[PATCH] x86_64: group memnodemap and memnodeshift in a memnode structure

pfn_to_page() and others need to access both memnode_shift and the very
first bytes of memnodemap[]. If we force memnode_shift to be just before the
memnodemap array, we can reduce the memory footprint to one cache line
instead of two for most setups. This patch introduce a 'memnode' structure
where shift and map[] are carefully placed.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/x86_64/mm/numa.c

@@ -25,8 +25,7 @@
 struct pglist_data *node_data[MAX_NUMNODES] __read_mostly;
 bootmem_data_t plat_node_bdata[MAX_NUMNODES];
 
-int memnode_shift;
-u8  memnodemap[NODEMAPSIZE];
+struct memnode memnode;
 
 unsigned char cpu_to_node[NR_CPUS] __read_mostly = {
 	[0 ... NR_CPUS-1] = NUMA_NO_NODE
@@ -367,8 +366,7 @@ void __init init_cpu_to_node(void)
 
 EXPORT_SYMBOL(cpu_to_node);
 EXPORT_SYMBOL(node_to_cpumask);
-EXPORT_SYMBOL(memnode_shift);
-EXPORT_SYMBOL(memnodemap);
+EXPORT_SYMBOL(memnode);
 EXPORT_SYMBOL(node_data);
 
 #ifdef CONFIG_DISCONTIGMEM

include/asm-x86_64/mmzone.h

@@ -15,8 +15,13 @@
 #define NODEMAPSIZE 0xfff
 
 /* Simple perfect hash to map physical addresses to node numbers */
-extern int memnode_shift; 
-extern u8  memnodemap[NODEMAPSIZE]; 
+struct memnode {
+	int shift;
+	u8 map[NODEMAPSIZE];
+} ____cacheline_aligned;
+extern struct memnode memnode;
+#define memnode_shift memnode.shift
+#define memnodemap memnode.map
 
 extern struct pglist_data *node_data[];