[RFC PATCH v2 0/6] mm/damon: add DAMOS_MIGRATE_{HOT,COLD} destination nodes and weights

[RFC PATCH v2 0/6] mm/damon: add DAMOS_MIGRATE_{HOT,COLD} destination nodes and weights

[SeongJae Park]

DAMOS_MIGRATE_{HOT,COLD} action can migrate pages to only single node.
It could be useful to allow it migrates pages to multiple nodes with
different weights.  A work for dynamic interleaving[1], which is in
progress, is an expected case.  We also discussed this could be useful
for memory tiering, e.g., when we want to move pages to multiple noes of
same tier.

Extend the API and ABI for specifying the multiple destination nodes and
their weights.

Note that this RFC is a prototype of the interface change for Bijan's
interleaving work[1].  Hence this patch series is only implementing the
interface part, not the real implementation of the migration behavior.

[1] https://lore.kernel.org/20250620180458.5041-1-bijan311@gmail.com
[2] https://lore.kernel.org/20240408175228.91414-1-sj@kernel.org

Changes from RFC
(https://lore.kernel.org/20250621173131.23917-1-sj@kernel.org)
- Add documentation patches
- Wordsmith commit messages
- Rebase on latest mm-new

SeongJae Park (6):
  mm/damon: add struct damos_migrate_dest
  mm/damon/core: add damos->migrate_dest field
  mm/damon/sysfs-schemes: implement DAMOS action destinations directory
  mm/damon/sysfs-schemes: set damos->migrate_dest
  Docs/ABI/damon: document schemes dests directory
  Docs/admin-guide/mm/damon/usage: document dests directory

 .../ABI/testing/sysfs-kernel-mm-damon         |  22 ++
 Documentation/admin-guide/mm/damon/usage.rst  |  33 ++-
 include/linux/damon.h                         |  29 +-
 mm/damon/core.c                               |   4 +
 mm/damon/sysfs-schemes.c                      | 253 +++++++++++++++++-
 5 files changed, 333 insertions(+), 8 deletions(-)


base-commit: 8a6d44984fa3076b444a6ddd8a8898b6ba254d25
-- 
2.39.5

[RFC PATCH v2 1/6] mm/damon: add struct damos_migrate_dest

[SeongJae Park]

Introduce a new struct, namely damos_migrate_dest, for specifying
multiple DAMOS' migration destination nodes and their weights.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/linux/damon.h | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index bb58e36f019e..d60addd0b7c8 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -447,6 +447,22 @@ struct damos_access_pattern {
 	unsigned int max_age_region;
 };
 
+/**
+ * struct damos_migrate_dest - Migration destination nodes and their weights.
+ * @node_id_arr:	Array of migration destination node ids.
+ * @weight_arr:		Array of migration weights for @node_id_arr.
+ * @nr_dests:		Length of the @node_id_arr and @weight_arr arrays.
+ *
+ * @node_id_arr is an array of the ids of migration destination nodes.
+ * @weight_arr is an array of the weights for those.  The weights in
+ * @weight_arr are for nodes in @node_id_arr of same array index.
+ */
+struct damos_migrate_dest {
+	unsigned int *node_id_arr;
+	unsigned int *weight_arr;
+	size_t nr_dests;
+};
+
 /**
  * struct damos - Represents a Data Access Monitoring-based Operation Scheme.
  * @pattern:		Access pattern of target regions.
-- 
2.39.5

[RFC PATCH v2 2/6] mm/damon/core: add damos->migrate_dest field

[SeongJae Park]

