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

RFC PATCH In review SJ Park 2 participants 19 messages Sep 28

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SJ Park

author maintainer
#0 lore raw

v5 cover 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.

Patches Sequence
================

Patch 1 introduces the quota goal complement flag API and implements its behavior. Patch 2 updates damos_new_quota_goal() to receive the flag. Patch 3 update DAMON sysfs interface to support the complement flag. Patches 4 and 5 extend existing kunit and kselftest to cover the new flag. Patches 6-8 update design, usage and ABI documents for the new feature.

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/[email protected]
- Fix a typo in test code (s/complementfalse/complement/).
- Extend sysfs.sh DAMON selftest for complement flag sysfs file. Changes from RFC v3
- RFC v3: https://lore.kernel.org/[email protected]
- Rebase to the latest mm-new.
- Add tests done to the cover letter.
Changes from RFC v2
- RFC v2: https://lore.kernel.org/[email protected]
- 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/[email protected]
- 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

SJ Park (8):
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 selftests/damon/sysfs.sh: test quota goal complement flag file 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 +-
 tools/testing/selftests/damon/sysfs.sh        |  3 ++
 11 files changed, 100 insertions(+), 21 deletions(-)

base-commit: f3528689602b1d578d582cb060e89fa25516fd67

Signature · 1 line
2.47.3
author maintainer
#1 lore raw

RFC PATCH v5 1/8 mm/damon/core: introduce damos_quota_goal->complement

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 <[email protected]>
---
 include/linux/damon.h |  2 ++
 mm/damon/core.c       | 26 +++++++++++++++++++++++++-
 2 files changed, 27 insertions(+), 1 deletion(-)
include/linux/damon.h +2 -0
index 844b175120f0..78b227875287 100644
@@ -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 */
mm/damon/core.c +25 -1
index 733025b36745..270ce9c85a2c 100644
@@ -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 */
Signature · 1 line
2.47.3
AI review
#2 lore raw

Re: [RFC PATCH v5 1/8] mm/damon/core: introduce damos_quota_goal->complement

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider: - [Low] mm/damon: integer overflow in damos_set_psi_current_val on 32-bit systems --

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] mm/damon: integer overflow in damos_set_psi_current_val on 32-bit systems --

commit 2c98b9664c0f8cdd559874386842cae96a9ea8cb
Author: SJ Park <[email protected]> mm/damon/core: introduce damos_quota_goal->complement

This commit introduces the complement flag to damos_quota_goal, allowing the system to use the complemented value of a target metric. It adds the field to the data structure and implements support for it during quota goal commits and metric value retrievals.

Quoted 4 lines
mm/damon/core.c +0 -0
index 733025b367457..270ce9c85a2ce 100644

[ ... ]

mm/damon/core.c static void damos_set_psi_current_val(u64 now_psi_total, · line 2971

Quoted 13 lines
mm/damon/core.c +5 -1
@@ -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;

[Severity: Low]
Does this multiplication risk an integer overflow on 32-bit systems?

On 32-bit systems, unsigned long is 32 bits, with a maximum value of ~4.29 billion. If a user configures reset_interval via sysfs to a value larger than 4,294,967 (about 71.5 minutes), the multiplication s->quota.reset_interval * 1000 will overflow unsigned long.

This causes the auto-tuning goal complement metric to evaluate with a truncated, incorrect value. While 32-bit systems running DAMON with 71+ minute intervals are extremely rare, could this cause unexpected behavior when long intervals are configured?

Quoted 6 lines
mm/damon/core.c +4 -0
+			else
+				val = 0;
+		}
+		goal->current_value = val;
 		return;
 	}
Signature · 1 line
Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=1
author maintainer
#3 lore raw

Re: [RFC PATCH v5 1/8] mm/damon/core: introduce damos_quota_goal->complement

Quoted 42 lines · On Mon, 28 Sep 2026 09:44:40 +0000 [email protected] wrote:

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] mm/damon: integer overflow in damos_set_psi_current_val on 32-bit systems --

commit 2c98b9664c0f8cdd559874386842cae96a9ea8cb
Author: SJ Park <[email protected]> mm/damon/core: introduce damos_quota_goal->complement

This commit introduces the complement flag to damos_quota_goal, allowing the system to use the complemented value of a target metric. It adds the field to the data structure and implements support for it during quota goal commits and metric value retrievals.

