[PATCH 00/12] mm/damon: cleanup code, add test cases, and update guidances in docs

[SJ Park]

Misc cleanup, improvements and updates of code, test, and documents.

Patches 1-5 cleanup DAMON code. Patches 6-10 adds kunit and selftest
test cases for recently fixed bugs and a new feature. Patches 11 and 12
update guidelines for AI review and what document to read, on DAMON
documents.

Changes from RFC v1.2
- RFC v1.2: https://lore.kernel.org/202607291402...@kernel.org
- Drop RFC tag.
- Rebase to latest mm-new.
Changes from RFC v1.1
- RFC v1.1: https://lore.kernel.org/2026072903375...@kernel.org
- Fix a typo: s/alingment/alignment/.
- Add damon probes parameter validation cleanup (patches 4 and 5).
Changes from RFC
- RFC: https://lore.kernel.org/2026072805281...@kernel.org
- Remove ctx parameter of __damon_va_init_regions().
- Fix damon_nr_samples_per_aggr() overflow kunit test.
- Rebase to the latest mm-new.

SJ Park (12):
mm/damon/core: use damon_nr_samples_per_aggr() for max merge threshold
mm/damon/core: remove debug messages
mm/damon/vaddr: remove a debug message
mm/damon/core: validate number of probes in valid_probe_params()
mm/damon/sysfs: remove probes number validation
mm/damon/tests/core-kunit: extend set_regions() test for error case
mm/damon/tests/core-kunit: test <=0 size damon_set_regions() inputs
mm/damon/tests/core-kunit: test overlapping ranges for set_regions()
mm/damon/tests/core-kunit: test damon_nr_samples_per_aggr()
selftests/damon/sysfs.sh: test hugepage_mem_bp quota goal
Docs/mm/damon/maintainer-profile: update AI review for Sashiko replies
Docs/ABI/damon: recommend subsystem doc instead of admin-guide

.../ABI/testing/sysfs-kernel-mm-damon | 2 +-
Documentation/mm/damon/maintainer-profile.rst | 19 ++----
mm/damon/core.c | 19 +++---
mm/damon/sysfs.c | 2 +-
mm/damon/tests/core-kunit.h | 65 ++++++++++++++++---
mm/damon/vaddr.c | 16 +----
tools/testing/selftests/damon/sysfs.sh | 1 +
7 files changed, 76 insertions(+), 48 deletions(-)


base-commit: 52315e1a031f7370a286d6f6c805e2c8eab5abbc
--
2.47.3

[SJ Park]

damon_test_set_regions_for() is designed to test only success-expected
damon_set_regions() calls. Extend it to cover error-expected calls,
too.

Signed-off-by: SJ Park <s...@kernel.org>
---
mm/damon/tests/core-kunit.h | 18 ++++++++++--------
1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h
index af26b3d60957b..2bcf3bafe2e29 100644
--- a/mm/damon/tests/core-kunit.h
+++ b/mm/damon/tests/core-kunit.h
@@ -469,11 +469,12 @@ static void damon_test_set_regions_for(struct kunit *test,
struct damon_addr_range *old_ranges, int sz_old_ranges,
struct damon_addr_range *new_ranges, int sz_new_ranges,
unsigned long min_region_sz,
- struct damon_addr_range *expect_ranges, int sz_expect_ranges)
+ struct damon_addr_range *expect_ranges, int sz_expect_ranges,
+ int expect_err)
{
struct damon_target *t;
struct damon_region *r;
- int i;
+ int i, err;

t = damon_new_target();
if (!t)
@@ -487,7 +488,8 @@ static void damon_test_set_regions_for(struct kunit *test,
damon_add_region(r, t);
}

- damon_set_regions(t, new_ranges, sz_new_ranges, min_region_sz);
+ err = damon_set_regions(t, new_ranges, sz_new_ranges, min_region_sz);
+ KUNIT_EXPECT_EQ(test, err, expect_err);

