[RFC PATCH v4 0/7] snapshot_set_swap_area() unpins the previously selected swap device and

[RFC PATCH v4 0/7] snapshot_set_swap_area() unpins the previously selected swap device and

[SJ Park]

Add repin_hibernation_swap_type(), which looks up the new device, clears
the old SWP_HIBERNATION flag and sets the new one under a single swap_lock
acquisition.  The same-device case is short- circuited so userspace can
re-select the same swap area without tripping WARN_ON_ONCE and -EBUSY. 
Switch snapshot_set_swap_area() to the new helper.

A failed lookup now preserves the previous pin instead of dropping it, so
a bad SNAPSHOT_SET_SWAP_AREA leaves the prior selection intact.  The open
and release paths keep using pin_hibernation_swap_type() and
unpin_hibernation_swap_type().

The race was identified during AI-assisted review of the SWP_HIBERNATION
pinning series.

SJ Park (7):
  mm/damon/core: introduce damos_quota_goal->complement
  mm/damon/core: add complement argument to damos_new_quota_goal()
  mm/damon/sysfs-schemes: support quota goal complement flag
  mm/damon/tests/core-kunit: test quota_goal->complement commit
  Docs/mm/damon/design: document damos quota goal complement flag
  Docs/admin-guide/mm/damon/usage: update for quota goal complement file
  Docs/ABI/damon: update for quota goal metric complement sysfs file

 .../ABI/testing/sysfs-kernel-mm-damon         |  6 ++++
 Documentation/admin-guide/mm/damon/usage.rst  | 15 +++++----
 Documentation/mm/damon/design.rst             | 15 ++++++---
 include/linux/damon.h                         |  4 ++-
 mm/damon/core.c                               | 33 ++++++++++++++++---
 mm/damon/lru_sort.c                           |  5 +--
 mm/damon/reclaim.c                            |  5 +--
 mm/damon/sysfs-schemes.c                      | 30 +++++++++++++++++
 mm/damon/tests/core-kunit.h                   |  3 ++
 samples/damon/mtier.c                         |  2 +-
 10 files changed, 97 insertions(+), 21 deletions(-)


base-commit: 1c2b8d2725f84b43fabe3b3e9628c91db8ca6c65
-- 
2.47.3

[RFC PATCH v4 1/7] mm/damon/core: introduce damos_quota_goal->complement

[SJ Park]

Introduce damos_quota_goal->complement for specifying whether to use a
complemented value of the given goal target metric.  Add the field to
the data structure and implement essential core support.  Handle the
flag in the quota goal commit and current quota goal metric value
retrieval.

Signed-off-by: SJ Park <sj@kernel.org>
---
 include/linux/damon.h |  2 ++
 mm/damon/core.c       | 26 +++++++++++++++++++++++++-
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 844b175120f0..78b227875287 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -175,6 +175,7 @@ enum damos_quota_goal_metric {
 /**
  * struct damos_quota_goal - DAMOS scheme quota auto-tuning goal.
  * @metric:		Metric to be used for representing the goal.
+ * @complement:		Use the complement of the metric.
  * @target_value:	Target value of @metric to achieve with the tuning.
  * @current_value:	Current value of @metric.
  * @nid:		Node id.
@@ -197,6 +198,7 @@ enum damos_quota_goal_metric {
  */
 struct damos_quota_goal {
 	enum damos_quota_goal_metric metric;
+	bool complement;
 	unsigned long target_value;
 	unsigned long current_value;
 	/* metric-dependent fields */
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 733025b36745..270ce9c85a2c 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -1224,6 +1224,7 @@ static int damos_commit_quota_goal(
 	if (!src->target_value)
 		return  -EINVAL;
 	dst->metric = src->metric;
+	dst->complement = src->complement;
 	dst->target_value = src->target_value;
 	if (dst->metric == DAMOS_QUOTA_USER_INPUT)
 		dst->current_value = src->current_value;
@@ -2960,10 +2961,18 @@ static void damos_set_psi_current_val(u64 now_psi_total,
 		struct damos_quota_goal *goal, struct damos *s)
 {
 	u64 last_psi_total = goal->last_psi_total;
+	unsigned long val;
 
