[PATCH 00/10] mm/damon: improve readability, clarity and test coverage

[PATCH 00/10] mm/damon: improve readability, clarity and test coverage

[SJ Park]

Yet another batch of miscellaneous DAMON minor improvements.  Mostly
focused on readability and clarity of code and document, and unit/self
test coverage.  No user-visible behavioral change is intended.

Changes from RFC v2
- RFC v2: https://lore.kernel.org/20260917040537.107341-1-sj@kernel.org
- Drop RFC tag.
- Rebase to the latest mm-new.
Changes from RFC
- RFC: https://lore.kernel.org/20260912200814.145612-1-sj@kernel.org
- Fix a typo in the selftest warning message.
- Collect A-b: from Randy.
- Split out damos_adjust_quota() fix to an individual hotfix patch.
- Add a patch for initializing walk_control_obsolete in damon_new_ctx().
- Add a patch for probe_hits_wsum damos filter commit kunit test.
- Trivial patch sequence update.
- Rebase to the latest mm-new.

SJ Park (10):
  mm/damon/api: remove NR_DAMOS_FILTER_TYPES
  mm/damon/core: use abs_diff() in damon_feed_loop_next_input()
  mm/damon/core: use mult_frac() in damon_feed_loop_next_input()
  mm/damon/core: set damon_ctx->walk_control_obsolete in damon_new_ctx()
  mm/damon/core: document damon_call()/damon_start() race hang issue
  mm/damon/paddr: remove pa parameter from damon_pa_filter_pass()
  mm/damon/tests/core-kunit: test eligible_mem_bp commitment
  mm/damon/tests/core-kunit: add probe_hits_wsum damos filter commit
    test
  selftests/damon/sysfs_memcg_path_leak: fail only for real DAMON leak
  Docs/mm/damon/design: clarify bp is basis point

 Documentation/mm/damon/design.rst             |  5 ++--
 include/linux/damon.h                         |  2 --
 mm/damon/core.c                               | 19 ++++--------
 mm/damon/paddr.c                              |  5 ++--
 mm/damon/tests/core-kunit.h                   | 30 +++++++++++++++++++
 .../selftests/damon/sysfs_memcg_path_leak.sh  |  7 +++++
 6 files changed, 48 insertions(+), 20 deletions(-)


base-commit: 942682790e570c9422a389bf34097e74c4777fe9
-- 
2.47.3

[PATCH 01/10] mm/damon/api: remove NR_DAMOS_FILTER_TYPES

[SJ Park]

Nobody uses NR_DAMOS_FILTER_TYPES.  Remove it.

Signed-off-by: SJ Park <sj@kernel.org>
---
 include/linux/damon.h | 2 --
 1 file changed, 2 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index bbb190b474015..836353c4ab9aa 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -400,7 +400,6 @@ struct damos_stat {
  * @DAMOS_FILTER_TYPE_ADDR:	Address range.
  * @DAMOS_FILTER_TYPE_TARGET:	Data Access Monitoring target.
  * @DAMOS_FILTER_TYPE_PROBE_HITS_WSUM:	probe_hits weighted sum range.
- * @NR_DAMOS_FILTER_TYPES:	Number of filter types.
  *
  * All types except &DAMOS_FILTER_TYPE_ADDR, &DAMOS_FILTER_TYPE_TARGET and
  * &DAMOS_FILTER_TYPE_PROBE_HITS_WSUM are handled by the underlying &struct
@@ -422,7 +421,6 @@ enum damos_filter_type {
 	DAMOS_FILTER_TYPE_ADDR,
 	DAMOS_FILTER_TYPE_TARGET,
 	DAMOS_FILTER_TYPE_PROBE_HITS_WSUM,
-	NR_DAMOS_FILTER_TYPES,
 };
 
 /**
-- 
2.47.3

Re: [PATCH 01/10] mm/damon/api: remove NR_DAMOS_FILTER_TYPES

[Gutierrez Asier]

