linux-kernel - Re: [PATCH] docs: update THP documentation to clarify sysfs "never" setting

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Message-ID: <39a75435-5fea-4816-b484-477d400c3564@redhat.com>
Date: Tue, 22 Jul 2025 09:20:19 +0200
From: David Hildenbrand <david@...hat.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: Zi Yan <ziy@...dia.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>,
 "Liam R . Howlett" <Liam.Howlett@...cle.com>, Nico Pache
 <npache@...hat.com>, Ryan Roberts <ryan.roberts@....com>,
 Dev Jain <dev.jain@....com>, Barry Song <baohua@...nel.org>,
 Jonathan Corbet <corbet@....net>, linux-mm@...ck.org,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] docs: update THP documentation to clarify sysfs "never"
 setting

On 21.07.25 17:55, Lorenzo Stoakes wrote:
> Rather confusingly, setting all Transparent Huge Page sysfs settings to
> "never" does not in fact result in THP being globally disabled.
> 
> Rather, it results in khugepaged being disabled, but one can still obtain
> THP pages using madvise(..., MADV_COLLAPSE).
> 
> This is something that has remained poorly documented for some time, and it
> is likely the received wisdom of most users of THP that never does, in
> fact, mean never.
> 
> It is therefore important to highlight, very clearly, that this is not the
> ase.
> 
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> ---

Can we also somehow tone down or clarify the "entirely disabled"?

Something as simple as

diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
index bd49b46398c92..2267d22277238 100644
--- a/Documentation/admin-guide/mm/transhuge.rst
+++ b/Documentation/admin-guide/mm/transhuge.rst
@@ -107,7 +107,7 @@ sysfs
  Global THP controls
  -------------------

-Transparent Hugepage Support for anonymous memory can be entirely disabled
+Transparent Hugepage Support for anonymous memory can be mostly disabled
  (mostly for debugging purposes) or only enabled inside MADV_HUGEPAGE
  regions (to avoid the risk of consuming more memory resources) or enabled
  system wide. This can be achieved per-supported-THP-size with one of::

-- 
Cheers,

David / dhildenb