[PATCH 5/8] mm/memory_hotplug: add __add_memory_driver_managed() with online_type arg

Gregory Price
2026-03-21T15:04:18Z

Existing callers of add_memory_driver_managed cannot select the
preferred online type (ZONE_NORMAL vs ZONE_MOVABLE), requiring it to
hot-add memory as offline blocks, and then follow up by onlining each
memory block individually.

Most drivers prefer the system default, but the CXL driver wants to
plumb a preferred policy through the dax kmem driver.

Refactor APIs to add a new interface which allows the dax kmem and
cxl_core modules to select a preferred policy. Only expose this
interface to those modules to avoid confusion among existing API users
and to limit usage in out-of-tree modules.

Refactor add_memory_driver_managed, extract __add_memory_driver_managed
- Add proper kernel-doc for add_memory_driver_managed while refactoring
- New helper accepts an explicit online_type.
- New help validates online_type is between OFFLINE and ONLINE_MOVABLE

Refactor: add_memory_resource, extract __add_memory_resource
- new helper accepts an explicit online_type

Original APIs now explicitly pass the system-default to new helpers.

No functional change for existing users.

Cc: David Hildenbrand <david@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Gregory Price <gourry@gourry.net>
---
include/linux/memory_hotplug.h | 3 ++
mm/memory_hotplug.c | 60 +++++++++++++++++++++++++++++-----
2 files changed, 55 insertions(+), 8 deletions(-)

diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index a8bcb36f93b8..1f19f08552ea 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -320,6 +320,9 @@ 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);
extern int add_memory_resource(int nid, struct resource *resource,
mhp_t mhp_flags);
+int __add_memory_driver_managed(int nid, u64 start, u64 size,
+ const char *resource_name, mhp_t mhp_flags,
+ enum mmop online_type);
extern int add_memory_driver_managed(int nid, u64 start, u64 size,
const char *resource_name,
mhp_t mhp_flags);
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index af9a6cb5a2f9..9081aad5078f 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1492,10 +1492,10 @@ static int create_altmaps_and_memory_blocks(int nid, struct memory_group *group,
*
* we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG
*/
-int add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
+static int __add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags,
+ enum mmop online_type)
{
struct mhp_params params = { .pgprot = pgprot_mhp(PAGE_KERNEL) };
- enum mmop online_type = mhp_get_default_online_type();
enum memblock_flags memblock_flags = MEMBLOCK_NONE;
struct memory_group *group = NULL;
u64 start, size;
@@ -1583,7 +1583,7 @@ int add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
merge_system_ram_resource(res);

/* online pages if requested */
- if (mhp_get_default_online_type() != MMOP_OFFLINE)
+ if (online_type != MMOP_OFFLINE)
walk_memory_blocks(start, size, &online_type,
online_memory_block);

@@ -1601,7 +1601,13 @@ int add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
return ret;
}

-/* requires device_hotplug_lock, see add_memory_resource() */
+int add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
+{
+ return __add_memory_resource(nid, res, mhp_flags,
+ mhp_get_default_online_type());
+}
+
+/* requires device_hotplug_lock, see __add_memory_resource() */
int __add_memory(int nid, u64 start, u64 size, mhp_t mhp_flags)
{
struct resource *res;
@@ -1629,7 +1635,15 @@ int add_memory(int nid, u64 start, u64 size, mhp_t mhp_flags)
}
EXPORT_SYMBOL_GPL(add_memory);

-/*
+/**
+ * __add_memory_driver_managed - add driver-managed memory with explicit online_type
+ * @nid: NUMA node ID where the memory will be added
+ * @start: Start physical address of the memory range
+ * @size: Size of the memory range in bytes
+ * @resource_name: Resource name in format "System RAM ($DRIVER)"
+ * @mhp_flags: Memory hotplug flags
+ * @online_type: Auto-Online behavior (offline, online, kernel, movable)
+ *
* Add special, driver-managed memory to the system as system RAM. Such
* memory is not exposed via the raw firmware-provided memmap as system
* RAM, instead, it is detected and added by a driver - during cold boot,
@@ -1649,9 +1663,12 @@ EXPORT_SYMBOL_GPL(add_memory);
*
* The resource_name (visible via /proc/iomem) has to have the format
* "System RAM ($DRIVER)".
+ *
+ * Return: 0 on success, negative error code on failure.
*/
-int add_memory_driver_managed(int nid, u64 start, u64 size,
- const char *resource_name, mhp_t mhp_flags)
+int __add_memory_driver_managed(int nid, u64 start, u64 size,
+ const char *resource_name, mhp_t mhp_flags,
+ enum mmop online_type)
{
struct resource *res;
int rc;
@@ -1661,6 +1678,9 @@ int add_memory_driver_managed(int nid, u64 start, u64 size,
resource_name[strlen(resource_name) - 1] != ')')
return -EINVAL;

+ if (online_type < MMOP_OFFLINE || online_type > MMOP_ONLINE_MOVABLE)
+ return -EINVAL;
+
lock_device_hotplug();

res = register_memory_resource(start, size, resource_name);
@@ -1669,7 +1689,7 @@ int add_memory_driver_managed(int nid, u64 start, u64 size,
goto out_unlock;
}

- rc = add_memory_resource(nid, res, mhp_flags);
+ rc = __add_memory_resource(nid, res, mhp_flags, online_type);
if (rc < 0)
release_memory_resource(res);

@@ -1677,6 +1697,30 @@ int add_memory_driver_managed(int nid, u64 start, u64 size,
unlock_device_hotplug();
return rc;
}
+EXPORT_SYMBOL_FOR_MODULES(__add_memory_driver_managed, "kmem,cxl_core");
+
+/**
+ * add_memory_driver_managed - add driver-managed memory
+ * @nid: NUMA node ID where the memory will be added
+ * @start: Start physical address of the memory range
+ * @size: Size of the memory range in bytes
+ * @resource_name: Resource name in format "System RAM ($DRIVER)"
+ * @mhp_flags: Memory hotplug flags
+ *
+ * Add driver-managed memory with the system default online type set by
+ * build config or kernel boot parameter.
+ *
+ * See __add_memory_driver_managed for more details.
+ *
+ * Return: 0 on success, negative error code on failure.
+ */
+int add_memory_driver_managed(int nid, u64 start, u64 size,
+ const char *resource_name, mhp_t mhp_flags)
+{
+ return __add_memory_driver_managed(nid, start, size, resource_name,
+ mhp_flags,
+ mhp_get_default_online_type());
+}
EXPORT_SYMBOL_GPL(add_memory_driver_managed);

/*
--
2.53.0