 	goal->last_psi_total = now_psi_total;
 	if (last_psi_total != U64_MAX) {
-		goal->current_value = now_psi_total - last_psi_total;
+		val = now_psi_total - last_psi_total;
+		if (goal->complement) {
+			if (val < s->quota.reset_interval * 1000)
+				val = s->quota.reset_interval * 1000 - val;
+			else
+				val = 0;
+		}
+		goal->current_value = val;
 		return;
 	}
 	/* uninitialized last_psi_total; make no effect this round */
@@ -3255,6 +3264,21 @@ static void damos_set_quota_goal_current_value(struct damon_ctx *c,
 	default:
 		break;
 	}
+	if (!goal->complement)
+		return;
+
+	/* updte current_value to complemented value */
+
+	/* for user_input, users set complemented value on their own */
+	if (goal->metric == DAMOS_QUOTA_USER_INPUT)
+		return;
+	/* damos_set_psi_current_val() handles complement flag itself */
+	if (goal->metric == DAMOS_QUOTA_SOME_MEM_PSI_US)
+		return;
+	if (goal->current_value < 10000)
+		goal->current_value = 10000 - goal->current_value;
+	else
+		goal->current_value = 0;
 }
 
 /* Return the highest score since it makes schemes least aggressive */
-- 
2.47.3

[RFC PATCH v4 2/7] mm/damon/core: add complement argument to damos_new_quota_goal()

[SJ Park]

damos_quota_goal->complement needs to be manually set by each API
callers.  It is easy to make mistakes.  Extend the quota goal
constructor, damos_new_quota_goal() to receive and set the complement
flag value. Also update all callers to use the new signature.

Signed-off-by: SJ Park <sj@kernel.org>
---
 include/linux/damon.h       | 2 +-
 mm/damon/core.c             | 7 ++++---
 mm/damon/lru_sort.c         | 5 +++--
 mm/damon/reclaim.c          | 5 +++--
 mm/damon/sysfs-schemes.c    | 2 +-
 mm/damon/tests/core-kunit.h | 1 +
 samples/damon/mtier.c       | 2 +-
 7 files changed, 14 insertions(+), 10 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 78b227875287..b310c40d6ceb 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -1098,7 +1098,7 @@ bool damos_filter_for_ops(enum damos_filter_type type);
 void damos_destroy_filter(struct damos_filter *f);
 
 struct damos_quota_goal *damos_new_quota_goal(
-		enum damos_quota_goal_metric metric,
+		enum damos_quota_goal_metric metric, bool complement,
 		unsigned long target_value);
 void damos_add_quota_goal(struct damos_quota *q, struct damos_quota_goal *g);
 void damos_destroy_quota_goal(struct damos_quota_goal *goal);
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 270ce9c85a2c..86f13411b91f 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -691,7 +691,7 @@ void damos_destroy_filter(struct damos_filter *f)
 }
 
 struct damos_quota_goal *damos_new_quota_goal(
-		enum damos_quota_goal_metric metric,
+		enum damos_quota_goal_metric metric, bool complement,
 		unsigned long target_value)
 {
 	struct damos_quota_goal *goal;
@@ -700,6 +700,7 @@ struct damos_quota_goal *damos_new_quota_goal(
 	if (!goal)
 		return NULL;
 	goal->metric = metric;
+	goal->complement = complement;
 	goal->target_value = target_value;
 	if (metric == DAMOS_QUOTA_SOME_MEM_PSI_US)
 		goal->last_psi_total = U64_MAX;
@@ -1262,8 +1263,8 @@ int damos_commit_quota_goals(struct damos_quota *dst, struct damos_quota *src)
 	damos_for_each_quota_goal_safe(src_goal, next, src) {
 		if (j++ < i)
 			continue;
-		new_goal = damos_new_quota_goal(
-				src_goal->metric, src_goal->target_value);
+		new_goal = damos_new_quota_goal(src_goal->metric,
+				src_goal->complement, src_goal->target_value);
 		if (!new_goal)
 			return -ENOMEM;
 		err = damos_commit_quota_goal(new_goal, src_goal);
diff --git a/mm/damon/lru_sort.c b/mm/damon/lru_sort.c
index 273efa3c913e..64e086985eb5 100644
--- a/mm/damon/lru_sort.c
+++ b/mm/damon/lru_sort.c
@@ -233,12 +233,13 @@ static int damon_lru_sort_add_quota_goals(struct damos *hot_scheme,
 