Add a new field to 'struct damos', namely migrate_dest, to allow DAMON
API callers specify multiple migration destination nodes and their
weights.  Also update 'struct damos' creation and destruction functions
accordingly to initialize the new field and free up the API
caller-allocated buffers on those, respectively.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/linux/damon.h | 13 ++++++++++---
 mm/damon/core.c       |  4 ++++
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index d60addd0b7c8..6370cf44486f 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -470,6 +470,7 @@ struct damos_migrate_dest {
  * @apply_interval_us:	The time between applying the @action.
  * @quota:		Control the aggressiveness of this scheme.
  * @wmarks:		Watermarks for automated (in)activation of this scheme.
+ * @migrate_dest:	Destination nodes if @action is "migrate_{hot,cold}".
  * @target_nid:		Destination node if @action is "migrate_{hot,cold}".
  * @filters:		Additional set of &struct damos_filter for &action.
  * @ops_filters:	ops layer handling &struct damos_filter objects list.
@@ -488,9 +489,12 @@ struct damos_migrate_dest {
  * monitoring context are inactive, DAMON stops monitoring either, and just
  * repeatedly checks the watermarks.
  *
+ * @migrate_dest specifies multiple migration target nodes with different
+ * weights for migrate_hot or migrate_cold actions.  @target_nid is ignored if
+ * this is set.
+ *
  * @target_nid is used to set the migration target node for migrate_hot or
- * migrate_cold actions, which means it's only meaningful when @action is either
- * "migrate_hot" or "migrate_cold".
+ * migrate_cold actions, and @migrate_dest is unset.
  *
  * Before applying the &action to a memory region, &struct damon_operations
  * implementation could check pages of the region and skip &action to respect
@@ -533,7 +537,10 @@ struct damos {
 	struct damos_quota quota;
 	struct damos_watermarks wmarks;
 	union {
-		int target_nid;
+		struct {
+			int target_nid;
+			struct damos_migrate_dest migrate_dest;
+		};
 	};
 	struct list_head filters;
 	struct list_head ops_filters;
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 979b29e16ef4..185aafa2e401 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -407,6 +407,7 @@ struct damos *damon_new_scheme(struct damos_access_pattern *pattern,
 	scheme->wmarks = *wmarks;
 	scheme->wmarks.activated = true;
 
+	scheme->migrate_dest = (struct damos_migrate_dest){};
 	scheme->target_nid = target_nid;
 
 	return scheme;
@@ -449,6 +450,9 @@ void damon_destroy_scheme(struct damos *s)
 
 	damos_for_each_filter_safe(f, next, s)
 		damos_destroy_filter(f);
+
+	kfree(s->migrate_dest.node_id_arr);
+	kfree(s->migrate_dest.weight_arr);
 	damon_del_scheme(s);
 	damon_free_scheme(s);
 }
-- 
2.39.5

[RFC PATCH v2 3/6] mm/damon/sysfs-schemes: implement DAMOS action destinations directory

[SeongJae Park]

DAMOS_MIGRATE_{HOT,COLD} can have multiple action destinations and their
weights.  Implement sysfs directory named 'dests' under each scheme
directory to let DAMON sysfs ABI users utilize the feature.  The
interface is similar to other multiple parameters directory like
kdamonds or filters.  The directory contains only nr_dests file
initially.  Writing a number of desired destinations to nr_dests creates
directories of the number.  Each of the created directories has two
files named id and weight.  Users can then write the destination's
identifier (node id in case of DAMOS_MIGRATE_*) and weight to the files.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs-schemes.c | 225 ++++++++++++++++++++++++++++++++++++++-
 1 file changed, 224 insertions(+), 1 deletion(-)

diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
index 601360e9b521..b9434cdaacdc 100644
--- a/mm/damon/sysfs-schemes.c
+++ b/mm/damon/sysfs-schemes.c
@@ -1655,6 +1655,204 @@ static const struct kobj_type damon_sysfs_access_pattern_ktype = {
 	.default_groups = damon_sysfs_access_pattern_groups,
 };
 
