linux-kernel - Re: [PATCH v2] mm: shmem/tmpfs hugepage defaults config choice

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Message-ID: <ivpba53svcfavp3f4pfqfm5z3goht346ri25rstz4dteggcbuf@73bnztkf53b2>
Date: Wed, 29 Oct 2025 11:16:45 +0000
From: Kiryl Shutsemau <kas@...nel.org>
To: Dmitry Ilvokhin <d@...okhin.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, 
	David Hildenbrand <david@...hat.com>, Lorenzo Stoakes <lorenzo.stoakes@...cle.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>, 
	Lance Yang <lance.yang@...ux.dev>, Vlastimil Babka <vbabka@...e.cz>, 
	Mike Rapoport <rppt@...nel.org>, Suren Baghdasaryan <surenb@...gle.com>, 
	Michal Hocko <mhocko@...e.com>, Jonathan Corbet <corbet@....net>, 
	Hugh Dickins <hughd@...gle.com>, linux-mm@...ck.org, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, kernel-team@...a.com
Subject: Re: [PATCH v2] mm: shmem/tmpfs hugepage defaults config choice

On Tue, Oct 28, 2025 at 05:49:50PM +0000, Dmitry Ilvokhin wrote:
> Allow to override defaults for shemem and tmpfs at config time. This is
> consistent with how transparent hugepages can be configured.
> 
> Same results can be achieved with the existing
> 'transparent_hugepage_shmem' and 'transparent_hugepage_tmpfs' settings
> in the kernel command line, but it is more convenient to define basic
> settings at config time instead of changing kernel command line later.
> 
> Defaults for shmem and tmpfs were not changed. They are remained the
> same as before: 'never' for both cases. Options 'deny' and 'force' are
> omitted intentionally since these are special values and supposed to be
> used for emergencies or testing and are not expected to be permanent
> ones.
> 
> Primary motivation for adding config option is to enable policy
> enforcement at build time. In large-scale production environments
> (Meta's for example), the kernel configuration is often maintained
> centrally close to the kernel code itself and owned by the kernel
> engineers, while boot parameters are managed independently (e.g.  by
> provisioning systems).  In such setups, the kernel build defines the
> supported and expected behavior in a single place, but there is no
> reliable or uniform control over the kernel command line options.
> 
> A build-time default allows kernel integrators to enforce a predictable
> hugepage policy for shmem/tmpfs on a base layer, ensuring reproducible
> behavior and avoiding configuration drift caused by possible boot-time
> differences.
> 
> In short, primary benefit is mostly operational: it provides a way to
> codify preferred policy in the kernel configuration, which is versioned,
> reviewed, and tested as part of the kernel build process, rather than
> depending on potentially variable boot parameters.
> 
> Signed-off-by: Dmitry Ilvokhin <d@...okhin.com>
> Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> Acked-by: Michal Hocko <mhocko@...e.com>
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

Acked-by: Kiryl Shutsemau <kas@...nel.org>

-- 
  Kiryl Shutsemau / Kirill A. Shutemov