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

[Kiryl Shutsemau <kas@kernel.org>]

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@ilvokhin.com>
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

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

-- 
  Kiryl Shutsemau / Kirill A. Shutemov