From: Quanmin Yan <yanquanmin1@huawei.com>

Adopting addr_unit would make DAMON_MINREGION 'addr_unit * 4096'
bytes and cause data alignment issues[1].

Add damon_ctx->min_sz_region to change DAMON_MIN_REGION from a global
macro value to per-context variable.

[1] https://lore.kernel.org/all/527714dd-0e33-43ab-bbbd-d89670ba79e7@huawei.com

Signed-off-by: Quanmin Yan <yanquanmin1@huawei.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/linux/damon.h        |  4 ++-
 mm/damon/core.c              | 67 ++++++++++++++++++++----------------
 mm/damon/sysfs.c             |  8 +++--
 mm/damon/tests/core-kunit.h  | 21 ++++++-----
 mm/damon/tests/vaddr-kunit.h |  2 +-
 mm/damon/vaddr.c             |  2 +-
 6 files changed, 61 insertions(+), 43 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 6fa52f7495d9..ec8716292c09 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -747,6 +747,7 @@ struct damon_attrs {
  *
  * @ops:	Set of monitoring operations for given use cases.
  * @addr_unit:	Scale factor for core to ops address conversion.
+ * @min_sz_region:		Minimum region size.
  * @adaptive_targets:	Head of monitoring targets (&damon_target) list.
  * @schemes:		Head of schemes (&damos) list.
  */
@@ -789,6 +790,7 @@ struct damon_ctx {
 
 	struct damon_operations ops;
 	unsigned long addr_unit;
+	unsigned long min_sz_region;
 
 	struct list_head adaptive_targets;
 	struct list_head schemes;
@@ -877,7 +879,7 @@ static inline void damon_insert_region(struct damon_region *r,
 void damon_add_region(struct damon_region *r, struct damon_target *t);
 void damon_destroy_region(struct damon_region *r, struct damon_target *t);
 int damon_set_regions(struct damon_target *t, struct damon_addr_range *ranges,
-		unsigned int nr_ranges);
+		unsigned int nr_ranges, unsigned long min_sz_region);
 void damon_update_region_access_rate(struct damon_region *r, bool accessed,
 		struct damon_attrs *attrs);
 
diff --git a/mm/damon/core.c b/mm/damon/core.c
index acea2964b9cc..7aeb3f24aae8 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -201,6 +201,7 @@ static int damon_fill_regions_holes(struct damon_region *first,
  * @t:		the given target.
  * @ranges:	array of new monitoring target ranges.
  * @nr_ranges:	length of @ranges.
+ * @min_sz_region:	minimum region size.
  *
  * This function adds new regions to, or modify existing regions of a
  * monitoring target to fit in specific ranges.
@@ -208,7 +209,7 @@ static int damon_fill_regions_holes(struct damon_region *first,
  * Return: 0 if success, or negative error code otherwise.
  */
 int damon_set_regions(struct damon_target *t, struct damon_addr_range *ranges,
-		unsigned int nr_ranges)
+		unsigned int nr_ranges, unsigned long min_sz_region)
 {
 	struct damon_region *r, *next;
 	unsigned int i;
@@ -245,16 +246,16 @@ int damon_set_regions(struct damon_target *t, struct damon_addr_range *ranges,
 			/* no region intersects with this range */
 			newr = damon_new_region(
 					ALIGN_DOWN(range->start,
-						DAMON_MIN_REGION),
-					ALIGN(range->end, DAMON_MIN_REGION));
+						min_sz_region),
+					ALIGN(range->end, min_sz_region));
 			if (!newr)
 				return -ENOMEM;
 			damon_insert_region(newr, damon_prev_region(r), r, t);
 		} else {
 			/* resize intersecting regions to fit in this range */
 			first->ar.start = ALIGN_DOWN(range->start,
-					DAMON_MIN_REGION);
-			last->ar.end = ALIGN(range->end, DAMON_MIN_REGION);
+					min_sz_region);
+			last->ar.end = ALIGN(range->end, min_sz_region);
 