Quoted 4 lines
mm/damon/core.c +0 -0
index 733025b367457..270ce9c85a2ce 100644

[ ... ]

mm/damon/core.c static void damos_set_psi_current_val(u64 now_psi_total, · line 2971

Quoted 13 lines
mm/damon/core.c +5 -1
@@ -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;

[Severity: Low]
Does this multiplication risk an integer overflow on 32-bit systems?

On 32-bit systems, unsigned long is 32 bits, with a maximum value of ~4.29 billion. If a user configures reset_interval via sysfs to a value larger than 4,294,967 (about 71.5 minutes), the multiplication s->quota.reset_interval * 1000 will overflow unsigned long.

Quoted 4 lines

This causes the auto-tuning goal complement metric to evaluate with a truncated, incorrect value. While 32-bit systems running DAMON with 71+ minute intervals are extremely rare, could this cause unexpected behavior when long intervals are configured?

Yes, that's extremely rare. Also sane users would use the new feature after testing. Not a blocker of this series in my opinion.

Quoted 11 lines
Quoted 7 lines
mm/damon/core.c +4 -0
+			else
+				val = 0;
+		}
+		goal->current_value = val;
 		return;
 	}
Signature · 1 line
Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=1

Thanks,
SJ

author maintainer
#4 lore raw

RFC PATCH v5 2/8 mm/damon/core: add complement argument to damos_new_quota_goal()

In reply to 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 <[email protected]>
---
 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(-)
include/linux/damon.h +1 -1
index 78b227875287..b310c40d6ceb 100644
@@ -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);
mm/damon/core.c +4 -3
index 270ce9c85a2c..86f13411b91f 100644
@@ -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);
mm/damon/lru_sort.c +3 -2
index 273efa3c913e..64e086985eb5 100644
@@ -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;
mm/damon/reclaim.c +3 -2
index 42a2c9cb1343..014b0779ea6d 100644
@@ -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;
mm/damon/sysfs-schemes.c +1 -1
index bfb6f0bc3f21..06af417bc9a2 100644
@@ -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;
mm/damon/tests/core-kunit.h +1 -0
index df84d9cc7d20..945037fe4be9 100644
@@ -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].complement,
 				dst_goals[i].target_value);
 		if (!goal)
 			goto out;
samples/damon/mtier.c +1 -1
index 27dc88bdf7a0..a2e311082cd4 100644
@@ -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;
Signature · 1 line
2.47.3
AI review
#5 lore raw

Re: [RFC PATCH v5 2/8] mm/damon/core: add complement argument to damos_new_quota_goal()

Sashiko has reviewed this patch and found no issues. It looks great!
Quoted 6 lines

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 <[email protected]>

Sashiko has reviewed this patch and found no issues. It looks great!

Signature · 1 line
Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=2
author maintainer
#6 lore raw

RFC PATCH v5 3/8 mm/damon/sysfs-schemes: support quota goal complement flag

In reply to 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 <[email protected]>
---
 mm/damon/sysfs-schemes.c | 32 +++++++++++++++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)
mm/damon/sysfs-schemes.c +31 -1
index 06af417bc9a2..8f083611741f 100644
@@ -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;
Signature · 1 line
2.47.3
AI review
#7 lore raw

Re: [RFC PATCH v5 3/8] mm/damon/sysfs-schemes: support quota goal complement flag

Sashiko has reviewed this patch and found no issues. It looks great!
Quoted 5 lines

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 <[email protected]>

Sashiko has reviewed this patch and found no issues. It looks great!