 	if (!active_mem_bp)
 		return 0;
-	goal = damos_new_quota_goal(DAMOS_QUOTA_ACTIVE_MEM_BP, active_mem_bp);
+	goal = damos_new_quota_goal(DAMOS_QUOTA_ACTIVE_MEM_BP, false,
+			active_mem_bp);
 	if (!goal)
 		return -ENOMEM;
 	damos_add_quota_goal(&hot_scheme->quota, goal);
 	/* aim 0.2 % goal conflict, to keep little ping pong */
-	goal = damos_new_quota_goal(DAMOS_QUOTA_INACTIVE_MEM_BP,
+	goal = damos_new_quota_goal(DAMOS_QUOTA_INACTIVE_MEM_BP, false,
 			10000 - active_mem_bp + 2);
 	if (!goal)
 		return -ENOMEM;
diff --git a/mm/damon/reclaim.c b/mm/damon/reclaim.c
index 42a2c9cb1343..014b0779ea6d 100644
--- a/mm/damon/reclaim.c
+++ b/mm/damon/reclaim.c
@@ -233,7 +233,7 @@ static int damon_reclaim_apply_parameters(void)
 	damon_set_schemes(param_ctx, &scheme, 1);
 
 	if (quota_mem_pressure_us) {
-		goal = damos_new_quota_goal(DAMOS_QUOTA_SOME_MEM_PSI_US,
+		goal = damos_new_quota_goal(DAMOS_QUOTA_SOME_MEM_PSI_US, false,
 				quota_mem_pressure_us);
 		if (!goal)
 			goto out;
@@ -241,7 +241,8 @@ static int damon_reclaim_apply_parameters(void)
 	}
 
 	if (quota_autotune_feedback) {
-		goal = damos_new_quota_goal(DAMOS_QUOTA_USER_INPUT, 10000);
+		goal = damos_new_quota_goal(DAMOS_QUOTA_USER_INPUT, false,
+				10000);
 		if (!goal)
 			goto out;
 		goal->current_value = quota_autotune_feedback;
diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
index bfb6f0bc3f21..06af417bc9a2 100644
--- a/mm/damon/sysfs-schemes.c
+++ b/mm/damon/sysfs-schemes.c
@@ -2869,7 +2869,7 @@ static int damos_sysfs_add_quota_score(
 		if (!sysfs_goal->target_value)
 			continue;
 
-		goal = damos_new_quota_goal(sysfs_goal->metric,
+		goal = damos_new_quota_goal(sysfs_goal->metric, false,
 				sysfs_goal->target_value);
 		if (!goal)
 			return -ENOMEM;
diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h
index df84d9cc7d20..20bba7421a40 100644
--- a/mm/damon/tests/core-kunit.h
+++ b/mm/damon/tests/core-kunit.h
@@ -930,6 +930,7 @@ static void damos_test_commit_quota_goals_for(struct kunit *test,
 		 * Make it kfree()-able.
 		 */
 		goal = damos_new_quota_goal(dst_goals[i].metric,
+				dst_goals[i].complementfalse,
 				dst_goals[i].target_value);
 		if (!goal)
 			goto out;
diff --git a/samples/damon/mtier.c b/samples/damon/mtier.c
index 27dc88bdf7a0..a2e311082cd4 100644
--- a/samples/damon/mtier.c
+++ b/samples/damon/mtier.c
@@ -163,7 +163,7 @@ static struct damon_ctx *damon_sample_mtier_build_ctx(bool promote)
 	damon_set_schemes(ctx, &scheme, 1);
 	quota_goal = damos_new_quota_goal(
 			promote ? DAMOS_QUOTA_NODE_MEM_USED_BP :
-			DAMOS_QUOTA_NODE_MEM_FREE_BP,
+			DAMOS_QUOTA_NODE_MEM_FREE_BP, false,
 			promote ? node0_mem_used_bp : node0_mem_free_bp);
 	if (!quota_goal)
 		goto free_out;
-- 
2.47.3

[RFC PATCH v4 3/7] mm/damon/sysfs-schemes: support quota goal complement flag

[SJ Park]

Add a new sysfs file, complement, under the quota goal directory.  It
works for setting and getting the quota goal metric complement flag
value.