 			/* fill possible holes in the range */
 			err = damon_fill_regions_holes(first, last, t);
@@ -545,6 +546,7 @@ struct damon_ctx *damon_new_ctx(void)
 	ctx->attrs.max_nr_regions = 1000;
 
 	ctx->addr_unit = 1;
+	ctx->min_sz_region = DAMON_MIN_REGION;
 
 	INIT_LIST_HEAD(&ctx->adaptive_targets);
 	INIT_LIST_HEAD(&ctx->schemes);
@@ -1127,8 +1129,8 @@ static struct damon_target *damon_nth_target(int n, struct damon_ctx *ctx)
  *
  * If @src has no region, @dst keeps current regions.
  */
-static int damon_commit_target_regions(
-		struct damon_target *dst, struct damon_target *src)
+static int damon_commit_target_regions(struct damon_target *dst,
+		struct damon_target *src, unsigned long src_min_sz_region)
 {
 	struct damon_region *src_region;
 	struct damon_addr_range *ranges;
@@ -1145,18 +1147,19 @@ static int damon_commit_target_regions(
 	i = 0;
 	damon_for_each_region(src_region, src)
 		ranges[i++] = src_region->ar;
-	err = damon_set_regions(dst, ranges, i);
+	err = damon_set_regions(dst, ranges, i, src_min_sz_region);
 	kfree(ranges);
 	return err;
 }
 
 static int damon_commit_target(
 		struct damon_target *dst, bool dst_has_pid,
-		struct damon_target *src, bool src_has_pid)
+		struct damon_target *src, bool src_has_pid,
+		unsigned long src_min_sz_region)
 {
 	int err;
 
-	err = damon_commit_target_regions(dst, src);
+	err = damon_commit_target_regions(dst, src, src_min_sz_region);
 	if (err)
 		return err;
 	if (dst_has_pid)
@@ -1178,7 +1181,8 @@ static int damon_commit_targets(
 		if (src_target) {
 			err = damon_commit_target(
 					dst_target, damon_target_has_pid(dst),
-					src_target, damon_target_has_pid(src));
+					src_target, damon_target_has_pid(src),
+					src->min_sz_region);
 			if (err)
 				return err;
 		} else {
@@ -1201,7 +1205,8 @@ static int damon_commit_targets(
 		if (!new_target)
 			return -ENOMEM;
 		err = damon_commit_target(new_target, false,
-				src_target, damon_target_has_pid(src));
+				src_target, damon_target_has_pid(src),
+				src->min_sz_region);
 		if (err) {
 			damon_destroy_target(new_target, NULL);
 			return err;
@@ -1248,6 +1253,7 @@ int damon_commit_ctx(struct damon_ctx *dst, struct damon_ctx *src)
 	}
 	dst->ops = src->ops;
 	dst->addr_unit = src->addr_unit;
+	dst->min_sz_region = src->min_sz_region;
 
 	return 0;
 }
@@ -1280,8 +1286,8 @@ static unsigned long damon_region_sz_limit(struct damon_ctx *ctx)
 
 	if (ctx->attrs.min_nr_regions)
 		sz /= ctx->attrs.min_nr_regions;
-	if (sz < DAMON_MIN_REGION)
-		sz = DAMON_MIN_REGION;
+	if (sz < ctx->min_sz_region)
+		sz = ctx->min_sz_region;
 
