[PATCH v2 0/4] Support dynamic (de)configuration of memory

[PATCH v2 0/4] Support dynamic (de)configuration of memory

[Sumanth Korikkar]

Hi,

Patchset provides a new interface for dynamic configuration and
deconfiguration of hotplug memory on s390, allowing with/without
memmap_on_memory support. It is a follow up on the discussion with David
when introducing memmap_on_memory support for s390 and support dynamic
(de)configuration of memory:
https://lore.kernel.org/all/ee492da8-74b4-4a97-8b24-73e07257f01d@redhat.com/
https://lore.kernel.org/all/20241202082732.3959803-1-sumanthk@linux.ibm.com/

The original motivation for introducing memmap_on_memory on s390 was to
avoid using online memory to store struct pages metadata, particularly
for standby memory blocks. This became critical in cases where there was
an imbalance between standby and online memory, potentially leading to
boot failures due to insufficient memory for metadata allocation.

To address this, memmap_on_memory was utilized on s390. However, in its
current form, it adds struct pages metadata at the start of each memory
block at the time of addition (only standby memory), and this
configuration is static. It cannot be changed at runtime  (When the user
needs continuous physical memory).

Inorder to provide more flexibility to the user and overcome the above
limitation, add an option to dynamically configure and deconfigure
hotpluggable memory block with/without memmap_on_memory.

With the new interface, s390 will not add all possible hotplug memory in
advance, like before, to make it visible in sysfs for online/offline
actions. Instead, before memory block can be set online, it has to be
configured via a new interface in /sys/firmware/memory/memoryX/config,
which makes s390 similar to others.  i.e. Adding of hotpluggable memory is
controlled by the user instead of adding it at boottime.

s390 kernel sysfs interface to configure/deconfigure memory with
memmap_on_memory (with upcoming lsmem changes):

* Initial memory layout:
lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY
RANGE                 SIZE   STATE BLOCK CONFIGURED MEMMAP_ON_MEMORY
0x00000000-0x7fffffff   2G  online 0-15  yes        no
0x80000000-0xffffffff   2G offline 16-31 no         yes

* Configure memory
echo 1 > /sys/firmware/memory/memory16/config
lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY
RANGE                  SIZE  STATE   BLOCK CONFIGURED MEMMAP_ON_MEMORY
0x00000000-0x7fffffff    2G  online  0-15  yes        no
0x80000000-0x87ffffff  128M offline    16  yes        yes
0x88000000-0xffffffff  1.9G offline 17-31  no         yes

* Deconfigure memory
echo 0 > /sys/firmware/memory/memory16/config
lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY
RANGE                 SIZE   STATE BLOCK CONFIGURED MEMMAP_ON_MEMORY
0x00000000-0x7fffffff   2G  online 0-15  yes        no
0x80000000-0xffffffff   2G offline 16-31 no         yes

* Enable memmap_on_memory and online it.
(Deconfigure first)
echo 0 > /sys/devices/system/memory/memory5/online
echo 0 > /sys/firmware/memory/memory5/config

lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY
RANGE                  SIZE  STATE  BLOCK CONFIGURED MEMMAP_ON_MEMORY
0x00000000-0x27ffffff  640M  online 0-4   yes        no
0x28000000-0x2fffffff  128M offline 5     no         no
0x30000000-0x7fffffff  1.3G  online 6-15  yes        no
0x80000000-0xffffffff    2G offline 16-31 no         yes

(Enable memmap_on_memory and online it)
echo 1 > /sys/firmware/memory/memory5/memmap_on_memory
echo 1 > /sys/firmware/memory/memory5/config
echo 1 > /sys/devices/system/memory/memory5/online

lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY
RANGE                  SIZE  STATE   BLOCK CONFIGURED MEMMAP_ON_MEMORY
0x00000000-0x27ffffff  640M  online  0-4   yes        no
0x28000000-0x2fffffff  128M  online  5     yes        yes
0x30000000-0x7fffffff  1.3G  online  6-15  yes        no
0x80000000-0xffffffff    2G  offline 16-31 no         yes

* Disable memmap_on_memory and online it.
(Deconfigure first)
echo 0 > /sys/devices/system/memory/memory5/online
echo 0 > /sys/firmware/memory/memory5/config

lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY
RANGE                  SIZE  STATE  BLOCK CONFIGURED MEMMAP_ON_MEMORY
0x00000000-0x27ffffff  640M  online 0-4   yes        no
0x28000000-0x2fffffff  128M offline 5     no         yes
0x30000000-0x7fffffff  1.3G  online 6-15  yes        no
0x80000000-0xffffffff    2G offline 16-31 no         yes

(Disable memmap_on_memory and online it)
echo 0 > /sys/firmware/memory/memory5/memmap_on_memory
echo 1 > /sys/firmware/memory/memory5/config
echo 1 > /sys/devices/system/memory/memory5/online

lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY
RANGE                  SIZE  STATE   BLOCK CONFIGURED MEMMAP_ON_MEMORY
0x00000000-0x7fffffff  2G    online  0-15  yes        no
0x80000000-0xffffffff  2G    offline 16-31 no         yes

* Userspace changes:
lsmem/chmem tool is also changed to use the new interface. I will send
it to util-linux soon.

Patch 1 adds support for removal of boot-allocated memory blocks.

Patch 2 provides option to dynamically configure and deconfigure memory
with/without memmap_on_memory.

Patch 3 removes MHP_OFFLINE_INACCESSIBLE from s390. The mhp flag was
used to mark memory as not accessible until memory hotplug online phase
begins.  However, with patch 2, it is no longer essential. Memory can be
brought to accessible state before adding memory, as the memory is added
during runttime now instead of boottime.

Patch 4 removes the MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE notifiers. It
is no longer needed.  Memory can be brought to accessible state before
adding memory now, with runtime (de)configuration of memory.

Note: The patches apply to the linux-next branch.

v2:
Thanks David
* Rename struct mblock/mblock_arg with struct sclp_mem/sclp_mem_arg.
* Rename all mblocks/mblock references with sclp_mems/sclp_mem -
  structures, functions.
* Rename create_online_mblock() with create_configured_sclp_mem().
* Rename config_mblock_show()/config_mblock_store() with
  config_sclp_mem_show()/config_sclp_mem_store().
* Remove contains_standby_increment() and
  sclp_mem_notifier. sclp mem state change is performed when
  adding/removing memory. sclp memory notifier - no longer needed with
  this patchset.
* Recover sclp mem state when add_memory() fails.
* Refactor and add function init_sclp_mem().
* Use unsigned long instead of unsigned long long.
* Simplify and correct kobj handling. Thanks Heiko.

