[PATCH 0/3] mm/damon/core: small cleanups

[PATCH 0/3] mm/damon/core: small cleanups

[Josh Law]

Three small cleanups for mm/damon/core.c:

1. Extract duplicated scheme-index-finding loops into a helper.

2. Use the already-maintained damon_nr_regions() instead of walking the
   region list to count in damon_commit_target_regions().

3. Move the static last_nr_regions variable in kdamond_split_regions()
   into struct damon_ctx so each kdamond tracks its own state.

Josh Law (3):
  mm/damon/core: deduplicate scheme index lookup into helper
  mm/damon/core: use damon_nr_regions() in damon_commit_target_regions()
  mm/damon/core: move last_nr_regions from static local to damon_ctx

 include/linux/damon.h |  2 ++
 mm/damon/core.c       | 54 ++++++++++++++++++-------------------------
 2 files changed, 24 insertions(+), 32 deletions(-)

-- 
2.34.1

[PATCH 1/3] mm/damon/core: deduplicate scheme index lookup into helper

[Josh Law]

Three functions (damos_apply_scheme, damos_trace_esz, damos_trace_stat)
contain identical loops walking the schemes list to find a scheme's
index for tracing.  Extract the common pattern into damon_scheme_idx().

Signed-off-by: Josh Law <objecting@objecting.org>
---
 mm/damon/core.c | 41 +++++++++++++++++------------------------
 1 file changed, 17 insertions(+), 24 deletions(-)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 6ee421141996..56372e577931 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -2045,6 +2045,19 @@ static void damos_walk_cancel(struct damon_ctx *ctx)
 	mutex_unlock(&ctx->walk_control_lock);
 }
 
+static unsigned int damon_scheme_idx(struct damon_ctx *c, struct damos *s)
+{
+	unsigned int idx = 0;
+	struct damos *siter;
+
+	damon_for_each_scheme(siter, c) {
+		if (siter == s)
+			break;
+		idx++;
+	}
+	return idx;
+}
+
 static void damos_apply_scheme(struct damon_ctx *c, struct damon_target *t,
 		struct damon_region *r, struct damos *s)
 {
@@ -2060,7 +2073,6 @@ static void damos_apply_scheme(struct damon_ctx *c, struct damon_target *t,
 	 * index here.
 	 */
 	unsigned int cidx = 0;
-	struct damos *siter;		/* schemes iterator */
 	unsigned int sidx = 0;
 	struct damon_target *titer;	/* targets iterator */
 	unsigned int tidx = 0;
@@ -2068,11 +2080,7 @@ static void damos_apply_scheme(struct damon_ctx *c, struct damon_target *t,
 
 	/* get indices for trace_damos_before_apply() */
 	if (trace_damos_before_apply_enabled()) {
-		damon_for_each_scheme(siter, c) {
-			if (siter == s)
-				break;
-			sidx++;
-		}
+		sidx = damon_scheme_idx(c, s);
 		damon_for_each_target(titer, c) {
 			if (titer == t)
 				break;
@@ -2394,15 +2402,7 @@ static void damos_set_effective_quota(struct damos_quota *quota)
 static void damos_trace_esz(struct damon_ctx *c, struct damos *s,
 		struct damos_quota *quota)
 {
-	unsigned int cidx = 0, sidx = 0;
-	struct damos *siter;
-
-	damon_for_each_scheme(siter, c) {
-		if (siter == s)
-			break;
-		sidx++;
-	}
-	trace_damos_esz(cidx, sidx, quota->esz);
+	trace_damos_esz(0, damon_scheme_idx(c, s), quota->esz);
 }
 
 static void damos_adjust_quota(struct damon_ctx *c, struct damos *s)
@@ -2469,18 +2469,11 @@ static void damos_adjust_quota(struct damon_ctx *c, struct damos *s)
 
 static void damos_trace_stat(struct damon_ctx *c, struct damos *s)
 {
-	unsigned int cidx = 0, sidx = 0;
-	struct damos *siter;
-
 	if (!trace_damos_stat_after_apply_interval_enabled())
 		return;
 
-	damon_for_each_scheme(siter, c) {
-		if (siter == s)
-			break;
-		sidx++;
-	}
-	trace_damos_stat_after_apply_interval(cidx, sidx, &s->stat);
+	trace_damos_stat_after_apply_interval(0, damon_scheme_idx(c, s),
+					      &s->stat);
 }
 
 static void kdamond_apply_schemes(struct damon_ctx *c)
-- 
2.34.1

[PATCH 2/3] mm/damon/core: use damon_nr_regions() in damon_commit_target_regions()

[Josh Law]

damon_commit_target_regions() walks the source region list twice: once
to count regions and again to copy their address ranges.  Use the
already-maintained damon_nr_regions() instead of the counting traversal.