 	return sz;
 }
@@ -1625,6 +1631,7 @@ static bool damos_valid_target(struct damon_ctx *c, struct damon_target *t,
  * @t:	The target of the region.
  * @rp:	The pointer to the region.
  * @s:	The scheme to be applied.
+ * @min_sz_region:	minimum region size.
  *
  * If a quota of a scheme has exceeded in a quota charge window, the scheme's
  * action would applied to only a part of the target access pattern fulfilling
@@ -1642,7 +1649,7 @@ static bool damos_valid_target(struct damon_ctx *c, struct damon_target *t,
  * Return: true if the region should be entirely skipped, false otherwise.
  */
 static bool damos_skip_charged_region(struct damon_target *t,
-		struct damon_region **rp, struct damos *s)
+		struct damon_region **rp, struct damos *s, unsigned long min_sz_region)
 {
 	struct damon_region *r = *rp;
 	struct damos_quota *quota = &s->quota;
@@ -1664,11 +1671,11 @@ static bool damos_skip_charged_region(struct damon_target *t,
 		if (quota->charge_addr_from && r->ar.start <
 				quota->charge_addr_from) {
 			sz_to_skip = ALIGN_DOWN(quota->charge_addr_from -
-					r->ar.start, DAMON_MIN_REGION);
+					r->ar.start, min_sz_region);
 			if (!sz_to_skip) {
-				if (damon_sz_region(r) <= DAMON_MIN_REGION)
+				if (damon_sz_region(r) <= min_sz_region)
 					return true;
-				sz_to_skip = DAMON_MIN_REGION;
+				sz_to_skip = min_sz_region;
 			}
 			damon_split_region_at(t, r, sz_to_skip);
 			r = damon_next_region(r);
@@ -1693,7 +1700,8 @@ static void damos_update_stat(struct damos *s,
 }
 
 static bool damos_filter_match(struct damon_ctx *ctx, struct damon_target *t,
-		struct damon_region *r, struct damos_filter *filter)
+		struct damon_region *r, struct damos_filter *filter,
+		unsigned long min_sz_region)
 {
 	bool matched = false;
 	struct damon_target *ti;
@@ -1710,8 +1718,8 @@ static bool damos_filter_match(struct damon_ctx *ctx, struct damon_target *t,
 		matched = target_idx == filter->target_idx;
 		break;
 	case DAMOS_FILTER_TYPE_ADDR:
-		start = ALIGN_DOWN(filter->addr_range.start, DAMON_MIN_REGION);
-		end = ALIGN_DOWN(filter->addr_range.end, DAMON_MIN_REGION);
+		start = ALIGN_DOWN(filter->addr_range.start, min_sz_region);
+		end = ALIGN_DOWN(filter->addr_range.end, min_sz_region);
 
 		/* inside the range */
 		if (start <= r->ar.start && r->ar.end <= end) {
@@ -1747,7 +1755,7 @@ static bool damos_filter_out(struct damon_ctx *ctx, struct damon_target *t,
 
 	s->core_filters_allowed = false;
 	damos_for_each_filter(filter, s) {
-		if (damos_filter_match(ctx, t, r, filter)) {
+		if (damos_filter_match(ctx, t, r, filter, ctx->min_sz_region)) {
 			if (filter->allow)
 				s->core_filters_allowed = true;
 			return !filter->allow;
@@ -1882,7 +1890,7 @@ static void damos_apply_scheme(struct damon_ctx *c, struct damon_target *t,
 	if (c->ops.apply_scheme) {
 		if (quota->esz && quota->charged_sz + sz > quota->esz) {
 			sz = ALIGN_DOWN(quota->esz - quota->charged_sz,
-					DAMON_MIN_REGION);
+					c->min_sz_region);
 			if (!sz)
 				goto update_stat;
 			damon_split_region_at(t, r, sz);
@@ -1930,7 +1938,7 @@ static void damon_do_apply_schemes(struct damon_ctx *c,
 		if (quota->esz && quota->charged_sz >= quota->esz)
 			continue;
 
-		if (damos_skip_charged_region(t, &r, s))
+		if (damos_skip_charged_region(t, &r, s, c->min_sz_region))
 			continue;
 
 		if (!damos_valid_target(c, t, r, s))
@@ -2328,7 +2336,8 @@ static void damon_split_region_at(struct damon_target *t,
 }
 
 /* Split every region in the given target into 'nr_subs' regions */
-static void damon_split_regions_of(struct damon_target *t, int nr_subs)
+static void damon_split_regions_of(struct damon_target *t, int nr_subs,
+				  unsigned long min_sz_region)
 {
 	struct damon_region *r, *next;
 	unsigned long sz_region, sz_sub = 0;
@@ -2338,13 +2347,13 @@ static void damon_split_regions_of(struct damon_target *t, int nr_subs)
 		sz_region = damon_sz_region(r);
 