+/*
+ * dest (action destination) directory
+ */
+
+struct damos_sysfs_dest {
+	struct kobject kobj;
+	unsigned int id;
+	unsigned int weight;
+};
+
+static struct damos_sysfs_dest *damos_sysfs_dest_alloc(void)
+{
+	return kzalloc(sizeof(struct damos_sysfs_dest), GFP_KERNEL);
+}
+
+static ssize_t id_show(
+		struct kobject *kobj, struct kobj_attribute *attr, char *buf)
+{
+	struct damos_sysfs_dest *dest = container_of(kobj,
+			struct damos_sysfs_dest, kobj);
+
+	return sysfs_emit(buf, "%u\n", dest->id);
+}
+
+static ssize_t id_store(struct kobject *kobj,
+		struct kobj_attribute *attr, const char *buf, size_t count)
+{
+	struct damos_sysfs_dest *dest = container_of(kobj,
+			struct damos_sysfs_dest, kobj);
+	int err = kstrtouint(buf, 0, &dest->id);
+
+	return err ? err : count;
+}
+
+static ssize_t weight_show(
+		struct kobject *kobj, struct kobj_attribute *attr, char *buf)
+{
+	struct damos_sysfs_dest *dest = container_of(kobj,
+			struct damos_sysfs_dest, kobj);
+
+	return sysfs_emit(buf, "%u\n", dest->weight);
+}
+
+static ssize_t weight_store(struct kobject *kobj,
+		struct kobj_attribute *attr, const char *buf, size_t count)
+{
+	struct damos_sysfs_dest *dest = container_of(kobj,
+			struct damos_sysfs_dest, kobj);
+	int err = kstrtouint(buf, 0, &dest->weight);
+
+	return err ? err : count;
+}
+
+static void damos_sysfs_dest_release(struct kobject *kobj)
+{
+	struct damos_sysfs_dest *dest = container_of(kobj,
+			struct damos_sysfs_dest, kobj);
+	kfree(dest);
+}
+
+static struct kobj_attribute damos_sysfs_dest_id_attr =
+		__ATTR_RW_MODE(id, 0600);
+
+static struct kobj_attribute damos_sysfs_dest_weight_attr =
+		__ATTR_RW_MODE(weight, 0600);
+
+static struct attribute *damos_sysfs_dest_attrs[] = {
+	&damos_sysfs_dest_id_attr.attr,
+	&damos_sysfs_dest_weight_attr.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(damos_sysfs_dest);
+
+static const struct kobj_type damos_sysfs_dest_ktype = {
+	.release = damos_sysfs_dest_release,
+	.sysfs_ops = &kobj_sysfs_ops,
+	.default_groups = damos_sysfs_dest_groups,
+};
+
+/*
+ * dests (action destinations) directory
+ */
+
+struct damos_sysfs_dests {
+	struct kobject kobj;
+	struct damos_sysfs_dest **dests_arr;
+	int nr;
+};
+
+static struct damos_sysfs_dests *
+damos_sysfs_dests_alloc(void)
+{
+	return kzalloc(sizeof(struct damos_sysfs_dests), GFP_KERNEL);
+}
+
+static void damos_sysfs_dests_rm_dirs(
+		struct damos_sysfs_dests *dests)
+{
+	struct damos_sysfs_dest **dests_arr = dests->dests_arr;
+	int i;
+
+	for (i = 0; i < dests->nr; i++)
+		kobject_put(&dests_arr[i]->kobj);
+	dests->nr = 0;
+	kfree(dests_arr);
+	dests->dests_arr = NULL;
+}
+
+static int damos_sysfs_dests_add_dirs(
+		struct damos_sysfs_dests *dests, int nr_dests)
+{
+	struct damos_sysfs_dest **dests_arr, *dest;
+	int err, i;
+
+	damos_sysfs_dests_rm_dirs(dests);
+	if (!nr_dests)
+		return 0;
+
+	dests_arr = kmalloc_array(nr_dests, sizeof(*dests_arr),
+			GFP_KERNEL | __GFP_NOWARN);
+	if (!dests_arr)
+		return -ENOMEM;
+	dests->dests_arr = dests_arr;
+
+	for (i = 0; i < nr_dests; i++) {
+		dest = damos_sysfs_dest_alloc();
+		if (!dest) {
+			damos_sysfs_dests_rm_dirs(dests);
+			return -ENOMEM;
+		}
+
+		err = kobject_init_and_add(&dest->kobj,
+				&damos_sysfs_dest_ktype,
+				&dests->kobj, "%d", i);
+		if (err) {
+			kobject_put(&dest->kobj);
+			damos_sysfs_dests_rm_dirs(dests);
+			return err;
+		}
+
+		dests_arr[i] = dest;
+		dests->nr++;
+	}
+	return 0;
+}
+
+static ssize_t nr_dests_show(struct kobject *kobj,
+		struct kobj_attribute *attr, char *buf)
+{
+	struct damos_sysfs_dests *dests = container_of(kobj,
+			struct damos_sysfs_dests, kobj);
+
+	return sysfs_emit(buf, "%d\n", dests->nr);
+}
+
+static ssize_t nr_dests_store(struct kobject *kobj,
+		struct kobj_attribute *attr, const char *buf, size_t count)
+{
+	struct damos_sysfs_dests *dests;
+	int nr, err = kstrtoint(buf, 0, &nr);
+
+	if (err)
+		return err;
+	if (nr < 0)
+		return -EINVAL;
+
+	dests = container_of(kobj, struct damos_sysfs_dests, kobj);
+
+	if (!mutex_trylock(&damon_sysfs_lock))
+		return -EBUSY;
+	err = damos_sysfs_dests_add_dirs(dests, nr);
+	mutex_unlock(&damon_sysfs_lock);
+	if (err)
+		return err;
+
+	return count;
+}
+
+static void damos_sysfs_dests_release(struct kobject *kobj)
+{
+	kfree(container_of(kobj, struct damos_sysfs_dests, kobj));
+}
+
+static struct kobj_attribute damos_sysfs_dests_nr_attr =
+		__ATTR_RW_MODE(nr_dests, 0600);
+
+static struct attribute *damos_sysfs_dests_attrs[] = {
+	&damos_sysfs_dests_nr_attr.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(damos_sysfs_dests);
+
+static const struct kobj_type damos_sysfs_dests_ktype = {
+	.release = damos_sysfs_dests_release,
+	.sysfs_ops = &kobj_sysfs_ops,
+	.default_groups = damos_sysfs_dests_groups,
+};
+
 /*
  * scheme directory
  */
@@ -1672,6 +1870,7 @@ struct damon_sysfs_scheme {
 	struct damon_sysfs_stats *stats;
 	struct damon_sysfs_scheme_regions *tried_regions;
 	int target_nid;
+	struct damos_sysfs_dests *dests;
 };
 