KUNIT_EXPECT_EQ(test, damon_nr_regions(t), sz_expect_ranges);
if (damon_nr_regions(t) != sz_expect_ranges) {
@@ -516,7 +518,7 @@ static void damon_test_set_regions(struct kunit *test)
(struct damon_addr_range[]){
{.start = 5, .end = 15},
{.start = 15, .end = 25},
- }, 2);
+ }, 2, 0);
/* Un-intersecting regions should be removed. */
damon_test_set_regions_for(test,
(struct damon_addr_range[]){
@@ -529,7 +531,7 @@ static void damon_test_set_regions(struct kunit *test)
1,
(struct damon_addr_range[]){
{.start = 18, .end = 23},
- }, 1);
+ }, 1, 0);
/*
* Holes should be filled up with new regions.
*
@@ -550,7 +552,7 @@ static void damon_test_set_regions(struct kunit *test)
{.start = 8, .end = 16},
{.start = 16, .end = 24},
{.start = 24, .end = 28},
- }, 3);
+ }, 3, 0);
/*
* New regions should be able to be appended.
*
@@ -572,7 +574,7 @@ static void damon_test_set_regions(struct kunit *test)
{.start = 0, .end = 4},
{.start = 4, .end = 15},
{.start = 25, .end = 40},
- }, 3);
+ }, 3, 0);
/*
* New regions should be able to be inserted.
*
@@ -595,7 +597,7 @@ static void damon_test_set_regions(struct kunit *test)
{.start = 0, .end = 15},
{.start = 25, .end = 40},
{.start = 44, .end = 50},
- }, 3);
+ }, 3, 0);
}

static void damon_test_update_monitoring_result(struct kunit *test)
--
2.47.3

[SJ Park]

damon_max_nr_accesses(), which is a previous version of
damon_nr_samples_per_aggr() before the renaming, was wrongly returning
zero or random overflowed values for extreme intervals setup. Commit
35d4a3cf70a8 ("mm/damon/ops-common: handle extreme intervals in
damon_hot_score()") updated the function to return correct or more valid
values. Add a kunit test to ensure it is working as expected.

Signed-off-by: SJ Park <s...@kernel.org>
---

mm/damon/tests/core-kunit.h | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)

diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h
index a4164ac489a61..d0bed01a5b7fe 100644
--- a/mm/damon/tests/core-kunit.h
+++ b/mm/damon/tests/core-kunit.h
@@ -625,6 +625,27 @@ static void damon_test_set_regions(struct kunit *test)
(struct damon_addr_range[]){}, 0, -EINVAL);
}

+static void damon_test_nr_samples_per_aggr(struct kunit *test)
+{
+ struct damon_attrs attrs = {
+ .sample_interval = 0,
+ .aggr_interval = 0,
+ };
+
+ /* Zero aggregation interval doesn't cause division by zero */
+ KUNIT_EXPECT_EQ(test, damon_nr_samples_per_aggr(&attrs), 1);
+
+ /*
+ * Too large aggregation interval on 64 bit system doesn't cause
+ * overflow
+ */
+ if (ULONG_MAX > UINT_MAX) {
+ attrs.aggr_interval = (unsigned long)UINT_MAX + 1;
+ KUNIT_EXPECT_EQ(test, damon_nr_samples_per_aggr(&attrs),
+ UINT_MAX);
+ }
+}
+

static void damon_test_update_monitoring_result(struct kunit *test)

{
struct damon_attrs old_attrs = {
@@ -1736,6 +1757,7 @@ static struct kunit_case damon_test_cases[] = {
KUNIT_CASE(damon_test_split_above_half_progresses),
KUNIT_CASE(damon_test_ops_registration),
KUNIT_CASE(damon_test_set_regions),
+ KUNIT_CASE(damon_test_nr_samples_per_aggr),
KUNIT_CASE(damon_test_update_monitoring_result),
KUNIT_CASE(damon_test_set_attrs),
KUNIT_CASE(damon_test_mvsum),
--
2.47.3

[SJ Park]

Commit 1292c0ecb1ca ("mm/damon/core: validate ranges in
damon_set_regions()") disallowed passing zero or negative size input
ranges to damon_set_regions(). Add kunit test cases for those inputs.

