mm/damon/reclaim: support online inputs update

DAMON_RECLAIM reads the user input parameters only when it starts.  To
allow more efficient online tuning, this commit implements a new input
parameter called 'commit_inputs'.  Writing true to the parameter makes
DAMON_RECLAIM reads the input parameters again.

Link: https://lkml.kernel.org/r/20220429160606.127307-14-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/damon/reclaim.c

@@ -29,6 +29,18 @@
  */
 static bool enabled __read_mostly;
 
+/*
+ * Make DAMON_RECLAIM reads the input parameters again, except ``enabled``.
+ *
+ * Input parameters that updated while DAMON_RECLAIM is running are not applied
+ * by default.  Once this parameter is set as ``Y``, DAMON_RECLAIM reads values
+ * of parametrs except ``enabled`` again.  Once the re-reading is done, this
+ * parameter is set as ``N``.  If invalid parameters are found while the
+ * re-reading, DAMON_RECLAIM will be disabled.
+ */
+static bool commit_inputs __read_mostly;
+module_param(commit_inputs, bool, 0600);
+
 /*
  * Time threshold for cold memory regions identification in microseconds.
  *
@@ -289,57 +301,56 @@ static struct damos *damon_reclaim_new_scheme(void)
 	return scheme;
 }
 
-static int damon_reclaim_turn(bool on)
+static int damon_reclaim_apply_parameters(void)
 {
-	struct damon_region *region;
 	struct damos *scheme;
-	int err;
-
-	if (!on) {
-		err = damon_stop(&ctx, 1);
-		if (!err)
-			kdamond_pid = -1;
-		return err;
-	}
+	struct damon_addr_range addr_range;
+	int err = 0;
 
 	err = damon_set_attrs(ctx, sample_interval, aggr_interval, 0,
 			min_nr_regions, max_nr_regions);
 	if (err)
 		return err;
 
+	/* Will be freed by next 'damon_set_schemes()' below */
+	scheme = damon_reclaim_new_scheme();
+	if (!scheme)
+		return -ENOMEM;
+	err = damon_set_schemes(ctx, &scheme, 1);
+	if (err)
+		return err;
+
 	if (monitor_region_start > monitor_region_end)
 		return -EINVAL;
 	if (!monitor_region_start && !monitor_region_end &&
 			!get_monitoring_region(&monitor_region_start,
 				&monitor_region_end))
 		return -EINVAL;
-	/* DAMON will free this on its own when finish monitoring */
-	region = damon_new_region(monitor_region_start, monitor_region_end);
-	if (!region)
-		return -ENOMEM;
-	damon_add_region(region, target);
+	addr_range.start = monitor_region_start;
+	addr_range.end = monitor_region_end;
+	return damon_set_regions(target, &addr_range, 1);
+}
 
-	/* Will be freed by 'damon_set_schemes()' below */
-	scheme = damon_reclaim_new_scheme();
-	if (!scheme) {
-		err = -ENOMEM;
-		goto free_region_out;
+static int damon_reclaim_turn(bool on)
+{
+	int err;
+
+	if (!on) {
+		err = damon_stop(&ctx, 1);
+		if (!err)
+			kdamond_pid = -1;
+		return err;
 	}
-	err = damon_set_schemes(ctx, &scheme, 1);
+
+	err = damon_reclaim_apply_parameters();
 	if (err)
-		goto free_scheme_out;
+		return err;
 
 	err = damon_start(&ctx, 1, true);
-	if (!err) {
-		kdamond_pid = ctx->kdamond->pid;
-		return 0;
-	}
-
-free_scheme_out:
-	damon_destroy_scheme(scheme);
-free_region_out:
-	damon_destroy_region(region, target);
-	return err;
+	if (err)
+		return err;
+	kdamond_pid = ctx->kdamond->pid;
+	return 0;
 }
 
 #define ENABLE_CHECK_INTERVAL_MS	1000
@@ -389,6 +400,7 @@ MODULE_PARM_DESC(enabled,
 static int damon_reclaim_after_aggregation(struct damon_ctx *c)
 {
 	struct damos *s;
+	int err = 0;
 
 	/* update the stats parameter */
 	damon_for_each_scheme(s, c) {
@@ -398,7 +410,23 @@ static int damon_reclaim_after_aggregation(struct damon_ctx *c)
 		bytes_reclaimed_regions = s->stat.sz_applied;
 		nr_quota_exceeds = s->stat.qt_exceeds;
 	}
-	return 0;
+
+	if (commit_inputs) {
+		err = damon_reclaim_apply_parameters();
+		commit_inputs = false;
+	}
+	return err;
+}
+
+static int damon_reclaim_after_wmarks_check(struct damon_ctx *c)
+{
+	int err = 0;
+
+	if (commit_inputs) {
+		err = damon_reclaim_apply_parameters();
+		commit_inputs = false;
+	}
+	return err;
 }
 
 static int __init damon_reclaim_init(void)
@@ -410,6 +438,7 @@ static int __init damon_reclaim_init(void)
 	if (damon_select_ops(ctx, DAMON_OPS_PADDR))
 		return -EINVAL;
 
+	ctx->callback.after_wmarks_check = damon_reclaim_after_wmarks_check;
 	ctx->callback.after_aggregation = damon_reclaim_after_aggregation;
 
 	target = damon_new_target();