[PATCH 0/2] mm/damon/core: Iterate over installed probes instead of DAMON_MAX_PROBES

[PATCH 0/2] mm/damon/core: Iterate over installed probes instead of DAMON_MAX_PROBES

[Suhaas Joshi]

Hello,

There were two "todo: " items of the same nature in mm/damon/core.c. Both
of these suggested that we should iterate over only installed probes while
updating (last_)probe_hits[] during merging/splitting regions, instead of
iterating over the entire array, which may have empty/unused indices.

So this patch series does exactly that. It replaces the for-loop over
[0, DAMON_MAX_PROBES) with a damon_for_each_probe() over the probe list of
the context.

These patches are based off mm-new. They pass all KUnit tests related to
damon. I have boot tested (but nothing beyond) on qemu-x86_64. Please do
let me know if I should do any specific tests and link the logs here.

Regards
Suhaas Joshi

Suhaas Joshi (2):
  mm/damon/core: Use only installed probe in damon_merge_two_regions()
  mm/damon/core: Copy only installed probe in damon_split_region_at()

 mm/damon/core.c             | 56 ++++++++++++++++++-------------
 mm/damon/tests/core-kunit.h | 67 +++++++++++++++++++++++++++++++------
 2 files changed, 89 insertions(+), 34 deletions(-)

-- 
2.55.0

[PATCH 1/2] mm/damon/core: Use only installed probe in damon_merge_two_regions()

[Suhaas Joshi]

While merging 2 regions, we iterate over the entire probe_hits[] array,
whose size is determined by the DAMON_MAX_PROBES macro. It is possible,
however, that we have fewer probes installed than DAMON_MAX_PROBES. In such
cases, we end up making redundant iterations. Therefore, to remedy this,
iterate over the list of installed probes instead of iterating over the
entire array. For doing this, start accepting a struct damon_ctx in
damon_merge_two_regions(), and update calling functions to pass this
argument.

Update the damon_test_merge_two() test to use this new signature for
damon_merge_two_regions() as well.

Signed-off-by: Suhaas Joshi <suhaas@s-joshi.in>
---
 mm/damon/core.c             | 14 +++++++++-----
 mm/damon/tests/core-kunit.h | 19 +++++++++++++++++--
 2 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 733025b36745..a3af5ee685e1 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -3499,20 +3499,24 @@ static void damon_verify_merge_two_regions(
 /*
  * Merge two adjacent regions into one region
  */
-static void damon_merge_two_regions(struct damon_target *t,
-		struct damon_region *l, struct damon_region *r)
+static void damon_merge_two_regions(struct damon_ctx *ctx, struct damon_target *t,
+				    struct damon_region *l, struct damon_region *r)
 {
 	unsigned long sz_l = damon_sz_region(l), sz_r = damon_sz_region(r);
 	int i;
+	struct damon_probe *p;
 
 	l->nr_accesses = (l->nr_accesses * sz_l + r->nr_accesses * sz_r) /
 			(sz_l + sz_r);
 	l->age = (l->age * sz_l + r->age * sz_r) / (sz_l + sz_r);
 	l->ar.end = r->ar.end;
-	/* todo: do this for only installed probes */
-	for (i = 0; i < DAMON_MAX_PROBES; i++)
+
+	i = 0;
+	damon_for_each_probe(p, ctx) {
 		l->probe_hits[i] = (l->probe_hits[i] * sz_l + r->probe_hits[i]
 				* sz_r) / (sz_l + sz_r);
+		++i;
+	}
 	damon_verify_merge_two_regions(l, r);
 	damon_destroy_region(r, t);
 }
@@ -3565,7 +3569,7 @@ static void damon_merge_regions_of(struct damon_target *t, unsigned int thres,
 			goto set_prev_continue;
 		if (damon_sz_region(prev) + damon_sz_region(r) > sz_limit)
 			goto set_prev_continue;
-		damon_merge_two_regions(t, prev, r);
+		damon_merge_two_regions(ctx, t, prev, r);
 		continue;
 set_prev_continue:
 		prev = r;
diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h
index df84d9cc7d20..5ad89c1d9fc2 100644
--- a/mm/damon/tests/core-kunit.h
+++ b/mm/damon/tests/core-kunit.h
@@ -182,13 +182,27 @@ static void damon_test_merge_two(struct kunit *test)
 {
 	struct damon_target *t;
 	struct damon_region *r, *r2, *r3;
+	struct damon_probe *p;
+	struct damon_ctx *ctx;
 	int i;
 
+	p = damon_new_probe();
+	if (!p)
+		kunit_skip(test, "probe alloc fail");
+	ctx = damon_new_ctx();
+	if (!ctx) {
+		damon_destroy_probe(p);
+		kunit_skip(test, "context alloc fail");
+	}
+	damon_add_probe(ctx, p);
 	t = damon_new_target();
-	if (!t)
+	if (!t) {
+		damon_destroy_ctx(ctx);
 		kunit_skip(test, "target alloc fail");
+	}
 	r = damon_new_region(0, 100);
 	if (!r) {
+		damon_destroy_ctx(ctx);
 		damon_free_target(t);
 		kunit_skip(test, "region alloc fail");
 	}
@@ -206,7 +220,7 @@ static void damon_test_merge_two(struct kunit *test)
 	r2->age = 21;
 	damon_add_region(r2, t);
 
-	damon_merge_two_regions(t, r, r2);
+	damon_merge_two_regions(ctx, t, r, r2);
 	KUNIT_EXPECT_EQ(test, r->ar.start, 0ul);
 	KUNIT_EXPECT_EQ(test, r->ar.end, 300ul);
 	KUNIT_EXPECT_EQ(test, r->nr_accesses, 16u);
@@ -220,6 +234,7 @@ static void damon_test_merge_two(struct kunit *test)
 	}
 	KUNIT_EXPECT_EQ(test, i, 1);
 