 struct damos_sysfs_action_name {
@@ -1762,6 +1961,22 @@ static int damon_sysfs_scheme_set_access_pattern(
 	return err;
 }
 
+static int damos_sysfs_set_dests(struct damon_sysfs_scheme *scheme)
+{
+	struct damos_sysfs_dests *dests = damos_sysfs_dests_alloc();
+	int err;
+
+	if (!dests)
+		return -ENOMEM;
+	err = kobject_init_and_add(&dests->kobj, &damos_sysfs_dests_ktype,
+			&scheme->kobj, "dests");
+	if (err)
+		kobject_put(&dests->kobj);
+	else
+		scheme->dests = dests;
+	return err;
+}
+
 static int damon_sysfs_scheme_set_quotas(struct damon_sysfs_scheme *scheme)
 {
 	struct damon_sysfs_quotas *quotas = damon_sysfs_quotas_alloc();
@@ -1894,9 +2109,12 @@ static int damon_sysfs_scheme_add_dirs(struct damon_sysfs_scheme *scheme)
 	err = damon_sysfs_scheme_set_access_pattern(scheme);
 	if (err)
 		return err;
-	err = damon_sysfs_scheme_set_quotas(scheme);
+	err = damos_sysfs_set_dests(scheme);
 	if (err)
 		goto put_access_pattern_out;
+	err = damon_sysfs_scheme_set_quotas(scheme);
+	if (err)
+		goto put_dests_out;
 	err = damon_sysfs_scheme_set_watermarks(scheme);
 	if (err)
 		goto put_quotas_access_pattern_out;
@@ -1927,6 +2145,9 @@ static int damon_sysfs_scheme_add_dirs(struct damon_sysfs_scheme *scheme)
 put_quotas_access_pattern_out:
 	kobject_put(&scheme->quotas->kobj);
 	scheme->quotas = NULL;
+put_dests_out:
+	kobject_put(&scheme->dests->kobj);
+	scheme->dests = NULL;
 put_access_pattern_out:
 	kobject_put(&scheme->access_pattern->kobj);
 	scheme->access_pattern = NULL;
@@ -1937,6 +2158,8 @@ static void damon_sysfs_scheme_rm_dirs(struct damon_sysfs_scheme *scheme)
 {
 	damon_sysfs_access_pattern_rm_dirs(scheme->access_pattern);
 	kobject_put(&scheme->access_pattern->kobj);
+	kobject_put(&scheme->dests->kobj);
+	damos_sysfs_dests_rm_dirs(scheme->dests);
 	damon_sysfs_quotas_rm_dirs(scheme->quotas);
 	kobject_put(&scheme->quotas->kobj);
 	kobject_put(&scheme->watermarks->kobj);
-- 
2.39.5