Sumanth Korikkar (4):
  s390/mm: Support removal of boot-allocated virtual memory map
  s390/sclp: Add support for dynamic (de)configuration of memory
  s390/sclp: Remove MHP_OFFLINE_INACCESSIBLE
  mm/memory_hotplug: Remove MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE
    notifiers

 arch/s390/mm/pgalloc.c         |   2 +
 arch/s390/mm/vmem.c            |  21 ++-
 drivers/base/memory.c          |  23 +--
 drivers/s390/char/sclp_mem.c   | 290 +++++++++++++++++++++++----------
 include/linux/memory.h         |   9 -
 include/linux/memory_hotplug.h |  18 +-
 include/linux/memremap.h       |   1 -
 mm/memory_hotplug.c            |  17 +-
 mm/sparse.c                    |   3 +-
 9 files changed, 227 insertions(+), 157 deletions(-)

-- 
2.48.1

[PATCH v2 1/4] s390/mm: Support removal of boot-allocated virtual memory map

[Sumanth Korikkar]

On s390, memory blocks are not currently removed via
arch_remove_memory(). With upcoming dynamic memory (de)configuration
support, runtime removal of memory blocks is possible. This internally
involves tearing down identity mapping, virtual memory mappings and
freeing the physical memory backing the struct pages metadata.

During early boot, physical memory used to back the struct pages
metadata in vmemmap is allocated through:

setup_arch()
  -> sparse_init()
    -> sparse_init_nid()
      -> __populate_section_memmap()
        -> vmemmap_alloc_block_buf()
          -> sparse_buffer_alloc()
            -> memblock_alloc()

Here, sparse_init_nid() sets up virtual-to-physical mapping for struct
pages backed by memblock_alloc(). This differs from runtime addition of
hotplug memory which uses the buddy allocator later.

To correctly free identity mappings, vmemmap mappings during hot-remove,
boot-time and runtime allocations must be distinguished using the
PageReserved bit:

* Boot-time memory, such as identity-mapped page tables allocated via
  boot_crst_alloc() and reserved via reserve_pgtables() is marked
  PageReserved in memmap_init_reserved_pages().

* Physical memory backing vmemmap (struct pages from memblock_alloc())
  is also marked PageReserved similarly.

During teardown, PageReserved bit is checked to distinguish between
boot-time allocation or buddy allocation.

This is similar to commit 645d5ce2f7d6 ("powerpc/mm/radix: Fix PTE/PMD
fragment count for early page table mappings")

Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
---
 arch/s390/mm/pgalloc.c |  2 ++
 arch/s390/mm/vmem.c    | 21 ++++++++++++---------
 2 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/arch/s390/mm/pgalloc.c b/arch/s390/mm/pgalloc.c
index 626fca116cd7..7df23528c01b 100644
--- a/arch/s390/mm/pgalloc.c
+++ b/arch/s390/mm/pgalloc.c
@@ -164,6 +164,8 @@ void page_table_free(struct mm_struct *mm, unsigned long *table)
 {
 	struct ptdesc *ptdesc = virt_to_ptdesc(table);
 
+	if (pagetable_is_reserved(ptdesc))
+		return free_reserved_ptdesc(ptdesc);
 	pagetable_dtor_free(ptdesc);
 }
 
diff --git a/arch/s390/mm/vmem.c b/arch/s390/mm/vmem.c
index f48ef361bc83..d96587b84e81 100644
--- a/arch/s390/mm/vmem.c
+++ b/arch/s390/mm/vmem.c
@@ -4,6 +4,7 @@
  */
 
 #include <linux/memory_hotplug.h>
+#include <linux/bootmem_info.h>
 #include <linux/cpufeature.h>
 #include <linux/memblock.h>
 #include <linux/pfn.h>
@@ -39,15 +40,21 @@ static void __ref *vmem_alloc_pages(unsigned int order)
 
 static void vmem_free_pages(unsigned long addr, int order, struct vmem_altmap *altmap)
 {
+	unsigned int nr_pages = 1 << order;
+	struct page *page;
+
 	if (altmap) {
 		vmem_altmap_free(altmap, 1 << order);
 		return;
 	}
-	/* We don't expect boot memory to be removed ever. */
-	if (!slab_is_available() ||
-	    WARN_ON_ONCE(PageReserved(virt_to_page((void *)addr))))
-		return;
-	free_pages(addr, order);
+	page = virt_to_page((void *)addr);
+	if (PageReserved(page)) {
+		/* allocated from memblock */
+		while (nr_pages--)
+			free_bootmem_page(page++);
+	} else {
+		free_pages(addr, order);
+	}
 }
 
 void *vmem_crst_alloc(unsigned long val)
@@ -79,10 +86,6 @@ pte_t __ref *vmem_pte_alloc(void)
 
 static void vmem_pte_free(unsigned long *table)
 {
-	/* We don't expect boot memory to be removed ever. */
-	if (!slab_is_available() ||
-	    WARN_ON_ONCE(PageReserved(virt_to_page(table))))
-		return;
 	page_table_free(&init_mm, table);
 }
 
-- 
2.48.1

[PATCH v2 2/4] s390/sclp: Add support for dynamic (de)configuration of memory

[Sumanth Korikkar]

Provide a new interface for dynamic configuration and deconfiguration of
hotplug memory, allowing with/without memmap_on_memory support. It is a
follow up on the discussion with David when introducing memmap_on_memory
support for s390 and support dynamic (de)configuration of memory:
https://lore.kernel.org/all/ee492da8-74b4-4a97-8b24-73e07257f01d@redhat.com/
https://lore.kernel.org/all/20241202082732.3959803-1-sumanthk@linux.ibm.com/

The original motivation for introducing memmap_on_memory on s390 was to
avoid using online memory to store struct pages metadata, particularly
for standby memory blocks. This became critical in cases where there was
an imbalance between standby and online memory, potentially leading to
boot failures due to insufficient memory for metadata allocation.

To address this, memmap_on_memory was utilized on s390. However, in its
current form, it adds struct pages metadata at the start of each memory
block at the time of addition and this configuration is static. It
cannot be changed at runtime. (When the user needs continuous physical
memory).

Inorder to provide more flexibility to the user and overcome the above
limitation, add option to dynamically configure and deconfigure
hotpluggable memory block with/without memmap_on_memory.

With the new interface, s390 will not add all possible hotplug memory in
advance, like before, to make it visible in sysfs for online/offline
actions. Instead, before memory block can be set online, it has to be
configured via a new interface in /sys/firmware/memory/memoryX/config,
which makes s390 similar to others.  i.e. Adding of hotpluggable memory is
controlled by the user instead of adding it at boottime.