+	damon_destroy_ctx(ctx);
 	damon_free_target(t);
 }
 
-- 
2.55.0

Re: [PATCH 1/2] mm/damon/core: Use only installed probe in damon_merge_two_regions()

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] mm: memory leak of ctx on r2 allocation failure in damon_test_merge_two()
--

commit ade902b9c0636f895031124ead4ff579818b8169
Author: Suhaas Joshi <suhaas@s-joshi.in>

mm/damon/core: Use only installed probe in damon_merge_two_regions()

While merging 2 regions, we iterate over the entire probe_hits[] array,
whose size is determined by the DAMON_MAX_PROBES macro. It is possible,
however, that we have fewer probes installed than DAMON_MAX_PROBES. In such
cases, we end up making redundant iterations. Therefore, to remedy this,
iterate over the list of installed probes instead of iterating over the
entire array. For doing this, start accepting a struct damon_ctx in
damon_merge_two_regions(), and update calling functions to pass this
argument.

> diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h
> index ef146ca2ae8aa..bea17b68f13c6 100644
> --- a/mm/damon/tests/core-kunit.h
> +++ b/mm/damon/tests/core-kunit.h
> @@ -182,13 +182,27 @@ static void damon_test_merge_two(struct kunit *test)
>  {
>  	struct damon_target *t;
>  	struct damon_region *r, *r2, *r3;
> +	struct damon_probe *p;
> +	struct damon_ctx *ctx;
>  	int i;
>  
> +	p = damon_new_probe();
> +	if (!p)
> +		kunit_skip(test, "probe alloc fail");
> +	ctx = damon_new_ctx();
> +	if (!ctx) {
> +		damon_destroy_probe(p);
> +		kunit_skip(test, "context alloc fail");
> +	}
> +	damon_add_probe(ctx, p);
>  	t = damon_new_target();
> -	if (!t)
> +	if (!t) {
> +		damon_destroy_ctx(ctx);
>  		kunit_skip(test, "target alloc fail");
> +	}
>  	r = damon_new_region(0, 100);
>  	if (!r) {
> +		damon_destroy_ctx(ctx);
>  		damon_free_target(t);
>  		kunit_skip(test, "region alloc fail");
>  	}

[Severity: Medium]
Is there a missing call to damon_destroy_ctx(ctx) if the allocation for
the second region (r2) fails?

Looking at damon_test_merge_two(), if r2 fails to allocate:

	r2 = damon_new_region(100, 300);
	if (!r2) {
		damon_free_target(t);
		kunit_skip(test, "second region alloc fail");
	}

Does this code leak the newly allocated ctx and its contained probe on this
error path?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261007154851.45368-2-suhaas@s-joshi.in?part=1

[PATCH 1/2] mm/damon/core: Use only installed probe in damon_merge_two_regions()

[Liew Rui Yan]

Hi Suhaas,

Thank you for your patches series!

On Wed, 07 Oct 2026 21:18:45 +0530 Suhaas Joshi <suhaas@s-joshi.in> wrote:

> While merging 2 regions, we iterate over the entire probe_hits[] array,
> whose size is determined by the DAMON_MAX_PROBES macro. It is possible,
> however, that we have fewer probes installed than DAMON_MAX_PROBES. In such

I find this a bit hard to read.  Could we change it to this?

    "However, it is possible that we have fewer probes installed than
    DAMON_MAX_PROBES."