[RFC PATCH v2 4/6] mm/damon/sysfs-schemes: set damos->migrate_dest

[SeongJae Park]

Pass user-specified multiple DAMOS action destinations and their weights
to DAMON core API, so that user requests can really work.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs-schemes.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
index b9434cdaacdc..507ca7708078 100644
--- a/mm/damon/sysfs-schemes.c
+++ b/mm/damon/sysfs-schemes.c
@@ -2576,6 +2576,29 @@ void damos_sysfs_update_effective_quotas(
 	}
 }
 
+static int damos_sysfs_add_migrate_dest(struct damos *scheme,
+		struct damos_sysfs_dests *sysfs_dests)
+{
+	struct damos_migrate_dest *dest = &scheme->migrate_dest;
+	int i;
+
+	dest->node_id_arr = kmalloc_array(sysfs_dests->nr,
+			sizeof(*dest->node_id_arr), GFP_KERNEL);
+	if (!dest->node_id_arr)
+		return -ENOMEM;
+	dest->weight_arr = kmalloc_array(sysfs_dests->nr,
+			sizeof(*dest->weight_arr), GFP_KERNEL);
+	if (!dest->weight_arr)
+		/* ->node_id_arr will be freed by scheme destruction */
+		return -ENOMEM;
+	for (i = 0; i < sysfs_dests->nr; i++) {
+		dest->node_id_arr[i] = sysfs_dests->dests_arr[i]->id;
+		dest->weight_arr[i] = sysfs_dests->dests_arr[i]->weight;
+	}
+	dest->nr_dests = sysfs_dests->nr;
+	return 0;
+}
+
 static struct damos *damon_sysfs_mk_scheme(
 		struct damon_sysfs_scheme *sysfs_scheme)
 {
@@ -2638,6 +2661,11 @@ static struct damos *damon_sysfs_mk_scheme(
 		damon_destroy_scheme(scheme);
 		return NULL;
 	}
+	err = damos_sysfs_add_migrate_dest(scheme, sysfs_scheme->dests);
+	if (err) {
+		damon_destroy_scheme(scheme);
+		return NULL;
+	}
 	return scheme;
 }
 
-- 
2.39.5

[RFC PATCH v2 5/6] Docs/ABI/damon: document schemes dests directory

[SeongJae Park]

Document the new DAMOS action destinations sysfs directories on ABI doc.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 .../ABI/testing/sysfs-kernel-mm-damon         | 22 +++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-kernel-mm-damon b/Documentation/ABI/testing/sysfs-kernel-mm-damon
index 5697ab154c1f..e98974dfac7a 100644
--- a/Documentation/ABI/testing/sysfs-kernel-mm-damon
+++ b/Documentation/ABI/testing/sysfs-kernel-mm-damon
@@ -431,6 +431,28 @@ Description:	Directory for DAMON operations set layer-handled DAMOS filters.
 		/sys/kernel/mm/damon/admin/kdamonds/<K>/contexts/<C>/schemes/<S>/filters
 		directory.
 
+What:		/sys/kernel/mm/damon/admin/kdamonds/<K>/contexts/<C>/schemes/<S>/dests/nr_dests
+Date:		Jul 2025
+Contact:	SeongJae Park <sj@kernel.org>
+Description:	Writing a number 'N' to this file creates the number of
+		directories for setting action destinations of the scheme named
+		'0' to 'N-1' under the dests/ directory.
+
+What:		/sys/kernel/mm/damon/admin/kdamonds/<K>/contexts/<C>/schemes/<S>/dests/<D>/id
+Date:		Jul 2025
+Contact:	SeongJae Park <sj@kernel.org>
+Description:	Writing to and reading from this file sets and gets the id of
+		the DAMOS action destination.  For DAMOS_MIGRATE_{HOT,COLD}
+		actions, the destination node's node id can be written and
+		read.
+
+What:		/sys/kernel/mm/damon/admin/kdamonds/<K>/contexts/<C>/schemes/<S>/dests/<D>/weight
+Date:		Jul 2025
+Contact:	SeongJae Park <sj@kernel.org>
+Description:	Writing to and reading from this file sets and gets the weight
+		of the DAMOS action destination to select as the destination of
+		each action among the destinations.
+
 What:		/sys/kernel/mm/damon/admin/kdamonds/<K>/contexts/<C>/schemes/<S>/stats/nr_tried
 Date:		Mar 2022
 Contact:	SeongJae Park <sj@kernel.org>
-- 
2.39.5

