The following "memhotplug testing" patches enable memory hotplug
operations to be performed on a system with no actual hardware
memory hotplug capabilities.

These are equivalent to the "fake cpu hotplug" patches that were
going around a while ago.  I would very much like them to stay in
-mm, but not be pushed up to mainline.

Index: linux-2.6.13/arch/i386/Kconfig
===================================================================
--- linux-2.6.13.orig/arch/i386/Kconfig	2005-08-30 12:10:18.000000000 -0700
+++ linux-2.6.13/arch/i386/Kconfig	2005-08-30 12:10:35.000000000 -0700
@@ -787,9 +787,9 @@ config ARCH_DISCONTIGMEM_ENABLE
 	def_bool y
 	depends on NUMA
 
-config ARCH_DISCONTIGMEM_DEFAULT
-	def_bool y
-	depends on NUMA && HIGHMEM
+config SIMULATED_MEM_HOTPLUG
+	bool "Simulate memory hotplug on non-hotplug hardware"
+	depends on EXPERIMENTAL && HIGHMEM
 
 config ARCH_SPARSEMEM_ENABLE
 	def_bool y
@@ -910,7 +910,7 @@ config HAVE_DEC_LOCK
 config BOOT_IOREMAP
 	bool
 	depends on (((X86_SUMMIT || X86_GENERICARCH) && NUMA) || (X86 && EFI))
-	default y
+	default y || SIMULATED_MEM_HOTPLUG
 
 config REGPARM
 	bool "Use register arguments (EXPERIMENTAL)"
Index: linux-2.6.13/arch/i386/kernel/setup.c
===================================================================
--- linux-2.6.13.orig/arch/i386/kernel/setup.c	2005-08-28 16:41:01.000000000 -0700
+++ linux-2.6.13/arch/i386/kernel/setup.c	2005-08-30 12:10:35.000000000 -0700
@@ -145,6 +145,7 @@ struct ist_info ist_info;
 EXPORT_SYMBOL(ist_info);
 #endif
 struct e820map e820;
+struct e820map bios_e820;
 
 extern void early_cpu_init(void);
 extern void dmi_scan_machine(void);
@@ -1512,6 +1513,7 @@ void __init setup_arch(char **cmdline_p)
 	else {
 		printk(KERN_INFO "BIOS-provided physical RAM map:\n");
 		print_memory_map(machine_specific_memory_setup());
+		bios_e820 = e820;
 	}
 
 	copy_edd();
Index: linux-2.6.13/arch/i386/mm/init.c
===================================================================
--- linux-2.6.13.orig/arch/i386/mm/init.c	2005-08-30 12:10:18.000000000 -0700
+++ linux-2.6.13/arch/i386/mm/init.c	2005-08-30 12:10:35.000000000 -0700
@@ -192,38 +192,42 @@ static inline int page_kills_ppro(unsign
 
 extern int is_available_memory(efi_memory_desc_t *);
 
-int page_is_ram(unsigned long pagenr)
+static int page_is_ram_efi(unsigned long pagenr)
 {
+#ifdef CONFIG_EFI
 	int i;
 	unsigned long addr, end;
+	efi_memory_desc_t *md;
 
-	if (efi_enabled) {
-		efi_memory_desc_t *md;
-
-		for (i = 0; i < memmap.nr_map; i++) {
-			md = &memmap.map[i];
-			if (!is_available_memory(md))
-				continue;
-			addr = (md->phys_addr+PAGE_SIZE-1) >> PAGE_SHIFT;
-			end = (md->phys_addr + (md->num_pages << EFI_PAGE_SHIFT)) >> PAGE_SHIFT;
-
-			if ((pagenr >= addr) && (pagenr < end))
-				return 1;
-		}
-		return 0;
+	for (i = 0; i < memmap.nr_map; i++) {
+		md = &memmap.map[i];
+		if (!is_available_memory(md))
+			continue;
+		addr = (md->phys_addr+PAGE_SIZE-1) >> PAGE_SHIFT;
+		end = (md->phys_addr + (md->num_pages << EFI_PAGE_SHIFT)) >> PAGE_SHIFT;
+		if ((pagenr >= addr) && (pagenr < end))
+			return 1;
 	}
+#endif /* CONFIG_EFI */
+	return 0;
+}
 
