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mm/damon/stat: add kdamond_pid parameter

RFC PATCH In review SeongJae Park 2 participants 5 messages Apr 30 – May 1

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Memory management Documentation MM misc DAMON
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SeongJae Park

author maintainer
#0 lore raw

cover mm/damon/stat: add kdamond_pid parameter

DAMON_STAT doesn't provide the pid of its kdamond, unlike DAMON_RECLAIM and DAMON_LRU_SORT. This makes user-space management of DAMON_STAT unnecessarily complicated. Provide the information via a new parameter, namely kdamond_pid, and document it.

Changes from RFC v2
- v2: https://lore.kernel.org/[email protected]
- Rebase to latest mm-new.
Changes from RFC v1.2
- rfc v1.2: https://lore.kernel.org/[email protected]
- Detect and use fresh kdamond pid.
Changes from RFC v1.1
- rfc v1.1: https://lore.kernel.org/[email protected]
- Close the parentheses of error handling block.
Changes from RFC
- rfc: https://lore.kernel.org/[email protected]
- Fix damon_kdamond_pid() failure handling.

SeongJae Park (2):
mm/damon/stat: add a parameter for reading kdamond pid Docs/admin-guide/mm/damon/stat: document kdamond_pid parameter

 Documentation/admin-guide/mm/damon/stat.rst |  7 ++++
 mm/damon/stat.c                             | 38 +++++++++++++++++++++
 2 files changed, 45 insertions(+)

base-commit: b8e00b62c650b2aa471195f663301118fde889c2

Signature · 1 line
2.47.3
author maintainer
#1 lore raw

RFC PATCH 1/2 mm/damon/stat: add a parameter for reading kdamond pid

Knowing the pid of the kdamonds can help user-space management including monitoring of DAMON's system resource consumption. To make it easier, DAMON_SYSFS, DAMON_RECLAIM and DAMON_LRU_SORT provide the pid information. DAMON_STAT is not providing it, though. Expose the pid of DAMON_STAT kdamond via a new read-only module parameter, namely kdamond_pid. This also makes DAMON modules usage more standardized, because DAMON_RECLAIM and DAMON_LRU_SORT also provide the information via their read-only parameters of the same name.

Signed-off-by SeongJae Park <[email protected]>
---
 mm/damon/stat.c | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)
mm/damon/stat.c +38 -0
index f4d3203e92639..37964683839d0 100644
@@ -266,6 +266,44 @@ static int damon_stat_enabled_load(char *buffer, const struct kernel_param *kp)
 	return sprintf(buffer, "%c\n", damon_stat_enabled() ? 'Y' : 'N');
 }
 
+static int damon_stat_kdamond_pid_store(
+		const char *val, const struct kernel_param *kp)
+{
+	/*
+	 * kdamond_pid is read-only, but kernel command line could write it.
+	 * Do nothing here.
+	 */
+	return 0;
+}
+
+static int damon_stat_kdamond_pid_load(
+		char *buffer, const struct kernel_param *kp)
+{
+	int pid;
+
+	if (!damon_stat_context) {
+		pid = -1;
+	} else {
+		pid = damon_kdamond_pid(damon_stat_context);
+		if (pid < 1)
+			pid = -1;
+	}
+	return sprintf(buffer, "%d\n", pid);
+}
+
+static const struct kernel_param_ops kdamond_pid_param_ops = {
+	.set = damon_stat_kdamond_pid_store,
+	.get = damon_stat_kdamond_pid_load,
+};
+
+/*
+ * PID of the DAMON thread
+ *
+ * If DAMON_STAT is enabled, this becomes the PID of the worker thread.
+ * Else, -1.
+ */
+module_param_cb(kdamond_pid, &kdamond_pid_param_ops, NULL, 0400);
+
 static int __init damon_stat_init(void)
 {
 	int err = 0;
Signature · 1 line
2.47.3
AI review
#2 lore raw

Re: [RFC PATCH v2.1 1/2] mm/damon/stat: add a parameter for reading kdamond pid

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider: - [Low] The newly added `kdamond_pid` module parameter lacks a `MODULE_PARM_DESC` declaration. --

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] The newly added kdamond_pid module parameter lacks a MODULE_PARM_DESC declaration. --

commit d56734720ba3e7838cd85a1ac6661cf5e54d9a3b
Author: SeongJae Park <[email protected]>

mm/damon/stat: add a parameter for reading kdamond pid

Expose the pid of DAMON_STAT kdamond via a new read-only module parameter named kdamond_pid. This standardizes DAMON module usage, as DAMON_RECLAIM and DAMON_LRU_SORT also provide this information.

