[RFC PATCH v3 0/4] Support large folios for tmpfs

[Baolin Wang <baolin.wang@linux.alibaba.com>]

Hi,

This RFC patch series attempts to support large folios for tmpfs. 

Considering that tmpfs already has the 'huge=' option to control the THP
allocation, it is necessary to maintain compatibility with the 'huge='
option, as well as considering the 'deny' and 'force' option controlled
by '/sys/kernel/mm/transparent_hugepage/shmem_enabled'.

Add a new huge option 'write_size' to support large folio allocation based
on the write size for tmpfs write and fallocate paths. So the huge pages
allocation strategy for tmpfs is that, if the 'huge=' option
(huge=always/within_size/advise) is enabled or the 'shmem_enabled' option
is 'force', it need just allow PMD sized THP to keep backward compatibility
for tmpfs. While 'huge=' option is disabled (huge=never) or the 'shmem_enabled'
option is 'deny', it will still disable any large folio allocations. Only
when the 'huge=' option is 'write_size', it will allow allocating large
folios based on the write size.

And I think the 'huge=write_size' option should be the default behavior
for tmpfs in future.

Any comments and suggestions are appreciated. Thanks.

Changes from RFC v2:
 - Drop mTHP interfaces to control huge page allocation, per Matthew.
 - Add a new helper to calculate the order, suggested by Matthew.
 - Add a new huge=write_size option to allocate large folios based on
   the write size.
 - Add a new patch to update the documentation.

Changes from RFC v1:
 - Drop patch 1.
 - Use 'write_end' to calculate the length in shmem_allowable_huge_orders().
 - Update shmem_mapping_size_order() per Daniel.

Baolin Wang (4):
  mm: factor out the order calculation into a new helper
  mm: shmem: change shmem_huge_global_enabled() to return huge order
    bitmap
  mm: shmem: add large folio support to the write and fallocate paths
    for tmpfs
  docs: tmpfs: add documention for 'write_size' huge option

 Documentation/filesystems/tmpfs.rst |   7 +-
 include/linux/pagemap.h             |  16 ++++-
 mm/shmem.c                          | 105 ++++++++++++++++++++--------
 3 files changed, 94 insertions(+), 34 deletions(-)

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