Re: [PATCH] use NODES_SHIFT to calculate ZONE_SHIFT

[Andrew Morton]

jbarnes@xxxxxxx (Jesse Barnes) wrote:
>
> Now that we have a proper NODES_SHIFT value, we need to use it to define
> ZONE_SHIFT otherwise we'll spill over 8 bits if we have more than 85
> nodes.  How does this look?  The '+2' should really be
> log2(MAX_NR_NODES), but I think this is an improvement over what was
> there.

You mean log2(MAX_NR_ZONES).

How about we do it this way, so at least the duplicated information is on
adjacent lines, and they are unlikely to get out of sync?


 
diff -puN include/linux/mm.h~ZONE_SHIFT-from-NODES_SHIFT include/linux/mm.h
--- 25/include/linux/mm.h~ZONE_SHIFT-from-NODES_SHIFT	Fri Nov  7 13:51:22 2003
+++ 25-akpm/include/linux/mm.h	Fri Nov  7 13:55:11 2003
@@ -322,8 +322,10 @@ static inline void put_page(struct page 
 /*
  * The zone field is never updated after free_area_init_core()
  * sets it, so none of the operations on it need to be atomic.
+ * We'll have up to log2(MAX_NUMNODES * MAX_NR_ZONES) zones
+ * total, so we use NODES_SHIFT here to get enough bits.
  */
-#define ZONE_SHIFT (BITS_PER_LONG - 8)
+#define ZONE_SHIFT (BITS_PER_LONG - NODES_SHIFT - MAX_NR_ZONES_SHIFT)
 
 struct zone;
 extern struct zone *zone_table[];
diff -puN include/linux/mmzone.h~ZONE_SHIFT-from-NODES_SHIFT include/linux/mmzone.h
--- 25/include/linux/mmzone.h~ZONE_SHIFT-from-NODES_SHIFT	Fri Nov  7 13:51:49 2003
+++ 25-akpm/include/linux/mmzone.h	Fri Nov  7 13:57:19 2003
@@ -159,7 +159,10 @@ struct zone {
 #define ZONE_DMA		0
 #define ZONE_NORMAL		1
 #define ZONE_HIGHMEM		2
-#define MAX_NR_ZONES		3
+
+#define MAX_NR_ZONES		3	/* Sync this with MAX_NR_ZONES_SHIFT */
+#define MAX_NR_ZONES_SHIFT	2	/* ceil(log2(MAX_NR_ZONES)) */
+
 #define GFP_ZONEMASK	0x03
 
 /*

_

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