Hi SJ,

On 9/17/2026 5:21 PM, SJ Park wrote:
> Nobody uses NR_DAMOS_FILTER_TYPES.  Remove it.
> 
> Signed-off-by: SJ Park <sj@kernel.org>
> ---
>  include/linux/damon.h | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/include/linux/damon.h b/include/linux/damon.h
> index bbb190b474015..836353c4ab9aa 100644
> --- a/include/linux/damon.h
> +++ b/include/linux/damon.h
> @@ -400,7 +400,6 @@ struct damos_stat {
>   * @DAMOS_FILTER_TYPE_ADDR:	Address range.
>   * @DAMOS_FILTER_TYPE_TARGET:	Data Access Monitoring target.
>   * @DAMOS_FILTER_TYPE_PROBE_HITS_WSUM:	probe_hits weighted sum range.
> - * @NR_DAMOS_FILTER_TYPES:	Number of filter types.
>   *
>   * All types except &DAMOS_FILTER_TYPE_ADDR, &DAMOS_FILTER_TYPE_TARGET and
>   * &DAMOS_FILTER_TYPE_PROBE_HITS_WSUM are handled by the underlying &struct
> @@ -422,7 +421,6 @@ enum damos_filter_type {
>  	DAMOS_FILTER_TYPE_ADDR,
>  	DAMOS_FILTER_TYPE_TARGET,
>  	DAMOS_FILTER_TYPE_PROBE_HITS_WSUM,
> -	NR_DAMOS_FILTER_TYPES,
>  };
>  
>  /**

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

-- 
Asier Gutierrez
Huawei

[PATCH 02/10] mm/damon/core: use abs_diff() in damon_feed_loop_next_input()

[SJ Park]

damon_feed_loop_next_input() is open-coding absolute diff calculation
instead of the dedicated helper, abs_diff(), for no good reason.  Use
the dedicated helper.

Signed-off-by: SJ Park <sj@kernel.org>
---
 mm/damon/core.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 444c97c184027..de46072dc1a2f 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -2926,10 +2926,7 @@ static unsigned long damon_feed_loop_next_input(unsigned long last_input,
 	if (score >= goal * 2)
 		return min_input;
 
-	if (over_achieving)
-		score_goal_diff = score - goal;
-	else
-		score_goal_diff = goal - score;
+	score_goal_diff = abs_diff(score, goal);
 
 	if (last_input < ULONG_MAX / score_goal_diff)
 		compensation = last_input * score_goal_diff / goal;
-- 
2.47.3

Re: [PATCH 02/10] mm/damon/core: use abs_diff() in damon_feed_loop_next_input()

[Gutierrez Asier]

On 9/17/2026 5:22 PM, SJ Park wrote:
> damon_feed_loop_next_input() is open-coding absolute diff calculation
> instead of the dedicated helper, abs_diff(), for no good reason.  Use
> the dedicated helper.
> 
> Signed-off-by: SJ Park <sj@kernel.org>
> ---
>  mm/damon/core.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index 444c97c184027..de46072dc1a2f 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -2926,10 +2926,7 @@ static unsigned long damon_feed_loop_next_input(unsigned long last_input,
>  	if (score >= goal * 2)
>  		return min_input;
>  
> -	if (over_achieving)
> -		score_goal_diff = score - goal;
> -	else
> -		score_goal_diff = goal - score;
> +	score_goal_diff = abs_diff(score, goal);
>  
>  	if (last_input < ULONG_MAX / score_goal_diff)
>  		compensation = last_input * score_goal_diff / goal;
LGTM

Reviewed-by: Asier Gutierrez <gutierrez.asier@huawei-partners.com>
-- 
Asier Gutierrez
Huawei

[PATCH 03/10] mm/damon/core: use mult_frac() in damon_feed_loop_next_input()

[SJ Park]

damon_feed_loop_next_input() does its best effort overflow protection.
score_goal_diff is always smaller than goal (10,000).  Hence the
calculation can be replaced to use mult_frac() without concerning the
overflow.  Use mult_frac().

Signed-off-by: SJ Park <sj@kernel.org>
---
 mm/damon/core.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index de46072dc1a2f..bc41ac7ecca43 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -2927,11 +2927,7 @@ static unsigned long damon_feed_loop_next_input(unsigned long last_input,
 		return min_input;
 
 	score_goal_diff = abs_diff(score, goal);
-
-	if (last_input < ULONG_MAX / score_goal_diff)
-		compensation = last_input * score_goal_diff / goal;
-	else
-		compensation = last_input / goal * score_goal_diff;
+	compensation = mult_frac(last_input, score_goal_diff, goal);
 
 	if (over_achieving)
 		return max(last_input - compensation, min_input);
-- 
2.47.3

Re: [PATCH 03/10] mm/damon/core: use mult_frac() in damon_feed_loop_next_input()

[Gutierrez Asier]