Signed-off-by: SJ Park <sj@kernel.org>
---
 mm/damon/sysfs-schemes.c | 32 +++++++++++++++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
index 06af417bc9a2..8f083611741f 100644
--- a/mm/damon/sysfs-schemes.c
+++ b/mm/damon/sysfs-schemes.c
@@ -1220,6 +1220,7 @@ static const struct kobj_type damon_sysfs_watermarks_ktype = {
 struct damos_sysfs_quota_goal {
 	struct kobject kobj;
 	enum damos_quota_goal_metric metric;
+	bool complement;
 	unsigned long target_value;
 	unsigned long current_value;
 	int nid;
@@ -1316,6 +1317,30 @@ static ssize_t target_metric_store(struct kobject *kobj,
 	return -EINVAL;
 }
 
+static ssize_t complement_show(struct kobject *kobj,
+		struct kobj_attribute *attr, char *buf)
+{
+	struct damos_sysfs_quota_goal *goal = container_of(kobj,
+			struct damos_sysfs_quota_goal, kobj);
+
+	return sysfs_emit(buf, "%c\n", goal->complement ? 'Y' : 'N');
+}
+
+static ssize_t complement_store(struct kobject *kobj,
+		struct kobj_attribute *attr, const char *buf, size_t count)
+{
+	struct damos_sysfs_quota_goal *goal = container_of(kobj,
+			struct damos_sysfs_quota_goal, kobj);
+	bool complement;
+	int err = kstrtobool(buf, &complement);
+
+	if (err)
+		return err;
+
+	goal->complement = complement;
+	return count;
+}
+
 static ssize_t target_value_show(struct kobject *kobj,
 		struct kobj_attribute *attr, char *buf)
 {
@@ -1424,6 +1449,9 @@ static void damos_sysfs_quota_goal_release(struct kobject *kobj)
 static struct kobj_attribute damos_sysfs_quota_goal_target_metric_attr =
 		__ATTR_RW_MODE(target_metric, 0600);
 
+static struct kobj_attribute damos_sysfs_quota_goal_complement_attr =
+		__ATTR_RW_MODE(complement, 0600);
+
 static struct kobj_attribute damos_sysfs_quota_goal_target_value_attr =
 		__ATTR_RW_MODE(target_value, 0600);
 
@@ -1438,6 +1466,7 @@ static struct kobj_attribute damos_sysfs_quota_goal_path_attr =
 
 static struct attribute *damos_sysfs_quota_goal_attrs[] = {
 	&damos_sysfs_quota_goal_target_metric_attr.attr,
+	&damos_sysfs_quota_goal_complement_attr.attr,
 	&damos_sysfs_quota_goal_target_value_attr.attr,
 	&damos_sysfs_quota_goal_current_value_attr.attr,
 	&damos_sysfs_quota_goal_nid_attr.attr,
@@ -2869,7 +2898,8 @@ static int damos_sysfs_add_quota_score(
 		if (!sysfs_goal->target_value)
 			continue;
 
-		goal = damos_new_quota_goal(sysfs_goal->metric, false,
+		goal = damos_new_quota_goal(sysfs_goal->metric,
+				sysfs_goal->complement,
 				sysfs_goal->target_value);
 		if (!goal)
 			return -ENOMEM;
-- 
2.47.3

[RFC PATCH v4 4/7] mm/damon/tests/core-kunit: test quota_goal->complement commit

[SJ Park]

Extend existing DAMOS quota goal commit unit test to test the complement
flag.  Set the source complement flag and confirm the destination is
updated to the given input.

