[RFC PATCH 0/7] Memory hotplug/hotremove at subsection size

Zi Yan zi.yan at sent.com
Fri May 7 01:26:16 AEST 2021

From: Zi Yan <ziy at nvidia.com>

Hi all,

This patchset tries to remove the restriction on memory hotplug/hotremove
granularity, which is always greater or equal to memory section size[1].
With the patchset, kernel is able to online/offline memory at a size independent
of memory section size, as small as 2MB (the subsection size).

The motivation is to increase MAX_ORDER of the buddy allocator and pageblock
size without increasing memory hotplug/hotremove granularity at the same time,
so that the kernel can allocator 1GB pages using buddy allocator and utilizes
existing pageblock based anti-fragmentation, paving the road for 1GB THP

The patchset utilizes the existing subsection support[3] and changes the
section size alignment checks to subsection size alignment checks. There are
also changes to pageblock code to support partial pageblocks, when pageblock
size is increased along with MAX_ORDER. Increasing pageblock size can enable
kernel to utilize existing anti-fragmentation mechanism for gigantic page

The last patch increases SECTION_SIZE_BITS to demonstrate the use of memory
hotplug/hotremove subsection, but is not intended to be merged as is. It is
there in case one wants to try this out and will be removed during the final

Feel free to give suggestions and comments. I am looking forward to your


Zi Yan (7):
  mm: sparse: set/clear subsection bitmap when pages are
  mm: set pageblock_order to the max of HUGETLB_PAGE_ORDER and
  mm: memory_hotplug: decouple memory_block size with section size.
  mm: pageblock: allow set/unset migratetype for partial pageblock
  mm: memory_hotplug, sparse: enable memory hotplug/hotremove
  arch: x86: no MAX_ORDER exceeds SECTION_SIZE check for 32bit vdso.
  [not for merge] mm: increase SECTION_SIZE_BITS to 31

 arch/ia64/Kconfig                |   1 -
 arch/powerpc/Kconfig             |   1 -
 arch/x86/Kconfig                 |  15 +++
 arch/x86/entry/vdso/Makefile     |   1 +
 arch/x86/include/asm/sparsemem.h |   2 +-
 drivers/base/memory.c            | 176 +++++++++++++++----------------
 drivers/base/node.c              |   2 +-
 include/linux/memory.h           |   8 +-
 include/linux/mmzone.h           |   2 +
 include/linux/page-isolation.h   |   8 +-
 include/linux/pageblock-flags.h  |   9 --
 mm/Kconfig                       |   7 --
 mm/memory_hotplug.c              |  22 ++--
 mm/page_alloc.c                  |  40 ++++---
 mm/page_isolation.c              |  30 +++---
 mm/sparse.c                      |  55 ++++++++--
 16 files changed, 219 insertions(+), 160 deletions(-)


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