[PATCH 1/1] mm/memory_hotplug: Adds option to hot-add memory in ZONE_MOVABLE

[Leonardo Bras <leonardo@linux.ibm.com>]

Adds an option on kernel config to make hot-added memory online in
ZONE_MOVABLE by default.

This would be great in systems with MEMORY_HOTPLUG_DEFAULT_ONLINE=y by
allowing to choose which zone it will be auto-onlined

Signed-off-by: Leonardo Bras <leonardo@linux.ibm.com>
---
 drivers/base/memory.c |  3 +++
 mm/Kconfig            | 14 ++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index f180427e48f4..378b585785c1 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -670,6 +670,9 @@ static int init_memory_block(struct memory_block **memory,
 	mem->state = state;
 	start_pfn = section_nr_to_pfn(mem->start_section_nr);
 	mem->phys_device = arch_get_memory_phys_device(start_pfn);
+#ifdef CONFIG_MEMORY_HOTPLUG_MOVABLE
+	mem->online_type = MMOP_ONLINE_MOVABLE;
+#endif
 
 	ret = register_memory(mem);
 
diff --git a/mm/Kconfig b/mm/Kconfig
index f0c76ba47695..74e793720f43 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -180,6 +180,20 @@ config MEMORY_HOTREMOVE
 	depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
 	depends on MIGRATION
 
+config MEMORY_HOTPLUG_MOVABLE
+	bool "Enhance the likelihood of hot-remove"
+	depends on MEMORY_HOTREMOVE
+	help
+	  This option sets the hot-added memory zone to MOVABLE which
+	  drastically reduces the chance of a hot-remove to fail due to
+	  unmovable memory segments. Kernel memory can't be allocated in
+	  this zone.
+
+	  Say Y here if you want to have better chance to hot-remove memory
+	  that have been previously hot-added.
+	  Say N here if you want to make all hot-added memory available to
+	  kernel space.
+
 # Heavily threaded applications may benefit from splitting the mm-wide
 # page_table_lock, so that faults on different parts of the user address
 # space can be handled with less contention: split it at this NR_CPUS.
-- 
2.20.1