[PATCH v1 1/1] Docs/mm/damon: Document DAMON actions when TRANSPARENT_HUGEPAGE is off

[PATCH v1 1/1] Docs/mm/damon: Document DAMON actions when TRANSPARENT_HUGEPAGE is off

[gutierrez.asier]

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/damon/66131775-180b-4b9f-b7ce-61a3e077b6e6@huawei-partners.com/T/#m278d3c9bbedcceaf2efa51e3dc7b40a40654e51c

Signed-off-by: Asier Gutierrez <gutierrez.asier@huawei-partners.com>
---
 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 29fff20b3c2a..478eab4a186a 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.
-- 
2.43.0

Re: [PATCH v1 1/1] Docs/mm/damon: Document DAMON actions when TRANSPARENT_HUGEPAGE is off

[SeongJae Park]

Hello Asier,


Thank you for sending this patch. :)

On Mon, 16 Mar 2026 14:08:21 +0000 <gutierrez.asier@huawei-partners.com> wrote:

> 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

checkpatch.pl shows a warning for the above line:

    WARNING: Prefer a maximum 75 chars per line (possible unwrapped commit description?)
    #12:
    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/damon/66131775-180b-4b9f-b7ce-61a3e077b6e6@huawei-partners.com/T/#m278d3c9bbedcceaf2efa51e3dc7b40a40654e51c
> 
> Signed-off-by: Asier Gutierrez <gutierrez.asier@huawei-partners.com>

Reviewed-by: SeongJae Park <sj@kernel.org>

Andrew might add this to mm.git while fixing the checkpatch warning on his own.
Let's give time for Andrew today.

I also added this to damon/next tree after fixing the warning.  If Andrew
doesn't pick this with the fix today, I will post mine as v2 of this patch
tomorrow.  If you prefer to do the v2 posting on your own, just let me know :)


Thanks,
SJ

[...]

Re: [PATCH v1 1/1] Docs/mm/damon: Document DAMON actions when TRANSPARENT_HUGEPAGE is off

[Gutierrez Asier]

Hi SJ,

On 3/16/2026 5:48 PM, SeongJae Park wrote:
> Hello Asier,
> 
> 
> Thank you for sending this patch. :)
> 
> On Mon, 16 Mar 2026 14:08:21 +0000 <gutierrez.asier@huawei-partners.com> wrote:
> 
>> 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
> 
> checkpatch.pl shows a warning for the above line:
> 
>     WARNING: Prefer a maximum 75 chars per line (possible unwrapped commit description?)
>     #12:
>     option. The DAMON behaviour is to silently fail[1] in when DAMOS_HUGEPAGE or

Yes, this is due to the link. I tried to keep this patch compact, without a
cover letter. I will submit a new version without the link.

>> DAMOS_NOHUGEPAGE are used, but TRANSPARENT_HUGEPAGE is disabled. Update the
>> DAMON documentation to reflect this behaviour.
>>
>> [1]: https://lore.kernel.org/damon/66131775-180b-4b9f-b7ce-61a3e077b6e6@huawei-partners.com/T/#m278d3c9bbedcceaf2efa51e3dc7b40a40654e51c
>>
>> Signed-off-by: Asier Gutierrez <gutierrez.asier@huawei-partners.com>
> 
> Reviewed-by: SeongJae Park <sj@kernel.org>
> 
> Andrew might add this to mm.git while fixing the checkpatch warning on his own.
> Let's give time for Andrew today.
> 
> I also added this to damon/next tree after fixing the warning.  If Andrew
> doesn't pick this with the fix today, I will post mine as v2 of this patch
> tomorrow.  If you prefer to do the v2 posting on your own, just let me know :)
> 
> 
> Thanks,
> SJ
> 
> [...]
> 

-- 
Asier Gutierrez
Huawei

Re: [PATCH v1 1/1] Docs/mm/damon: Document DAMON actions when TRANSPARENT_HUGEPAGE is off

[SeongJae Park]

On Mon, 16 Mar 2026 17:56:55 +0300 Gutierrez Asier <gutierrez.asier@huawei-partners.com> wrote:

> Hi SJ,
> 
> On 3/16/2026 5:48 PM, SeongJae Park wrote:
> > Hello Asier,
> > 
> > 
> > Thank you for sending this patch. :)
> > 
> > On Mon, 16 Mar 2026 14:08:21 +0000 <gutierrez.asier@huawei-partners.com> wrote:
> > 
> >> 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
> > 
> > checkpatch.pl shows a warning for the above line:
> > 
> >     WARNING: Prefer a maximum 75 chars per line (possible unwrapped commit description?)
> >     #12:
> >     option. The DAMON behaviour is to silently fail[1] in when DAMOS_HUGEPAGE or
> 
> Yes, this is due to the link. I tried to keep this patch compact, without a
> cover letter. I will submit a new version without the link.

The above warning is not for the link.  After wrapping the line, however,
checkpatch does warn the link line like below.

    WARNING: Prefer a maximum 75 chars per line (possible unwrapped commit description?)
    #13:
    [1]: https://lore.kernel.org/damon/66131775-180b-4b9f-b7ce-61a3e077b6e6@huawei-partners.com/T/#m278d3c9bbedcceaf2efa51e3dc7b40a40654e51c

But, it should be ok to just ignore the warning for the link line.  So, please
wrap the line, but keep the link.


Thanks,
SJ

[...]