mm/damon/lru_sort: enable and disable synchronously

Writing a value to DAMON_RECLAIM's 'enabled' parameter turns on or off
DAMON in an ansychronous way.  This means the parameter cannot be used to
read the current status of DAMON_RECLAIM.  'kdamond_pid' parameter should
be used instead for the purpose.  The documentation is easy to be read as
it works in a synchronous way, so it is a little bit confusing.  It also
makes the user space tooling dirty.

There's no real reason to have the asynchronous behavior, though.  Simply
make the parameter works synchronously, rather than updating the document.

Link: https://lkml.kernel.org/r/20221025173650.90624-4-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/damon/lru_sort.c

@@ -9,7 +9,6 @@
 
 #include <linux/damon.h>
 #include <linux/module.h>
-#include <linux/workqueue.h>
 
 #include "modules-common.h"
 
@@ -235,38 +234,31 @@ static int damon_lru_sort_turn(bool on)
 	return 0;
 }
 
-static struct delayed_work damon_lru_sort_timer;
-static void damon_lru_sort_timer_fn(struct work_struct *work)
-{
-	static bool last_enabled;
-	bool now_enabled;
-
-	now_enabled = enabled;
-	if (last_enabled != now_enabled) {
-		if (!damon_lru_sort_turn(now_enabled))
-			last_enabled = now_enabled;
-		else
-			enabled = last_enabled;
-	}
-}
-static DECLARE_DELAYED_WORK(damon_lru_sort_timer, damon_lru_sort_timer_fn);
-
-static bool damon_lru_sort_initialized;
-
 static int damon_lru_sort_enabled_store(const char *val,
 		const struct kernel_param *kp)
 {
-	int rc = param_set_bool(val, kp);
+	bool is_enabled = enabled;
+	bool enable;
+	int err;
+
+	err = strtobool(val, &enable);
+	if (err)
+		return err;
 
-	if (rc < 0)
-		return rc;
+	if (is_enabled == enable)
+		return 0;
 
-	if (!damon_lru_sort_initialized)
-		return rc;
+	/* Called before init function.  The function will handle this. */
+	if (!ctx)
+		goto set_param_out;
 
-	schedule_delayed_work(&damon_lru_sort_timer, 0);
+	err = damon_lru_sort_turn(enable);
+	if (err)
+		return err;
 
-	return 0;
+set_param_out:
+	enabled = enable;
+	return err;
 }
 
 static const struct kernel_param_ops enabled_param_ops = {
@@ -320,10 +312,11 @@ static int __init damon_lru_sort_init(void)
 	ctx->callback.after_wmarks_check = damon_lru_sort_after_wmarks_check;
 	ctx->callback.after_aggregation = damon_lru_sort_after_aggregation;
 
-	schedule_delayed_work(&damon_lru_sort_timer, 0);
+	/* 'enabled' has set before this function, probably via command line */
+	if (enabled)
+		err = damon_lru_sort_turn(true);
 
-	damon_lru_sort_initialized = true;
-	return 0;
+	return err;
 }
 
 module_init(damon_lru_sort_init);