powerpc/powernv: Set memory_block_size_bytes to 256MB

powerpc sets a low SECTION_SIZE_BITS to accomodate small pseries
boxes. We default to 16MB memory blocks, and boxes with a lot
of memory end up with enormous numbers of sysfs memory nodes.

Set a more reasonable default for powernv of 256MB.
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/platforms/powernv/setup.c

@@ -244,6 +244,13 @@ static void pnv_kexec_cpu_down(int crash_shutdown, int secondary)
 }
 #endif /* CONFIG_KEXEC */
 
+#ifdef CONFIG_MEMORY_HOTPLUG_SPARSE
+static unsigned long pnv_memory_block_size(void)
+{
+	return 256UL * 1024 * 1024;
+}
+#endif
+
 static void __init pnv_setup_machdep_opal(void)
 {
 	ppc_md.get_boot_time = opal_get_boot_time;
@@ -326,4 +333,7 @@ define_machine(powernv) {
 #ifdef CONFIG_KEXEC
 	.kexec_cpu_down		= pnv_kexec_cpu_down,
 #endif
+#ifdef CONFIG_MEMORY_HOTPLUG_SPARSE
+	.memory_block_size	= pnv_memory_block_size,
+#endif
 };