diff options
| author | Dmitry Ilvokhin <d@ilvokhin.com> | 2025-10-23 18:12:02 +0000 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2025-11-16 17:28:23 -0800 |
| commit | e97d7c5165227e6e4423b4a869d7805b01706392 (patch) | |
| tree | ac03dabe36af2713116c0192db97a44abcba95a1 /Documentation/admin-guide/mm | |
| parent | f46dbea0d95668dbbaf0aaa5f2c3aabf8f4d8fda (diff) | |
mm: shmem/tmpfs hugepage defaults config choice
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.
[d@ilvokhin.com: v2]
Link: https://lkml.kernel.org/r/aQECPpjd-fU_TC79@shell.ilvokhin.com
Link: https://lkml.kernel.org/r/aPpv8sAa2sYgNu3L@shell.ilvokhin.com
Signed-off-by: Dmitry Ilvokhin <d@ilvokhin.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Acked-by: Kiryl Shutsemau <kas@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'Documentation/admin-guide/mm')
| -rw-r--r-- | Documentation/admin-guide/mm/transhuge.rst | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst index 1654211cc6cf..5fbc3d89bb07 100644 --- a/Documentation/admin-guide/mm/transhuge.rst +++ b/Documentation/admin-guide/mm/transhuge.rst @@ -381,6 +381,11 @@ hugepage allocation policy for the tmpfs mount by using the kernel parameter four valid policies for tmpfs (``always``, ``within_size``, ``advise``, ``never``). The tmpfs mount default policy is ``never``. +Additionally, Kconfig options are available to set the default hugepage +policies for shmem (``CONFIG_TRANSPARENT_HUGEPAGE_SHMEM_HUGE_*``) and tmpfs +(``CONFIG_TRANSPARENT_HUGEPAGE_TMPFS_HUGE_*``) at build time. Refer to the +Kconfig help for more details. + In the same manner as ``thp_anon`` controls each supported anonymous THP size, ``thp_shmem`` controls each supported shmem THP size. ``thp_shmem`` has the same format as ``thp_anon``, but also supports the policy |