Re: [PATCH v2 0/5] Support large folios for tmpfs

[Daniel Gomez <da.gomez@samsung.com>]

On Tue Nov 12, 2024 at 8:45 AM CET, Baolin Wang wrote:
> Traditionally, tmpfs only supported PMD-sized huge folios. However nowadays

Nitpick:
We are mixing here folios/page, PMD-size huge. For anyone not aware of
Memory Folios conversion in the kernel I think this makes it confusing.
Tmpfs has never supported folios so, this is not true. Can we rephrase
it?

Below you are also mixing terms huge/large folios etc. Can we be
consistent? I'd stick with folios (for order-0), and large folios (!
order-0). I'd use huge term only when referring to PMD-size pages.

> with other file systems supporting any sized large folios, and extending
> anonymous to support mTHP, we should not restrict tmpfs to allocating only
> PMD-sized huge folios, making it more special. Instead, we should allow

Again here.

> tmpfs can allocate any sized large folios.
>
> Considering that tmpfs already has the 'huge=' option to control the huge
> folios allocation, we can extend the 'huge=' option to allow any sized huge

'huge=' has never controlled folios.

> folios. The semantics of the 'huge=' mount option are:
>
> huge=never: no any sized huge folios
> huge=always: any sized huge folios
> huge=within_size: like 'always' but respect the i_size
> huge=advise: like 'always' if requested with fadvise()/madvise()
>
> Note: for tmpfs mmap() faults, due to the lack of a write size hint, still
> allocate the PMD-sized huge folios if huge=always/within_size/advise is set.
>
> Moreover, the 'deny' and 'force' testing options controlled by
> '/sys/kernel/mm/transparent_hugepage/shmem_enabled', still retain the same
> semantics. The 'deny' can disable any sized large folios for tmpfs, while
> the 'force' can enable PMD sized large folios for tmpfs.
>
> Any comments and suggestions are appreciated. Thanks.
>
> Changes from v1:
>  - Add reviewed tag from Barry and David. Thanks.
>  - Fix building warnings reported by kernel test robot.
>  - Add a new patch to control the default huge policy for tmpfs.
>
> Changes from RFC v3:
>  - Drop the huge=write_size option.
>  - Allow any sized huge folios for 'hgue' option.
>  - Update the documentation, per David.
>
> 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 for tmpfs
>   mm: shmem: add a kernel command line to change the default huge policy
>     for tmpfs
>
> David Hildenbrand (1):
>   docs: tmpfs: update the huge folios policy for tmpfs and shmem
>
>  .../admin-guide/kernel-parameters.txt         |   7 +
>  Documentation/admin-guide/mm/transhuge.rst    |  64 ++++++--
>  include/linux/pagemap.h                       |  16 +-
>  mm/shmem.c                                    | 148 ++++++++++++++----
>  4 files changed, 183 insertions(+), 52 deletions(-)