The s390 kernel sysfs interface to configure and deconfigure memory is
as follows (considering the upcoming lsmem changes):

* Initial memory layout:
lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY
RANGE                 SIZE   STATE BLOCK CONFIGURED MEMMAP_ON_MEMORY
0x00000000-0x7fffffff   2G  online 0-15  yes        no
0x80000000-0xffffffff   2G offline 16-31 no         yes

* Configure memory
sys="/sys"
echo 1 > $sys/firmware/memory/memory16/config
lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY
RANGE                  SIZE  STATE   BLOCK CONFIGURED MEMMAP_ON_MEMORY
0x00000000-0x7fffffff    2G  online  0-15  yes        no
0x80000000-0x87ffffff  128M offline    16  yes        yes
0x88000000-0xffffffff  1.9G offline 17-31  no         yes

* Deconfigure memory
echo 0 > $sys/firmware/memory/memory16/config
lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY
RANGE                 SIZE   STATE BLOCK CONFIGURED MEMMAP_ON_MEMORY
0x00000000-0x7fffffff   2G  online 0-15  yes        no
0x80000000-0xffffffff   2G offline 16-31 no         yes

3. Enable memmap_on_memory and online it.
echo 0 > $sys/devices/system/memory/memory5/online
echo 0 > $sys/firmware/memory/memory5/config

lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY
RANGE                  SIZE  STATE  BLOCK CONFIGURED MEMMAP_ON_MEMORY
0x00000000-0x27ffffff  640M  online 0-4   yes        no
0x28000000-0x2fffffff  128M offline 5     no         no
0x30000000-0x7fffffff  1.3G  online 6-15  yes        no
0x80000000-0xffffffff    2G offline 16-31 no         yes

echo 1 > $sys/firmware/memory/memory5/memmap_on_memory
echo 1 > $sys/firmware/memory/memory5/config
echo 1 > $sys/devices/system/memory/memory5/online

lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY
RANGE                  SIZE  STATE   BLOCK CONFIGURED MEMMAP_ON_MEMORY
0x00000000-0x27ffffff  640M  online  0-4   yes        no
0x28000000-0x2fffffff  128M  online  5     yes        yes
0x30000000-0x7fffffff  1.3G  online  6-15  yes        no
0x80000000-0xffffffff    2G  offline 16-31 no         yes

4. Disable memmap_on_memory and online it.
echo 0 > $sys/devices/system/memory/memory5/online
echo 0 > $sys/firmware/memory/memory5/config

lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY
RANGE                  SIZE  STATE  BLOCK CONFIGURED MEMMAP_ON_MEMORY
0x00000000-0x27ffffff  640M  online 0-4   yes        no
0x28000000-0x2fffffff  128M offline 5     no         yes
0x30000000-0x7fffffff  1.3G  online 6-15  yes        no
0x80000000-0xffffffff    2G offline 16-31 no         yes

echo 0 > $sys/firmware/memory/memory5/memmap_on_memory
echo 1 > $sys/firmware/memory/memory5/config
echo 1 > $sys/devices/system/memory/memory5/online

lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY
RANGE                  SIZE  STATE   BLOCK CONFIGURED MEMMAP_ON_MEMORY
0x00000000-0x7fffffff  2G    online  0-15  yes        no
0x80000000-0xffffffff  2G    offline 16-31 no         yes

Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
---
 drivers/s390/char/sclp_mem.c | 290 +++++++++++++++++++++++++----------
 1 file changed, 207 insertions(+), 83 deletions(-)

diff --git a/drivers/s390/char/sclp_mem.c b/drivers/s390/char/sclp_mem.c
index 27f49f5fd358..e1302b1c98ac 100644
--- a/drivers/s390/char/sclp_mem.c
+++ b/drivers/s390/char/sclp_mem.c
@@ -9,9 +9,12 @@
 #define pr_fmt(fmt) KMSG_COMPONENT ": " fmt
 
 #include <linux/cpufeature.h>
+#include <linux/container_of.h>
 #include <linux/err.h>
 #include <linux/errno.h>
 #include <linux/init.h>
+#include <linux/kobject.h>
+#include <linux/kstrtox.h>
 #include <linux/memory.h>
 #include <linux/memory_hotplug.h>
 #include <linux/mm.h>
@@ -27,7 +30,6 @@
 #define SCLP_CMDW_ASSIGN_STORAGE		0x000d0001
 #define SCLP_CMDW_UNASSIGN_STORAGE		0x000c0001
 
-static DEFINE_MUTEX(sclp_mem_mutex);
 static LIST_HEAD(sclp_mem_list);
 static u8 sclp_max_storage_id;
 static DECLARE_BITMAP(sclp_storage_ids, 256);
@@ -38,6 +40,18 @@ struct memory_increment {
 	int standby;
 };
 
+struct sclp_mem {
+	struct kobject kobj;
+	unsigned int id;
+	unsigned int memmap_on_memory;
+	unsigned int config;
+};
+
+struct sclp_mem_arg {
+	struct sclp_mem *sclp_mems;
+	struct kset *kset;
+};
+
 struct assign_storage_sccb {
 	struct sccb_header header;
 	u16 rn;
@@ -163,92 +177,165 @@ static int sclp_mem_change_state(unsigned long start, unsigned long size,
 	return rc ? -EIO : 0;
 }
 
-static bool contains_standby_increment(unsigned long start, unsigned long end)
+static ssize_t config_sclp_mem_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf)
 {
-	struct memory_increment *incr;
-	unsigned long istart;
+	struct sclp_mem *sclp_mem = container_of(kobj, struct sclp_mem, kobj);
 
-	list_for_each_entry(incr, &sclp_mem_list, list) {
-		istart = rn2addr(incr->rn);
-		if (end - 1 < istart)
-			continue;
-		if (start > istart + sclp.rzm - 1)
-			continue;
-		if (incr->standby)
-			return true;
-	}
-	return false;
+	return sysfs_emit(buf, "%u\n", READ_ONCE(sclp_mem->config));
 }
 
-static int sclp_mem_notifier(struct notifier_block *nb,
-			     unsigned long action, void *data)
+static ssize_t config_sclp_mem_store(struct kobject *kobj, struct kobj_attribute *attr,
+				     const char *buf, size_t count)
 {
-	unsigned long start, size;
-	struct memory_notify *arg;
+	unsigned long addr, block_size;
+	struct sclp_mem *sclp_mem;
+	struct memory_block *mem;
 	unsigned char id;
-	int rc = 0;
+	bool value;
+	int rc;
 