> cases, we end up making redundant iterations. Therefore, to remedy this,
> iterate over the list of installed probes instead of iterating over the
> entire array. For doing this, start accepting a struct damon_ctx in
> damon_merge_two_regions(), and update calling functions to pass this
> argument.
> 
> Update the damon_test_merge_two() test to use this new signature for
> damon_merge_two_regions() as well.
> 
> Signed-off-by: Suhaas Joshi <suhaas@s-joshi.in>
> ---
>  mm/damon/core.c             | 14 +++++++++-----
>  mm/damon/tests/core-kunit.h | 19 +++++++++++++++++--
>  2 files changed, 26 insertions(+), 7 deletions(-)
> 
> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index 733025b36745..a3af5ee685e1 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -3499,20 +3499,24 @@ static void damon_verify_merge_two_regions(
>  /*
>   * Merge two adjacent regions into one region
>   */
> -static void damon_merge_two_regions(struct damon_target *t,
> -		struct damon_region *l, struct damon_region *r)
> +static void damon_merge_two_regions(struct damon_ctx *ctx, struct damon_target *t,
> +				    struct damon_region *l, struct damon_region *r)
>  {
>  	unsigned long sz_l = damon_sz_region(l), sz_r = damon_sz_region(r);
>  	int i;
> +	struct damon_probe *p;
>  
>  	l->nr_accesses = (l->nr_accesses * sz_l + r->nr_accesses * sz_r) /
>  			(sz_l + sz_r);
>  	l->age = (l->age * sz_l + r->age * sz_r) / (sz_l + sz_r);
>  	l->ar.end = r->ar.end;
> -	/* todo: do this for only installed probes */
> -	for (i = 0; i < DAMON_MAX_PROBES; i++)
> +
> +	i = 0;
> +	damon_for_each_probe(p, ctx) {
>  		l->probe_hits[i] = (l->probe_hits[i] * sz_l + r->probe_hits[i]
>  				* sz_r) / (sz_l + sz_r);
> +		++i;
> +	}
>  	damon_verify_merge_two_regions(l, r);
>  	damon_destroy_region(r, t);
>  }
> @@ -3565,7 +3569,7 @@ static void damon_merge_regions_of(struct damon_target *t, unsigned int thres,
>  			goto set_prev_continue;
>  		if (damon_sz_region(prev) + damon_sz_region(r) > sz_limit)
>  			goto set_prev_continue;
> -		damon_merge_two_regions(t, prev, r);
> +		damon_merge_two_regions(ctx, t, prev, r);
>  		continue;
>  set_prev_continue:
>  		prev = r;
> diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h
> index df84d9cc7d20..5ad89c1d9fc2 100644
> --- a/mm/damon/tests/core-kunit.h
> +++ b/mm/damon/tests/core-kunit.h
> @@ -182,13 +182,27 @@ static void damon_test_merge_two(struct kunit *test)
>  {
>  	struct damon_target *t;
>  	struct damon_region *r, *r2, *r3;
> +	struct damon_probe *p;
> +	struct damon_ctx *ctx;
>  	int i;
>  
> +	p = damon_new_probe();
> +	if (!p)
> +		kunit_skip(test, "probe alloc fail");
> +	ctx = damon_new_ctx();
> +	if (!ctx) {
> +		damon_destroy_probe(p);
> +		kunit_skip(test, "context alloc fail");
> +	}
> +	damon_add_probe(ctx, p);
>  	t = damon_new_target();
> -	if (!t)
> +	if (!t) {
> +		damon_destroy_ctx(ctx);
>  		kunit_skip(test, "target alloc fail");
> +	}
>  	r = damon_new_region(0, 100);
>  	if (!r) {
> +		damon_destroy_ctx(ctx);
>  		damon_free_target(t);
>  		kunit_skip(test, "region alloc fail");
>  	}
> @@ -206,7 +220,7 @@ static void damon_test_merge_two(struct kunit *test)
>  	r2->age = 21;
>  	damon_add_region(r2, t);
>  
> -	damon_merge_two_regions(t, r, r2);
> +	damon_merge_two_regions(ctx, t, r, r2);
>  	KUNIT_EXPECT_EQ(test, r->ar.start, 0ul);
>  	KUNIT_EXPECT_EQ(test, r->ar.end, 300ul);
>  	KUNIT_EXPECT_EQ(test, r->nr_accesses, 16u);
> @@ -220,6 +234,7 @@ static void damon_test_merge_two(struct kunit *test)
>  	}
>  	KUNIT_EXPECT_EQ(test, i, 1);
>  
> +	damon_destroy_ctx(ctx);
>  	damon_free_target(t);
>  }
>  
> -- 
> 2.55.0

Other than the commit message I just mentioned, and the issue reported
[1] by Sashiko, LGTM.

Reviewed-by: Liew Rui Yan <aethernet65535@gmail.com>

[1] https://lore.kernel.org/damon/sashiko-outbox-163177@kernel.org

Best regards,
Rui Yan

Re: [PATCH 1/2] mm/damon/core: Use only installed probe in damon_merge_two_regions()

[SJ Park]

Hello Suhaas,

On Wed,  7 Oct 2026 21:18:45 +0530 Suhaas Joshi <suhaas@s-joshi.in> wrote:

> While merging 2 regions, we iterate over the entire probe_hits[] array,
> whose size is determined by the DAMON_MAX_PROBES macro. It is possible,
> however, that we have fewer probes installed than DAMON_MAX_PROBES. In such
> cases, we end up making redundant iterations. Therefore, to remedy this,
> iterate over the list of installed probes instead of iterating over the
> entire array. For doing this, start accepting a struct damon_ctx in
> damon_merge_two_regions(), and update calling functions to pass this
> argument.
> 
> Update the damon_test_merge_two() test to use this new signature for
> damon_merge_two_regions() as well.

Thank you for this patch.

[...]
> --- a/mm/damon/tests/core-kunit.h
> +++ b/mm/damon/tests/core-kunit.h
> @@ -182,13 +182,27 @@ static void damon_test_merge_two(struct kunit *test)
>  {
>  	struct damon_target *t;
>  	struct damon_region *r, *r2, *r3;
> +	struct damon_probe *p;
> +	struct damon_ctx *ctx;
>  	int i;
>  
> +	p = damon_new_probe();
> +	if (!p)
> +		kunit_skip(test, "probe alloc fail");
> +	ctx = damon_new_ctx();
> +	if (!ctx) {
> +		damon_destroy_probe(p);
> +		kunit_skip(test, "context alloc fail");
> +	}
> +	damon_add_probe(ctx, p);
>  	t = damon_new_target();
> -	if (!t)
> +	if (!t) {
> +		damon_destroy_ctx(ctx);
>  		kunit_skip(test, "target alloc fail");
> +	}
>  	r = damon_new_region(0, 100);
>  	if (!r) {
> +		damon_destroy_ctx(ctx);
>  		damon_free_target(t);
>  		kunit_skip(test, "region alloc fail");
>  	}
> @@ -206,7 +220,7 @@ static void damon_test_merge_two(struct kunit *test)
>  	r2->age = 21;
>  	damon_add_region(r2, t);

As also found [1] by Sashiko, seems this patch mistakenly not calling
damon_destroy_ctx() for r2 allocation failure.  Could you please add that?

[1] https://lore.kernel.org/sashiko-outbox-163177@kernel.org


Thanks,
SJ

[PATCH 2/2] mm/damon/core: Copy only installed probe in damon_split_region_at()

[Suhaas Joshi]

In damon_split_region_at(), we copy the entire probe_hits[] and
last_probe_hits[] arrays of DAMON_MAX_PROBES size. However it is possible
that the number of probes installed is less than DAMON_MAX_PROBES, in which
case one or more iterations is/are redundant. To remedy this, iterate over
only as many times as the number of installed probes. To do so, accept a
struct damon_ctx pointer in damon_split_region_at(), and update all
invocations of the function to pass the new argument.

