[PATCH 0/8] implement "memmap on memory" feature on s390

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Hi All,

The patch series implements "memmap on memory" feature on s390 and
provides the necessary fixes for it.

Patch 1  addresses the locking order in memory hotplug operations,
ensuring that the mem_hotplug_lock is held during critical operations
like mhp_init_memmap_on_memory() and mhp_deinit_memmap_on_memory()

Patch 2 deals with error handling in add_memory_resource() and considers
the possibility of altmap support. This ensures proper deallocation of
struct pages, aligning with the allocation strategy.

Patch 3 relocates the vmem_altmap code to sparse-vmemmap.c, enabling the
utilization of vmem_altmap_free() and vmem_altmap_offset() without the
dependency on CONFIG_ZONE_DEVICE. Note: These functions are also used in
arm64 architecture. However, ZONE_DEVICE or ARCH_HAS_ZONE_DEVICE doesnt
seems to be enabled in arm64.

Patch 4 introduces MEM_PHYS_ONLINE/OFFLINE memory notifiers. It
facilitates the emulation of dynamic ACPI event-triggered logic for
memory hotplug on platforms lacking such events. This sets the stage for
implementing the "memmap on memory" feature for s390 in subsequent
patches. All architecture/codepaths have the default cases handled in
memory notifiers. Hence, introducing new memory notifiers will have no
functional impact.

Patches 5 allocates vmemmap pages from self-contained memory range for
s390. It allocates memory map (struct pages array) from the hotplugged
memory range, rather than using system memory by passing altmap to
vmemmap functions.

Patch 6 implements MEM_PHYS_ONLINE and MEM_PHYS_OFFLINE memory notifiers
on s390. It involves making the memory block physically accessible and
then calling __add_pages()/__remove_pages() with altmap parameter.

Patch 7 removes unhandled memory notifier types. This is currently
handled in default case

Patch 8 finally enables MHP_MEMMAP_ON_MEMORY on s390

Thank you

Sumanth Korikkar (8):
  mm/memory_hotplug: fix memory hotplug locking order
  mm/memory_hotplug: fix error handling in add_memory_resource()
  mm: use vmem_altmap code without CONFIG_ZONE_DEVICE
  mm/memory_hotplug: introduce MEM_PHYS_ONLINE/OFFLINE memory notifiers
  s390/mm: allocate vmemmap pages from self-contained memory range
  s390/mm: implement MEM_PHYS_ONLINE MEM_PHYS_OFFLINE memory notifiers
  s390/sclp: remove unhandled memory notifier type
  s390: enable MHP_MEMMAP_ON_MEMORY

 arch/s390/Kconfig            |  1 +
 arch/s390/mm/init.c          | 19 ++++++++---
 arch/s390/mm/vmem.c          | 62 ++++++++++++++++++++----------------
 drivers/base/memory.c        | 28 ++++++++++++++--
 drivers/s390/char/sclp_cmd.c | 37 +++++++++++++++------
 include/linux/memory.h       |  2 ++
 include/linux/memremap.h     | 12 -------
 include/linux/mm.h           |  2 ++
 mm/memory_hotplug.c          | 15 ++++-----
 mm/memremap.c                | 14 +-------
 mm/sparse-vmemmap.c          | 13 ++++++++
 11 files changed, 129 insertions(+), 76 deletions(-)


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