On 9/17/2026 5:22 PM, SJ Park wrote:
> damon_feed_loop_next_input() does its best effort overflow protection.
> score_goal_diff is always smaller than goal (10,000).  Hence the
> calculation can be replaced to use mult_frac() without concerning the
> overflow.  Use mult_frac().
> 
> Signed-off-by: SJ Park <sj@kernel.org>
> ---
>  mm/damon/core.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index de46072dc1a2f..bc41ac7ecca43 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -2927,11 +2927,7 @@ static unsigned long damon_feed_loop_next_input(unsigned long last_input,
>  		return min_input;
>  
>  	score_goal_diff = abs_diff(score, goal);
> -
> -	if (last_input < ULONG_MAX / score_goal_diff)
> -		compensation = last_input * score_goal_diff / goal;
> -	else
> -		compensation = last_input / goal * score_goal_diff;
> +	compensation = mult_frac(last_input, score_goal_diff, goal);
>  
>  	if (over_achieving)
>  		return max(last_input - compensation, min_input);
LGTM

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


-- 
Asier Gutierrez
Huawei

[PATCH 04/10] mm/damon/core: set damon_ctx->walk_control_obsolete in damon_new_ctx()

[SJ Park]

damos_walk() should be called for a damon_ctx context that has
successfully started at least once.  That's because
damon_ctx->walk_control_obsolete is initialized when kdamond starts.  If
the rule is violated, an indefinite wait can happen.  There is no
existing violation of the rule.

damon_call() had a similar rule, and it turned out keeping the rule is
not easy for damon_call()'s case.  Hence, commit 8023b5f47e09
("mm/damon/core: set ctx->call_controls_obsolete in damon_new_ctx()")
added the initialization in damon_new_ctx() and removed the rule.

Keeping the rule for damos_walk() is relatively easier.  But having
slightly different rules for similar functions could be confusing.
Sashiko, for example, repeatedly asked questions about this.  Do the
initialization of walk_control_obsolete in damon_new_ctx() for
consistency.

[1] https://lore.kernel.org/20260915011614.102342-1-sj@kernel.org

Signed-off-by: SJ Park <sj@kernel.org>
---
 mm/damon/core.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index bc41ac7ecca43..c63b09d4a2d0d 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -939,6 +939,7 @@ struct damon_ctx *damon_new_ctx(void)
 	INIT_LIST_HEAD(&ctx->schemes);
 
 	ctx->call_controls_obsolete = true;
+	ctx->walk_control_obsolete = true;
 	prandom_seed_state(&ctx->rnd_state, get_random_u64());
 
 	return ctx;
@@ -2308,10 +2309,6 @@ int damon_call(struct damon_ctx *ctx, struct damon_call_control *control)
  * passed at least one &damos->apply_interval_us, kdamond marks the request as
  * completed so that damos_walk() can wakeup and return.
  *
- * Note that this function should be called only after damon_start() with the
- * @ctx has succeeded.  Otherwise, this function could fall into an indefinite
- * wait.
- *
  * Return: 0 on success, negative error code otherwise.
  */
 int damos_walk(struct damon_ctx *ctx, struct damos_walk_control *control)
-- 
2.47.3

[PATCH 05/10] mm/damon/core: document damon_call()/damon_start() race hang issue

[SJ Park]

Let's suppose damon_start() and damon_call() are executed in parallel
for the same DAMON context.  Then, damon_call() could show
ctx->damon_calls_obsolete set while ctx->kdamond is unset.  If
damon_start() sets ctx->kdamond before damon_call() starts the
cancelling, damon_call() can indefinitely hang.  No DAMON API caller
does such parallel execution of damon_start() and damon_call(), so the
issue doesn't exist.  But who knows what will happen in future.  Add a
clarification comment for caution.

Signed-off-by: SJ Park <sj@kernel.org>
---
 mm/damon/core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index c63b09d4a2d0d..2258b72da7a78 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -2258,6 +2258,9 @@ int damon_kdamond_pid(struct damon_ctx *ctx)
  *
  * When this function is failed, the @ctx is guaranteed to be stopped.
  *
+ * This function should not be called in parallel to damon_start() for the
+ * @ctx.  In the case, this function could indefinitely hang.
+ *
  * Return: 0 on success, negative error code otherwise.
  */
 int damon_call(struct damon_ctx *ctx, struct damon_call_control *control)
-- 
2.47.3

[PATCH 06/10] mm/damon/paddr: remove pa parameter from damon_pa_filter_pass()

[SJ Park]

damon_pa_filter_pass() receives the 'pa' parameter, but doesn't use it.
Remove the parameter from the function signature.

