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

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Message-ID: <37934c20-4cf9-480f-847d-212e7efb350a@infradead.org>
Date: Mon, 1 Dec 2025 10:52:00 -0800
From: Randy Dunlap <rdunlap@...radead.org>
To: Nico Pache <npache@...hat.com>, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, linux-mm@...ck.org,
 linux-doc@...r.kernel.org
Cc: david@...hat.com, ziy@...dia.com, baolin.wang@...ux.alibaba.com,
 lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com, ryan.roberts@....com,
 dev.jain@....com, corbet@....net, rostedt@...dmis.org, mhiramat@...nel.org,
 mathieu.desnoyers@...icios.com, akpm@...ux-foundation.org,
 baohua@...nel.org, willy@...radead.org, peterx@...hat.com,
 wangkefeng.wang@...wei.com, usamaarif642@...il.com, sunnanyong@...wei.com,
 vishal.moola@...il.com, thomas.hellstrom@...ux.intel.com,
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 cl@...two.org, jglisse@...gle.com, surenb@...gle.com, zokeefe@...gle.com,
 hannes@...xchg.org, rientjes@...gle.com, mhocko@...e.com, hughd@...gle.com,
 richard.weiyang@...il.com, lance.yang@...ux.dev, vbabka@...e.cz,
 rppt@...nel.org, jannh@...gle.com, pfalcato@...e.de,
 Bagas Sanjaya <bagasdotme@...il.com>
Subject: Re: [PATCH v13 mm-new 16/16] Documentation: mm: update the admin
 guide for mTHP collapse



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@...il.com>
> Signed-off-by: Nico Pache <npache@...hat.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