Re: [RFC PATCH v1 1/1] This patch set introces a new action: DAMOS_COLLAPSE.

[Gutierrez Asier <gutierrez.asier@huawei-partners.com>]

On 3/24/2026 3:39 AM, SeongJae Park wrote:
> Hello Asier,
> 
> On Mon, 23 Mar 2026 14:56:45 +0000 <gutierrez.asier@huawei-partners.com> wrote:
> 
>> From: Asier Gutierrez <gutierrez.asier@huawei-partners.com>
>>
>> For DAMOS_HUGEPAGE and DAMOS_NOHUGEPAGE to work, khugepaged should be
>> working, since it relies on hugepage_madvise to add a new slot. This
>> slot should be picked up by khugepaged and eventually collapse (or
>> not, if we are using DAMOS_NOHUGEPAGE) the pages. If THP is not
>> enabled, khugepaged will not be working, and therefore no collapse
>> will happen.
>>
>> DAMOS_COLLAPSE eventually calls madvise_collapse, which will collapse
>> the address range synchronously.
>>
>> This new action may be required to support autotuning with hugepage as
>> a goal[1].
>>
>> [1]: https://lore.kernel.org/damon/20260313000816.79933-1-sj@kernel.org/
>>
>> ---------
>> Benchmarks:
>>
>> T n: THP never
>> T m: THP madvise
>> D h: DAMON action hugepage
>> D c: DAMON action collapse
>>
>> +------------------+----------+----------+----------+
>> |                  | T n, D h | T m, D h | T n, D c |
>> +------------------+----------+----------+----------+
>> | Total memory use | 2.07     | 2.09     | 2.07     |
>> | Huge pages       | 0        | 1.3      | 1.25     |
>> +------------------+----------+----------+----------+
> 
> Thank you for sharing the benchmark results!  But, I'm having a hard time to
> understand what this really means.  Could you please further clarify the setup
> of the benchmarks and interpretation of the results?
I will fix the cover in the next version, which I will submit soon.

I tested the patch in a physical server with MariaDB 10.5. I run
sysbench to load the server.

I check 3 scenarios:
- DAMON action hugepage for the database task, THP as never
- DAMON action hugepage, THP madvise
- DAMON action collapse, THP never

I compared the memory consumption, both in overall in the server and
anonymous huge page consumption. The results are in the table

T n: THP never
T m: THP madvise
D h: DAMON action hugepage
D c: DAMON action collapse