Signed-off-by: SJ Park <sj@kernel.org>
---
 mm/damon/paddr.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/mm/damon/paddr.c b/mm/damon/paddr.c
index 5abfabaa339e0..2cfdc356b4157 100644
--- a/mm/damon/paddr.c
+++ b/mm/damon/paddr.c
@@ -163,8 +163,7 @@ static bool damon_pa_filter_match(struct damon_filter *filter,
 	return matched == filter->matching;
 }
 
-static bool damon_pa_filter_pass(phys_addr_t pa, struct folio *folio,
-		struct damon_probe *p)
+static bool damon_pa_filter_pass(struct folio *folio, struct damon_probe *p)
 {
 	struct damon_filter *f;
 	bool pass = true;
@@ -200,7 +199,7 @@ static unsigned int damon_pa_apply_probes(struct damon_ctx *ctx,
 					ctx->addr_unit);
 			folio = damon_get_folio(PHYS_PFN(pa));
 			damon_for_each_probe(p, ctx) {
-				if (damon_pa_filter_pass(pa, folio, p))
+				if (damon_pa_filter_pass(folio, p))
 					r->probe_hits[i]++;
 				i++;
 			}
-- 
2.47.3

[PATCH 07/10] mm/damon/tests/core-kunit: test eligible_mem_bp commitment

[SJ Park]

There was a DAMOS quota goal commit bug [1] that doesn't update the nid
field for DAMOS_QUOTA_NODE_ELIGIBLE_MEM_BP metric goal.  Add a kunit
test case for confirming nid commitment.

[1] https://lore.kkernel.org/20260827045035.94611-1-sj@kernel.org

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

diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h
index 5da84caf4124d..1f19fefdd98c3 100644
--- a/mm/damon/tests/core-kunit.h
+++ b/mm/damon/tests/core-kunit.h
@@ -835,6 +835,9 @@ static void damos_test_commit_quota_goal_for(struct kunit *test,
 		KUNIT_EXPECT_EQ(test, dst->nid, src->nid);
 		KUNIT_EXPECT_EQ(test, dst->memcg_id, src->memcg_id);
 		break;
+	case DAMOS_QUOTA_NODE_ELIGIBLE_MEM_BP:
+		KUNIT_EXPECT_EQ(test, dst->nid, src->nid);
+		break;
 	default:
 		break;
 	}
@@ -898,6 +901,13 @@ static void damos_test_commit_quota_goal(struct kunit *test)
 			.current_value = 345,
 			.last_psi_total = 567,
 			});
+	damos_test_commit_quota_goal_for(test, &dst,
+			&(struct damos_quota_goal){
+			.metric = DAMOS_QUOTA_NODE_ELIGIBLE_MEM_BP,
+			.target_value = 12,
+			.current_value = 345,
+			.nid = 6,
+			});
 }
 
 static void damos_test_commit_quota_goals_for(struct kunit *test,
-- 
2.47.3

[PATCH 08/10] mm/damon/tests/core-kunit: add probe_hits_wsum damos filter commit test

[SJ Park]

DAMOS filter commit kunit test lacks test cases for probe_hits_wsum
filter type.  Add test cases for probe_hits_wsum type DAMOS filter
commit.

Signed-off-by: SJ Park <sj@kernel.org>
---
 mm/damon/tests/core-kunit.h | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h
index 1f19fefdd98c3..5ff0436c58441 100644
--- a/mm/damon/tests/core-kunit.h
+++ b/mm/damon/tests/core-kunit.h
@@ -1166,6 +1166,10 @@ static void damos_test_commit_filter_for(struct kunit *test,
 		KUNIT_EXPECT_EQ(test, dst->sz_range.min, src->sz_range.min);
 		KUNIT_EXPECT_EQ(test, dst->sz_range.max, src->sz_range.max);
 		break;
+	case DAMOS_FILTER_TYPE_PROBE_HITS_WSUM:
+		KUNIT_EXPECT_EQ(test, dst->range_min, src->range_min);
+		KUNIT_EXPECT_EQ(test, dst->range_max, src->range_max);
+		break;
 	default:
 		break;
 	}
@@ -1239,6 +1243,22 @@ static void damos_test_commit_filter(struct kunit *test)
 			.allow = true,
 			.target_idx = 6,
 			}, false);
+	damos_test_commit_filter_for(test, &dst,
+			&(struct damos_filter){
+			.type = DAMOS_FILTER_TYPE_PROBE_HITS_WSUM,
+			.matching = false,
+			.allow = true,
+			.range_min = 12,
+			.range_max = 34,
+			}, false);
+	damos_test_commit_filter_for(test, &dst,
+			&(struct damos_filter){
+			.type = DAMOS_FILTER_TYPE_PROBE_HITS_WSUM,
+			.matching = false,
+			.allow = true,
+			.range_min = 34,
+			.range_max = 12,
+			}, true);
 }
 
 static void damos_test_help_initailize_scheme(struct damos *scheme)
-- 
2.47.3

[PATCH 09/10] selftests/damon/sysfs_memcg_path_leak: fail only for real DAMON leak

[SJ Park]

The selftest can fail for any leak if it happens while the test is
running.  Remove the false positive test failures by further checking if
the expected leaking function is called out on the report.