Signed-off-by: SJ Park <sj@kernel.org>
---
 mm/damon/tests/core-kunit.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h
index 20bba7421a40..6a13d9bd377c 100644
--- a/mm/damon/tests/core-kunit.h
+++ b/mm/damon/tests/core-kunit.h
@@ -819,6 +819,7 @@ static void damos_test_commit_quota_goal_for(struct kunit *test,
 	damos_commit_quota_goal(dst, src);
 
 	KUNIT_EXPECT_EQ(test, dst->metric, src->metric);
+	KUNIT_EXPECT_EQ(test, dst->complement, src->complement);
 	KUNIT_EXPECT_EQ(test, dst->target_value, src->target_value);
 	if (src->metric == DAMOS_QUOTA_USER_INPUT)
 		KUNIT_EXPECT_EQ(test, dst->current_value, src->current_value);
@@ -862,6 +863,7 @@ static void damos_test_commit_quota_goal(struct kunit *test)
 	damos_test_commit_quota_goal_for(test, &dst,
 			&(struct damos_quota_goal){
 			.metric = DAMOS_QUOTA_USER_INPUT,
+			.complement = true,
 			.target_value = 789,
 			.current_value = 12});
 	damos_test_commit_quota_goal_for(test, &dst,
-- 
2.47.3

[RFC PATCH v4 5/7] Docs/mm/damon/design: document damos quota goal complement flag

[SJ Park]

Update DAMON design document for the newly added damos quota goal metric
value complement flag.

Signed-off-by: SJ Park <sj@kernel.org>
---
 Documentation/mm/damon/design.rst | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/Documentation/mm/damon/design.rst b/Documentation/mm/damon/design.rst
index e82390e77a70..5cd651b1b7aa 100644
--- a/Documentation/mm/damon/design.rst
+++ b/Documentation/mm/damon/design.rst
@@ -702,10 +702,10 @@ There are two such tuning algorithms that users can select as they need.
   that the zero quota is a valid quota, and therefore ``qt_exceeds`` :ref:`stat
   <damon_design_damos_stat>` will keep increasing in this case.
 
-The goal can be specified with five parameters, namely ``target_metric``,
-``target_value``, ``current_value``, ``nid`` and ``path``.  The auto-tuning
-mechanism tries to make ``current_value`` of ``target_metric`` be same to
-``target_value``.
+The goal can be specified with six parameters, namely ``target_metric``,
+``complement``, ``target_value``, ``current_value``, ``nid`` and ``path``.  The
+auto-tuning mechanism tries to make ``current_value`` of ``complement``-ed
+``target_metric`` be same to ``target_value``.
 
 - ``user_input``: User-provided value.  Users could use any metric that they
   has interest in for the value.  Use space main workload's latency or
@@ -733,6 +733,13 @@ mechanism tries to make ``current_value`` of ``target_metric`` be same to
 - ``hugepage_mem_bp``: Total huge page to total used memory ratio in bp
   (1/10,000).
 
+``complement`` is a boolean parameter that determines whether to use
+complemented value of the target metric.  For example, if ``complement`` is set
+and target metric is ``active_mem_bp``, it is effectively same to
+``inactive_mem_bp``.  ``complement`` is no-op when the target metric type is
+``user_input``.  For the metric type, the user should be able to emit
+complemented metric values on their own.
+
 ``nid`` is optionally required for ``node_mem_used_bp``, ``node_mem_free_bp``,
 ``node_memcg_used_bp``, ``node_memcg_free_bp`` and ``node_eligible_mem_bp`` to
 point the specific NUMA node.
-- 
2.47.3

[RFC PATCH v4 6/7] Docs/admin-guide/mm/damon/usage: update for quota goal complement file

[SJ Park]

Update DAMON usage document for the newly added quota goal metric
complement sysfs file.

Signed-off-by: SJ Park <sj@kernel.org>
---
 Documentation/admin-guide/mm/damon/usage.rst | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/Documentation/admin-guide/mm/damon/usage.rst b/Documentation/admin-guide/mm/damon/usage.rst
index ba4725544856..3d43954c7046 100644
--- a/Documentation/admin-guide/mm/damon/usage.rst
+++ b/Documentation/admin-guide/mm/damon/usage.rst
@@ -98,7 +98,8 @@ comma (",").
     │ │ │ │ │ │ │     fail_charge_num,fail_charge_denom
     │ │ │ │ │ │ │ │ weights/sz_permil,nr_accesses_permil,age_permil
     │ │ │ │ │ │ │ │ :ref:`goals <sysfs_schemes_quota_goals>`/nr_goals
-    │ │ │ │ │ │ │ │ │ 0/target_metric,target_value,current_value,nid,path
+    │ │ │ │ │ │ │ │ │ 0/target_metric,complement,target_value,
+    │ │ │ │ │ │ │ │ │  current_value,nid,path
     │ │ │ │ │ │ │ :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,damon_target_idx,min,max
@@ -492,12 +493,12 @@ number (``N``) to the file creates the number of child directories named ``0``
 to ``N-1``.  Each directory represents each goal and current achievement.
 Among the multiple feedback, the best one is used.
 