-	arg = data;
-	start = arg->start_pfn << PAGE_SHIFT;
-	size = arg->nr_pages << PAGE_SHIFT;
-	mutex_lock(&sclp_mem_mutex);
+	rc = kstrtobool(buf, &value);
+	if (rc)
+		return rc;
+	sclp_mem = container_of(kobj, struct sclp_mem, kobj);
+	block_size = memory_block_size_bytes();
+	addr = sclp_mem->id * block_size;
+	/*
+	 * Hold device_hotplug_lock when adding/removing memory blocks.
+	 * Additionally, also protect calls to find_memory_block() and
+	 * sclp_attach_storage().
+	 */
+	rc = lock_device_hotplug_sysfs();
+	if (rc)
+		goto out;
 	for_each_clear_bit(id, sclp_storage_ids, sclp_max_storage_id + 1)
 		sclp_attach_storage(id);
-	switch (action) {
-	case MEM_GOING_OFFLINE:
-		/*
-		 * Do not allow to set memory blocks offline that contain
-		 * standby memory. This is done to simplify the "memory online"
-		 * case.
-		 */
-		if (contains_standby_increment(start, start + size))
-			rc = -EPERM;
-		break;
-	case MEM_PREPARE_ONLINE:
+	if (value) {
+		if (sclp_mem->config)
+			goto out_unlock;
+		rc = sclp_mem_change_state(addr, block_size, 1);
+		if (rc)
+			goto out_unlock;
 		/*
-		 * Access the altmap_start_pfn and altmap_nr_pages fields
-		 * within the struct memory_notify specifically when dealing
-		 * with only MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE notifiers.
-		 *
-		 * When altmap is in use, take the specified memory range
-		 * online, which includes the altmap.
+		 * Set entire memory block CMMA state to nodat. Later, when
+		 * page tables pages are allocated via __add_memory(), those
+		 * regions are marked __arch_set_page_dat().
 		 */
-		if (arg->altmap_nr_pages) {
-			start = PFN_PHYS(arg->altmap_start_pfn);
-			size += PFN_PHYS(arg->altmap_nr_pages);
+		__arch_set_page_nodat((void *)__va(addr), block_size >> PAGE_SHIFT);
+		rc = __add_memory(0, addr, block_size,
+				  sclp_mem->memmap_on_memory ?
+				  MHP_MEMMAP_ON_MEMORY | MHP_OFFLINE_INACCESSIBLE : MHP_NONE);
+		if (rc) {
+			sclp_mem_change_state(addr, block_size, 0);
+			goto out_unlock;
 		}
-		rc = sclp_mem_change_state(start, size, 1);
-		if (rc || !arg->altmap_nr_pages)
-			break;
-		/*
-		 * Set CMMA state to nodat here, since the struct page memory
-		 * at the beginning of the memory block will not go through the
-		 * buddy allocator later.
-		 */
-		__arch_set_page_nodat((void *)__va(start), arg->altmap_nr_pages);
-		break;
-	case MEM_FINISH_OFFLINE:
-		/*
-		 * When altmap is in use, take the specified memory range
-		 * offline, which includes the altmap.
-		 */
-		if (arg->altmap_nr_pages) {
-			start = PFN_PHYS(arg->altmap_start_pfn);
-			size += PFN_PHYS(arg->altmap_nr_pages);
+		mem = find_memory_block(pfn_to_section_nr(PFN_DOWN(addr)));
+		put_device(&mem->dev);
+		WRITE_ONCE(sclp_mem->config, 1);
+	} else {
+		if (!sclp_mem->config)
+			goto out_unlock;
+		mem = find_memory_block(pfn_to_section_nr(PFN_DOWN(addr)));
+		if (mem->state != MEM_OFFLINE) {
+			put_device(&mem->dev);
+			rc = -EBUSY;
+			goto out_unlock;
 		}
-		sclp_mem_change_state(start, size, 0);
-		break;
-	default:
-		break;
+		/* drop the ref just got via find_memory_block() */
+		put_device(&mem->dev);
+		sclp_mem_change_state(addr, block_size, 0);
+		__remove_memory(addr, block_size);
+		WRITE_ONCE(sclp_mem->config, 0);
 	}
-	mutex_unlock(&sclp_mem_mutex);
-	return rc ? NOTIFY_BAD : NOTIFY_OK;
+out_unlock:
+	unlock_device_hotplug();
+out:
+	return rc ? rc : count;
 }
 
-static struct notifier_block sclp_mem_nb = {
-	.notifier_call = sclp_mem_notifier,
+static ssize_t memmap_on_memory_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf)
+{
+	struct sclp_mem *sclp_mem = container_of(kobj, struct sclp_mem, kobj);
+
+	return sysfs_emit(buf, "%u\n", READ_ONCE(sclp_mem->memmap_on_memory));
+}
+
+static ssize_t memmap_on_memory_store(struct kobject *kobj, struct kobj_attribute *attr,
+				      const char *buf, size_t count)
+{
+	struct sclp_mem *sclp_mem;
+	unsigned long block_size;
+	struct memory_block *mem;
+	bool value;
+	int rc;
+
+	rc = kstrtobool(buf, &value);
+	if (rc)
+		return rc;
+	rc = lock_device_hotplug_sysfs();
+	if (rc)
+		return rc;
+	block_size = memory_block_size_bytes();
+	sclp_mem = container_of(kobj, struct sclp_mem, kobj);
+	mem = find_memory_block(pfn_to_section_nr(PFN_DOWN(sclp_mem->id * block_size)));
+	if (!mem) {
+		WRITE_ONCE(sclp_mem->memmap_on_memory, value);
+	} else {
+		put_device(&mem->dev);
+		rc = -EBUSY;
+	}
+	unlock_device_hotplug();
+	return rc ? rc : count;
+}
+
+static const struct kobj_type ktype = {
+	.sysfs_ops = &kobj_sysfs_ops,
 };
 
+static struct kobj_attribute memmap_attr =
+	__ATTR(memmap_on_memory, 0644, memmap_on_memory_show, memmap_on_memory_store);
+static struct kobj_attribute config_attr =
+	__ATTR(config, 0644, config_sclp_mem_show, config_sclp_mem_store);
+
+static struct attribute *sclp_mem_attrs[] = {
+	&memmap_attr.attr,
+	&config_attr.attr,
+	NULL,
+};
+
+static struct attribute_group sclp_mem_attr_group = {
+	.attrs = sclp_mem_attrs,
+};
+
+static int create_sclp_mem(struct sclp_mem *sclp_mem, struct kset *kset,
+			   unsigned int id, bool config, bool memmap_on_memory)
+{
+	int rc;
+
+	sclp_mem->memmap_on_memory = memmap_on_memory;
+	sclp_mem->config = config;
+	sclp_mem->id = id;
+	kobject_init(&sclp_mem->kobj, &ktype);
+	rc = kobject_add(&sclp_mem->kobj, &kset->kobj, "memory%d", id);
+	if (rc)
+		return rc;
+	return sysfs_create_group(&sclp_mem->kobj, &sclp_mem_attr_group);
+}
+
+static int create_configured_sclp_mem(struct memory_block *mem, void *argument)
+{
+	struct sclp_mem *sclp_mems;
+	struct sclp_mem_arg *arg;
+	struct kset *kset;
+	unsigned int id;
+
+	id = mem->dev.id;
+	arg = (struct sclp_mem_arg *)argument;
+	sclp_mems = arg->sclp_mems;
+	kset = arg->kset;
+	return create_sclp_mem(&sclp_mems[id], kset, id, true, false);
+}
+
 static void __init align_to_block_size(unsigned long *start,
 				       unsigned long *size,
 				       unsigned long alignment)
@@ -264,14 +351,17 @@ static void __init align_to_block_size(unsigned long *start,
 	*size = size_align;
 }
 
