Implement a sysfs file to expose addr_unit for DAMON_LRU_SORT
users. During parameter application, use the configured
addr_unit parameter to perform the necessary initialization.
Similar to the core layer, prevent setting addr_unit to zero.

It is worth noting that when monitor_region_start and
monitor_region_end are unset (i.e., 0), their values will
later be set to biggest_system_ram. At that point, addr_unit
may not be the default value 1. Although we could divide the
biggest_system_ram value by addr_unit, changing addr_unit
without setting monitor_region_start/end should be considered
a user misoperation. And biggest_system_ram is only within
the 0~ULONG_MAX range, system can clearly work correctly with
addr_unit=1. Therefore, if monitor_region_start/end are unset,
always silently reset addr_unit to 1.

Signed-off-by: Quanmin Yan <yanquanmin1@huawei.com>
---
 mm/damon/lru_sort.c | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/mm/damon/lru_sort.c b/mm/damon/lru_sort.c
index b5a5ed16a7a5..14d31009c09e 100644
--- a/mm/damon/lru_sort.c
+++ b/mm/damon/lru_sort.c
@@ -111,6 +111,13 @@ module_param(monitor_region_start, ulong, 0600);
 static unsigned long monitor_region_end __read_mostly;
 module_param(monitor_region_end, ulong, 0600);
 
+/*
+ * Scale factor for DAMON_LRU_SORT to ops address conversion.
+ *
+ * This parameter must not be set to 0.
+ */
+static unsigned long addr_unit __read_mostly = 1;
+
 /*
  * PID of the DAMON thread
  *
@@ -198,6 +205,15 @@ static int damon_lru_sort_apply_parameters(void)
 	if (err)
 		return err;
 
+	/*
+	 * If monitor_region_start/end are unset, always silently
+	 * reset addr_unit to 1.
+	 */
+	if (!monitor_region_start && !monitor_region_end)
+		addr_unit = 1;
+	param_ctx->addr_unit = addr_unit;
+	param_ctx->min_sz_region = max(DAMON_MIN_REGION / addr_unit, 1);
+
 	if (!damon_lru_sort_mon_attrs.sample_interval) {
 		err = -EINVAL;
 		goto out;
@@ -290,6 +306,30 @@ static int damon_lru_sort_turn(bool on)
 	return damon_call(ctx, &call_control);
 }
 
+static int damon_lru_sort_addr_unit_store(const char *val,
+		const struct kernel_param *kp)
+{
+	unsigned long input_addr_unit;
+	int err = kstrtoul(val, 0, &input_addr_unit);
+
+	if (err)
+		return err;
+	if (!input_addr_unit)
+		return -EINVAL;
+
+	addr_unit = input_addr_unit;
+	return 0;
+}
+
+static const struct kernel_param_ops addr_unit_param_ops = {
+	.set = damon_lru_sort_addr_unit_store,
+	.get = param_get_ulong,
+};
+
+module_param_cb(addr_unit, &addr_unit_param_ops, &addr_unit, 0600);
+MODULE_PARM_DESC(addr_unit,
+	"Scale factor for DAMON_LRU_SORT to ops address conversion (default: 1)");
+
 static int damon_lru_sort_enabled_store(const char *val,
 		const struct kernel_param *kp)
 {
-- 
2.43.0