 		for (i = 0; i < nr_subs - 1 &&
-				sz_region > 2 * DAMON_MIN_REGION; i++) {
+				sz_region > 2 * min_sz_region; i++) {
 			/*
 			 * Randomly select size of left sub-region to be at
 			 * least 10 percent and at most 90% of original region
 			 */
 			sz_sub = ALIGN_DOWN(damon_rand(1, 10) *
-					sz_region / 10, DAMON_MIN_REGION);
+					sz_region / 10, min_sz_region);
 			/* Do not allow blank region */
 			if (sz_sub == 0 || sz_sub >= sz_region)
 				continue;
@@ -2384,7 +2393,7 @@ static void kdamond_split_regions(struct damon_ctx *ctx)
 		nr_subregions = 3;
 
 	damon_for_each_target(t, ctx)
-		damon_split_regions_of(t, nr_subregions);
+		damon_split_regions_of(t, nr_subregions, ctx->min_sz_region);
 
 	last_nr_regions = nr_regions;
 }
@@ -2773,7 +2782,7 @@ int damon_set_region_biggest_system_ram_default(struct damon_target *t,
 
 	addr_range.start = *start;
 	addr_range.end = *end;
-	return damon_set_regions(t, &addr_range, 1);
+	return damon_set_regions(t, &addr_range, 1, DAMON_MIN_REGION);
 }
 
 /*
diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index 98bf15d403b2..0ed404c89f80 100644
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -1329,7 +1329,8 @@ static int damon_sysfs_set_attrs(struct damon_ctx *ctx,
 }
 
 static int damon_sysfs_set_regions(struct damon_target *t,
-		struct damon_sysfs_regions *sysfs_regions)
+		struct damon_sysfs_regions *sysfs_regions,
+		unsigned long min_sz_region)
 {
 	struct damon_addr_range *ranges = kmalloc_array(sysfs_regions->nr,
 			sizeof(*ranges), GFP_KERNEL | __GFP_NOWARN);
@@ -1351,7 +1352,7 @@ static int damon_sysfs_set_regions(struct damon_target *t,
 		if (ranges[i - 1].end > ranges[i].start)
 			goto out;
 	}
-	err = damon_set_regions(t, ranges, sysfs_regions->nr);
+	err = damon_set_regions(t, ranges, sysfs_regions->nr, min_sz_region);
 out:
 	kfree(ranges);
 	return err;
@@ -1372,7 +1373,7 @@ static int damon_sysfs_add_target(struct damon_sysfs_target *sys_target,
 			/* caller will destroy targets */
 			return -EINVAL;
 	}
-	return damon_sysfs_set_regions(t, sys_target->regions);
+	return damon_sysfs_set_regions(t, sys_target->regions, ctx->min_sz_region);
 }
 
 static int damon_sysfs_add_targets(struct damon_ctx *ctx,
@@ -1430,6 +1431,7 @@ static int damon_sysfs_apply_inputs(struct damon_ctx *ctx,
 	if (err)
 		return err;
 	ctx->addr_unit = sys_ctx->addr_unit;
+	ctx->min_sz_region = max(DAMON_MIN_REGION / sys_ctx->addr_unit, 1);
 	err = damon_sysfs_set_attrs(ctx, sys_ctx->attrs);
 	if (err)
 		return err;
diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h
index 5f5dc9db2e90..51369e35298b 100644
--- a/mm/damon/tests/core-kunit.h
+++ b/mm/damon/tests/core-kunit.h
@@ -230,14 +230,14 @@ static void damon_test_split_regions_of(struct kunit *test)
 	t = damon_new_target();
 	r = damon_new_region(0, 22);
 	damon_add_region(r, t);
-	damon_split_regions_of(t, 2);
+	damon_split_regions_of(t, 2, DAMON_MIN_REGION);
 	KUNIT_EXPECT_LE(test, damon_nr_regions(t), 2u);
 	damon_free_target(t);
 
 	t = damon_new_target();
 	r = damon_new_region(0, 220);
 	damon_add_region(r, t);
-	damon_split_regions_of(t, 4);
+	damon_split_regions_of(t, 4, DAMON_MIN_REGION);
 	KUNIT_EXPECT_LE(test, damon_nr_regions(t), 4u);
 	damon_free_target(t);
 	damon_destroy_ctx(c);
@@ -303,7 +303,7 @@ static void damon_test_set_regions(struct kunit *test)
 
 	damon_add_region(r1, t);
 	damon_add_region(r2, t);
-	damon_set_regions(t, &range, 1);
+	damon_set_regions(t, &range, 1, DAMON_MIN_REGION);
 
