Re: [PATCH v3] docs: update THP admin guide about non-tmpfs filesystem support

[Luis Chamberlain <mcgrof@kernel.org>]

On Fri, Apr 04, 2025 at 04:06:57PM +0200, Pankaj Raghav (Samsung) wrote:
> From: Pankaj Raghav <p.raghav@samsung.com>
> 
> THP support for non-tmpfs filesystem has been around for some time now.
> Update the admin guide to reflect it.
> 
> While we are at it, move FilePmdMapped to previous paragraph for clarity,
> and clarify ShmemPmdMapped & ShmemHugePage.
> 
> Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
> Acked-by: David Hildenbrand <david@redhat.com>
> ---
> 
> Changes since v2:
> - Address comment from Bagas Sanjaya
> - Squash commits and Ack from David
> 
>  Documentation/admin-guide/mm/transhuge.rst | 22 +++++++++++++++-------
>  1 file changed, 15 insertions(+), 7 deletions(-)
> 
> diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
> index dff8d5985f0f..f8aae64e38d0 100644
> --- a/Documentation/admin-guide/mm/transhuge.rst
> +++ b/Documentation/admin-guide/mm/transhuge.rst
> @@ -12,8 +12,8 @@ using huge pages for the backing of virtual memory with huge pages
>  that supports the automatic promotion and demotion of page sizes and
>  without the shortcomings of hugetlbfs.
>  
> -Currently THP only works for anonymous memory mappings and tmpfs/shmem.
> -But in the future it can expand to other filesystems.
> +Currently, THP only works for anonymous memory mappings, tmpfs/shmem and
> +filesystems that support large folios.

That seems to allude that THP can be supported on filesystems
that suppor large folios. I don't think we want to call that THP
and that can confuse folks. Leaving "currently" also seems to
indicate that there is more work to be done for THP for filesystems
but that's not true as well. So how about something like:

THP only works for anonymous memory mappings, and the tmpfs/shmem is the only
filesystem to support it. The alternative to THP for other filesystems is to
support large folios and with it you can end up using huge pages
opportunistically.

  Luis