[05/18] Page flags: Add PageVcompound()

[Christoph Lameter <clameter@sgi.com>]

Add a another page flag that can be used to figure out if a compound
page is virtually mapped. The mark is necessary since we have to know
when freeing pages if we have to destroy a virtual mapping. No additional
flag is consumed through the use of PG_swapcache together with PG_compound
(similar to PageHead() and PageTail()).

Signed-off-by: Christoph Lameter <clameter@sgi.com>

---
 include/linux/page-flags.h |   18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

Index: linux-2.6/include/linux/page-flags.h
===================================================================
--- linux-2.6.orig/include/linux/page-flags.h	2007-10-03 19:31:51.000000000 -0700
+++ linux-2.6/include/linux/page-flags.h	2007-10-03 19:34:37.000000000 -0700
@@ -248,6 +248,24 @@ static inline void __ClearPageTail(struc
 #define __SetPageHead(page)	__SetPageCompound(page)
 #define __ClearPageHead(page)	__ClearPageCompound(page)
 
+/*
+ * PG_swapcache is used in combination with PG_compound to indicate
+ * that a compound page was allocated via vmalloc.
+ */
+#define PG_vcompound_mask ((1L << PG_compound) | (1L << PG_swapcache))
+#define PageVcompound(page)	((page->flags & PG_vcompound_mask) \
+					== PG_vcompound_mask)
+
+static inline void __SetPageVcompound(struct page *page)
+{
+	page->flags |= PG_vcompound_mask;
+}
+
+static inline void __ClearPageVcompound(struct page *page)
+{
+	page->flags &= ~PG_vcompound_mask;
+}
+
 #ifdef CONFIG_SWAP
 #define PageSwapCache(page)	test_bit(PG_swapcache, &(page)->flags)
 #define SetPageSwapCache(page)	set_bit(PG_swapcache, &(page)->flags)

-- 
-
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