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

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Message-Id: <20231128155227.1315063-1-sumanthk@linux.ibm.com>
Date:   Tue, 28 Nov 2023 16:52:22 +0100
From:   Sumanth Korikkar <sumanthk@...ux.ibm.com>
To:     linux-mm <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>
Cc:     Oscar Salvador <osalvador@...e.de>, Michal Hocko <mhocko@...e.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        linux-s390 <linux-s390@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH v5 0/5] implement "memmap on memory" feature on s390

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(-)

-- 
2.40.1