Allow SPARSEMEM without NUMA

Build on the previous patch to allow DISCONTIGMEM without NUMA, which actually turns out to be most of the work in allowing SPARSEMEM without NUMA to compile. Beyond that, the changes are:

* Extend the definition of NEED_MULTIPLE_NODES.
SPARSEMEM kind of includes DISCONTIGMEM from a compile point of view, but the config symbols don't represent that. I guess a new symbol could be created. But it seems logical enough the way it is below.

* Create a dummy early_pfn_to_nid() as that function is
in numa.c and thus only exists if CONFIG_NUMA (and CONFIG_SPARSEMEM) is set. Its just used to allow mm/sparse.c:node_memmap_size_bytes() to compile, a function that is never used in IA64 (or anywhere else outside of i386 according to its comment), but is compiled anyway. I guess the hope is by having it there other arches will use it in the future. In any case, making a bogus early_pfn_to_nid(), though untidy, shouldn't break anything.

The main drawback of this approach as suddenly there is a spruious early_pfn_to_nid() in disctontig.c - I couldn't think of a better place for it off hand.

Booted up on a HP RX2620, but not tested beyond that.

Index: linux-2.6/mm/Kconfig
=================================--- linux-2.6.orig/mm/Kconfig 2007-05-11 10:18:13.000000000 +0900
+++ linux-2.6/mm/Kconfig 2007-05-11 10:27:13.000000000 +0900
@@ -78,13 +78,13 @@ config FLAT_NODE_MEM_MAP
depends on !SPARSEMEM

#
-# Both the NUMA code and DISCONTIGMEM use arrays of pg_data_t's +# The NUMA, DISCONTIGMEM and SPARSEMEM code all use arrays of pg_data_t's

 # to represent different areas of memory.  This variable allows
 # those dependencies to exist individually.
 #
 config NEED_MULTIPLE_NODES
 	def_bool y
-	depends on DISCONTIGMEM || NUMA
+	depends on DISCONTIGMEM || SPARSEMEM || NUMA

config HAVE_MEMORY_PRESENT
def_bool y
Index: linux-2.6/arch/ia64/mm/discontig.c
=================================--- linux-2.6.orig/arch/ia64/mm/discontig.c 2007-05-11 10:27:12.000000000 +0900
+++ linux-2.6/arch/ia64/mm/discontig.c 2007-05-11 10:48:08.000000000 +0900
@@ -731,3 +731,7 @@ void arch_refresh_nodedata(int update_no
scatter_node_data();
}
#endif
+
+#if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_NUMA) +int early_pfn_to_nid(unsigned long pfn) { BUG(); }; +#endif