Also update damon_test_split_at() and damos_test_filter_out() in
core-kunit.h to supply a context to function paths that call
damon_split_region_at().

Signed-off-by: Suhaas Joshi <suhaas@s-joshi.in>
---
 mm/damon/core.c             | 42 +++++++++++++++++---------------
 mm/damon/tests/core-kunit.h | 48 ++++++++++++++++++++++++++++++-------
 2 files changed, 63 insertions(+), 27 deletions(-)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index a3af5ee685e1..025df4d19e20 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -2049,8 +2049,8 @@ static unsigned long damon_region_sz_limit(struct damon_ctx *ctx)
 	return sz;
 }
 
-static int damon_split_region_at(struct damon_target *t,
-				  struct damon_region *r, unsigned long sz_r);
+static int damon_split_region_at(struct damon_ctx *ctx, struct damon_target *t,
+				 struct damon_region *r, unsigned long sz_r);
 
 /*
  * damon_apply_min_nr_regions() - Make effect of min_nr_regions parameter.
@@ -2075,7 +2075,7 @@ static unsigned long damon_apply_min_nr_regions(struct damon_ctx *ctx)
 	damon_for_each_target(t, ctx) {
 		damon_for_each_region_safe(r, next, t) {
 			while (damon_sz_region(r) > max_region_sz) {
-				if (damon_split_region_at(t, r, max_region_sz))
+				if (damon_split_region_at(ctx, t, r, max_region_sz))
 					goto out;
 				r = damon_next_region(r);
 			}
@@ -2494,9 +2494,9 @@ static bool damos_valid_target(struct damon_ctx *c, struct damon_region *r,
  *
  * Return: true if the region should be skipped, false otherwise.
  */
-static bool damos_skip_charged_region(struct damon_target *t,
-		struct damon_region *r, struct damos *s,
-		unsigned long min_region_sz)
+static bool damos_skip_charged_region(struct damon_ctx *ctx, struct damon_target *t,
+				      struct damon_region *r, struct damos *s,
+				      unsigned long min_region_sz)
 {
 	struct damos_quota *quota = &s->quota;
 	unsigned long sz_to_skip;
@@ -2523,7 +2523,7 @@ static bool damos_skip_charged_region(struct damon_target *t,
 				}
 				sz_to_skip = min_region_sz;
 			}
-			damon_split_region_at(t, r, sz_to_skip);
+			damon_split_region_at(ctx, t, r, sz_to_skip);
 			skip = true;
 		}
 	}
@@ -2581,12 +2581,12 @@ static bool damos_filter_match(struct damon_ctx *ctx, struct damon_target *t,
 		}
 		/* start before the range and overlap */
 		if (r->ar.start < start) {
-			damon_split_region_at(t, r, start - r->ar.start);
+			damon_split_region_at(ctx, t, r, start - r->ar.start);
 			matched = false;
 			break;
 		}
 		/* start inside the range */
-		damon_split_region_at(t, r, end - r->ar.start);
+		damon_split_region_at(ctx, t, r, end - r->ar.start);
 		matched = true;
 		break;
 	case DAMOS_FILTER_TYPE_PROBE_HITS_WSUM:
@@ -2779,7 +2779,7 @@ static void damos_apply_scheme(struct damon_ctx *c, struct damon_target *t,
 					c->min_region_sz);
 			if (!sz)
 				goto update_stat;
-			if (damon_split_region_at(t, r, sz))
+			if (damon_split_region_at(c, t, r, sz))
 				goto update_stat;
 		}
 		if (damos_core_filter_out(c, t, r, s))
@@ -2826,7 +2826,7 @@ static void damon_do_apply_schemes(struct damon_ctx *c,
 		if (damos_quota_is_full(quota, c->min_region_sz))
 			continue;
 
-		if (damos_skip_charged_region(t, r, s, c->min_region_sz))
+		if (damos_skip_charged_region(c, t, r, s, c->min_region_sz))
 			continue;
 
 		if (s->max_nr_snapshots &&
@@ -3643,10 +3643,12 @@ static void damon_verify_split_region_at(struct damon_region *r,
  *
  * Return: 0 on success, negative error code otherwise.
  */
-static int damon_split_region_at(struct damon_target *t,
-				  struct damon_region *r, unsigned long sz_r)
+static int damon_split_region_at(struct damon_ctx *ctx, struct damon_target *t,
+				 struct damon_region *r, unsigned long sz_r)
 {
 	struct damon_region *new;
+	struct damon_probe *p;
+	int i;
 
 	damon_verify_split_region_at(r, sz_r);
 	new = damon_new_region(r->ar.start + sz_r, r->ar.end);
@@ -3658,11 +3660,13 @@ static int damon_split_region_at(struct damon_target *t,
 	new->age = r->age;
 	new->last_nr_accesses = r->last_nr_accesses;
 	new->nr_accesses = r->nr_accesses;
-	/* todo: do this for only installed probes */
-	memcpy(new->probe_hits, r->probe_hits, sizeof(r->probe_hits));
-	memcpy(new->last_probe_hits, r->last_probe_hits,
-			sizeof(r->last_probe_hits));
 
+	i = 0;
+	damon_for_each_probe(p, ctx) {
+		new->probe_hits[i] = r->probe_hits[i];
+		new->last_probe_hits[i] = r->last_probe_hits[i];
+		++i;
+	}
 	damon_insert_region(new, r, damon_next_region(r), t);
 	return 0;
 }
@@ -3691,7 +3695,7 @@ static void damon_split_regions_of(struct damon_ctx *ctx,
 			if (sz_sub == 0 || sz_sub >= sz_region)
 				continue;
 