-Each goal directory contains five files, namely ``target_metric``,
-``target_value``, ``current_value``, ``nid``, and ``path``.  Users can set and
-get the five parameters for the quota auto-tuning goals that specified on the
-:ref:`design doc <damon_design_damos_quotas_auto_tuning>` by writing to and
-reading from each of the files.  Because the kernel does not update
-``current_value``, reading it only makes sense when ``target_metric`` is
+Each goal directory contains six files, namely ``target_metric``,
+``complement``, ``target_value``, ``current_value``, ``nid``, and ``path``.
+Users can set and get the six parameters for the quota auto-tuning goals that
+specified on the :ref:`design doc <damon_design_damos_quotas_auto_tuning>` by
+writing to and reading from each of the files.  Because the kernel does not
+update ``current_value``, reading it only makes sense when ``target_metric`` is
 ``user_input``.  Note that users should further write
 ``commit_schemes_quota_goals`` to the ``state`` file of the :ref:`kdamond
 directory <sysfs_kdamond>` to pass the feedback to DAMON.
-- 
2.47.3

[RFC PATCH v4 7/7] Docs/ABI/damon: update for quota goal metric complement sysfs file

[SJ Park]

Update DAMON ABI document for the newly added damos quota goal metric
complement sysfs file.

Signed-off-by: SJ Park <sj@kernel.org>
---
 Documentation/ABI/testing/sysfs-kernel-mm-damon | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-kernel-mm-damon b/Documentation/ABI/testing/sysfs-kernel-mm-damon
index 55df688ea596..4acb2015c2f4 100644
--- a/Documentation/ABI/testing/sysfs-kernel-mm-damon
+++ b/Documentation/ABI/testing/sysfs-kernel-mm-damon
@@ -375,6 +375,12 @@ Contact:	SJ Park <sj@kernel.org>
 Description:	Writing to and reading from this file sets and gets the quota
 		auto-tuning goal metric.
 
+What:		/sys/kernel/mm/damon/admin/kdamonds/<K>/contexts/<C>/schemes/<S>/quotas/goals/<G>/complement
+Date:		Sep 2026
+Contact:	SJ Park <sj@kernel.org>
+Description:	Writing to and reading from this file sets and gets whether to
+		use the complement value of the quota auto-tuning goal metric.
+
 What:		/sys/kernel/mm/damon/admin/kdamonds/<K>/contexts/<C>/schemes/<S>/quotas/goals/<G>/target_value
 Date:		Nov 2023
 Contact:	SJ Park <sj@kernel.org>
-- 
2.47.3

[RFC PATCH v4 0/7] mm/damon: introduce damos quota goal target metric complement flag (was: "Re: [RFC PATCH v4 0/7] snapshot_set_swap_area() unpins the previously selected swap device and")

[SJ Park]

On Sun, 27 Sep 2026 05:05:24 -0700 SJ Park <sj@kernel.org> wrote:

> Add repin_hibernation_swap_type(), which looks up the new device, clears
> the old SWP_HIBERNATION flag and sets the new one under a single swap_lock
> acquisition.  The same-device case is short- circuited so userspace can
> re-select the same swap area without tripping WARN_ON_ONCE and -EBUSY. 
> Switch snapshot_set_swap_area() to the new helper.
[...]

Oops, this cover letter is completely wrong...  Please ignore.  My tool was
using the commit message of unrelated commit due to my mistake.  I'm so sorry
for the noise.

Attaching the correct cover letter below.


