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Message-ID: <20260114085201.3222597-3-gourry@gourry.net>
Date: Wed, 14 Jan 2026 03:51:54 -0500
From: Gregory Price <gourry@...rry.net>
To: linux-mm@...ck.org
Cc: linux-cxl@...r.kernel.org,
nvdimm@...ts.linux.dev,
linux-kernel@...r.kernel.org,
virtualization@...ts.linux.dev,
kernel-team@...a.com,
dan.j.williams@...el.com,
vishal.l.verma@...el.com,
dave.jiang@...el.com,
david@...nel.org,
mst@...hat.com,
jasowang@...hat.com,
xuanzhuo@...ux.alibaba.com,
eperezma@...hat.com,
osalvador@...e.de,
akpm@...ux-foundation.org
Subject: [PATCH 2/8] mm/memory_hotplug: extract __add_memory_resource() and __offline_memory()
Extract internal helper functions with explicit parameters to prepare
for adding new APIs that allow explicit online type control:
- __add_memory_resource(): accepts an explicit online_type parameter.
Add MMOP_SYSTEM_DEFAULT as a new value that instructs the function
to use mhp_get_default_online_type() for the actual online type.
The existing add_memory_resource() becomes a thin wrapper that
passes MMOP_SYSTEM_DEFAULT to preserve existing behavior.
- __offline_memory(): extracted from offline_and_remove_memory() to
handle the offline operation with rollback support. The caller
now handles locking and the remove step separately.
This refactoring enables future callers to specify explicit online
types (MMOP_OFFLINE, MMOP_ONLINE, MMOP_ONLINE_MOVABLE) or use
MMOP_SYSTEM_DEFAULT for the system default policy. The offline logic
can also be used independently of the remove step.
Mild functional change: if try_remove_memory() failed after successfully
offlining, we would re-online the memory. We no longer do this, and in
practice removal doesn't fail if offline succeeds.
Signed-off-by: Gregory Price <gourry@...rry.net>
---
include/linux/memory_hotplug.h | 2 +
mm/memory_hotplug.c | 69 ++++++++++++++++++++++------------
2 files changed, 48 insertions(+), 23 deletions(-)
diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index f2f16cdd73ee..d5407264d72a 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -29,6 +29,8 @@ enum {
MMOP_ONLINE_KERNEL,
/* Online the memory to ZONE_MOVABLE. */
MMOP_ONLINE_MOVABLE,
+ /* Use system default online type from mhp_get_default_online_type(). */
+ MMOP_SYSTEM_DEFAULT,
};
/* Flags for add_memory() and friends to specify memory hotplug details. */
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 5718556121f0..ab73c8fcc0f1 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1490,7 +1490,8 @@ 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;
@@ -1499,6 +1500,10 @@ int add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
bool new_node = false;
int ret;
+ /* Convert system default to actual online type */
+ if (online_type == MMOP_SYSTEM_DEFAULT)
+ online_type = mhp_get_default_online_type();
+
start = res->start;
size = resource_size(res);
@@ -1580,12 +1585,9 @@ 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)
walk_memory_blocks(start, size, &online_type,
online_memory_block);
- }
return ret;
error:
@@ -1601,7 +1603,12 @@ 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, MMOP_SYSTEM_DEFAULT);
+}
+
+/* requires device_hotplug_lock, see __add_memory_resource() */
int __add_memory(int nid, u64 start, u64 size, mhp_t mhp_flags)
{
struct resource *res;
@@ -2357,12 +2364,12 @@ static int try_reonline_memory_block(struct memory_block *mem, void *arg)
}
/*
- * Try to offline and remove memory. Might take a long time to finish in case
- * memory is still in use. Primarily useful for memory devices that logically
- * unplugged all memory (so it's no longer in use) and want to offline + remove
- * that memory.
+ * Offline a memory range. In case of failure, already offlined memory blocks
+ * will be re-onlined.
+ *
+ * Caller must hold device hotplug lock.
*/
-int offline_and_remove_memory(u64 start, u64 size)
+static int __offline_memory(u64 start, u64 size)
{
const unsigned long mb_count = size / memory_block_size_bytes();
uint8_t *online_types, *tmp;
@@ -2388,11 +2395,37 @@ int offline_and_remove_memory(u64 start, u64 size)
*/
memset(online_types, MMOP_OFFLINE, mb_count);
- lock_device_hotplug();
-
tmp = online_types;
rc = walk_memory_blocks(start, size, &tmp, try_offline_memory_block);
+ /*
+ * Rollback what we did. While memory onlining might theoretically fail
+ * (nacked by a notifier), it barely ever happens.
+ */
+ if (rc) {
+ tmp = online_types;
+ walk_memory_blocks(start, size, &tmp,
+ try_reonline_memory_block);
+ }
+
+ kfree(online_types);
+ return rc;
+}
+
+/*
+ * Try to offline and remove memory. Might take a long time to finish in case
+ * memory is still in use. Primarily useful for memory devices that logically
+ * unplugged all memory (so it's no longer in use) and want to offline + remove
+ * that memory.
+ */
+int offline_and_remove_memory(u64 start, u64 size)
+{
+ int rc;
+
+ lock_device_hotplug();
+
+ rc = __offline_memory(start, size);
+
/*
* In case we succeeded to offline all memory, remove it.
* This cannot fail as it cannot get onlined in the meantime.
@@ -2403,18 +2436,8 @@ int offline_and_remove_memory(u64 start, u64 size)
pr_err("%s: Failed to remove memory: %d", __func__, rc);
}
- /*
- * Rollback what we did. While memory onlining might theoretically fail
- * (nacked by a notifier), it barely ever happens.
- */
- if (rc) {
- tmp = online_types;
- walk_memory_blocks(start, size, &tmp,
- try_reonline_memory_block);
- }
unlock_device_hotplug();
- kfree(online_types);
return rc;
}
EXPORT_SYMBOL_GPL(offline_and_remove_memory);
--
2.52.0
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