add hugetlb_optimize_vmemmap sysctl

This series is based on next-20220428.

This series amis to add hugetlb_optimize_vmemmap sysctl to enable or disable
the feature of optimizing vmemmap pages associated with HugeTLB pages.

v9:
  - Go back to v3 since checking the size of struct page at config time is
    very complex.

v8:
  - Fix compilation (scripts/selinux/mdp/mdp.c) error when
    CONFIG_SECURITY_SELINUX is selected.

v7:
  - Fix circular dependency issue reported by kernel test robot.
  - Introduce CONFIG_HUGETLB_PAGE_HAS_OPTIMIZE_VMEMMAP instead of
    STRUCT_PAGE_SIZE_IS_POWER_OF_2.
  - Add more comments into vm.rst to explain hugetlb_optimize_vmemmap (Andrew).
  - Drop the patch "sysctl: allow to set extra1 to SYSCTL_ONE".
  - Add a new patch "use kstrtobool for hugetlb_vmemmap param parsing".
  - Reuse static_key's refcount to count the number of HugeTLB pages with
    vmemmap pages optimized to simplify the lock scheme.

v6:
  - Remove "make syncconfig" from Kbuild.

v5:
  - Fix not working properly if one is workig off of a very clean build
    reported by Luis Chamberlain.
  - Add Suggested-by for Luis Chamberlain.

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@intel.com>.
  - Move sysctl code from kernel/sysctl.c to mm/hugetlb_vmemmap.c.

Muchun Song (4):
  mm: hugetlb_vmemmap: disable hugetlb_optimize_vmemmap when struct page
    crosses page boundaries
  mm: memory_hotplug: override memmap_on_memory when
    hugetlb_free_vmemmap=on
  mm: hugetlb_vmemmap: use kstrtobool for hugetlb_vmemmap param parsing
  mm: hugetlb_vmemmap: add hugetlb_optimize_vmemmap sysctl

 Documentation/admin-guide/kernel-parameters.txt |   6 +-
 Documentation/admin-guide/sysctl/vm.rst         |  30 +++++++
 include/linux/memory_hotplug.h                  |   9 ++
 mm/hugetlb_vmemmap.c                            | 104 ++++++++++++++++++++----
 mm/hugetlb_vmemmap.h                            |   4 +-
 mm/memory_hotplug.c                             |  27 ++++--
 6 files changed, 155 insertions(+), 25 deletions(-)

-- 
2.11.0