mm/damon/reclaim: support addr_unit for DAMON_RECLAIM

Implement a sysfs file to expose addr_unit for DAMON_RECLAIM 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.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Quanmin Yan <[e-mail]>
Reviewed-by: SeongJae Park <[e-mail]>
Cc: Kefeng Wang <[e-mail]>
Cc: ze zuo <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

mm/damon/reclaim.c

···
 module_param(monitor_region_end, ulong, 0600);
 
 /*
+ * Scale factor for DAMON_RECLAIM to ops address conversion.
+ *
+ * This parameter must not be set to 0.
+ */
+static unsigned long addr_unit __read_mostly = 1;
+
+/*
  * Skip anonymous pages reclamation.
  *
  * If this parameter is set as ``Y``, DAMON_RECLAIM does not reclaim anonymous
···
 	err = damon_modules_new_paddr_ctx_target(&param_ctx, &param_target);
 	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_reclaim_mon_attrs.aggr_interval) {
 		err = -EINVAL;
···
 	kdamond_pid = ctx->kdamond->pid;
 	return damon_call(ctx, &call_control);
 }
+
+static int damon_reclaim_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_reclaim_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_RECLAIM to ops address conversion (default: 1)");
 
 static int damon_reclaim_enabled_store(const char *val,
 		const struct kernel_param *kp)