-static void __init add_memory_merged(u16 rn)
+static int __init create_standby_sclp_mems_merged(struct sclp_mem *sclp_mems,
+						  struct kset *kset, u16 rn)
 {
 	unsigned long start, size, addr, block_size;
 	static u16 first_rn, num;
+	unsigned int id;
+	int rc = 0;
 
 	if (rn && first_rn && (first_rn + num == rn)) {
 		num++;
-		return;
+		return rc;
 	}
 	if (!first_rn)
 		goto skip_add;
@@ -286,24 +376,61 @@ static void __init add_memory_merged(u16 rn)
 	if (!size)
 		goto skip_add;
 	for (addr = start; addr < start + size; addr += block_size) {
-		add_memory(0, addr, block_size,
-			   cpu_has_edat1() ?
-			   MHP_MEMMAP_ON_MEMORY | MHP_OFFLINE_INACCESSIBLE : MHP_NONE);
+		id = addr / block_size;
+		rc = create_sclp_mem(&sclp_mems[id], kset, id, false,
+				     mhp_supports_memmap_on_memory());
+		if (rc)
+			break;
 	}
 skip_add:
 	first_rn = rn;
 	num = 1;
+	return rc;
 }
 
-static void __init sclp_add_standby_memory(void)
+static int __init create_standby_sclp_mems(struct sclp_mem *sclp_mems, struct kset *kset)
 {
 	struct memory_increment *incr;
+	int rc = 0;
 
 	list_for_each_entry(incr, &sclp_mem_list, list) {
 		if (incr->standby)
-			add_memory_merged(incr->rn);
+			rc = create_standby_sclp_mems_merged(sclp_mems, kset, incr->rn);
+		if (rc)
+			goto out;
 	}
-	add_memory_merged(0);
+	rc = create_standby_sclp_mems_merged(sclp_mems, kset, 0);
+out:
+	return rc;
+}
+
+static int __init init_sclp_mem(void)
+{
+	const u64 block_size = memory_block_size_bytes();
+	const u64 max_sclp_mems = roundup(sclp.rnmax * sclp.rzm, block_size) / block_size;
+	struct sclp_mem *sclp_mems;
+	struct sclp_mem_arg arg;
+	struct kset *kset;
+	int rc;
+
+	/* Allocate memory for all blocks ahead of time. */
+	sclp_mems = kcalloc(max_sclp_mems, sizeof(struct sclp_mem), GFP_KERNEL);
+	if (!sclp_mems)
+		return -ENOMEM;
+
+	kset = kset_create_and_add("memory", NULL, firmware_kobj);
+	if (!kset)
+		return -ENOMEM;
+
+	/* Initial memory is in the "configured" state already. */
+	arg.sclp_mems = sclp_mems;
+	arg.kset = kset;
+	rc = for_each_memory_block(&arg, create_configured_sclp_mem);
+	if (rc)
+		return rc;
+
+	/* Standby memory is "deconfigured". */
+	return create_standby_sclp_mems(sclp_mems, kset);
 }
 
 static void __init insert_increment(u16 rn, int standby, int assigned)
@@ -336,7 +463,7 @@ static void __init insert_increment(u16 rn, int standby, int assigned)
 	list_add(&new_incr->list, prev);
 }
 
-static int __init sclp_detect_standby_memory(void)
+static int __init sclp_setup_memory(void)
 {
 	struct read_storage_sccb *sccb;
 	int i, id, assigned, rc;
@@ -388,12 +515,9 @@ static int __init sclp_detect_standby_memory(void)
 		goto out;
 	for (i = 1; i <= sclp.rnmax - assigned; i++)
 		insert_increment(0, 1, 0);
-	rc = register_memory_notifier(&sclp_mem_nb);
-	if (rc)
-		goto out;
-	sclp_add_standby_memory();
+	rc = init_sclp_mem();
 out:
 	free_page((unsigned long)sccb);
 	return rc;
 }
-__initcall(sclp_detect_standby_memory);
+__initcall(sclp_setup_memory);
-- 
2.48.1

[PATCH v2 3/4] s390/sclp: Remove MHP_OFFLINE_INACCESSIBLE

[Sumanth Korikkar]

mhp_flag MHP_OFFLINE_INACCESSIBLE was used to mark memory as not
accessible until memory hotplug online phase begins.

Earlier, standby memory blocks were added upfront during boottime and
MHP_OFFLINE_INACCESSIBLE flag avoided page_init_poison() on memmap
during mhp addtion phase.

However with dynamic runtime configuration of memory, standby memory can
be brought to accessible state before performing add_memory(). Hence,
remove MHP_OFFLINE_INACCESSIBLE.

Acked-by: Heiko Carstens <hca@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
---
 drivers/s390/char/sclp_mem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/s390/char/sclp_mem.c b/drivers/s390/char/sclp_mem.c
index e1302b1c98ac..0f8c0a4dbdd3 100644
--- a/drivers/s390/char/sclp_mem.c
+++ b/drivers/s390/char/sclp_mem.c
@@ -224,7 +224,7 @@ static ssize_t config_sclp_mem_store(struct kobject *kobj, struct kobj_attribute
 		__arch_set_page_nodat((void *)__va(addr), block_size >> PAGE_SHIFT);
 		rc = __add_memory(0, addr, block_size,
 				  sclp_mem->memmap_on_memory ?
-				  MHP_MEMMAP_ON_MEMORY | MHP_OFFLINE_INACCESSIBLE : MHP_NONE);
+				  MHP_MEMMAP_ON_MEMORY : MHP_NONE);
 		if (rc) {
 			sclp_mem_change_state(addr, block_size, 0);
 			goto out_unlock;
-- 
2.48.1

[PATCH v2 4/4] mm/memory_hotplug: Remove MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE notifiers

[Sumanth Korikkar]

MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE memory notifiers were introduced
to prepare the transition of memory to and from a physically accessible
state. This enhancement was crucial for implementing the "memmap on memory"
feature for s390.