Signed-off-by: SJ Park <sj@kernel.org>
---
 tools/testing/selftests/damon/sysfs_memcg_path_leak.sh | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/tools/testing/selftests/damon/sysfs_memcg_path_leak.sh b/tools/testing/selftests/damon/sysfs_memcg_path_leak.sh
index 33a7ff43ed6cc..34c37129c49fe 100755
--- a/tools/testing/selftests/damon/sysfs_memcg_path_leak.sh
+++ b/tools/testing/selftests/damon/sysfs_memcg_path_leak.sh
@@ -41,5 +41,12 @@ if [ "$kmemleak_report" = "" ]
 then
 	exit 0
 fi
+if ! echo "$kmemleak_report" | grep "memcg_path_store" --quiet
+then
+	echo "[WARN] memleak found; apparently not from DAMON, though"
+	echo "$kmemleak_report"
+	exit 0
+fi
+
 echo "$kmemleak_report"
 exit 1
-- 
2.47.3

[PATCH 10/10] Docs/mm/damon/design: clarify bp is basis point

[SJ Park]

DAMON design document uses "bp" for "basis point" in multiple places.
Because it is not clearly mentioned, it is difficult to understand what
"bp" stands for.  Add the clarification.

Reported-by: Randy Dunlap <rdunlap@infradead.org>
Closes: https://lore.kernel.org/107dc6ba-697e-4b25-ba3e-8ce2499cac9a@infradead.org
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: SJ Park <sj@kernel.org>
---
 Documentation/mm/damon/design.rst | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/Documentation/mm/damon/design.rst b/Documentation/mm/damon/design.rst
index 0a86792f90a18..e82390e77a70a 100644
--- a/Documentation/mm/damon/design.rst
+++ b/Documentation/mm/damon/design.rst
@@ -445,7 +445,7 @@ users to set the aimed amount of access events to observe via DAMON within
 given time interval.  The target can be specified by the user as a ratio of
 DAMON-observed access events to the theoretical maximum amount of the events
 (``access_bp``) that measured within a given number of aggregations
-(``aggrs``).
+(``aggrs``).  The ratio is in basis point (bp or 1/10,000).
 
 The DAMON-observed access events are calculated in byte granularity based on
 DAMON :ref:`region assumption <damon_design_region_based_sampling>`.  For
@@ -717,7 +717,8 @@ mechanism tries to make ``current_value`` of ``target_metric`` be same to
   in microseconds that measured from last quota reset to next quota reset.
   DAMOS does the measurement on its own, so only ``target_value`` need to be
   set by users at the initial time.  In other words, DAMOS does self-feedback.
-- ``node_mem_used_bp``: Specific NUMA node's used memory ratio in bp (1/10,000).
+- ``node_mem_used_bp``: Specific NUMA node's used memory ratio in basis point
+  (bp or 1/10,000).
 - ``node_mem_free_bp``: Specific NUMA node's free memory ratio in bp (1/10,000).
 - ``node_memcg_used_bp``: Specific cgroup's node used memory ratio for a
   specific NUMA node, in bp (1/10,000).
-- 
2.47.3

Re: [PATCH 00/10] mm/damon: improve readability, clarity and test coverage

[SJ Park]

On Thu, 17 Sep 2026 07:21:58 -0700 SJ Park <sj@kernel.org> wrote:

> Yet another batch of miscellaneous DAMON minor improvements.  Mostly
> focused on readability and clarity of code and document, and unit/self
> test coverage.  No user-visible behavioral change is intended.

Sashiko found no blocker for this series.  Sashiko send its findings to damon@
mailing list [1], and I reply those if anything needs to be clarified.  Please
refer to those for details.

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


Thanks,
SJ

Re: [PATCH 00/10] mm/damon: improve readability, clarity and test coverage

[Andrew Morton]

On Thu, 17 Sep 2026 07:21:58 -0700 SJ Park <sj@kernel.org> wrote:

> Yet another batch of miscellaneous DAMON minor improvements.  Mostly
> focused on readability and clarity of code and document, and unit/self
> test coverage.  No user-visible behavioral change is intended.

Thanks, all queued up in mm-new.