Signed-off-by: SJ Park <s...@kernel.org>
---

mm/damon/tests/core-kunit.h | 14 ++++++++++++++
1 file changed, 14 insertions(+)

diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h
index 2bcf3bafe2e29..3cbbbcbfbef8f 100644
--- a/mm/damon/tests/core-kunit.h
+++ b/mm/damon/tests/core-kunit.h
@@ -598,6 +598,20 @@ static void damon_test_set_regions(struct kunit *test)

{.start = 25, .end = 40},
{.start = 44, .end = 50},

}, 3, 0);
+ /* Zero size regions should return -EINVAL. */
+ damon_test_set_regions_for(test,
+ (struct damon_addr_range[]){}, 0,
+ (struct damon_addr_range[]){
+ {.start = 42, .end = 42},
+ }, 1, 1,
+ (struct damon_addr_range[]){}, 0, -EINVAL);
+ /* Negative size regions should return -EINVAL. */
+ damon_test_set_regions_for(test,
+ (struct damon_addr_range[]){}, 0,
+ (struct damon_addr_range[]){
+ {.start = 42, .end = 21},
+ }, 1, 1,
+ (struct damon_addr_range[]){}, 0, -EINVAL);

}

static void damon_test_update_monitoring_result(struct kunit *test)

--
2.47.3

[SJ Park]

Commit 954157679ec3 ("mm/damon/core: disallow overlapping input ranges
for damon_set_regions()") disallowed passing overlapping input ranges to
damon_set_regions(). Add a kunit test case for the overlapping input.

Signed-off-by: SJ Park <s...@kernel.org>
---

mm/damon/tests/core-kunit.h | 11 +++++++++++
1 file changed, 11 insertions(+)

diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h
index 3cbbbcbfbef8f..a4164ac489a61 100644
--- a/mm/damon/tests/core-kunit.h
+++ b/mm/damon/tests/core-kunit.h
@@ -612,6 +612,17 @@ static void damon_test_set_regions(struct kunit *test)

{.start = 42, .end = 21},

}, 1, 1,

(struct damon_addr_range[]){}, 0, -EINVAL);
+ /*

+ * Regions resulting in same region after alignment should return
+ * -EINVAL.
+ */

+ damon_test_set_regions_for(test,
+ (struct damon_addr_range[]){}, 0,
+ (struct damon_addr_range[]){

+ {.start = 10, .end = 20},
+ {.start = 20, .end = 30},
+ }, 2, 4096,

[SJ Park]

On Tue, 1 Sep 2026 22:47:33 -0700 SJ Park <s...@kernel.org> wrote:

> Misc cleanup, improvements and updates of code, test, and documents.

Sashiko found one better-to-do change for patch 2. Since it is quite trivial
in my opinion, I asked Andrew to pick a fixup patch as a reply to the patch 2.
Andrew, please feel free to let me know if you prefer reposting.

Sashiko sent findings to damon@ mailing list [1], and I replied to all the
comments having some findings. Please read those for details.

[1] https://lore.kernel.org/damon/


Thanks,
SJ

[...]

[Kunwu Chan]

On Tue, 1 Sep 2026 22:47:42 -0700 SJ Park <s...@kernel.org> wrote:

> damon_max_nr_accesses(), which is a previous version of
> damon_nr_samples_per_aggr() before the renaming, was wrongly returning
> zero or random overflowed values for extreme intervals setup. Commit
> 35d4a3cf70a8 ("mm/damon/ops-common: handle extreme intervals in
> damon_hot_score()") updated the function to return correct or more valid
> values. Add a kunit test to ensure it is working as expected.
>
> Signed-off-by: SJ Park <s...@kernel.org>
> ---
> mm/damon/tests/core-kunit.h | 22 ++++++++++++++++++++++
> 1 file changed, 22 insertions(+)
>
> diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h
> index a4164ac489a61..d0bed01a5b7fe 100644
> --- a/mm/damon/tests/core-kunit.h
> +++ b/mm/damon/tests/core-kunit.h
> @@ -625,6 +625,27 @@ static void damon_test_set_regions(struct kunit *test)
> (struct damon_addr_range[]){}, 0, -EINVAL);
> }
>
> +static void damon_test_nr_samples_per_aggr(struct kunit *test)
> +{
> + struct damon_attrs attrs = {
> + .sample_interval = 0,
> + .aggr_interval = 0,
> + };
> +

Hi SJ,

A small question about the first test case.

