[rfc 06/10] Sparsemem: Vmemmap does not need section bits

[Christoph Lameter]

Sparsemem vmemmap does not need any section bits. This patch has
the effect of reducing the number of bits used in page->flags
by at least 6.

Signed-off-by: Christoph Lameter <clameter@xxxxxxx>

---
 include/linux/mm.h |   11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

Index: linux-2.6/include/linux/mm.h
===================================================================
--- linux-2.6.orig/include/linux/mm.h	2008-03-03 15:45:07.047305876 -0800
+++ linux-2.6/include/linux/mm.h	2008-03-03 15:49:04.686432973 -0800
@@ -390,11 +390,11 @@ static inline void set_compound_order(st
  * we have run out of space and have to fall back to an
  * alternate (slower) way of determining the node.
  *
- *        No sparsemem: |       NODE     | ZONE | ... | FLAGS |
- * with space for node: | SECTION | NODE | ZONE | ... | FLAGS |
- *   no space for node: | SECTION |     ZONE    | ... | FLAGS |
+ * No sparsemem or sparsemem vmemmap: |       NODE     | ZONE | ... | FLAGS |
+ * classic sparse with space for node:| SECTION | NODE | ZONE | ... | FLAGS |
+ * classic sparse no space for node:  | SECTION |     ZONE    | ... | FLAGS |
  */
-#ifdef CONFIG_SPARSEMEM
+#if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
 #define SECTIONS_WIDTH		SECTIONS_SHIFT
 #else
 #define SECTIONS_WIDTH		0
@@ -405,6 +405,9 @@ static inline void set_compound_order(st
 #if SECTIONS_WIDTH+ZONES_WIDTH+NODES_SHIFT <= FLAGS_RESERVED
 #define NODES_WIDTH		NODES_SHIFT
 #else
+#ifdef CONFIG_SPARSEMEM_VMEMMAP
+#error "Vmemmap: No space for nodes field in page flags"
+#endif
 #define NODES_WIDTH		0
 #endif
 

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