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

[Bagas Sanjaya <bagasdotme@gmail.com>]

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On Fri, Apr 04, 2025 at 04:06:57PM +0200, Pankaj Raghav (Samsung) wrote:
> 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.
>  
>  .. note::
>     in the examples below we presume that the basic page size is 4K and
> @@ -463,11 +463,19 @@ fields for each mapping. (Note that AnonHugePages only applies to traditional
>  PMD-sized THP for historical reasons and should have been called
>  AnonHugePmdMapped).
>  
> -The number of file transparent huge pages mapped to userspace is available
> -by reading ShmemPmdMapped and ShmemHugePages fields in ``/proc/meminfo``.
> -To identify what applications are mapping file transparent huge pages, it
> -is necessary to read ``/proc/PID/smaps`` and count the FilePmdMapped fields
> -for each mapping.
> +The number of PMD-sized transparent huge pages currently used by
> +filesystem data (page cache) is available by reading the FileHugePages field
> +in ``/proc/meminfo``. The number of these huge pages that are mapped to userspace
> +is available by reading FilePmdMapped field in ``proc/meminfo``. To identify
> +what applications are mapping these huge pages, it is necessary to read
> +``/proc/PID/smaps`` and count the FilePmdMapped fields for each mapping.
> +
> +In similar fashion, the number of PMD-sized transparent huge pages currently
> +used by tmpfs/shmem is available by reading the ShmemHugePages field
> +in ``/proc/meminfo``. The number of these huge pages that are mapped to userspace
> +is available by reading ShmemPmdMapped field in ``proc/meminfo``. To identify
> +what applications are mapping these huge pages, it is necessary to read
> +``/proc/PID/smaps`` and count the ShmemPmdMapped fields for each mapping.
>  
>  Note that reading the smaps file is expensive and reading it
>  frequently will incur overhead.
> 

Looks good, thanks!

Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com>

-- 
An old man doll... just what I always wanted! - Clara

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