-	for (i = 0; i < e820.nr_map; i++) {
+int page_is_ram_e820(unsigned long pagenr, struct e820map *local_e820)
+{
+	int i;
+	unsigned long addr, end;
+
+	for (i = 0; i < local_e820->nr_map; i++) {
 
-		if (e820.map[i].type != E820_RAM)	/* not usable memory */
+		if (local_e820->map[i].type != E820_RAM) /* not usable memory */
 			continue;
 		/*
 		 *	!!!FIXME!!! Some BIOSen report areas as RAM that
 		 *	are not. Notably the 640->1Mb area. We need a sanity
 		 *	check here.
 		 */
-		addr = (e820.map[i].addr+PAGE_SIZE-1) >> PAGE_SHIFT;
-		end = (e820.map[i].addr+e820.map[i].size) >> PAGE_SHIFT;
+		addr = (local_e820->map[i].addr+PAGE_SIZE-1) >> PAGE_SHIFT;
+		end = (local_e820->map[i].addr+local_e820->map[i].size) >> PAGE_SHIFT;
 		if  ((pagenr >= addr) && (pagenr < end))
 			return 1;
 	}
@@ -745,3 +749,10 @@ void free_initrd_mem(unsigned long start
 	}
 }
 #endif
+
+int page_is_ram(unsigned long pagenr)
+{
+	if (efi_enabled)
+		return page_is_ram_efi(pagenr);
+	return page_is_ram_e820(pagenr, &e820);
+}
Index: linux-2.6.13/drivers/base/memory.c
===================================================================
--- linux-2.6.13.orig/drivers/base/memory.c	2005-08-30 12:10:12.000000000 -0700
+++ linux-2.6.13/drivers/base/memory.c	2005-08-30 12:10:35.000000000 -0700
@@ -303,15 +303,25 @@ static int block_size_init(void)
  * as well as ppc64 will do all of their discovery in userspace
  * and will require this interface.
  */
+extern int page_is_hotpluggable_ram(unsigned long pfn);
 #ifdef CONFIG_ARCH_MEMORY_PROBE
 static ssize_t
 memory_probe_store(struct class *class, const char __user *buf, size_t count)
 {
 	u64 phys_addr;
+	unsigned long offset;
 	int ret;
 
 	phys_addr = simple_strtoull(buf, NULL, 0);
 
+	for (offset = 0; offset < PAGES_PER_SECTION; offset++) {
+		unsigned long page_nr = (phys_addr >> PAGE_SHIFT) + offset;
+		if (page_is_hotpluggable_ram(page_nr))
+			break;
+	}
+	if (offset == PAGES_PER_SECTION)
+		return -EINVAL;
+
 	ret = add_memory(phys_addr, PAGES_PER_SECTION << PAGE_SHIFT);
 
 	if (ret)
Index: linux-2.6.13/mm/memory_hotplug.c
===================================================================
--- linux-2.6.13.orig/mm/memory_hotplug.c	2005-08-30 12:10:17.000000000 -0700
+++ linux-2.6.13/mm/memory_hotplug.c	2005-08-30 12:10:35.000000000 -0700
@@ -108,6 +108,21 @@ static void grow_pgdat_span(struct pglis
 		pgdat->node_spanned_pages = end_pfn - pgdat->node_spanned_pages;
 }
 
+#ifdef CONFIG_SIMULATED_MEM_HOTPLUG
+int page_is_hotpluggable_ram(unsigned long pfn)
+{
+	extern struct e820map bios_e820;
+	extern int page_is_ram_e820(unsigned long, struct e820map*);
+
+	return page_is_ram_e820(pfn, &bios_e820);
+}
+#else
+int page_is_hotpluggable_ram(unsigned long pfn)
+{
+	return 1;
+}
+#endif
+
 int online_pages(unsigned long pfn, unsigned long nr_pages)
 {
 	unsigned long i;