB_DEBUG
-	ClearPageError(page);
-#endif
+	page->flags &= ~SLABDEBUG;
 }
 
 /*