Docs/mm/damon/design: document DAMON actions when TRANSPARENT_HUGEPAGE is off

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.

Link: https://lkml.kernel.org/r/20260318035349.88715-1-sj@kernel.org
Link: 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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/Documentation/mm/damon/design.rst b/Documentation/mm/damon/design.rst
index dc37402c0fee91582b98f6cc8493769d20f19f19..838b14d2251932e5b66db031f50dfb48c94488ad 100644 (file)
--- 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.