[PATCH v4 0/4] add hugetlb_free_vmemmap sysctl

[Muchun Song]

This series is based on next-20220310.

This series amis to add hugetlb_free_vmemmap sysctl to enable the feature
of freeing vmemmap pages of HugeTLB pages.

v4:
  - Introduce STRUCT_PAGE_SIZE_IS_POWER_OF_2 inspired by Luis.

v3:
  - Add pr_warn_once() (Mike).
  - Handle the transition from enabling to disabling (Luis)

v2:
  - Fix compilation when !CONFIG_MHP_MEMMAP_ON_MEMORY reported by kernel
    test robot <lkp@xxxxxxxxx>.
  - Move sysctl code from kernel/sysctl.c to mm/hugetlb_vmemmap.c.

Muchun Song (4):
  mm: hugetlb_vmemmap: introduce STRUCT_PAGE_SIZE_IS_POWER_OF_2
  mm: memory_hotplug: override memmap_on_memory when
    hugetlb_free_vmemmap=on
  sysctl: allow to set extra1 to SYSCTL_ONE
  mm: hugetlb_vmemmap: add hugetlb_free_vmemmap sysctl

 Documentation/admin-guide/sysctl/vm.rst |  14 +++++
 Kbuild                                  |  12 ++++
 fs/Kconfig                              |   2 +-
 include/linux/memory_hotplug.h          |   9 +++
 include/linux/mm_types.h                |   2 +
 kernel/sysctl.c                         |   2 +-
 mm/Kconfig                              |   3 +
 mm/hugetlb_vmemmap.c                    | 107 ++++++++++++++++++++++++--------
 mm/hugetlb_vmemmap.h                    |   4 +-
 mm/memory_hotplug.c                     |  27 ++++++--
 mm/struct_page_size.c                   |  19 ++++++
 scripts/check_struct_page_po2.sh        |  11 ++++
 12 files changed, 177 insertions(+), 35 deletions(-)
 create mode 100644 mm/struct_page_size.c
 create mode 100755 scripts/check_struct_page_po2.sh

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2.11.0