[RFC PATCH v2 6/6] Docs/admin-guide/mm/damon/usage: document dests directory

[SeongJae Park]

Document the newly added DAMOS action destination directory of the DAMON
sysfs interface on the usage document.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 Documentation/admin-guide/mm/damon/usage.rst | 33 +++++++++++++++++---
 1 file changed, 29 insertions(+), 4 deletions(-)

diff --git a/Documentation/admin-guide/mm/damon/usage.rst b/Documentation/admin-guide/mm/damon/usage.rst
index d960aba72b82..fc5c962353ed 100644
--- a/Documentation/admin-guide/mm/damon/usage.rst
+++ b/Documentation/admin-guide/mm/damon/usage.rst
@@ -85,6 +85,8 @@ comma (",").
     │ │ │ │ │ │ │ :ref:`watermarks <sysfs_watermarks>`/metric,interval_us,high,mid,low
     │ │ │ │ │ │ │ :ref:`{core_,ops_,}filters <sysfs_filters>`/nr_filters
     │ │ │ │ │ │ │ │ 0/type,matching,allow,memcg_path,addr_start,addr_end,target_idx,min,max
+    │ │ │ │ │ │ │ :ref:`dests <damon_sysfs_dests>`/nr_dests
+    │ │ │ │ │ │ │ │ 0/id,weight
     │ │ │ │ │ │ │ :ref:`stats <sysfs_schemes_stats>`/nr_tried,sz_tried,nr_applied,sz_applied,sz_ops_filter_passed,qt_exceeds
     │ │ │ │ │ │ │ :ref:`tried_regions <sysfs_schemes_tried_regions>`/total_bytes
     │ │ │ │ │ │ │ │ 0/start,end,nr_accesses,age,sz_filter_passed
@@ -307,10 +309,10 @@ to ``N-1``.  Each directory represents each DAMON-based operation scheme.
 schemes/<N>/
 ------------
 
-In each scheme directory, seven directories (``access_pattern``, ``quotas``,
-``watermarks``, ``core_filters``, ``ops_filters``, ``filters``, ``stats``, and
-``tried_regions``) and three files (``action``, ``target_nid`` and
-``apply_interval``) exist.
+In each scheme directory, eight directories (``access_pattern``, ``quotas``,
+``watermarks``, ``core_filters``, ``ops_filters``, ``filters``, ``dests``,
+``stats``, and ``tried_regions``) and three files (``action``, ``target_nid``
+and ``apply_interval``) exist.
 
 The ``action`` file is for setting and getting the scheme's :ref:`action
 <damon_design_damos_action>`.  The keywords that can be written to and read
@@ -484,6 +486,29 @@ Refer to the :ref:`DAMOS filters design documentation
 of different ``allow`` works, when each of the filters are supported, and
 differences on stats.
 
+.. _damon_sysfs_dests:
+
+schemes/<N>/dests/
+------------------
+
+Directory for specifying the destinations of given DAMON-based operation
+scheme's action.  This directory is ignored if the action of the given scheme
+is not supporting multiple destinations.  Only ``DAMOS_MIGRATE_{HOT,COLD}``
+actions are supporting multiple destinations.
+
+In the beginning, the directory has only one file, ``nr_dests``.  Writing a
+number (``N``) to the file creates the number of child directories named ``0``
+to ``N-1``.  Each directory represents each action destination.
+
+Each destination directory contains two files, namely ``id`` and ``weight``.
+Users can write and read the identifier of the destination to ``id`` file.
+For ``DAMOS_MIGRATE_{HOT,COLD}`` actions, the migrate destination node's node
+id should be written to ``id`` file.  Users can write and read the weight of
+the destination among the given destinations to the ``weight`` file.  The
+weight can be an arbitrary integer.  When DAMOS apply the action to each entity
+of the memory region, it will select the destination of the action based on the
+relative weights of the destinations.
+
 .. _sysfs_schemes_stats:
 
 schemes/<N>/stats/
-- 
2.39.5