Thanks,
SJ

=== >8 ===
mm/damon: introduce damos quota goal target metric complement flag

Aim-oriented DAMOS quota auto-tuning assumes the aggressiveness of the
scheme (quota) and the quota goal metric are directly proportional.
Depending on the scheme setup and usage, keeping the relationship can be
challenging.

For example, let's suppose a memory tiering approach for higher upper
tier utilization.  One common idea for that (TPP) is utilizing two
schemes, one for promotion and the other one for demotion.  The
promotion scheme migrates hot pages from lower tier to upper tier,
aiming for high utilization of the upper tier.  The demotion scheme
migrates cold pages from upper tier to lower tier, aiming for head room
free memory of the upper tier.  Both schemes and their goals are in
direct proportion.  However, for this kind of use case, we need to
implement two different goal metrics (per-node memory utilization and
free memory ratio) while essentially the free memory ratio is just a
complemented value of the utilization.

To avoid adding too many new metrics, we are adding metrics that turn
out to be really needed for each found use case.  For example,
some_mem_psi_us, node_eligible_mem_bp and hugepage_mem_bp don't have
their complemented value version.  But it is not really difficult to
expect use cases that their complemented version can be useful.  For
example, hugepage_mem_bp use case may need a way to reduce the hugepage
ratio.  That would require a complemented version of hugepage_mem_bp.
Adding a new metric for each of such use cases could make the number of
metrics unnecessarily high, and discourage flexible usages of DAMOS.

Add a new flag, quota goal complement, to allow flexible tuning goal
setup without unnecessarily increasing the number of metrics.  The flag
specifies whether to use the complemented value of the given goal metric
for the tuning.  For example, if the complement flag is set, the upper
tier memory utilization ratio metric works the same as the free memory
ratio metric for the tier.

Note: Below is additional information that is not intended to be added
to the final commit message.

Test
====

I tested this feature using the latest version of DAMON user-space tool,
damo [1], as below.

On an idle system having 10 GiB single node memory (node id 0), fill up
80% of memory with page cache.

    $ dd if=/dev/zero of=foo bs=1M count=$((1024*8))

Run DAMOS with pageout action for 80% of free memory, but using
node_mem_used_bp metric like below.

    $ sudo ./damo start --damos_action pageout \
            --damos_quota_space 100M --damos_quota_interval 1s \
            --damos_quota_fail_charge_ratio 1 4096 \
            --damos_quota_goal_tuner temporal \
            --damos_quota_goal node_mem_used_bp 20% 0

Because the system has more than 20% node 0 memory utilization, DAMOS
does nothing, as expected.

Run DAMOS with pageout action for 80% of free memory, using
node_mem_used_bp metrics with complement flag like below.

    $ sudo ./damo start --damos_action pageout \
            --damos_quota_space 100M --damos_quota_interval 1s \
            --damos_quota_fail_charge_ratio 1 4096 \
            --damos_quota_goal_tuner temporal \
            --damos_quota_goal node_mem_used_bp 80% complement 0

Because the complement flag is given, it is effectively the same as
node_mem_freepbp metrics with a target of 80%.  DAMOS reclaims the page
cache ~100 MiB per second, until the free memory ratio (complemented
memory utilization ratio) reaches the goal, 80%.

Changes from RFC v4
- RFC v4: https://lore.kernel.org/20260927120533.50484-1-sj@kernel.org
- Fix a typo in test code (s/complementfalse/complement/)
Changes from RFC v3
- RFC v3: https://lore.kernel.org/20260923101454.5748-1-sj@kernel.org
- Rebase to the latest mm-new.
- Add tests done to the cover letter.
Changes from RFC v2
- RFC v2: https://lore.kernel.org/20260919011359.88921-1-sj@kernel.org
- Avoid quota goal value underflow for some_mem_psi.
- Handle complement flag for psi goal with unset last_psi_total.
- Pass complement argument to damos_new_quota_goal() from core and
  core-kunit.
- Explicitly document no-op complement behavior for user_input.
Changes from RFC
- RFC: https://lore.kernel.org/20260918142827.85303-1-sj@kernel.org
- Avoid quota goal value underflow.
- Fix usage doc for number of files in each goal directory.
- Rebase to the latest mm-new.

[1] https://github.com/damonitor/damo