-			damon_split_region_at(t, r, sz_sub);
+			damon_split_region_at(ctx, t, r, sz_sub);
 			sz_region = sz_sub;
 		}
 	}
@@ -3723,7 +3727,7 @@ static void damon_split_some_regions(struct damon_ctx *ctx,
 			if (sz_sub == 0 || sz_sub >= sz_region)
 				continue;
 
-			damon_split_region_at(t, r, sz_sub);
+			damon_split_region_at(ctx, t, r, sz_sub);
 		}
 	}
 }
diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h
index 5ad89c1d9fc2..e02604c7e0bc 100644
--- a/mm/damon/tests/core-kunit.h
+++ b/mm/damon/tests/core-kunit.h
@@ -141,12 +141,26 @@ static void damon_test_split_at(struct kunit *test)
 {
 	struct damon_target *t;
 	struct damon_region *r, *r_new;
+	struct damon_ctx *ctx;
+	struct damon_probe *p;
 
+	p = damon_new_probe();
+	if (!p)
+		kunit_skip(test, "probe alloc fail");
+	ctx = damon_new_ctx();
+	if (!ctx) {
+		damon_destroy_probe(p);
+		kunit_skip(test, "context alloc fail");
+	}
+	damon_add_probe(ctx, p);
 	t = damon_new_target();
-	if (!t)
+	if (!t) {
+		damon_destroy_ctx(ctx);
 		kunit_skip(test, "target alloc fail");
+	}
 	r = damon_new_region(0, 100);
 	if (!r) {
+		damon_destroy_ctx(ctx);
 		damon_free_target(t);
 		kunit_skip(test, "region alloc fail");
 	}
@@ -156,7 +170,7 @@ static void damon_test_split_at(struct kunit *test)
 	r->last_probe_hits[0] = 3;
 	r->age = 10;
 	damon_add_region(r, t);
-	damon_split_region_at(t, r, 25);
+	damon_split_region_at(ctx, t, r, 25);
 	KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 2);
 	if (damon_nr_regions(t) != 2)
 		goto out;
@@ -176,6 +190,7 @@ static void damon_test_split_at(struct kunit *test)
 
 out:
 	damon_free_target(t);
+	damon_destroy_ctx(ctx);
 }
 
 static void damon_test_merge_two(struct kunit *test)
@@ -1648,19 +1663,35 @@ static void damos_test_filter_out(struct kunit *test)
 	struct damon_target *t;
 	struct damon_region *r, *r2;
 	struct damos_filter *f;
+	struct damon_ctx *ctx;
+	struct damon_probe *p;
+
+	p = damon_new_probe();
+	if (!p)
+		kunit_skip(test, "probe alloc fail");
+	ctx = damon_new_ctx();
+	if (!ctx) {
+		damon_destroy_probe(p);
+		kunit_skip(test, "context alloc fail");
+	}
+	damon_add_probe(ctx, p);
 
 	f = damos_new_filter(DAMOS_FILTER_TYPE_ADDR, true, false);
-	if (!f)
+	if (!f) {
+		damon_destroy_ctx(ctx);
 		kunit_skip(test, "filter alloc fail");
+	}
 	f->addr_range = (struct damon_addr_range){.start = 2, .end = 6};
 
 	t = damon_new_target();
 	if (!t) {
+		damon_destroy_ctx(ctx);
 		damos_destroy_filter(f);
 		kunit_skip(test, "target alloc fail");
 	}
 	r = damon_new_region(3, 5);
 	if (!r) {
+		damon_destroy_ctx(ctx);
 		damos_destroy_filter(f);
 		damon_free_target(t);
 		kunit_skip(test, "region alloc fail");
@@ -1668,27 +1699,27 @@ static void damos_test_filter_out(struct kunit *test)
 	damon_add_region(r, t);
 
 	/* region in the range */
-	KUNIT_EXPECT_TRUE(test, damos_filter_match(NULL, t, r, f, 1));
+	KUNIT_EXPECT_TRUE(test, damos_filter_match(ctx, t, r, f, 1));
 	KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 1);
 
 	/* region before the range */
 	r->ar.start = 1;
 	r->ar.end = 2;
 	KUNIT_EXPECT_FALSE(test,
-			damos_filter_match(NULL, t, r, f, 1));
+			damos_filter_match(ctx, t, r, f, 1));
 	KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 1);
 
 	/* region after the range */
 	r->ar.start = 6;
 	r->ar.end = 8;
 	KUNIT_EXPECT_FALSE(test,
-			damos_filter_match(NULL, t, r, f, 1));
+			damos_filter_match(ctx, t, r, f, 1));
 	KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 1);
 
 	/* region started before the range */
 	r->ar.start = 1;
 	r->ar.end = 4;
-	KUNIT_EXPECT_FALSE(test, damos_filter_match(NULL, t, r, f, 1));
+	KUNIT_EXPECT_FALSE(test, damos_filter_match(ctx, t, r, f, 1));
 	/* filter should have split the region */
 	KUNIT_EXPECT_EQ(test, r->ar.start, 1);
 	KUNIT_EXPECT_EQ(test, r->ar.end, 2);
@@ -1704,7 +1735,7 @@ static void damos_test_filter_out(struct kunit *test)
 	r->ar.start = 2;
 	r->ar.end = 8;
 	KUNIT_EXPECT_TRUE(test,
-			damos_filter_match(NULL, t, r, f, 1));
+			damos_filter_match(ctx, t, r, f, 1));
 	/* filter should have split the region */
 	KUNIT_EXPECT_EQ(test, r->ar.start, 2);
 	KUNIT_EXPECT_EQ(test, r->ar.end, 6);
@@ -1717,6 +1748,7 @@ static void damos_test_filter_out(struct kunit *test)
 	damon_destroy_region(r2, t);
 
 out:
+	damon_destroy_ctx(ctx);
 	damon_free_target(t);
 	damos_free_filter(f);
 }
-- 
2.55.0