With introduction of dynamic (de)configuration of hotpluggable memory,
memory can be brought to accessible state before add_memory(). Memory
can be brought to inaccessible state before remove_memory(). Hence,
there is no need of MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE memory
notifiers anymore.

This basically reverts commit
c5f1e2d18909 ("mm/memory_hotplug: introduce MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE notifiers")
Additionally, apply minor adjustments to the function parameters of
move_pfn_range_to_zone() and mhp_supports_memmap_on_memory() to ensure
compatibility with the latest branch.

Signed-off-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
---
 drivers/base/memory.c          | 23 +----------------------
 include/linux/memory.h         |  9 ---------
 include/linux/memory_hotplug.h | 18 +-----------------
 include/linux/memremap.h       |  1 -
 mm/memory_hotplug.c            | 17 +++--------------
 mm/sparse.c                    |  3 +--
 6 files changed, 6 insertions(+), 65 deletions(-)

diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index 6d84a02cfa5d..fc43f2703ae0 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -226,7 +226,6 @@ static int memory_block_online(struct memory_block *mem)
 	unsigned long start_pfn = section_nr_to_pfn(mem->start_section_nr);
 	unsigned long nr_pages = PAGES_PER_SECTION * sections_per_block;
 	unsigned long nr_vmemmap_pages = 0;
-	struct memory_notify arg;
 	struct zone *zone;
 	int ret;
 
@@ -246,19 +245,9 @@ static int memory_block_online(struct memory_block *mem)
 	if (mem->altmap)
 		nr_vmemmap_pages = mem->altmap->free;
 
-	arg.altmap_start_pfn = start_pfn;
-	arg.altmap_nr_pages = nr_vmemmap_pages;
-	arg.start_pfn = start_pfn + nr_vmemmap_pages;
-	arg.nr_pages = nr_pages - nr_vmemmap_pages;
 	mem_hotplug_begin();
-	ret = memory_notify(MEM_PREPARE_ONLINE, &arg);
-	ret = notifier_to_errno(ret);
-	if (ret)
-		goto out_notifier;
-
 	if (nr_vmemmap_pages) {
-		ret = mhp_init_memmap_on_memory(start_pfn, nr_vmemmap_pages,
-						zone, mem->altmap->inaccessible);
+		ret = mhp_init_memmap_on_memory(start_pfn, nr_vmemmap_pages, zone);
 		if (ret)
 			goto out;
 	}
@@ -280,11 +269,7 @@ static int memory_block_online(struct memory_block *mem)
 					  nr_vmemmap_pages);
 
 	mem->zone = zone;
-	mem_hotplug_done();
-	return ret;
 out:
-	memory_notify(MEM_FINISH_OFFLINE, &arg);
-out_notifier:
 	mem_hotplug_done();
 	return ret;
 }
@@ -297,7 +282,6 @@ static int memory_block_offline(struct memory_block *mem)
 	unsigned long start_pfn = section_nr_to_pfn(mem->start_section_nr);
 	unsigned long nr_pages = PAGES_PER_SECTION * sections_per_block;
 	unsigned long nr_vmemmap_pages = 0;
-	struct memory_notify arg;
 	int ret;
 
 	if (!mem->zone)
@@ -329,11 +313,6 @@ static int memory_block_offline(struct memory_block *mem)
 		mhp_deinit_memmap_on_memory(start_pfn, nr_vmemmap_pages);
 
 	mem->zone = NULL;
-	arg.altmap_start_pfn = start_pfn;
-	arg.altmap_nr_pages = nr_vmemmap_pages;
-	arg.start_pfn = start_pfn + nr_vmemmap_pages;
-	arg.nr_pages = nr_pages - nr_vmemmap_pages;
-	memory_notify(MEM_FINISH_OFFLINE, &arg);
 out:
 	mem_hotplug_done();
 	return ret;
diff --git a/include/linux/memory.h b/include/linux/memory.h
index 0c214256216f..ba1515160894 100644
--- a/include/linux/memory.h
+++ b/include/linux/memory.h
@@ -96,17 +96,8 @@ int set_memory_block_size_order(unsigned int order);
 #define	MEM_GOING_ONLINE	(1<<3)
 #define	MEM_CANCEL_ONLINE	(1<<4)
 #define	MEM_CANCEL_OFFLINE	(1<<5)
-#define	MEM_PREPARE_ONLINE	(1<<6)
-#define	MEM_FINISH_OFFLINE	(1<<7)
 
 struct memory_notify {
-	/*
-	 * The altmap_start_pfn and altmap_nr_pages fields are designated for
-	 * specifying the altmap range and are exclusively intended for use in
-	 * MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE notifiers.
-	 */
-	unsigned long altmap_start_pfn;
-	unsigned long altmap_nr_pages;
 	unsigned long start_pfn;
 	unsigned long nr_pages;
 };
diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 23f038a16231..f2f16cdd73ee 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -58,22 +58,6 @@ typedef int __bitwise mhp_t;
  * implies the node id (nid).
  */
 #define MHP_NID_IS_MGID		((__force mhp_t)BIT(2))
-/*
- * The hotplugged memory is completely inaccessible while the memory is
- * offline. The memory provider will handle MEM_PREPARE_ONLINE /
- * MEM_FINISH_OFFLINE notifications and make the memory accessible.
- *
- * This flag is only relevant when used along with MHP_MEMMAP_ON_MEMORY,
- * because the altmap cannot be written (e.g., poisoned) when adding
- * memory -- before it is set online.
- *
- * This allows for adding memory with an altmap that is not currently
- * made available by a hypervisor. When onlining that memory, the
- * hypervisor can be instructed to make that memory available, and
- * the onlining phase will not require any memory allocations, which is
- * helpful in low-memory situations.
- */
-#define MHP_OFFLINE_INACCESSIBLE	((__force mhp_t)BIT(3))
 
 /*
  * Extended parameters for memory hotplug:
@@ -123,7 +107,7 @@ extern void adjust_present_page_count(struct page *page,
 				      long nr_pages);
 /* VM interface that may be used by firmware interface */
 extern int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages,
-				     struct zone *zone, bool mhp_off_inaccessible);
+				     struct zone *zone);
 extern void mhp_deinit_memmap_on_memory(unsigned long pfn, unsigned long nr_pages);
 extern int online_pages(unsigned long pfn, unsigned long nr_pages,
 			struct zone *zone, struct memory_group *group);
diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index e5951ba12a28..30c7aecbd245 100644
--- a/include/linux/memremap.h
+++ b/include/linux/memremap.h
@@ -25,7 +25,6 @@ struct vmem_altmap {
 	unsigned long free;
 	unsigned long align;
 	unsigned long alloc;
-	bool inaccessible;
 };
 
