[PATCH v2] Docs/mm/damon/design: document DAMON actions when TRANSPARENT_HUGEPAGE is off

[PATCH v2] Docs/mm/damon/design: document DAMON actions when TRANSPARENT_HUGEPAGE is off

[SeongJae Park]

From: Asier Gutierrez <gutierrez.asier@huawei-partners.com>

MADV_HUGEPAGE and MADV_NOHUGEPAGE are guarded and they are not available
when compiling the kernel without TRANSPARENT_HUGEPAGE option. The DAMON
behaviour is to silently fail [1] in when DAMOS_HUGEPAGE or
DAMOS_NOHUGEPAGE are used, but TRANSPARENT_HUGEPAGE is disabled. Update
the DAMON documentation to reflect this behaviour.

[1]: https://lore.kernel.org/66131775-180b-4b9f-b7ce-61a3e077b6e6@huawei-partners.com/

Signed-off-by: Asier Gutierrez <gutierrez.asier@huawei-partners.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Signed-off-by: SeongJae Park <sj@kernel.org>
---
Changes from v1
(https://lore.kernel.org/20260316140822.2033181-1-gutierrez.asier@huawei-partners.com)
- Wordsmith description.
- Rebase to latest mm-new.

 Documentation/mm/damon/design.rst | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/Documentation/mm/damon/design.rst b/Documentation/mm/damon/design.rst
index dc37402c0fee9..838b14d225193 100644
--- a/Documentation/mm/damon/design.rst
+++ b/Documentation/mm/damon/design.rst
@@ -460,9 +460,13 @@ that supports each action are as below.
  - ``pageout``: Reclaim the region.
    Supported by ``vaddr``, ``fvaddr`` and ``paddr`` operations set.
  - ``hugepage``: Call ``madvise()`` for the region with ``MADV_HUGEPAGE``.
-   Supported by ``vaddr`` and ``fvaddr`` operations set.
+   Supported by ``vaddr`` and ``fvaddr`` operations set. When
+   TRANSPARENT_HUGEPAGE is disabled, the application of the action will just
+   fail.
  - ``nohugepage``: Call ``madvise()`` for the region with ``MADV_NOHUGEPAGE``.
-   Supported by ``vaddr`` and ``fvaddr`` operations set.
+   Supported by ``vaddr`` and ``fvaddr`` operations set. When
+   TRANSPARENT_HUGEPAGE is disabled, the application of the action will just
+   fail.
  - ``lru_prio``: Prioritize the region on its LRU lists.
    Supported by ``paddr`` operations set.
  - ``lru_deprio``: Deprioritize the region on its LRU lists.

base-commit: 809b8b9fc1374abb1b1b50fbd0260085b0832b2e
-- 
2.47.3