[PATCH v5 0/5] implement "memmap on memory" feature on s390

Sumanth Korikkar
2023-11-28T15:52:49Z

Hi All,

The patch series implements "memmap on memory" feature on s390.

Patch 1 introduces MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE memory
notifiers to prepare the transition of memory to and from a physically
accessible state. New mhp_flag MHP_OFFLINE_INACCESSIBLE is introduced to
ensure altmap cannot be written when addidng memory - before it is set
online. This enhancement is crucial for implementing the "memmap on
memory" feature for s390 in a subsequent patch.

Patches 2 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 3 removes unhandled memory notifier types on s390.

Patch 4 implements MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE memory
notifiers on s390. MEM_PREPARE_ONLINE memory notifier makes memory block
physical accessible via sclp assign command. The notifier ensures
self-contained memory maps are accessible and hence enabling the "memmap
on memory" on s390. MEM_FINISH_OFFLINE memory notifier shifts the memory
block to an inaccessible state via sclp unassign command

Patch 5 finally enables MHP_MEMMAP_ON_MEMORY on s390

Note:
These patches are rebased on top of three fixes:
mm: use vmem_altmap code without CONFIG_ZONE_DEVICE
mm/memory_hotplug: fix error handling in add_memory_resource()
mm/memory_hotplug: add missing mem_hotplug_lock

v5:
* Added reviewed-by
* Removed variables altmap_start, altmap_size in sclp_cmd.c
* Used PFN_PHYS macro.

Thanks for the valualble feedback.

v4:
* Introduced two new fields, altmap_start_pfn and altmap_nr_pages, in
the memory_notify structure and document it that it is used only in
MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE callbacks.
* Incorporated the newly added fields into s390's
MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE notifier callbacks.
* Prevent access to memblock->altmap->free in the s390 notifier callback.
* page_init_poison() could be performed similar to when adding new
memory in sparse_add_section(). Perform it without cond_resched().

v3:
* added comments to MHP_OFFLINE_ACCESSIBLE as suggested by David.
* Squashed three commits related to new memory notifier.

v2:
* Fixes are integrated and hence removed from this patch series
Suggestions from David:
* Add new flag MHP_OFFLINE_INACCESSIBLE to avoid accessing memory
during memory hotplug addition phase.
* Avoid page_init_poison() on memmap during mhp addition phase, when
MHP_OFFLINE_INACCESSIBLE mhp_flag is passed in add_memory().
* Do not skip add_pages() in arch_add_memory(). Similarly, remove
similar hacks in arch_remove_memory().
* Use MHP_PREPARE_ONLINE/MHP_FINISH_OFFLINE naming convention for
new memory notifiers.
* Rearrange removal of unused s390 memory notifier.
* Necessary commit messages changes.

Thank you

Sumanth Korikkar (5):
mm/memory_hotplug: introduce MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE
notifiers
s390/mm: allocate vmemmap pages from self-contained memory range
s390/sclp: remove unhandled memory notifier type
s390/mm: implement MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE notifiers
s390: enable MHP_MEMMAP_ON_MEMORY

arch/s390/Kconfig | 1 +
arch/s390/mm/init.c | 3 --
arch/s390/mm/vmem.c | 62 +++++++++++++++++++---------------
drivers/base/memory.c | 23 ++++++++++++-
drivers/s390/char/sclp_cmd.c | 44 +++++++++++++++++++-----
include/linux/memory.h | 9 +++++
include/linux/memory_hotplug.h | 18 +++++++++-
include/linux/memremap.h | 1 +
mm/memory_hotplug.c | 13 ++++++-
mm/sparse.c | 3 +-
10 files changed, 134 insertions(+), 43 deletions(-)

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2.40.1