 /*
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 0be83039c3b5..238a6712738e 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1088,7 +1088,7 @@ void adjust_present_page_count(struct page *page, struct memory_group *group,
 }
 
 int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages,
-			      struct zone *zone, bool mhp_off_inaccessible)
+			      struct zone *zone)
 {
 	unsigned long end_pfn = pfn + nr_pages;
 	int ret, i;
@@ -1097,15 +1097,6 @@ int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages,
 	if (ret)
 		return ret;
 
-	/*
-	 * Memory block is accessible at this stage and hence poison the struct
-	 * pages now.  If the memory block is accessible during memory hotplug
-	 * addition phase, then page poisining is already performed in
-	 * sparse_add_section().
-	 */
-	if (mhp_off_inaccessible)
-		page_init_poison(pfn_to_page(pfn), sizeof(struct page) * nr_pages);
-
 	move_pfn_range_to_zone(zone, pfn, nr_pages, NULL, MIGRATE_UNMOVABLE,
 			       false);
 
@@ -1444,7 +1435,7 @@ static void remove_memory_blocks_and_altmaps(u64 start, u64 size)
 }
 
 static int create_altmaps_and_memory_blocks(int nid, struct memory_group *group,
-					    u64 start, u64 size, mhp_t mhp_flags)
+					    u64 start, u64 size)
 {
 	unsigned long memblock_size = memory_block_size_bytes();
 	u64 cur_start;
@@ -1460,8 +1451,6 @@ static int create_altmaps_and_memory_blocks(int nid, struct memory_group *group,
 		};
 
 		mhp_altmap.free = memory_block_memmap_on_memory_pages();
-		if (mhp_flags & MHP_OFFLINE_INACCESSIBLE)
-			mhp_altmap.inaccessible = true;
 		params.altmap = kmemdup(&mhp_altmap, sizeof(struct vmem_altmap),
 					GFP_KERNEL);
 		if (!params.altmap) {
@@ -1555,7 +1544,7 @@ int add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
 	 */
 	if ((mhp_flags & MHP_MEMMAP_ON_MEMORY) &&
 	    mhp_supports_memmap_on_memory()) {
-		ret = create_altmaps_and_memory_blocks(nid, group, start, size, mhp_flags);
+		ret = create_altmaps_and_memory_blocks(nid, group, start, size);
 		if (ret)
 			goto error;
 	} else {
diff --git a/mm/sparse.c b/mm/sparse.c
index 17c50a6415c2..b5b2b6f7041b 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -951,8 +951,7 @@ int __meminit sparse_add_section(int nid, unsigned long start_pfn,
 	 * Poison uninitialized struct pages in order to catch invalid flags
 	 * combinations.
 	 */
-	if (!altmap || !altmap->inaccessible)
-		page_init_poison(memmap, sizeof(struct page) * nr_pages);
+	page_init_poison(memmap, sizeof(struct page) * nr_pages);
 
 	ms = __nr_to_section(section_nr);
 	set_section_nid(section_nr, nid);
-- 
2.48.1

Re: [PATCH v2 4/4] mm/memory_hotplug: Remove MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE notifiers

[David Hildenbrand]

On 09.10.25 15:18, Sumanth Korikkar wrote:
> MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE memory notifiers were introduced
> to prepare the transition of memory to and from a physically accessible
> state. This enhancement was crucial for implementing the "memmap on memory"
> feature for s390.
> 
> With introduction of dynamic (de)configuration of hotpluggable memory,
> memory can be brought to accessible state before add_memory(). Memory
> can be brought to inaccessible state before remove_memory(). Hence,
> there is no need of MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE memory
> notifiers anymore.
> 
> This basically reverts commit
> c5f1e2d18909 ("mm/memory_hotplug: introduce MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE notifiers")
> Additionally, apply minor adjustments to the function parameters of
> move_pfn_range_to_zone() and mhp_supports_memmap_on_memory() to ensure
> compatibility with the latest branch.
> 
> Signed-off-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
> ---

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Cheers

David / dhildenb

Re: [PATCH v2 2/4] s390/sclp: Add support for dynamic (de)configuration of memory

[David Hildenbrand]

Just a couple of nits

> ---
>   drivers/s390/char/sclp_mem.c | 290 +++++++++++++++++++++++++----------
>   1 file changed, 207 insertions(+), 83 deletions(-)
> 
> diff --git a/drivers/s390/char/sclp_mem.c b/drivers/s390/char/sclp_mem.c
> index 27f49f5fd358..e1302b1c98ac 100644
> --- a/drivers/s390/char/sclp_mem.c
> +++ b/drivers/s390/char/sclp_mem.c
> @@ -9,9 +9,12 @@
>   #define pr_fmt(fmt) KMSG_COMPONENT ": " fmt
>   
>   #include <linux/cpufeature.h>
> +#include <linux/container_of.h>
>   #include <linux/err.h>
>   #include <linux/errno.h>
>   #include <linux/init.h>
> +#include <linux/kobject.h>
> +#include <linux/kstrtox.h>
>   #include <linux/memory.h>
>   #include <linux/memory_hotplug.h>
>   #include <linux/mm.h>
> @@ -27,7 +30,6 @@
>   #define SCLP_CMDW_ASSIGN_STORAGE		0x000d0001
>   #define SCLP_CMDW_UNASSIGN_STORAGE		0x000c0001
>   
> -static DEFINE_MUTEX(sclp_mem_mutex);
>   static LIST_HEAD(sclp_mem_list);
>   static u8 sclp_max_storage_id;
>   static DECLARE_BITMAP(sclp_storage_ids, 256);
> @@ -38,6 +40,18 @@ struct memory_increment {
>   	int standby;
>   };
>   
> +struct sclp_mem {
> +	struct kobject kobj;
> +	unsigned int id;
> +	unsigned int memmap_on_memory;
> +	unsigned int config;
> +};
> +
> +struct sclp_mem_arg {
> +	struct sclp_mem *sclp_mems;
> +	struct kset *kset;
> +};

Just one thought: if you keep either as global variable you wouldn't 
need this. (I would just keep both as globals, but whatever you prefer)

Whatever you prefer.

[...]

>   
> -static void __init sclp_add_standby_memory(void)
> +static int __init create_standby_sclp_mems(struct sclp_mem *sclp_mems, struct kset *kset)
>   {
>   	struct memory_increment *incr;
> +	int rc = 0;
>   
>   	list_for_each_entry(incr, &sclp_mem_list, list) {
>   		if (incr->standby)
> -			add_memory_merged(incr->rn);
> +			rc = create_standby_sclp_mems_merged(sclp_mems, kset, incr->rn);
> +		if (rc)
> +			goto out;

Why not "return rc;" to avoid the goto label?