Signed-off-by: Josh Law <objecting@objecting.org>
---
 mm/damon/core.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 56372e577931..6c1f738e265c 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -1217,17 +1217,15 @@ static int damon_commit_target_regions(struct damon_target *dst,
 {
 	struct damon_region *src_region;
 	struct damon_addr_range *ranges;
+	unsigned int nr = damon_nr_regions(src);
 	int i = 0, err;
 
-	damon_for_each_region(src_region, src)
-		i++;
-	if (!i)
+	if (!nr)
 		return 0;
 
-	ranges = kmalloc_objs(*ranges, i, GFP_KERNEL | __GFP_NOWARN);
+	ranges = kmalloc_objs(*ranges, nr, GFP_KERNEL | __GFP_NOWARN);
 	if (!ranges)
 		return -ENOMEM;
-	i = 0;
 	damon_for_each_region(src_region, src)
 		ranges[i++] = src_region->ar;
 	err = damon_set_regions(dst, ranges, i, src_min_region_sz);
-- 
2.34.1

[PATCH 3/3] mm/damon/core: move last_nr_regions from static local to damon_ctx

[Josh Law]

kdamond_split_regions() uses a function-level static variable to
remember the previous iteration's region count.  This is shared across
all kdamond threads, so one kdamond's region count leaks into another's
splitting decision.  Move the variable into struct damon_ctx so each
kdamond tracks its own state.

Signed-off-by: Josh Law <objecting@objecting.org>
---
 include/linux/damon.h | 2 ++
 mm/damon/core.c       | 5 ++---
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 438fe6f3eab4..85fe33ce7be4 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -803,6 +803,8 @@ struct damon_ctx {
 	struct completion kdamond_started;
 	/* for scheme quotas prioritization */
 	unsigned long *regions_score_histogram;
+	/* for kdamond_split_regions() heuristic */
+	unsigned int last_nr_regions;
 
 	/* lists of &struct damon_call_control */
 	struct list_head call_controls;
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 6c1f738e265c..50e8bdeb70dd 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -2722,7 +2722,6 @@ static void kdamond_split_regions(struct damon_ctx *ctx)
 {
 	struct damon_target *t;
 	unsigned int nr_regions = 0;
-	static unsigned int last_nr_regions;
 	int nr_subregions = 2;
 
 	damon_for_each_target(t, ctx)
@@ -2732,14 +2731,14 @@ static void kdamond_split_regions(struct damon_ctx *ctx)
 		return;
 
 	/* Maybe the middle of the region has different access frequency */
-	if (last_nr_regions == nr_regions &&
+	if (ctx->last_nr_regions == nr_regions &&
 			nr_regions < ctx->attrs.max_nr_regions / 3)
 		nr_subregions = 3;
 
 	damon_for_each_target(t, ctx)
 		damon_split_regions_of(t, nr_subregions, ctx->min_region_sz);
 
-	last_nr_regions = nr_regions;
+	ctx->last_nr_regions = nr_regions;
 }
 
 /*
-- 
2.34.1

Re: (sashiko status) [PATCH 0/3] mm/damon/core: small cleanups

[SeongJae Park]

Forwarding sashiko.dev review status for this thread.

# review url: https://sashiko.dev/#/patchset/20260325073800.141756-1-objecting@objecting.org

- [PATCH 1/3] mm/damon/core: deduplicate scheme index lookup into helper
  - status: Reviewed
  - review: No issues found.
- [PATCH 2/3] mm/damon/core: use damon_nr_regions() in damon_commit_target_regions()
  - status: Reviewed
  - review: No issues found.
- [PATCH 3/3] mm/damon/core: move last_nr_regions from static local to damon_ctx
  - status: Reviewed
  - review: No issues found.

# hkml [1] generated a draft of this mail.  It can be regenerated
# using below command:
#
#     hkml patch sashiko_dev --thread_status --for_forwarding \
#             20260325073800.141756-1-objecting@objecting.org
#
# [1] https://github.com/sjp38/hackermail

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

Re: (sashiko status) [PATCH 0/3] mm/damon/core: small cleanups

[Josh Law]

On 25 March 2026 14:58:26 GMT, SeongJae Park <sj@kernel.org> wrote:
>Forwarding sashiko.dev review status for this thread.
>
># review url: https://sashiko.dev/#/patchset/20260325073800.141756-1-objecting@objecting.org
>
>- [PATCH 1/3] mm/damon/core: deduplicate scheme index lookup into helper
>  - status: Reviewed
>  - review: No issues found.
>- [PATCH 2/3] mm/damon/core: use damon_nr_regions() in damon_commit_target_regions()
>  - status: Reviewed
>  - review: No issues found.
>- [PATCH 3/3] mm/damon/core: move last_nr_regions from static local to damon_ctx
>  - status: Reviewed
>  - review: No issues found.
>
># hkml [1] generated a draft of this mail.  It can be regenerated
># using below command:
>#
>#     hkml patch sashiko_dev --thread_status --for_forwarding \
>#             20260325073800.141756-1-objecting@objecting.org
>#
># [1] https://github.com/sjp38/hackermail
>
>Sent using hkml (https://github.com/sjp38/hackermail)



Yay! No regressions