[PATCH v3 0/4] Better split_huge_page_test result check

[Zi Yan]

This patchset uses kpageflags to get after-split folio orders for a better
split_huge_page_test result check[1]. The added gather_folio_orders() scans
through a VPN range and collects the numbers of folios at different orders.
check_folio_orders() compares the result of gather_folio_orders() to
a given list of numbers of different orders.

This patchset also added new order and in folio offset to the split huge
page debugfs's pr_debug()s;

Changelog
===
>From V2[3]:
1. Added two missing free()s in check_folio_orders().
2. Reimplemented is_backed_by_thp() to use kpageflags to get precise
   folio order information and renamed it to is_backed_by_folio() in new
   Patch 3.
3. Renamed *_file to *_fd in Patch 2.
4. Indentation fixes.
5. Fixed vaddr stepping issue in gather_folio_orders() when a compound
   tail page is encountered.
6. Used pmd_order in place of max_order in split_huge_page_test.c.
7. Documented gather_folio_orders().

>From V1[2]:
1. Dropped split_huge_pages_pid() for loop step change to avoid messing
   up with PTE-mapped THP handling. split_huge_page_test.c is changed to
   perform split at [addr, addr + pagesize) range to limit one
   folio_split() per folio.
2. Moved pr_debug changes in Patch 2 to Patch 1.
3. Moved KPF_* to vm_util.h and used PAGEMAP_PFN instead of local PFN_MASK.
4. Used pagemap_get_pfn() helper.
5. Used char *vaddr and size_t len as inputs to gather_folio_orders() and
   check_folio_orders() instead of vpn and nr_pages.
6. Removed variable length variables and used malloc instead.

[1] https://lore.kernel.org/linux-mm/e2f32bdb-e4a4-447c-867c-31405cbba151@xxxxxxxxxx/
[2] https://lore.kernel.org/linux-mm/20250806022045.342824-1-ziy@xxxxxxxxxx/
[3] https://lore.kernel.org/linux-mm/20250808190144.797076-1-ziy@xxxxxxxxxx/

Zi Yan (4):
  mm/huge_memory: add new_order and offset to split_huge_pages*()
    pr_debug.
  selftests/mm: add check_folio_orders() helper.
  selftests/mm: reimplement is_backed_by_thp() with more precise check
  selftests/mm: check after-split folio orders in split_huge_page_test.

 mm/huge_memory.c                              |   8 +-
 .../selftests/mm/split_huge_page_test.c       | 154 +++++++++++-----
 tools/testing/selftests/mm/vm_util.c          | 173 ++++++++++++++++++
 tools/testing/selftests/mm/vm_util.h          |   8 +
 4 files changed, 292 insertions(+), 51 deletions(-)

-- 
2.47.2