>   	}
> -	add_memory_merged(0);
> +	rc = create_standby_sclp_mems_merged(sclp_mems, kset, 0);
> +out:
> +	return rc;
> +}
> +
> +static int __init init_sclp_mem(void)
> +{
> +	const u64 block_size = memory_block_size_bytes();

Instead of "u64" maybe "unsigned long" like memory_block_size_bytes() 
returns?

> +	const u64 max_sclp_mems = roundup(sclp.rnmax * sclp.rzm, block_size) / block_size;

Instead of u64 maybe "unsigned int" like the ids you store per sclp_mem?

> +	struct sclp_mem *sclp_mems;
> +	struct sclp_mem_arg arg;
> +	struct kset *kset;
> +	int rc;
> +
> +	/* Allocate memory for all blocks ahead of time. */
> +	sclp_mems = kcalloc(max_sclp_mems, sizeof(struct sclp_mem), GFP_KERNEL);
> +	if (!sclp_mems)
> +		return -ENOMEM;
> +
> +	kset = kset_create_and_add("memory", NULL, firmware_kobj);
> +	if (!kset)
> +		return -ENOMEM;

I guess we don't care about freeing sclp_mems in that case? Likely it 
should never ever happen either way.

-- 
Cheers

David / dhildenb

Re: [PATCH v2 2/4] s390/sclp: Add support for dynamic (de)configuration of memory

[Sumanth Korikkar]

> > +struct sclp_mem {
> > +	struct kobject kobj;
> > +	unsigned int id;
> > +	unsigned int memmap_on_memory;
> > +	unsigned int config;
> > +};
> > +
> > +struct sclp_mem_arg {
> > +	struct sclp_mem *sclp_mems;
> > +	struct kset *kset;
> > +};
> 
> Just one thought: if you keep either as global variable you wouldn't need
> this. (I would just keep both as globals, but whatever you prefer)
> 
> Whatever you prefer.

Hi David,

I prefer to preserve the ones we have.

> > -static void __init sclp_add_standby_memory(void)
> > +static int __init create_standby_sclp_mems(struct sclp_mem *sclp_mems, struct kset *kset)
> >   {
> >   	struct memory_increment *incr;
> > +	int rc = 0;
> >   	list_for_each_entry(incr, &sclp_mem_list, list) {
> >   		if (incr->standby)
> > -			add_memory_merged(incr->rn);
> > +			rc = create_standby_sclp_mems_merged(sclp_mems, kset, incr->rn);
> > +		if (rc)
> > +			goto out;
> 
> Why not "return rc;" to avoid the goto label?

Sure. Will add it.

> >   	}
> > -	add_memory_merged(0);
> > +	rc = create_standby_sclp_mems_merged(sclp_mems, kset, 0);
> > +out:
> > +	return rc;
> > +}
> > +
> > +static int __init init_sclp_mem(void)
> > +{
> > +	const u64 block_size = memory_block_size_bytes();
> 
> Instead of "u64" maybe "unsigned long" like memory_block_size_bytes()
> returns?

Noted.

> > +	const u64 max_sclp_mems = roundup(sclp.rnmax * sclp.rzm, block_size) / block_size;
> 
> Instead of u64 maybe "unsigned int" like the ids you store per sclp_mem?

Sure.

> > +	struct sclp_mem *sclp_mems;
> > +	struct sclp_mem_arg arg;
> > +	struct kset *kset;
> > +	int rc;
> > +
> > +	/* Allocate memory for all blocks ahead of time. */
> > +	sclp_mems = kcalloc(max_sclp_mems, sizeof(struct sclp_mem), GFP_KERNEL);
> > +	if (!sclp_mems)
> > +		return -ENOMEM;
> > +
> > +	kset = kset_create_and_add("memory", NULL, firmware_kobj);
> > +	if (!kset)
> > +		return -ENOMEM;
> 
> I guess we don't care about freeing sclp_mems in that case? Likely it should
> never ever happen either way.

Right. We dont care about freeing sclp_mems here.

Thank you.

Re: [PATCH v2 2/4] s390/sclp: Add support for dynamic (de)configuration of memory

[David Hildenbrand]

On 10.10.25 10:09, Sumanth Korikkar wrote:
>>> +struct sclp_mem {
>>> +	struct kobject kobj;
>>> +	unsigned int id;
>>> +	unsigned int memmap_on_memory;
>>> +	unsigned int config;
>>> +};
>>> +
>>> +struct sclp_mem_arg {
>>> +	struct sclp_mem *sclp_mems;
>>> +	struct kset *kset;
>>> +};
>>
>> Just one thought: if you keep either as global variable you wouldn't need
>> this. (I would just keep both as globals, but whatever you prefer)
>>
>> Whatever you prefer.
> 

Feel free to add my

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Cheers

David / dhildenb

Re: [PATCH v2 0/4] Support dynamic (de)configuration of memory

[Heiko Carstens]

On Thu, Oct 09, 2025 at 03:18:35PM +0200, Sumanth Korikkar wrote:
> Hi,
> 
> Patchset provides a new interface for dynamic configuration and
> deconfiguration of hotplug memory on s390, allowing with/without
> memmap_on_memory support. It is a follow up on the discussion with David
> when introducing memmap_on_memory support for s390 and support dynamic
> (de)configuration of memory:
> https://lore.kernel.org/all/ee492da8-74b4-4a97-8b24-73e07257f01d@redhat.com/
> https://lore.kernel.org/all/20241202082732.3959803-1-sumanthk@linux.ibm.com/

Andrew, David, we would like to carry this series via the s390 tree,
including the fourth patch, which is common code only.

Is this ok for both of you?

Re: [PATCH v2 0/4] Support dynamic (de)configuration of memory

[David Hildenbrand]

On 10.10.25 10:24, Heiko Carstens wrote:
> On Thu, Oct 09, 2025 at 03:18:35PM +0200, Sumanth Korikkar wrote:
>> Hi,
>>
>> Patchset provides a new interface for dynamic configuration and
>> deconfiguration of hotplug memory on s390, allowing with/without
>> memmap_on_memory support. It is a follow up on the discussion with David
>> when introducing memmap_on_memory support for s390 and support dynamic
>> (de)configuration of memory:
>> https://lore.kernel.org/all/ee492da8-74b4-4a97-8b24-73e07257f01d@redhat.com/
>> https://lore.kernel.org/all/20241202082732.3959803-1-sumanthk@linux.ibm.com/
> 
> Andrew, David, we would like to carry this series via the s390 tree,
> including the fourth patch, which is common code only.
> 
> Is this ok for both of you?

Fine with me, I don't expect a lot of memory hotplug changes that could 
interact.

As an alternative, we could route #4 separately later through mm.

But this one feels like it can just all go through the mm tree if Andrew 
is fine with it.

-- 
Cheers

David / dhildenb