 	KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 3);
 	damon_for_each_region(r, t) {
@@ -450,25 +450,29 @@ 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));
+	KUNIT_EXPECT_TRUE(test,
+			damos_filter_match(NULL, t, r, f, DAMON_MIN_REGION));
 	KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 1);
 
 	/* region before the range */
 	r->ar.start = DAMON_MIN_REGION * 1;
 	r->ar.end = DAMON_MIN_REGION * 2;
-	KUNIT_EXPECT_FALSE(test, damos_filter_match(NULL, t, r, f));
+	KUNIT_EXPECT_FALSE(test,
+			damos_filter_match(NULL, t, r, f, DAMON_MIN_REGION));
 	KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 1);
 
 	/* region after the range */
 	r->ar.start = DAMON_MIN_REGION * 6;
 	r->ar.end = DAMON_MIN_REGION * 8;
-	KUNIT_EXPECT_FALSE(test, damos_filter_match(NULL, t, r, f));
+	KUNIT_EXPECT_FALSE(test,
+			damos_filter_match(NULL, t, r, f, DAMON_MIN_REGION));
 	KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 1);
 
 	/* region started before the range */
 	r->ar.start = DAMON_MIN_REGION * 1;
 	r->ar.end = DAMON_MIN_REGION * 4;
-	KUNIT_EXPECT_FALSE(test, damos_filter_match(NULL, t, r, f));
+	KUNIT_EXPECT_FALSE(test,
+			damos_filter_match(NULL, t, r, f, DAMON_MIN_REGION));
 	/* filter should have split the region */
 	KUNIT_EXPECT_EQ(test, r->ar.start, DAMON_MIN_REGION * 1);
 	KUNIT_EXPECT_EQ(test, r->ar.end, DAMON_MIN_REGION * 2);
@@ -481,7 +485,8 @@ static void damos_test_filter_out(struct kunit *test)
 	/* region started in the range */
 	r->ar.start = DAMON_MIN_REGION * 2;
 	r->ar.end = DAMON_MIN_REGION * 8;
-	KUNIT_EXPECT_TRUE(test, damos_filter_match(NULL, t, r, f));
+	KUNIT_EXPECT_TRUE(test,
+			damos_filter_match(NULL, t, r, f, DAMON_MIN_REGION));
 	/* filter should have split the region */
 	KUNIT_EXPECT_EQ(test, r->ar.start, DAMON_MIN_REGION * 2);
 	KUNIT_EXPECT_EQ(test, r->ar.end, DAMON_MIN_REGION * 6);
diff --git a/mm/damon/tests/vaddr-kunit.h b/mm/damon/tests/vaddr-kunit.h
index d2b37ccf2cc0..fce38dd53cf8 100644
--- a/mm/damon/tests/vaddr-kunit.h
+++ b/mm/damon/tests/vaddr-kunit.h
@@ -141,7 +141,7 @@ static void damon_do_test_apply_three_regions(struct kunit *test,
 		damon_add_region(r, t);
 	}
 
-	damon_set_regions(t, three_regions, 3);
+	damon_set_regions(t, three_regions, 3, DAMON_MIN_REGION);
 
 	for (i = 0; i < nr_expected / 2; i++) {
 		r = __nth_region_of(t, i);
diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
index 66ef9869eafe..8c048f9b129e 100644
--- a/mm/damon/vaddr.c
+++ b/mm/damon/vaddr.c
@@ -299,7 +299,7 @@ static void damon_va_update(struct damon_ctx *ctx)
 	damon_for_each_target(t, ctx) {
 		if (damon_va_three_regions(t, three_regions))
 			continue;
-		damon_set_regions(t, three_regions, 3);
+		damon_set_regions(t, three_regions, 3, DAMON_MIN_REGION);
 	}
 }
 