Re: [PATCH 2/2] mm/damon/core: Copy only installed probe in damon_split_region_at()

[sashiko-bot]

> In damon_split_region_at(), we copy the entire probe_hits[] and
> last_probe_hits[] arrays of DAMON_MAX_PROBES size. However it is possible
> that the number of probes installed is less than DAMON_MAX_PROBES, in which
> case one or more iterations is/are redundant. To remedy this, iterate over
> only as many times as the number of installed probes. To do so, accept a
> struct damon_ctx pointer in damon_split_region_at(), and update all
> invocations of the function to pass the new argument.
> 
> Also update damon_test_split_at() and damos_test_filter_out() in
> core-kunit.h to supply a context to function paths that call
> damon_split_region_at().
> 
> Signed-off-by: Suhaas Joshi <suhaas@s-joshi.in>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261007154851.45368-2-suhaas@s-joshi.in?part=2

[PATCH 2/2] mm/damon/core: Copy only installed probe in damon_split_region_at()

[Liew Rui Yan]

On Wed, 07 Oct 2026 21:18:46 +0530 Suhaas Joshi <suhaas@s-joshi.in> wrote:

> In damon_split_region_at(), we copy the entire probe_hits[] and
> last_probe_hits[] arrays of DAMON_MAX_PROBES size. However it is possible
> that the number of probes installed is less than DAMON_MAX_PROBES, in which
> case one or more iterations is/are redundant. To remedy this, iterate over
> only as many times as the number of installed probes. To do so, accept a
> struct damon_ctx pointer in damon_split_region_at(), and update all
> invocations of the function to pass the new argument.
> 
> Also update damon_test_split_at() and damos_test_filter_out() in
> core-kunit.h to supply a context to function paths that call
> damon_split_region_at().
> 
> Signed-off-by: Suhaas Joshi <suhaas@s-joshi.in>
> ---
>  mm/damon/core.c             | 42 +++++++++++++++++---------------
>  mm/damon/tests/core-kunit.h | 48 ++++++++++++++++++++++++++++++-------
>  2 files changed, 63 insertions(+), 27 deletions(-)
> 
> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index a3af5ee685e1..025df4d19e20 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -2049,8 +2049,8 @@ static unsigned long damon_region_sz_limit(struct damon_ctx *ctx)
>  	return sz;
>  }
>  
> -static int damon_split_region_at(struct damon_target *t,
> -				  struct damon_region *r, unsigned long sz_r);
> +static int damon_split_region_at(struct damon_ctx *ctx, struct damon_target *t,
> +				 struct damon_region *r, unsigned long sz_r);
>  
>  /*
>   * damon_apply_min_nr_regions() - Make effect of min_nr_regions parameter.
> @@ -2075,7 +2075,7 @@ static unsigned long damon_apply_min_nr_regions(struct damon_ctx *ctx)
>  	damon_for_each_target(t, ctx) {
>  		damon_for_each_region_safe(r, next, t) {
>  			while (damon_sz_region(r) > max_region_sz) {
> -				if (damon_split_region_at(t, r, max_region_sz))
> +				if (damon_split_region_at(ctx, t, r, max_region_sz))
>  					goto out;
>  				r = damon_next_region(r);
>  			}
> @@ -2494,9 +2494,9 @@ static bool damos_valid_target(struct damon_ctx *c, struct damon_region *r,
>   *
>   * Return: true if the region should be skipped, false otherwise.
>   */
> -static bool damos_skip_charged_region(struct damon_target *t,
> -		struct damon_region *r, struct damos *s,
> -		unsigned long min_region_sz)
> +static bool damos_skip_charged_region(struct damon_ctx *ctx, struct damon_target *t,
> +				      struct damon_region *r, struct damos *s,
> +				      unsigned long min_region_sz)
>  {
>  	struct damos_quota *quota = &s->quota;
>  	unsigned long sz_to_skip;
> @@ -2523,7 +2523,7 @@ static bool damos_skip_charged_region(struct damon_target *t,
>  				}
>  				sz_to_skip = min_region_sz;
>  			}
> -			damon_split_region_at(t, r, sz_to_skip);
> +			damon_split_region_at(ctx, t, r, sz_to_skip);
>  			skip = true;
>  		}
>  	}
> @@ -2581,12 +2581,12 @@ static bool damos_filter_match(struct damon_ctx *ctx, struct damon_target *t,
>  		}
>  		/* start before the range and overlap */
>  		if (r->ar.start < start) {
> -			damon_split_region_at(t, r, start - r->ar.start);
> +			damon_split_region_at(ctx, t, r, start - r->ar.start);
>  			matched = false;
>  			break;
>  		}
>  		/* start inside the range */
> -		damon_split_region_at(t, r, end - r->ar.start);
> +		damon_split_region_at(ctx, t, r, end - r->ar.start);
>  		matched = true;
>  		break;
>  	case DAMOS_FILTER_TYPE_PROBE_HITS_WSUM:
> @@ -2779,7 +2779,7 @@ static void damos_apply_scheme(struct damon_ctx *c, struct damon_target *t,
>  					c->min_region_sz);
>  			if (!sz)
>  				goto update_stat;
> -			if (damon_split_region_at(t, r, sz))
> +			if (damon_split_region_at(c, t, r, sz))
>  				goto update_stat;
>  		}
>  		if (damos_core_filter_out(c, t, r, s))
> @@ -2826,7 +2826,7 @@ static void damon_do_apply_schemes(struct damon_ctx *c,
>  		if (damos_quota_is_full(quota, c->min_region_sz))
>  			continue;
>  
> -		if (damos_skip_charged_region(t, r, s, c->min_region_sz))
> +		if (damos_skip_charged_region(c, t, r, s, c->min_region_sz))
>  			continue;
>  
>  		if (s->max_nr_snapshots &&
> @@ -3643,10 +3643,12 @@ static void damon_verify_split_region_at(struct damon_region *r,
>   *
>   * Return: 0 on success, negative error code otherwise.
>   */
> -static int damon_split_region_at(struct damon_target *t,
> -				  struct damon_region *r, unsigned long sz_r)
> +static int damon_split_region_at(struct damon_ctx *ctx, struct damon_target *t,
> +				 struct damon_region *r, unsigned long sz_r)
>  {
>  	struct damon_region *new;
> +	struct damon_probe *p;
