[RFC PATCH V3 12/17] sysfs: Add sysfs support to tune scanning

Raghavendra K T
2025-08-14T15:35:49Z

Support below tunables:
scan_enable: turn on or turn off mm_struct scanning
scan_period: initial scan_period (default: 2sec)
scan_sleep_ms: sleep time between two successive round of scanning and
migration.
mms_to_scan: total mm_struct to scan before taking a pause.
target_node: default regular node to which migration of accessed pages
is done (this is only fall back mechnism, otherwise target_node
heuristic is used).

Signed-off-by: Raghavendra K T <raghavendra.kt@amd.com>
---
mm/kscand.c | 205 ++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 205 insertions(+)

diff --git a/mm/kscand.c b/mm/kscand.c
index 41321d373be7..a73606f7ca3c 100644
--- a/mm/kscand.c
+++ b/mm/kscand.c
@@ -21,6 +21,7 @@
#include <linux/delay.h>
#include <linux/cleanup.h>
#include <linux/minmax.h>
+#include <trace/events/kmem.h>

#include <asm/pgalloc.h>
#include "internal.h"
@@ -173,6 +174,171 @@ static bool kscand_eligible_srcnid(int nid)
return !node_is_toptier(nid);
}

+#ifdef CONFIG_SYSFS
+static ssize_t scan_sleep_ms_show(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ char *buf)
+{
+ return sysfs_emit(buf, "%u\n", kscand_scan_sleep_ms);
+}
+
+static ssize_t scan_sleep_ms_store(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ const char *buf, size_t count)
+{
+ unsigned int msecs;
+ int err;
+
+ err = kstrtouint(buf, 10, &msecs);
+ if (err)
+ return -EINVAL;
+
+ kscand_scan_sleep_ms = msecs;
+ kscand_sleep_expire = 0;
+ wake_up_interruptible(&kscand_wait);
+
+ return count;
+}
+
+static struct kobj_attribute scan_sleep_ms_attr =
+ __ATTR_RW(scan_sleep_ms);
+
+static ssize_t mm_scan_period_ms_show(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ char *buf)
+{
+ return sysfs_emit(buf, "%u\n", kscand_mm_scan_period_ms);
+}
+
+/* If a value less than MIN or greater than MAX asked for store value is clamped */
+static ssize_t mm_scan_period_ms_store(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ const char *buf, size_t count)
+{
+ unsigned int msecs, stored_msecs;
+ int err;
+
+ err = kstrtouint(buf, 10, &msecs);
+ if (err)
+ return -EINVAL;
+
+ stored_msecs = clamp(msecs, KSCAND_SCAN_PERIOD_MIN, KSCAND_SCAN_PERIOD_MAX);
+
+ kscand_mm_scan_period_ms = stored_msecs;
+ kscand_sleep_expire = 0;
+ wake_up_interruptible(&kscand_wait);
+
+ return count;
+}
+
+static struct kobj_attribute mm_scan_period_ms_attr =
+ __ATTR_RW(mm_scan_period_ms);
+
+static ssize_t mms_to_scan_show(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ char *buf)
+{
+ return sysfs_emit(buf, "%lu\n", kscand_mms_to_scan);
+}
+
+static ssize_t mms_to_scan_store(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ const char *buf, size_t count)
+{
+ unsigned long val;
+ int err;
+
+ err = kstrtoul(buf, 10, &val);
+ if (err)
+ return -EINVAL;
+
+ kscand_mms_to_scan = val;
+ kscand_sleep_expire = 0;
+ wake_up_interruptible(&kscand_wait);
+
+ return count;
+}
+
+static struct kobj_attribute mms_to_scan_attr =
+ __ATTR_RW(mms_to_scan);
+
+static ssize_t scan_enabled_show(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ char *buf)
+{
+ return sysfs_emit(buf, "%u\n", kscand_scan_enabled ? 1 : 0);
+}
+
+static ssize_t scan_enabled_store(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ const char *buf, size_t count)
+{
+ unsigned int val;
+ int err;
+
+ err = kstrtouint(buf, 10, &val);
+ if (err || val > 1)
+ return -EINVAL;
+
+ if (val) {
+ kscand_scan_enabled = true;
+ need_wakeup = true;
+ } else
+ kscand_scan_enabled = false;
+
+ kscand_sleep_expire = 0;
+ wake_up_interruptible(&kscand_wait);
+
+ return count;
+}
+
+static struct kobj_attribute scan_enabled_attr =
+ __ATTR_RW(scan_enabled);
+
+static ssize_t target_node_show(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ char *buf)
+{
+ return sysfs_emit(buf, "%u\n", kscand_target_node);
+}
+
+static ssize_t target_node_store(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ const char *buf, size_t count)
+{
+ int err, node;
+
+ err = kstrtoint(buf, 10, &node);
+ if (err)
+ return -EINVAL;
+
+ kscand_sleep_expire = 0;
+ if (!node_is_toptier(node))
+ return -EINVAL;
+
+ kscand_target_node = node;
+ wake_up_interruptible(&kscand_wait);
+
+ return count;
+}
+static struct kobj_attribute target_node_attr =
+ __ATTR_RW(target_node);
+
+static struct attribute *kscand_attr[] = {
+ &scan_sleep_ms_attr.attr,
+ &mm_scan_period_ms_attr.attr,
+ &mms_to_scan_attr.attr,
+ &scan_enabled_attr.attr,
+ &target_node_attr.attr,
+ NULL,
+};
+
+struct attribute_group kscand_attr_group = {
+ .attrs = kscand_attr,
+ .name = "kscand",
+};
+#endif
+
static inline int kscand_has_work(void)
{
return !list_empty(&kscand_scan.mm_head);
@@ -1231,11 +1397,45 @@ static int kscand(void *none)
return 0;
}

+#ifdef CONFIG_SYSFS
+extern struct kobject *mm_kobj;
+static int __init kscand_init_sysfs(struct kobject **kobj)
+{
+ int err;
+
+ err = sysfs_create_group(*kobj, &kscand_attr_group);
+ if (err) {
+ pr_err("failed to register kscand group\n");
+ goto err_kscand_attr;
+ }
+
+ return 0;
+
+err_kscand_attr:
+ sysfs_remove_group(*kobj, &kscand_attr_group);
+ return err;
+}
+
+static void __init kscand_exit_sysfs(struct kobject *kobj)
+{
+ sysfs_remove_group(kobj, &kscand_attr_group);
+}
+#else
+static inline int __init kscand_init_sysfs(struct kobject **kobj)
+{
+ return 0;
+}
+static inline void __init kscand_exit_sysfs(struct kobject *kobj)
+{
+}
+#endif
+
static inline void kscand_destroy(void)
{
kmem_cache_destroy(kscand_slot_cache);
/* XXX: move below to kmigrated thread */
kmem_cache_destroy(kmigrated_slot_cache);
+ kscand_exit_sysfs(mm_kobj);
}

void __kscand_enter(struct mm_struct *mm)
@@ -1421,6 +1621,10 @@ static int __init kscand_init(void)
return -ENOMEM;
}

+ err = kscand_init_sysfs(&mm_kobj);
+ if (err)
+ goto err_init_sysfs;
+
init_list();
err = start_kscand();
if (err)
@@ -1437,6 +1641,7 @@ static int __init kscand_init(void)

err_kscand:
stop_kscand();
+err_init_sysfs:
kscand_destroy();

return err;
--
2.34.1