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

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Message-ID: <bea04294-3302-42f1-ade1-e4ec6aa80b99@linux.alibaba.com>
Date: Tue, 22 Jul 2025 13:59:42 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: David Hildenbrand <david@...hat.com>, Zi Yan <ziy@...dia.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 2025/7/22 13:34, Lorenzo Stoakes wrote:
> 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>

Thanks.
Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.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