[PATCH v1 00/10] Remove READ_ONLY_THP_FOR_FS Kconfig

[Zi Yan <ziy@nvidia.com>]

Hi all,

This patchset removes READ_ONLY_THP_FOR_FS Kconfig and enables creating
read-only THPs for FSes with large folio support (the supported orders
need to include PMD_ORDER) by default.

The changes are:
1. collapse_file() from mm/khugepaged.c, instead of checking
   CONFIG_READ_ONLY_THP_FOR_FS, makes sure the mapping_max_folio_order()
   of struct address_space of the file is at least PMD_ORDER.
2. file_thp_enabled() also checks mapping_max_folio_order() instead.
3. truncate_inode_partial_folio() calls folio_split() directly instead
   of the removed try_folio_split_to_order(), since large folios can
   only show up on a FS with large folio support.
4. nr_thps is removed from struct address_space, since it is no longer
   needed to drop all read-only THPs from a FS without large folio
   support when the fd becomes writable. Its related filemap_nr_thps*()
   are removed too.
5. folio_check_splittable() no longer checks READ_ONLY_THP_FOR_FS.
6. Updated comments in various places.

Changelog
===
From RFC[1]:
1. instead of removing READ_ONLY_THP_FOR_FS function entirely, turn it
   on by default for all FSes with large folio support and the supported
   orders includes PMD_ORDER.

Suggestions and comments are welcome.

Link: https://lore.kernel.org/all/20260323190644.1714379-1-ziy@nvidia.com/ [1]

Zi Yan (10):
  mm: remove READ_ONLY_THP_FOR_FS Kconfig option
  mm/khugepaged: remove READ_ONLY_THP_FOR_FS check
  mm: fs: remove filemap_nr_thps*() functions and their users
  fs: remove nr_thps from struct address_space
  mm/huge_memory: remove READ_ONLY_THP_FOR_FS from file_thp_enabled()
  mm/huge_memory: remove folio split check for READ_ONLY_THP_FOR_FS
  mm/truncate: use folio_split() in truncate_inode_partial_folio()
  fs/btrfs: remove a comment referring to READ_ONLY_THP_FOR_FS
  selftests/mm: remove READ_ONLY_THP_FOR_FS in khugepaged
  selftests/mm: remove READ_ONLY_THP_FOR_FS from comments in
    guard-regions

 fs/btrfs/defrag.c                          |  3 --
 fs/inode.c                                 |  3 --
 fs/open.c                                  | 27 ----------------
 include/linux/fs.h                         |  5 ---
 include/linux/huge_mm.h                    | 25 ++-------------
 include/linux/pagemap.h                    | 29 -----------------
 mm/Kconfig                                 | 11 -------
 mm/filemap.c                               |  1 -
 mm/huge_memory.c                           | 29 ++---------------
 mm/khugepaged.c                            | 36 +++++-----------------
 mm/truncate.c                              |  8 ++---
 tools/testing/selftests/mm/guard-regions.c |  9 +++---
 tools/testing/selftests/mm/khugepaged.c    |  4 +--
 13 files changed, 23 insertions(+), 167 deletions(-)

-- 
2.43.0