Re: [PATCH v13 mm-new 16/16] Documentation: mm: update the admin guide for mTHP collapse

Randy Dunlap
2025-12-01T18:52:09Z

On 12/1/25 9:46 AM, Nico Pache wrote:
> Now that we can collapse to mTHPs lets update the admin guide to
> reflect these changes and provide proper guidance on how to utilize it.
>
> Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com>
> Signed-off-by: Nico Pache <npache@redhat.com>
> ---
> Documentation/admin-guide/mm/transhuge.rst | 48 +++++++++++++---------
> 1 file changed, 28 insertions(+), 20 deletions(-)
>
> diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
> index d396d1bfb274..87bcfa80886a 100644
> --- a/Documentation/admin-guide/mm/transhuge.rst
> +++ b/Documentation/admin-guide/mm/transhuge.rst
> @@ -63,7 +63,8 @@ often.
> THP can be enabled system wide or restricted to certain tasks or even
> memory ranges inside task's address space. Unless THP is completely
> disabled, there is ``khugepaged`` daemon that scans memory and
> -collapses sequences of basic pages into PMD-sized huge pages.
> +collapses sequences of basic pages into huge pages of either PMD size
> +or mTHP sizes, if the system is configured to do so

so.

>
> The THP behaviour is controlled via :ref:`sysfs <thp_sysfs>`
> interface and using madvise(2) and prctl(2) system calls.
> @@ -219,10 +220,10 @@ this behaviour by writing 0 to shrink_underused, and enable it by writing
> echo 0 > /sys/kernel/mm/transparent_hugepage/shrink_underused
> echo 1 > /sys/kernel/mm/transparent_hugepage/shrink_underused
>
> -khugepaged will be automatically started when PMD-sized THP is enabled
> +khugepaged will be automatically started when any THP size is enabled
> (either of the per-size anon control or the top-level control are set
> to "always" or "madvise"), and it'll be automatically shutdown when
> -PMD-sized THP is disabled (when both the per-size anon control and the
> +all THP sizes are disabled (when both the per-size anon control and the
> top-level control are "never")

"never").

>
> process THP controls

[snip]

--
~Randy