[RFC PATCH 0/5] Split a huge page to any lower order pages

[Zi Yan <zi.yan@sent.com>]

From: Zi Yan <ziy@nvidia.com>

Hi all,

With Matthew's huge pagecache page patches merged, we are able to handle any
size pagecache pages, but currently split_huge_page can only split a huge page
to order-0 pages. This can easily erase the benefit of having huge pagecache
pages, when operations like truncate might want to keep pages larger than
order-0. In response, here is the patches to add support for splitting a huge
page to any lower order pages.

The patchset is on top of mmotm-2022-03-16-17-42.

* Patch 1 and 2 add new_order parameter split_page_memcg() and
  split_page_owner() and prepare for upcoming changes.
* Patch 3 adds split_huge_page_to_list_to_order() to split a huge page
  to any lower order. The original split_huge_page_to_list() calls
  split_huge_page_to_list_to_order() with new_order = 0.
* Patch 4 uses split_huge_page_to_list_to_order() in huge pagecache page
  truncation instead of split the huge page all the way down to order-0.
* Patch 5 adds a test API to debugfs and test cases in
  split_huge_page_test selftests.

Comments and/or suggestions are welcome.

Zi Yan (5):
  mm: memcg: make memcg huge page split support any order split.
  mm: page_owner: add support for splitting to any order in split
    page_owner.
  mm: thp: split huge page to any lower order pages.
  mm: truncate: split huge page cache page to a non-zero order if
    possible.
  mm: huge_memory: enable debugfs to split huge pages to any order.

 include/linux/huge_mm.h                       |   8 +
 include/linux/memcontrol.h                    |   2 +-
 include/linux/page_owner.h                    |  12 +-
 mm/huge_memory.c                              | 139 +++++++----
 mm/memcontrol.c                               |  10 +-
 mm/page_alloc.c                               |   4 +-
 mm/page_owner.c                               |  13 +-
 mm/truncate.c                                 |  33 ++-
 .../selftests/vm/split_huge_page_test.c       | 219 +++++++++++++++---
 9 files changed, 347 insertions(+), 93 deletions(-)

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2.35.1