Quoted 4 lines
mm/damon/stat.c +0 -0
index f4d3203e92639..37964683839d0 100644

[ ... ]

mm/damon/stat.c static int damon_stat_enabled_load(char *buffer, const struct kernel_param *kp) · line 305

Quoted 12 lines
mm/damon/stat.c +12 -0
+static const struct kernel_param_ops kdamond_pid_param_ops = {
+	.set = damon_stat_kdamond_pid_store,
+	.get = damon_stat_kdamond_pid_load,
+};
+
+/*
+ * PID of the DAMON thread
+ *
+ * If DAMON_STAT is enabled, this becomes the PID of the worker thread.
+ * Else, -1.
+ */
+module_param_cb(kdamond_pid, &kdamond_pid_param_ops, NULL, 0400);

This isn't a bug, but should this module parameter include a MODULE_PARM_DESC() declaration?

Other parameters in mm/damon/stat.c like enabled, estimated_memory_bandwidth, and memory_idle_ms_percentiles have corresponding MODULE_PARM_DESC() declarations.

Quoted 4 lines
mm/damon/stat.c +1 -0
+
 static int __init damon_stat_init(void)
 {
 	int err = 0;
Signature · 1 line
Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=1
author maintainer
#3 lore raw

Re: [RFC PATCH v2.1 1/2] mm/damon/stat: add a parameter for reading kdamond pid

Quoted 34 lines · On Thu, 30 Apr 2026 15:14:18 +0000 [email protected] wrote:

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] The newly added kdamond_pid module parameter lacks a MODULE_PARM_DESC declaration. --

commit d56734720ba3e7838cd85a1ac6661cf5e54d9a3b
Author: SeongJae Park <[email protected]>

mm/damon/stat: add a parameter for reading kdamond pid

Expose the pid of DAMON_STAT kdamond via a new read-only module parameter named kdamond_pid. This standardizes DAMON module usage, as DAMON_RECLAIM and DAMON_LRU_SORT also provide this information.

Quoted 4 lines
mm/damon/stat.c +0 -0
index f4d3203e92639..37964683839d0 100644

[ ... ]

mm/damon/stat.c static int damon_stat_enabled_load(char *buffer, const struct kernel_param *kp) · line 305

Quoted 12 lines
mm/damon/stat.c +12 -0
+static const struct kernel_param_ops kdamond_pid_param_ops = {
+	.set = damon_stat_kdamond_pid_store,
+	.get = damon_stat_kdamond_pid_load,
+};
+
+/*
+ * PID of the DAMON thread
+ *
+ * If DAMON_STAT is enabled, this becomes the PID of the worker thread.
+ * Else, -1.
+ */
+module_param_cb(kdamond_pid, &kdamond_pid_param_ops, NULL, 0400);

This isn't a bug, but should this module parameter include a MODULE_PARM_DESC() declaration?

Quoted 3 lines

Other parameters in mm/damon/stat.c like enabled, estimated_memory_bandwidth, and memory_idle_ms_percentiles have corresponding MODULE_PARM_DESC() declarations.

Good finding, I will add that.

Thanks,
SJ

[...]

author maintainer
#4 lore raw

RFC PATCH 2/2 Docs/admin-guide/mm/damon/stat: document kdamond_pid parameter

In reply to SeongJae Park

Update DAMON_STAT usage document for newly added kdamond_pid parameter.

Signed-off-by SeongJae Park <[email protected]>
---
 Documentation/admin-guide/mm/damon/stat.rst | 7 +++++++
 1 file changed, 7 insertions(+)
Documentation/admin-guide/mm/damon/stat.rst +7 -0
index c4b14daeb2dd6..46c5dd96aa2ed 100644
@@ -89,3 +89,10 @@ percentiles of the idle time values via this read-only parameter.  Reading the
 parameter returns 101 idle time values in milliseconds, separated by comma.
 Each value represents 0-th, 1st, 2nd, 3rd, ..., 99th and 100th percentile idle
 times.
+
+kdamond_pid
+-----------
+
+PID of the DAMON thread.
+
+If DAMON_STAT is enabled, this becomes the PID of the worker thread.  Else, -1.
Signature · 1 line
2.47.3