Both `sample_interval` and `aggr_interval` are zero here. Since
`sample_interval` is the denominator in `damon_nr_samples_per_aggr()`,
would it be better to keep `aggr_interval` non-zero when testing the
zero `sample_interval` case?

This would make the test explicitly cover the divide-by-zero protection.
If the `aggr_interval == 0` behavior is also worth covering, perhaps it
could be tested separately.

Thanks,
Kunwu

Sent using hkml (https://github.com/sjp38/hackermail)

[SJ Park]

On Wed, 2 Sep 2026 23:08:41 +0800 Kunwu Chan <kunwu...@gmail.com> wrote:

> On Tue, 1 Sep 2026 22:47:42 -0700 SJ Park <s...@kernel.org> wrote:

[...]

> Both `sample_interval` and `aggr_interval` are zero here. Since
> `sample_interval` is the denominator in `damon_nr_samples_per_aggr()`,
> would it be better to keep `aggr_interval` non-zero when testing the
> zero `sample_interval` case?
>
> This would make the test explicitly cover the divide-by-zero protection.
> If the `aggr_interval == 0` behavior is also worth covering, perhaps it
> could be tested separately.

Thank you for your review and question, Kunwu!

Yes, that kind of additional test case would be nice. Please feel free to post
a patch if you'd like to! :) And no pressure, no rush. I will also consider
doing it myself if it seems you are not interested.


Thanks,
SJ

[...]

[Kunwu Chan]

Thanks for the feedback, SJ!

I will prepare a small follow-up patch for this test
clarity improvement.

Reviewed-by: Kunwu Chan <kunwu...@gmail.com>

Thanks,
Kunwu

>
>
> Thanks,
> SJ
>
> [...]

[Andrew Morton]

On Tue, 1 Sep 2026 22:47:33 -0700 SJ Park <s...@kernel.org> wrote:

> Misc cleanup, improvements and updates of code, test, and documents.
>
> Patches 1-5 cleanup DAMON code. Patches 6-10 adds kunit and selftest
> test cases for recently fixed bugs and a new feature. Patches 11 and 12
> update guidelines for AI review and what document to read, on DAMON
> documents.

Thanks, I added all this. Along with the fixup for [02/12].

[SJ Park]

On Wed, 2 Sep 2026 23:49:42 +0800 Kunwu Chan <kunwu...@gmail.com> wrote:

> On Wed, 2 Sep 2026 08:19:54 -0700 SJ Park <s...@kernel.org> wrote:
>
> > On Wed, 2 Sep 2026 23:08:41 +0800 Kunwu Chan <kunwu...@gmail.com> wrote:
> >
> > > On Tue, 1 Sep 2026 22:47:42 -0700 SJ Park <s...@kernel.org> wrote:
> > [...]
> > > Both `sample_interval` and `aggr_interval` are zero here. Since
> > > `sample_interval` is the denominator in `damon_nr_samples_per_aggr()`,
> > > would it be better to keep `aggr_interval` non-zero when testing the
> > > zero `sample_interval` case?
> > >
> > > This would make the test explicitly cover the divide-by-zero protection.
> > > If the `aggr_interval == 0` behavior is also worth covering, perhaps it
> > > could be tested separately.
> >
> > Thank you for your review and question, Kunwu!
> >
> > Yes, that kind of additional test case would be nice. Please feel free to post
> > a patch if you'd like to! :) And no pressure, no rush. I will also consider
> > doing it myself if it seems you are not interested.
>
> Thanks for the feedback, SJ!
>
> I will prepare a small follow-up patch for this test
> clarity improvement.

Looking forward to!

>
> Reviewed-by: Kunwu Chan <kunwu...@gmail.com>

Thank you! Also appreciate your R-b: for other patches!


Thanks,
SJ

[...]

[Kunwu Chan]

Hi SJ,

I reviewed patches 6-8. The test helper extension and the added
error cases look correct to me, including the overlap case after
range alignment.

Reviewed-by: Kunwu Chan <kunwu...@gmail.com>

Thanks,
Kunwu