Re: [PATCH 2/9] mm/memory_hotplug: add __add_memory_driver_managed() with online_type arg
From: Jonathan Cameron <jonathan.cameron@huawei.com>
Date: 2026-02-02 17:25:29
Also in:
linux-cxl, linux-fsdevel, linux-mm, lkml, nvdimm
On Thu, 29 Jan 2026 16:04:35 -0500 Gregory Price [off-list ref] wrote:
Enable dax kmem driver to select how to online the memory rather than implicitly depending on the system default. This will allow users of dax to plumb through a preferred auto-online policy for their region. Refactor and new interface: Add __add_memory_driver_managed() which accepts an explicit online_type and export mhp_get_default_online_type() so callers can pass it when they want the default behavior.
Hi Gregory, I think maybe I'd have left the export for the first user outside of memory_hotplug.c. Not particularly important however. Maybe talk about why a caller of __add_memory_driver_managed() might want the default? Feels like that's for the people who don't... Or is this all a dance to avoid an if (special mode) __add_memory_driver_managed(); else add_memory_driver_managed(); ? Other comments are mostly about using a named enum. I'm not sure if there is some existing reason why that doesn't work? -Errno pushed through this variable or anything like that?
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Refactor: Extract __add_memory_resource() to take an explicit online_type parameter, and update add_memory_resource() to pass the system default. 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 | 91 ++++++++++++++++++++++++---------- 2 files changed, 67 insertions(+), 27 deletions(-)diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h index f2f16cdd73ee..1eb63d1a247d 100644 --- a/include/linux/memory_hotplug.h +++ b/include/linux/memory_hotplug.h@@ -293,6 +293,9 @@ 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, + int online_type);
Given online_type values are from an enum anyway, maybe we can name that enum and use it explicitly?
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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 87796b617d9e..d3ca95b872bd 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c@@ -239,6 +239,7 @@ int mhp_get_default_online_type(void) return mhp_default_online_type; } +EXPORT_SYMBOL_GPL(mhp_get_default_online_type); void mhp_set_default_online_type(int online_type) {@@ -1490,7 +1491,8 @@ 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, + int online_type) { struct mhp_params params = { .pgprot = pgprot_mhp(PAGE_KERNEL) }; enum memblock_flags memblock_flags = MEMBLOCK_NONE;@@ -1580,12 +1582,9 @@ 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) { - int online_type = mhp_get_default_online_type(); - + if (online_type != MMOP_OFFLINE)
Ah. Fair enough, ignore comment in previous patch. I should have read on...
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walk_memory_blocks(start, size, &online_type, online_memory_block); - } return ret; error:@@ -1601,7 +1600,13 @@ 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;@@ -1629,29 +1634,24 @@ int add_memory(int nid, u64 start, u64 size, mhp_t mhp_flags) } EXPORT_SYMBOL_GPL(add_memory); -/* - * 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, - * after a reboot, and after kexec. - * - * Reasons why this memory should not be used for the initial memmap of a - * kexec kernel or for placing kexec images: - * - The booting kernel is in charge of determining how this memory will be - * used (e.g., use persistent memory as system RAM) - * - Coordination with a hypervisor is required before this memory - * can be used (e.g., inaccessible parts). +/** + * __add_memory_driver_managed - add driver-managed memory with explicit online_type
It's a little odd to add nice kernel-doc formatted documentation when the non __ variant has free form docs. Maybe tidy that up first if we want to go kernel-doc in this file? (I'm in favor, but no idea on general feelings...)
+ * @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 ($DRIVER)" + * @mhp_flags: Memory hotplug flags + * @online_type: Online behavior (MMOP_ONLINE, MMOP_ONLINE_KERNEL, + * MMOP_ONLINE_MOVABLE, or MMOP_OFFLINE)
Given that's currently the full set, seems like enum wins out here over an int.
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* - * For this memory, no entries in /sys/firmware/memmap ("raw firmware-provided - * memory map") are created. Also, the created memory resource is flagged - * with IORESOURCE_SYSRAM_DRIVER_MANAGED, so in-kernel users can special-case - * this memory as well (esp., not place kexec images onto it). + * Add driver-managed memory with explicit online_type specification. + * The resource_name must have the format "System RAM ($DRIVER)". * - * 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, + int online_type) { struct resource *res; int rc;@@ -1661,6 +1661,9 @@ int add_memory_driver_managed(int nid, u64 start, u64 size, resource_name[strlen(resource_name) - 1] != ')') return -EINVAL; + if (online_type < 0 || online_type > MMOP_ONLINE_MOVABLE)
This is where using an enum would help compiler know what is going on and maybe warn if anyone writes something that isn't defined.
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+ return -EINVAL; + lock_device_hotplug(); res = register_memory_resource(start, size, resource_name);@@ -1669,7 +1672,7 @@ 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 +1680,40 @@ 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"); + +/* + * 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, + * after a reboot, and after kexec. + * + * Reasons why this memory should not be used for the initial memmap of a + * kexec kernel or for placing kexec images: + * - The booting kernel is in charge of determining how this memory will be + * used (e.g., use persistent memory as system RAM) + * - Coordination with a hypervisor is required before this memory + * can be used (e.g., inaccessible parts). + * + * For this memory, no entries in /sys/firmware/memmap ("raw firmware-provided + * memory map") are created. Also, the created memory resource is flagged + * with IORESOURCE_SYSRAM_DRIVER_MANAGED, so in-kernel users can special-case + * this memory as well (esp., not place kexec images onto it). + * + * The resource_name (visible via /proc/iomem) has to have the format + * "System RAM ($DRIVER)". + * + * Memory will be onlined using the system default online type. + * + * Returns 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); /*