[PATCH v2 1/2] mm/damon/core: Use only installed probe in damon_merge_two_regions()

[PATCH v2 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. However, it is
possible 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             | 16 +++++++++++-----
 mm/damon/tests/core-kunit.h | 20 ++++++++++++++++++--
 2 files changed, 29 insertions(+), 7 deletions(-)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index b63e60ef8990..fc202f90991b 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -3524,20 +3524,26 @@ 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);
 }
@@ -3590,7 +3596,7 @@ 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 ef146ca2ae8a..4e380c6c5eb2 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");
 	}
@@ -198,6 +212,7 @@ static void damon_test_merge_two(struct kunit *test)
 	damon_add_region(r, t);
 	r2 = damon_new_region(100, 300);
 	if (!r2) {
+		damon_destroy_ctx(ctx);
 		damon_free_target(t);
 		kunit_skip(test, "second region alloc fail");
 	}
@@ -206,7 +221,7 @@ 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 +235,7 @@ 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

[PATCH v2 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             | 45 +++++++++++++++++++---------------
 mm/damon/tests/core-kunit.h | 48 ++++++++++++++++++++++++++++++-------
 2 files changed, 66 insertions(+), 27 deletions(-)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index fc202f90991b..9e5a19c2a19d 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -2051,8 +2051,8 @@ 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.
@@ -2077,7 +2077,7 @@ 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);
 			}
@@ -2474,6 +2474,7 @@ static bool damos_valid_target(struct damon_ctx *c, struct damon_region *r,
 /*
  * damos_skip_charged_region() - Check if the given region or starting part of
  * it is already charged for the DAMOS quota.
+ * @ctx: The pointer to the context.
  * @t:	The target of the region.
  * @rp:	The pointer to the region.
  * @s:	The scheme to be applied.
@@ -2496,9 +2497,10 @@ 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;
@@ -2525,7 +2527,7 @@ 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;
 		}
 	}
@@ -2583,12 +2585,12 @@ 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:
@@ -2781,7 +2783,7 @@ 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))
@@ -2828,7 +2830,7 @@ 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 &&
@@ -3666,15 +3668,18 @@ static void damon_verify_split_region_at(struct damon_region *r,
 /*
  * Split a region in two
  *
+ * ctx		pointer to the region's context
  * r		the region to be split
  * sz_r		size of the first sub-region that will be made
  *
  * 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);
@@ -3686,11 +3691,13 @@ 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;
 }
@@ -3719,7 +3726,7 @@ 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;
 		}
 	}
@@ -3751,7 +3758,7 @@ 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 4e380c6c5eb2..b942598e8dc2 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)
@@ -1799,19 +1814,35 @@ 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");
@@ -1819,27 +1850,27 @@ 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);
@@ -1855,7 +1886,7 @@ 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);
@@ -1868,6 +1899,7 @@ 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 v2 1/2] mm/damon/core: Use only installed probe in damon_merge_two_regions()

[Suhaas Joshi]

For some inexplicable reason, the cover-letter hasn't been sent again.

I am just adding the changelog here, in case the cover letter never arrives.

Changelog v1->v2:

1. Simplified patch 1's commit message to make it clearer 
   (Liew's suggestion)
2. Added comment docs for extra arguments I am adding to functions
   (SJ's suggestion)
3. Destroyed the context in case r2 allocation fails in damon_test_merge_two()
   (Sashiko/Liew/SJ suggestion)
4. Wrapped lines at 80 characters 
   (SJ's suggestion)

As for why the cover-letter isn't being sent, I have no idea. Everything seems
fine during `git send-email --dry-run`. Also seemed fine when I sent the series
to myself as a test.
Apologies for the inconvenience. I will make sure I fix this issue before sending
v3 or any more series in the future.

Thanks
Suhaas

On Thu, Oct 08, 2026 at 08:49:25PM +0530, Suhaas Joshi wrote:
> While merging 2 regions, we iterate over the entire probe_hits[] array,
> whose size is determined by the DAMON_MAX_PROBES macro. However, it is
> possible 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             | 16 +++++++++++-----
>  mm/damon/tests/core-kunit.h | 20 ++++++++++++++++++--
>  2 files changed, 29 insertions(+), 7 deletions(-)
> 
> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index b63e60ef8990..fc202f90991b 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -3524,20 +3524,26 @@ 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);
>  }
> @@ -3590,7 +3596,7 @@ 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 ef146ca2ae8a..4e380c6c5eb2 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");
>  	}
> @@ -198,6 +212,7 @@ static void damon_test_merge_two(struct kunit *test)
>  	damon_add_region(r, t);
>  	r2 = damon_new_region(100, 300);
>  	if (!r2) {
> +		damon_destroy_ctx(ctx);
>  		damon_free_target(t);
>  		kunit_skip(test, "second region alloc fail");
>  	}
> @@ -206,7 +221,7 @@ 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 +235,7 @@ 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
>