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

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Message-ID: <77b19486-28ca-47e1-b506-6de604f6ec0a@redhat.com>
Date: Thu, 3 Apr 2025 15:49:27 +0200
From: David Hildenbrand <david@...hat.com>
To: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>,
 Andrew Morton <akpm@...ux-foundation.org>, Jonathan Corbet <corbet@....net>
Cc: linux-kernel@...r.kernel.org, willy@...radead.org, linux-mm@...ck.org,
 da.gomez@...nel.org, mcgrof@...nel.org, gost.dev@...sung.com,
 linux-doc@...r.kernel.org, Pankaj Raghav <p.raghav@...sung.com>
Subject: Re: [PATCH] docs: update THP admin guide about non-tmpfs filesystem
 support

On 03.04.25 12:38, Pankaj Raghav (Samsung) wrote:
> From: Pankaj Raghav <p.raghav@...sung.com>
> 
> THP support for non-tmpfs filesystem has been around for some time now.
> Update the admin guide to reflect it.
> 
> Signed-off-by: Pankaj Raghav <p.raghav@...sung.com>
> ---
>   Documentation/admin-guide/mm/transhuge.rst | 8 ++++++--
>   1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
> index dff8d5985f0f..01b7ce90d693 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
> @@ -463,6 +463,10 @@ 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 PMD-sized transparent huge pages currently used by
> +filesystem data (page cache) is available by reading the FileHugePages field
> +in ``/proc/meminfo``.
> +

These changed look good. Do we also want to talk about FilePmdMapped? 
(PMD-sized THPs in the page cache that are mapped in to user space using 
a PMD ?)

Do we have to distinguish it from below? (shmem also uses the page cache)

>   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

Previously here, but: this reads rather odd. "file transparent huge 
pages". "PMD-sized THPs specific to shmem are tracked separately ..." ?

-- 
Cheers,

David / dhildenb