[PATCH] Tighten CONFIG_NUMA preconditions

Patch from Martin J. Bligh and Dave Hansen

People with ordinary PCs are accidentally turning on NUMA support, and people
with NUMA machines are finding the NUMA option mysteriously disappearing.
This patch sets the defaults to sane things for everyone, and only allows you
to turn on NUMA with both SMP and 64Gb support on (it's useful for the
distros on non-Summit boxes, but not on their UP kernels ;-)).

I've also moved it below the highmem options, as it logically depends on
them, so this makes more sense.  For those searching for NUMA support on
*real* NUMA machine, Dave has provided some guiding comments to show them
what they messed up (it's totally non-obvious).  Hopefully this will stop
people's recent unfortunate foot-wounds (I think UP machines were defaulting
to NUMA on ...  oops).

arch/i386/Kconfig

@@ -476,21 +476,6 @@ config NR_CPUS
 	  This is purely to save memory - each supported CPU adds
 	  approximately eight kilobytes to the kernel image.
 
-# Common NUMA Features
-config NUMA
-	bool "Numa Memory Allocation Support"
-	depends on (HIGHMEM64G && (X86_NUMAQ || (X86_SUMMIT && ACPI && !ACPI_HT_ONLY))) || X86_PC
-
-config DISCONTIGMEM
-	bool
-	depends on NUMA
-	default y
-
-config HAVE_ARCH_BOOTMEM_NODE
-	bool
-	depends on NUMA
-	default y
-
 config X86_TSC
 	bool
 	depends on (MWINCHIP3D || MWINCHIP2 || MCRUSOE || MCYRIXIII || MK7 || MK6 || MPENTIUM4 || MPENTIUMIII || MPENTIUMII || M686 || M586MMX || M586TSC || MK8 || MVIAC3_2) && !X86_NUMAQ
@@ -680,6 +665,30 @@ config X86_PAE
 	depends on HIGHMEM64G
 	default y
 
+# Common NUMA Features
+config NUMA
+	bool "Numa Memory Allocation Support"
+	depends on SMP && HIGHMEM64G && (X86_PC || X86_NUMAQ || (X86_SUMMIT && ACPI && !ACPI_HT_ONLY))
+	default n if X86_PC
+	default y if (X86_NUMAQ || X86_SUMMIT)
+
+# Need comments to help the hapless user trying to turn on NUMA support
+comment "NUMA (NUMA-Q) requires SMP, 64GB highmem support"
+	depends on X86_NUMAQ && (!HIGHMEM64G || !SMP)
+
+comment "NUMA (Summit) requires SMP, 64GB highmem support, full ACPI"
+	depends on X86_SUMMIT && (!HIGHMEM64G || !ACPI || ACPI_HT_ONLY)
+
+config DISCONTIGMEM
+	bool
+	depends on NUMA
+	default y
+
+config HAVE_ARCH_BOOTMEM_NODE
+	bool
+	depends on NUMA
+	default y
+
 config HIGHPTE
 	bool "Allocate 3rd-level pagetables from highmem"
 	depends on HIGHMEM4G || HIGHMEM64G