> +	int i;
>  
>  	damon_verify_split_region_at(r, sz_r);
>  	new = damon_new_region(r->ar.start + sz_r, r->ar.end);
> @@ -3658,11 +3660,13 @@ static int damon_split_region_at(struct damon_target *t,
>  	new->age = r->age;
>  	new->last_nr_accesses = r->last_nr_accesses;
>  	new->nr_accesses = r->nr_accesses;
> -	/* todo: do this for only installed probes */
> -	memcpy(new->probe_hits, r->probe_hits, sizeof(r->probe_hits));
> -	memcpy(new->last_probe_hits, r->last_probe_hits,
> -			sizeof(r->last_probe_hits));
>  
> +	i = 0;
> +	damon_for_each_probe(p, ctx) {
> +		new->probe_hits[i] = r->probe_hits[i];
> +		new->last_probe_hits[i] = r->last_probe_hits[i];
> +		++i;
> +	}
>  	damon_insert_region(new, r, damon_next_region(r), t);
>  	return 0;
>  }
> @@ -3691,7 +3695,7 @@ static void damon_split_regions_of(struct damon_ctx *ctx,
>  			if (sz_sub == 0 || sz_sub >= sz_region)
>  				continue;
>  
> -			damon_split_region_at(t, r, sz_sub);
> +			damon_split_region_at(ctx, t, r, sz_sub);
>  			sz_region = sz_sub;
>  		}
>  	}
> @@ -3723,7 +3727,7 @@ static void damon_split_some_regions(struct damon_ctx *ctx,
>  			if (sz_sub == 0 || sz_sub >= sz_region)
>  				continue;
>  
> -			damon_split_region_at(t, r, sz_sub);
> +			damon_split_region_at(ctx, t, r, sz_sub);
>  		}
>  	}
>  }
> diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h
> index 5ad89c1d9fc2..e02604c7e0bc 100644
> --- a/mm/damon/tests/core-kunit.h
> +++ b/mm/damon/tests/core-kunit.h
> @@ -141,12 +141,26 @@ static void damon_test_split_at(struct kunit *test)
>  {
>  	struct damon_target *t;
>  	struct damon_region *r, *r_new;
> +	struct damon_ctx *ctx;
> +	struct damon_probe *p;
>  
> +	p = damon_new_probe();
> +	if (!p)
> +		kunit_skip(test, "probe alloc fail");
> +	ctx = damon_new_ctx();
> +	if (!ctx) {
> +		damon_destroy_probe(p);
> +		kunit_skip(test, "context alloc fail");
> +	}
> +	damon_add_probe(ctx, p);
>  	t = damon_new_target();
> -	if (!t)
> +	if (!t) {
> +		damon_destroy_ctx(ctx);
>  		kunit_skip(test, "target alloc fail");
> +	}
>  	r = damon_new_region(0, 100);
>  	if (!r) {
> +		damon_destroy_ctx(ctx);
>  		damon_free_target(t);
>  		kunit_skip(test, "region alloc fail");
>  	}
> @@ -156,7 +170,7 @@ static void damon_test_split_at(struct kunit *test)
>  	r->last_probe_hits[0] = 3;
>  	r->age = 10;
>  	damon_add_region(r, t);
> -	damon_split_region_at(t, r, 25);
> +	damon_split_region_at(ctx, t, r, 25);
>  	KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 2);
>  	if (damon_nr_regions(t) != 2)
>  		goto out;
> @@ -176,6 +190,7 @@ static void damon_test_split_at(struct kunit *test)
>  
>  out:
>  	damon_free_target(t);
> +	damon_destroy_ctx(ctx);
>  }
>  
>  static void damon_test_merge_two(struct kunit *test)
> @@ -1648,19 +1663,35 @@ static void damos_test_filter_out(struct kunit *test)
>  	struct damon_target *t;
>  	struct damon_region *r, *r2;
>  	struct damos_filter *f;
> +	struct damon_ctx *ctx;
> +	struct damon_probe *p;
> +
> +	p = damon_new_probe();
> +	if (!p)
> +		kunit_skip(test, "probe alloc fail");
> +	ctx = damon_new_ctx();
> +	if (!ctx) {
> +		damon_destroy_probe(p);
> +		kunit_skip(test, "context alloc fail");
> +	}
> +	damon_add_probe(ctx, p);
>  
>  	f = damos_new_filter(DAMOS_FILTER_TYPE_ADDR, true, false);
> -	if (!f)
> +	if (!f) {
> +		damon_destroy_ctx(ctx);
>  		kunit_skip(test, "filter alloc fail");
> +	}
>  	f->addr_range = (struct damon_addr_range){.start = 2, .end = 6};
>  
>  	t = damon_new_target();
>  	if (!t) {
> +		damon_destroy_ctx(ctx);
>  		damos_destroy_filter(f);
>  		kunit_skip(test, "target alloc fail");
>  	}
>  	r = damon_new_region(3, 5);
>  	if (!r) {
> +		damon_destroy_ctx(ctx);
>  		damos_destroy_filter(f);
>  		damon_free_target(t);
>  		kunit_skip(test, "region alloc fail");
> @@ -1668,27 +1699,27 @@ static void damos_test_filter_out(struct kunit *test)
>  	damon_add_region(r, t);
>  
>  	/* region in the range */
> -	KUNIT_EXPECT_TRUE(test, damos_filter_match(NULL, t, r, f, 1));
> +	KUNIT_EXPECT_TRUE(test, damos_filter_match(ctx, t, r, f, 1));
>  	KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 1);
>  
>  	/* region before the range */
>  	r->ar.start = 1;
>  	r->ar.end = 2;
>  	KUNIT_EXPECT_FALSE(test,
> -			damos_filter_match(NULL, t, r, f, 1));
> +			damos_filter_match(ctx, t, r, f, 1));
>  	KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 1);
>  
>  	/* region after the range */
>  	r->ar.start = 6;
>  	r->ar.end = 8;
>  	KUNIT_EXPECT_FALSE(test,
> -			damos_filter_match(NULL, t, r, f, 1));
> +			damos_filter_match(ctx, t, r, f, 1));
>  	KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 1);
>  
>  	/* region started before the range */
>  	r->ar.start = 1;
>  	r->ar.end = 4;
> -	KUNIT_EXPECT_FALSE(test, damos_filter_match(NULL, t, r, f, 1));
> +	KUNIT_EXPECT_FALSE(test, damos_filter_match(ctx, t, r, f, 1));
>  	/* filter should have split the region */
>  	KUNIT_EXPECT_EQ(test, r->ar.start, 1);
>  	KUNIT_EXPECT_EQ(test, r->ar.end, 2);
> @@ -1704,7 +1735,7 @@ static void damos_test_filter_out(struct kunit *test)
>  	r->ar.start = 2;
>  	r->ar.end = 8;
>  	KUNIT_EXPECT_TRUE(test,
> -			damos_filter_match(NULL, t, r, f, 1));
> +			damos_filter_match(ctx, t, r, f, 1));
>  	/* filter should have split the region */
>  	KUNIT_EXPECT_EQ(test, r->ar.start, 2);
>  	KUNIT_EXPECT_EQ(test, r->ar.end, 6);
> @@ -1717,6 +1748,7 @@ static void damos_test_filter_out(struct kunit *test)
>  	damon_destroy_region(r2, t);
>  
>  out:
> +	damon_destroy_ctx(ctx);
>  	damon_free_target(t);
>  	damos_free_filter(f);
>  }
> -- 
> 2.55.0