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author maintainer
#8 lore raw

RFC PATCH v5 4/8 mm/damon/tests/core-kunit: test quota_goal->complement commit

In reply to 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 <[email protected]>
---
 mm/damon/tests/core-kunit.h | 2 ++
 1 file changed, 2 insertions(+)
mm/damon/tests/core-kunit.h +2 -0
index 945037fe4be9..251b300eaa50 100644
@@ -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,
Signature · 1 line
2.47.3
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#9 lore raw

Re: [RFC PATCH v5 4/8] mm/damon/tests/core-kunit: test quota_goal->complement commit

Sashiko has reviewed this patch and found no issues. It looks great!
Quoted 5 lines

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 <[email protected]>

Sashiko has reviewed this patch and found no issues. It looks great!

Signature · 1 line
Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=4
author maintainer
#10 lore raw

RFC PATCH v5 5/8 selftests/damon/sysfs.sh: test quota goal complement flag file

In reply to SJ Park

Test the existence and the valid input acceptance of the newly added quota goal complement flag sysfs file.

Signed-off-by SJ Park <[email protected]>
---
 tools/testing/selftests/damon/sysfs.sh | 3 +++
 1 file changed, 3 insertions(+)
tools/testing/selftests/damon/sysfs.sh +3 -0
index b66593c9ac47..1cc7ab2d7e22 100755
@@ -212,6 +212,9 @@ test_goal()
 	ensure_write_succ "$fpath" "node_eligible_mem_bp" "valid input"
 	ensure_write_succ "$fpath" "hugepage_mem_bp" "valid input"
 	ensure_write_fail "$fpath" "foo" "invalid input"
+	ensure_file "$goal_dir/complement" "exist" "600"
+	ensure_write_succ "$goal_dir/complement" "Y" "valid input"
+	ensure_write_succ "$goal_dir/complement" "N" "valid input"
 	ensure_file "$goal_dir/nid" "exist" "600"
 	ensure_file "$goal_dir/path" "exist" "600"
 }
Signature · 1 line
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#11 lore raw

Re: [RFC PATCH v5 5/8] selftests/damon/sysfs.sh: test quota goal complement flag file

Sashiko has reviewed this patch and found no issues. It looks great!
Quoted 4 lines

Test the existence and the valid input acceptance of the newly added quota goal complement flag sysfs file.

Signed-off-by SJ Park <[email protected]>

Sashiko has reviewed this patch and found no issues. It looks great!

Signature · 1 line
Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=5
author maintainer
#12 lore raw

RFC PATCH v5 6/8 Docs/mm/damon/design: document damos quota goal complement flag

In reply to SJ Park

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

Signed-off-by SJ Park <[email protected]>
---
 Documentation/mm/damon/design.rst | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)
Documentation/mm/damon/design.rst +11 -4
index e82390e77a70..5cd651b1b7aa 100644
@@ -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.
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2.47.3
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#13 lore raw

Re: [RFC PATCH v5 6/8] Docs/mm/damon/design: document damos quota goal complement flag

Sashiko has reviewed this patch and found no issues. It looks great!
Quoted 4 lines

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

Signed-off-by SJ Park <[email protected]>

Sashiko has reviewed this patch and found no issues. It looks great!

Signature · 1 line
Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=6
author maintainer
#14 lore raw

RFC PATCH v5 7/8 Docs/admin-guide/mm/damon/usage: update for quota goal complement file

In reply to SJ Park

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

Signed-off-by SJ Park <[email protected]>
---
 Documentation/admin-guide/mm/damon/usage.rst | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)
Documentation/admin-guide/mm/damon/usage.rst +8 -7
index ba4725544856..3d43954c7046 100644
@@ -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.
Signature · 1 line
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#15 lore raw

Re: [RFC PATCH v5 7/8] Docs/admin-guide/mm/damon/usage: update for quota goal complement file

Sashiko has reviewed this patch and found no issues. It looks great!
Quoted 4 lines

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

Signed-off-by SJ Park <[email protected]>

Sashiko has reviewed this patch and found no issues. It looks great!