+------------------+----------+----------+----------+
|                  | T n, D h | T m, D h | T n, D c |
+------------------+----------+----------+----------+
| Total memory use | 2.07     | 2.09     | 2.07     |
| Huge pages       | 0        | 1.3      | 1.25     |
+------------------+----------+----------+----------+
> 
>>
>> Changes
>> ---------
>> v1-v2:
>> Added benchmarks
>> Added damos_filter_type documentation for new action to fix kernel-doc
> 
> Please add Changelog on the commentary section [1].  Also, please consider
> adding links to previous versions.
> 
>>
>> Signed-off-by: Asier Gutierrez <gutierrez.asier@huawei-partners.com>
>> ---
>>  Documentation/mm/damon/design.rst      |  4 ++++
>>  include/linux/damon.h                  |  2 ++
>>  mm/damon/sysfs-schemes.c               |  4 ++++
>>  mm/damon/vaddr.c                       |  3 +++
>>  tools/testing/selftests/damon/sysfs.py | 11 ++++++-----
>>  5 files changed, 19 insertions(+), 5 deletions(-)
>>
>> diff --git a/Documentation/mm/damon/design.rst b/Documentation/mm/damon/design.rst
>> index 838b14d22519..405142641e55 100644
>> --- a/Documentation/mm/damon/design.rst
>> +++ b/Documentation/mm/damon/design.rst
>> @@ -467,6 +467,10 @@ that supports each action are as below.
>>     Supported by ``vaddr`` and ``fvaddr`` operations set. When
>>     TRANSPARENT_HUGEPAGE is disabled, the application of the action will just
>>     fail.
>> + - ``collapse``: Call ``madvise()`` for the region with ``MADV_COLLAPSE``.
>> +   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.
>> diff --git a/include/linux/damon.h b/include/linux/damon.h
>> index d9a3babbafc1..6941113968ec 100644
>> --- a/include/linux/damon.h
>> +++ b/include/linux/damon.h
>> @@ -121,6 +121,7 @@ struct damon_target {
>>   * @DAMOS_PAGEOUT:	Reclaim the region.
>>   * @DAMOS_HUGEPAGE:	Call ``madvise()`` for the region with MADV_HUGEPAGE.
>>   * @DAMOS_NOHUGEPAGE:	Call ``madvise()`` for the region with MADV_NOHUGEPAGE.
>> + * @DAMOS_COLLAPSE:	Call ``madvise()`` for the region with MADV_COLLAPSE.
>>   * @DAMOS_LRU_PRIO:	Prioritize the region on its LRU lists.
>>   * @DAMOS_LRU_DEPRIO:	Deprioritize the region on its LRU lists.
>>   * @DAMOS_MIGRATE_HOT:  Migrate the regions prioritizing warmer regions.
>> @@ -140,6 +141,7 @@ enum damos_action {
>>  	DAMOS_PAGEOUT,
>>  	DAMOS_HUGEPAGE,
>>  	DAMOS_NOHUGEPAGE,
>> +	DAMOS_COLLAPSE,
>>  	DAMOS_LRU_PRIO,
>>  	DAMOS_LRU_DEPRIO,
>>  	DAMOS_MIGRATE_HOT,
>> diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
>> index 5186966dafb3..aa08a8f885fb 100644
>> --- a/mm/damon/sysfs-schemes.c
>> +++ b/mm/damon/sysfs-schemes.c
>> @@ -2041,6 +2041,10 @@ static struct damos_sysfs_action_name damos_sysfs_action_names[] = {
>>  		.action = DAMOS_NOHUGEPAGE,
>>  		.name = "nohugepage",
>>  	},
>> +	{
>> +		.action = DAMOS_COLLAPSE,
>> +		.name = "collapse",
>> +	},
>>  	{
>>  		.action = DAMOS_LRU_PRIO,
>>  		.name = "lru_prio",
>> diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
>> index b069dbc7e3d2..dd5f2d7027ac 100644
>> --- a/mm/damon/vaddr.c
>> +++ b/mm/damon/vaddr.c
>> @@ -903,6 +903,9 @@ static unsigned long damon_va_apply_scheme(struct damon_ctx *ctx,
>>  	case DAMOS_NOHUGEPAGE:
>>  		madv_action = MADV_NOHUGEPAGE;
>>  		break;
>> +	case DAMOS_COLLAPSE:
>> +		madv_action = MADV_COLLAPSE;
>> +		break;
>>  	case DAMOS_MIGRATE_HOT:
>>  	case DAMOS_MIGRATE_COLD:
>>  		return damos_va_migrate(t, r, scheme, sz_filter_passed);
>> diff --git a/tools/testing/selftests/damon/sysfs.py b/tools/testing/selftests/damon/sysfs.py
>> index 3aa5c91548a5..c6476e63f4fb 100755
>> --- a/tools/testing/selftests/damon/sysfs.py
>> +++ b/tools/testing/selftests/damon/sysfs.py
>> @@ -123,11 +123,12 @@ def assert_scheme_committed(scheme, dump):
>>              'pageout': 2,
>>              'hugepage': 3,
>>              'nohugeapge': 4,
>> -            'lru_prio': 5,
>> -            'lru_deprio': 6,
>> -            'migrate_hot': 7,
>> -            'migrate_cold': 8,
>> -            'stat': 9,
>> +            'collapse': 5
> 
> Comman is missed?
> 
>> +            'lru_prio': 6,
>> +            'lru_deprio': 7,
>> +            'migrate_hot': 8,
>> +            'migrate_cold': 9,
>> +            'stat': 10,
>>              }
>>      assert_true(dump['action'] == action_val[scheme.action], 'action', dump)
>>      assert_true(dump['apply_interval_us'] == scheme. apply_interval_us,
>> -- 
>> 2.43.0
> 
> Other than the selftest part, code looks good.  Please consider dropping RFC
> tag from the next spin.  Clarifying more details about the test would be
> helpful, though.
> 
> [1] https://docs.kernel.org/process/submitting-patches.html#commentary
> 
> 
> Thanks,
> SJ
> 

SJ, should I remove the RFC tag for the next version?

-- 
Asier Gutierrez
Huawei