-- 
2.39.5

On Thu, 28 Aug 2025 10:12:42 -0700 SeongJae Park <sj@kernel.org> wrote:

> From: Quanmin Yan <yanquanmin1@huawei.com>
> 
> Adopting addr_unit would make DAMON_MINREGION 'addr_unit * 4096'
> bytes and cause data alignment issues[1].
> 
> Add damon_ctx->min_sz_region to change DAMON_MIN_REGION from a global
> macro value to per-context variable.
> 
> [1] https://lore.kernel.org/all/527714dd-0e33-43ab-bbbd-d89670ba79e7@huawei.com

I think I found an issue of this patch.  Please refer to the attaching patch
for details.

This patch is in the mm tree and not yet merged into the mainline.  Andrew,
could you please add the attached patch as a fixup of this one?


Thanks,
SJ

==== Attachment 0 (0001-mm-damon-sysfs-set-damon_ctx-min_sz_region-only-for-.patch) ====
From af4a31405f4d8c4e5b32f7244f0cdcf960dce30f Mon Sep 17 00:00:00 2001
From: SeongJae Park <sj@kernel.org>
Date: Wed, 17 Sep 2025 08:31:54 -0700
Subject: [PATCH] mm/damon/sysfs: set damon_ctx->min_sz_region only for paddr
 use case

damon_ctx->addr_unit is respected only for physical address space
monitoring use case.  Meanwhile, damon_ctx->min_sz_region is used by the
core layer for aligning regions, regardless of whether it is set for
physical address space monitoring or virtual address spaces monitoring.
And it is set as 'DAMON_MIN_REGION / damon_ctx->addr_unit'.  Hence, if
user sets ->addr_unit on virtual address spaces monitoring mode, regions
can be unexpectedly aligned in <PAGE_SIZE granularity.  It shouldn't
cause crash-like issues but make monitoring and DAMOS behavior difficult
to understand.

Fix the unexpected behavior by setting ->min_sz_region only when it is
configured for physical address space monitoring.

The issue was found from a result of Chris' experiments that thankfully
shared with me off-list.

Cc: Chris Mason <clm@fb.com>
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index fe4e73d0ebbb..883b0d886d68 100644
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -1435,7 +1435,10 @@ static int damon_sysfs_apply_inputs(struct damon_ctx *ctx,
 	if (err)
 		return err;
 	ctx->addr_unit = sys_ctx->addr_unit;
-	ctx->min_sz_region = max(DAMON_MIN_REGION / sys_ctx->addr_unit, 1);
+	/* addr_unit is respected by only DAMON_OPS_PADDR */
+	if (sys_ctx->ops_id == DAMON_OPS_PADDR)
+		ctx->min_sz_region = max(
+				DAMON_MIN_REGION / sys_ctx->addr_unit, 1);
 	err = damon_sysfs_set_attrs(ctx, sys_ctx->attrs);
 	if (err)
 		return err;
-- 
2.39.5

On Wed, 17 Sep 2025 09:00:41 -0700 SeongJae Park <sj@kernel.org> wrote:

> On Thu, 28 Aug 2025 10:12:42 -0700 SeongJae Park <sj@kernel.org> wrote:
> 
> > From: Quanmin Yan <yanquanmin1@huawei.com>
> > 
> > Adopting addr_unit would make DAMON_MINREGION 'addr_unit * 4096'
> > bytes and cause data alignment issues[1].
> > 
> > Add damon_ctx->min_sz_region to change DAMON_MIN_REGION from a global
> > macro value to per-context variable.
> > 
> > [1] https://lore.kernel.org/all/527714dd-0e33-43ab-bbbd-d89670ba79e7@huawei.com
> 
> I think I found an issue of this patch.  Please refer to the attaching patch
> for details.
> 
> This patch is in the mm tree and not yet merged into the mainline.  Andrew,
> could you please add the attached patch as a fixup of this one?

The flawed patch is actually in mm.git's mm-stable branch, which is
supposedly non-rebasing.  So I queued this patch as separate commit, with

Fixes: d8f867fa0825 ("mm/damon: add damon_ctx->min_sz_region")