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Message-ID: <d54d1dfb-f06d-4979-983b-73998f05867e@lucifer.local>
Date: Tue, 22 Jul 2025 06:34:08 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: David Hildenbrand <david@...hat.com>, 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

Hi Andrew,

Could you apply this fix-patch? It adds the caveat regarding MADV_COLLAPSE in a
couple other places whwere the sysfs 'never' mode is mentioned.

Thanks, Lorenzo

----8<----
>From 7c0bdda6a633bc38e7d5a3b0acf2cef7bdc961af Mon Sep 17 00:00:00 2001
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Date: Tue, 22 Jul 2025 06:32:18 +0100
Subject: [PATCH] docs: update admin guide transhuge page to mention
 MADV_COLLAPSE everywhere

We previously missed a couple places where the 'never' mode was described,
put the caveat regarding MADV_COLLAPSE in these locations also.

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.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 182519197ef7..370fba113460 100644
--- a/Documentation/admin-guide/mm/transhuge.rst
+++ b/Documentation/admin-guide/mm/transhuge.rst
@@ -385,7 +385,9 @@ always
     Attempt to allocate huge pages every time we need a new page;

 never
-    Do not allocate huge pages;
+    Do not allocate huge pages. Note that ``madvise(..., MADV_COLLAPSE)``
+    can still cause transparent huge pages to be obtained even if this mode
+    is specified everywhere;

 within_size
     Only allocate huge page if it will be fully within i_size.
@@ -441,7 +443,9 @@ inherit
     have enabled="inherit" and all other hugepage sizes have enabled="never";

 never
-    Do not allocate <size> huge pages;
+    Do not allocate <size> huge pages. Note that ``madvise(...,
+    MADV_COLLAPSE)`` can still cause transparent huge pages to be obtained
+    even if this mode is specified everywhere;

 within_size
     Only allocate <size> huge page if it will be fully within i_size.
--
2.50.1

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