Add CONFIG_MIGRATION for page migration support

Include page migration if the system is NUMA or having a memory model
that allows distinct areas of memory (SPARSEMEM, DISCONTIGMEM).

And:
- Only include lru_add_drain_per_cpu if building for an SMP system.

This patch is independent of the rest of the direct migration patchset
and is also needed to complete the swap migration patchset.

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

Index: linux-2.6.14-rc5-mm1/include/linux/swap.h
===================================================================
--- linux-2.6.14-rc5-mm1.orig/include/linux/swap.h	2005-11-02 11:39:01.000000000 -0800
+++ linux-2.6.14-rc5-mm1/include/linux/swap.h	2005-11-02 11:42:00.000000000 -0800
@@ -179,7 +179,9 @@ extern int vm_swappiness;
 extern int isolate_lru_page(struct page *p);
 extern int putback_lru_pages(struct list_head *l);
 
+#ifdef CONFIG_MIGRATION
 extern int migrate_pages(struct list_head *l, struct list_head *t);
+#endif
 
 #ifdef CONFIG_MMU
 /* linux/mm/shmem.c */
Index: linux-2.6.14-rc5-mm1/mm/Kconfig
===================================================================
--- linux-2.6.14-rc5-mm1.orig/mm/Kconfig	2005-10-31 14:10:53.000000000 -0800
+++ linux-2.6.14-rc5-mm1/mm/Kconfig	2005-11-02 11:44:57.000000000 -0800
@@ -132,3 +132,11 @@ config SPLIT_PTLOCK_CPUS
 	default "4096" if ARM && !CPU_CACHE_VIPT
 	default "4096" if PARISC && DEBUG_SPINLOCK && !64BIT
 	default "4"
+
+#
+# support for page migration
+#
+config MIGRATION
+	def_bool y if NUMA || SPARSEMEM || DISCONTIGMEM
+
+
Index: linux-2.6.14-rc5-mm1/mm/vmscan.c
===================================================================
--- linux-2.6.14-rc5-mm1.orig/mm/vmscan.c	2005-11-02 11:39:01.000000000 -0800
+++ linux-2.6.14-rc5-mm1/mm/vmscan.c	2005-11-02 11:54:00.000000000 -0800
@@ -572,6 +572,7 @@ keep:
 	return reclaimed;
 }
 
+#ifdef CONFIG_MIGRATION
 /*
  * swapout a single page
  * page is locked upon entry, unlocked on exit
@@ -721,6 +722,7 @@ retry_later:
 
 	return nr_failed + retry;
 }
+#endif
 
 /*
  * zone->lru_lock is heavily contended.  Some of the functions that
@@ -766,10 +768,12 @@ static int isolate_lru_pages(struct zone
 	return scanned;
 }
 
+#ifdef CONFIG_SMP
 static void lru_add_drain_per_cpu(void *dummy)
 {
 	lru_add_drain();
 }
+#endif
 
 /*
  * Isolate one page from the LRU lists and put it on the