mm: optimize compound_head() by avoiding a shared page flag

[sfrench/cifs-2.6.git] / include / linux / page-flags.h

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 96326594e55d9fec9ae803ea61f9659c1e7f6b64..a3c8b60a9c3a72519ef2356a5bf4b2ecb9000c35 100644 (file)
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -6,6 +6,7 @@
 #define PAGE_FLAGS_H
 
 #include <linux/types.h>
+#include <linux/mm_types.h>
 
 /*
  * Various page->flags bits:
@@ -241,6 +242,34 @@ static inline void SetPageUptodate(struct page *page)
 #define __SetPageCompound(page)        __set_bit(PG_compound, &(page)->flags)
 #define __ClearPageCompound(page) __clear_bit(PG_compound, &(page)->flags)
 
+/*
+ * PG_reclaim is used in combination with PG_compound to mark the
+ * head and tail of a compound page
+ *
+ * PG_compound & PG_reclaim    => Tail page
+ * PG_compound & ~PG_reclaim   => Head page
+ */
+
+#define PG_head_tail_mask ((1L << PG_compound) | (1L << PG_reclaim))
+
+#define PageTail(page) ((page->flags & PG_head_tail_mask) \
+                               == PG_head_tail_mask)
+
+static inline void __SetPageTail(struct page *page)
+{
+       page->flags |= PG_head_tail_mask;
+}
+
+static inline void __ClearPageTail(struct page *page)
+{
+       page->flags &= ~PG_head_tail_mask;
+}
+
+#define PageHead(page) ((page->flags & PG_head_tail_mask) \
+                               == (1L << PG_compound))
+#define __SetPageHead(page)    __SetPageCompound(page)
+#define __ClearPageHead(page)  __ClearPageCompound(page)
+
 #ifdef CONFIG_SWAP
 #define PageSwapCache(page)    test_bit(PG_swapcache, &(page)->flags)
 #define SetPageSwapCache(page) set_bit(PG_swapcache, &(page)->flags)