Signature · 1 line
Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=7
author maintainer
#16 lore raw

RFC PATCH v5 8/8 Docs/ABI/damon: update for quota goal metric complement sysfs file

In reply to SJ Park

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

Signed-off-by SJ Park <[email protected]>
---
 Documentation/ABI/testing/sysfs-kernel-mm-damon | 6 ++++++
 1 file changed, 6 insertions(+)
Documentation/ABI/testing/sysfs-kernel-mm-damon +6 -0
index 55df688ea596..4acb2015c2f4 100644
@@ -375,6 +375,12 @@ Contact:	SJ Park <[email protected]>
 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 <[email protected]>
+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 <[email protected]>
Signature · 1 line
2.47.3
AI review
#17 lore raw

Re: [RFC PATCH v5 8/8] Docs/ABI/damon: update for quota goal metric complement sysfs file

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider: - [Medium] mm: integer overflow in damos_set_psi_current_val() on 32-bit --

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] mm: integer overflow in damos_set_psi_current_val() on 32-bit
--

commit 5d7327c0afcb5fe144677a675b1eea685917f61e
Author: SJ Park <[email protected]>
Docs/ABI/damon: update for quota goal metric complement sysfs file

This commit introduces a complement flag for the quota auto-tuning goal metric and updates the sysfs ABI documentation to reflect this addition. It also modifies the core DAMON tuning logic to support the complement calculation.

Quoted 4 lines
mm/damon/core.c +0 -0
index 733025b367457..86f13411b91fa 100644

[ ... ]

mm/damon/core.c static void damos_set_psi_current_val(u64 now_psi_total, · line 2972

Quoted 13 lines
mm/damon/core.c +5 -1
@@ -2960,10 +2962,18 @@ 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;

[Severity: Medium]
Could this multiplication in mm/damon/core.c:damos_set_psi_current_val() overflow on 32-bit systems? If reset_interval is configured to a value greater than 4,294,967 (about 71 minutes) via sysfs, s->quota.reset_interval * 1000 will exceed the maximum value of a 32-bit unsigned long.

This could cause the complement calculation to yield corrupted values or premature zeros, breaking the auto-tuning logic.

Quoted 7 lines
mm/damon/core.c +4 -0
+			else
+				val = 0;
+		}
+		goal->current_value = val;
 		return;
 	}
 	/* uninitialized last_psi_total; make no effect this round */
Signature · 1 line
Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=8
author maintainer
#18 lore raw

Re: [RFC PATCH v5 8/8] Docs/ABI/damon: update for quota goal metric complement sysfs file

Quoted 40 lines · On Mon, 28 Sep 2026 09:43:59 +0000 [email protected] wrote:

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] mm: integer overflow in damos_set_psi_current_val() on 32-bit
--

commit 5d7327c0afcb5fe144677a675b1eea685917f61e
Author: SJ Park <[email protected]>
Docs/ABI/damon: update for quota goal metric complement sysfs file

This commit introduces a complement flag for the quota auto-tuning goal metric and updates the sysfs ABI documentation to reflect this addition. It also modifies the core DAMON tuning logic to support the complement calculation.

Quoted 4 lines
mm/damon/core.c +0 -0
index 733025b367457..86f13411b91fa 100644

[ ... ]

mm/damon/core.c static void damos_set_psi_current_val(u64 now_psi_total, · line 2972

Quoted 13 lines
mm/damon/core.c +5 -1
@@ -2960,10 +2962,18 @@ 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;

[Severity: Medium]
Could this multiplication in mm/damon/core.c:damos_set_psi_current_val() overflow on 32-bit systems? If reset_interval is configured to a value greater than 4,294,967 (about 71 minutes) via sysfs, s->quota.reset_interval * 1000 will exceed the maximum value of a 32-bit unsigned long.

Quoted 2 lines

This could cause the complement calculation to yield corrupted values or premature zeros, breaking the auto-tuning logic.

It is an extreme setup. Also, sane users would test it before using the new feature. No blocker of this series in my opinion.

Quoted 12 lines
Quoted 8 lines
mm/damon/core.c +4 -0
+			else
+				val = 0;
+		}
+		goal->current_value = val;
 		return;
 	}
 	/* uninitialized last_psi_total; make no effect this round */
Signature · 1 line
Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=8

Thanks,
SJ