[PATCH] mm: add build-time option to set hotplug default type

[Gregory Price <gourry@gourry.net>]

When memory hotplug auto-online is enabled, hotplug memory blocks are
onlined into ZONE_NORMAL by default. The `memhp_default_state` boot
param allows runtime configuration, but no build-time config exists.

Add a build-time configuration option to change default hotplug zone.

build config:
  MEMHP_DEFAULT_TYPE

Selections:
  MEMHP_DEFAULT_TYPE_NORMAL  => mhp_default_online_type = "online"
  MEMHP_DEFAULT_TYPE_MOVABLE => mhp_default_online_type = "online_movable"

When MEMORY_HOTPLUG_DEFAULT_ONLINE is disabled, MEMHP_DEFAULT_TYPE is
set to "offline" to match the current system behavior.

ZONE_NORMAL still remains the default, because for systems with a large
amount of hotplug memory, defaulting it to ZONE_MOVABLE may result in
portions failing to online if sufficient ZONE_NORMAL memory does not
exist to describe it.

Signed-off-by: Gregory Price <gourry@gourry.net>
---
 drivers/base/memory.c          |  4 ++--
 include/linux/memory_hotplug.h |  5 +++--
 mm/Kconfig                     | 33 +++++++++++++++++++++++++++++++++
 mm/memory_hotplug.c            | 29 ++++++++++++++++++++++-------
 4 files changed, 60 insertions(+), 11 deletions(-)

diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index 67858eeb92ed..6f69b01abe51 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -512,7 +512,7 @@ static ssize_t auto_online_blocks_show(struct device *dev,
 				       struct device_attribute *attr, char *buf)
 {
 	return sysfs_emit(buf, "%s\n",
-			  online_type_to_str[mhp_default_online_type]);
+			  online_type_to_str[memhp_default_type()]);
 }
 
 static ssize_t auto_online_blocks_store(struct device *dev,
@@ -524,7 +524,7 @@ static ssize_t auto_online_blocks_store(struct device *dev,
 	if (online_type < 0)
 		return -EINVAL;
 
-	mhp_default_online_type = online_type;
+	memhp_set_default_type(online_type);
 	return count;
 }
 
diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index b27ddce5d324..a43470f0d93c 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -144,8 +144,6 @@ extern u64 max_mem_size;
 
 extern int mhp_online_type_from_str(const char *str);
 
-/* Default online_type (MMOP_*) when new memory blocks are added. */
-extern int mhp_default_online_type;
 /* If movable_node boot option specified */
 extern bool movable_node_enabled;
 static inline bool movable_node_is_enabled(void)
@@ -303,6 +301,9 @@ static inline void __remove_memory(u64 start, u64 size) {}
 #endif /* CONFIG_MEMORY_HOTREMOVE */
 
 #ifdef CONFIG_MEMORY_HOTPLUG
+/* Default online_type (MMOP_*) when new memory blocks are added. */
+extern int memhp_default_type(void);
+extern void memhp_set_default_type(int online_type);
 extern void __ref free_area_init_core_hotplug(struct pglist_data *pgdat);
 extern int __add_memory(int nid, u64 start, u64 size, mhp_t mhp_flags);
 extern int add_memory(int nid, u64 start, u64 size, mhp_t mhp_flags);
diff --git a/mm/Kconfig b/mm/Kconfig
index 7949ab121070..b6e63e5306b1 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -565,6 +565,39 @@ config MEMORY_HOTPLUG_DEFAULT_ONLINE
 	  Say N here if you want the default policy to keep all hot-plugged
 	  memory blocks in 'offline' state.
 
+choice
+	prompt "Memory Hotplug Default Type"
+	depends on MEMORY_HOTPLUG_DEFAULT_ONLINE
+	default MEMHP_DEFAULT_TYPE_NORMAL
+	help
+	  Default memory zone for driver managed hotplug memory.
+	  Select normal to generally allow kernel usage of this memory.
+	  Select movable to generally disallow kernel usage of this memory.
+	  Example typical kernel usage would be page structs and page tables.
+
+
+config MEMHP_DEFAULT_TYPE_NORMAL
+	bool "Normal"
+	help
+	  Online driver managed hotplug memory into zone normal.
+	  Select this if you want the kernel to be able to utilize
+	  this memory for kernel data (e.g. page tables).
+
+config MEMHP_DEFAULT_TYPE_MOVABLE
+	bool "Movable"
+	help
+	  Online driver managed hotplug memory into zone movable.
+	  Select this if you do not want the kernel to be able to
+	  utilize this memory for kernel data (e.g. page tables).
+
+endchoice
+
+config MEMHP_DEFAULT_TYPE
+       string
+       default "online" if MEMHP_DEFAULT_TYPE_NORMAL
+       default "online_movable" if MEMHP_DEFAULT_TYPE_MOVABLE
+       default "offline"
+
 config MEMORY_HOTREMOVE
 	bool "Allow for memory hot remove"
 	select HAVE_BOOTMEM_INFO_NODE if (X86_64 || PPC64)
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 3b6f93962481..1e4340fa9f07 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -219,11 +219,26 @@ void put_online_mems(void)
 
 bool movable_node_enabled = false;
 
-#ifndef CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE
-int mhp_default_online_type = MMOP_OFFLINE;
-#else
-int mhp_default_online_type = MMOP_ONLINE;
-#endif
+static int mhp_default_online_type = -1;
+int memhp_default_type(void)
+{
+	int type;
+
+	if (mhp_default_online_type >= 0)
+		return mhp_default_online_type;
+
+	type = mhp_online_type_from_str(CONFIG_MEMHP_DEFAULT_TYPE);
+	if (type < 0)
+		type = MMOP_OFFLINE;
+
+	mhp_default_online_type = type;
+	return mhp_default_online_type;
+}
+
+void memhp_set_default_type(int online_type)
+{
+	mhp_default_online_type = online_type;
+}
 
 static int __init setup_memhp_default_state(char *str)
 {
@@ -1328,7 +1343,7 @@ static int check_hotplug_memory_range(u64 start, u64 size)
 
 static int online_memory_block(struct memory_block *mem, void *arg)
 {
-	mem->online_type = mhp_default_online_type;
+	mem->online_type = memhp_default_type();
 	return device_online(&mem->dev);
 }
 
@@ -1575,7 +1590,7 @@ int add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
 		merge_system_ram_resource(res);
 
 	/* online pages if requested */
-	if (mhp_default_online_type != MMOP_OFFLINE)
+	if (memhp_default_type() != MMOP_OFFLINE)
 		walk_memory_blocks(start, size, NULL, online_memory_block);
 
 	return ret;
-- 
2.47.1