Thank you for your patches!  LGTM.

Reviewed-by: Liew Rui Yan <aethernet65535@gmail.com>

Best regards,
Rui Yan

Re: [PATCH 2/2] mm/damon/core: Copy only installed probe in damon_split_region_at()

[SJ Park]

Hello Suhaas,


From the next time, please send a patch series as a single thread, with a cover
letter.

On Wed,  7 Oct 2026 21:18:46 +0530 Suhaas Joshi <suhaas@s-joshi.in> wrote:

> In damon_split_region_at(), we copy the entire probe_hits[] and
> last_probe_hits[] arrays of DAMON_MAX_PROBES size. However it is possible
> that the number of probes installed is less than DAMON_MAX_PROBES, in which
> case one or more iterations is/are redundant. To remedy this, iterate over
> only as many times as the number of installed probes. To do so, accept a
> struct damon_ctx pointer in damon_split_region_at(), and update all
> invocations of the function to pass the new argument.
> 
> Also update damon_test_split_at() and damos_test_filter_out() in
> core-kunit.h to supply a context to function paths that call
> damon_split_region_at().
> 
> Signed-off-by: Suhaas Joshi <suhaas@s-joshi.in>
> ---
>  mm/damon/core.c             | 42 +++++++++++++++++---------------
>  mm/damon/tests/core-kunit.h | 48 ++++++++++++++++++++++++++++++-------
>  2 files changed, 63 insertions(+), 27 deletions(-)
> 
> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index a3af5ee685e1..025df4d19e20 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -2049,8 +2049,8 @@ static unsigned long damon_region_sz_limit(struct damon_ctx *ctx)
>  	return sz;
>  }
>  
> -static int damon_split_region_at(struct damon_target *t,
> -				  struct damon_region *r, unsigned long sz_r);
> +static int damon_split_region_at(struct damon_ctx *ctx, struct damon_target *t,
> +				 struct damon_region *r, unsigned long sz_r);

Please wrap lines for 80 columns [1] limit per line.  Same for below.

[...]
> @@ -2494,9 +2494,9 @@ static bool damos_valid_target(struct damon_ctx *c, struct damon_region *r,
>   *
>   * Return: true if the region should be skipped, false otherwise.
>   */
> -static bool damos_skip_charged_region(struct damon_target *t,
> -		struct damon_region *r, struct damos *s,
> -		unsigned long min_region_sz)
> +static bool damos_skip_charged_region(struct damon_ctx *ctx, struct damon_target *t,
> +				      struct damon_region *r, struct damos *s,
> +				      unsigned long min_region_sz)

Please update the comment above to document the new parameter.

[...]
> @@ -3643,10 +3643,12 @@ static void damon_verify_split_region_at(struct damon_region *r,
>   *
>   * Return: 0 on success, negative error code otherwise.
>   */
> -static int damon_split_region_at(struct damon_target *t,
> -				  struct damon_region *r, unsigned long sz_r)
> +static int damon_split_region_at(struct damon_ctx *ctx, struct damon_target *t,
> +				 struct damon_region *r, unsigned long sz_r)

Ditto.

[...]

[1] https://docs.kernel.org/process/coding-style.html#breaking-long-lines-and-strings


Thanks,
SJ