mm/damon/reclaim: enable and disable synchronously

Patch series "mm/damon/reclaim,lru_sort: enable/disable synchronously".

Writing a value to DAMON_RECLAIM and DAMON_LRU_SORT's 'enabled' parameters
turns on or off DAMON in an ansychronous way.  This means the parameter
cannot be used to read the current status of them.  '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.

The first and second patches changes the behavior of the 'enabled'
parameter for DAMON_RECLAIM and adds a selftest for the changed behavior,
respectively.  Following two patches make the same changes for
DAMON_LRU_SORT.


This patch (of 4):

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/20221025173650.90624-1-sj@kernel.org
Link: https://lkml.kernel.org/r/20221025173650.90624-2-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/reclaim.c

@@ -9,7 +9,6 @@
 
 #include <linux/damon.h>
 #include <linux/module.h>
-#include <linux/workqueue.h>
 
 #include "modules-common.h"
 
@@ -181,38 +180,31 @@ static int damon_reclaim_turn(bool on)
 	return 0;
 }
 
-static struct delayed_work damon_reclaim_timer;
-static void damon_reclaim_timer_fn(struct work_struct *work)
-{
-	static bool last_enabled;
-	bool now_enabled;
-
-	now_enabled = enabled;
-	if (last_enabled != now_enabled) {
-		if (!damon_reclaim_turn(now_enabled))
-			last_enabled = now_enabled;
-		else
-			enabled = last_enabled;
-	}
-}
-static DECLARE_DELAYED_WORK(damon_reclaim_timer, damon_reclaim_timer_fn);
-
-static bool damon_reclaim_initialized;
-
 static int damon_reclaim_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;
 
-	if (rc < 0)
-		return rc;
+	err = strtobool(val, &enable);
+	if (err)
+		return err;
 
-	/* system_wq might not initialized yet */
-	if (!damon_reclaim_initialized)
-		return rc;
+	if (is_enabled == enable)
+		return 0;
 
-	schedule_delayed_work(&damon_reclaim_timer, 0);
-	return 0;
+	/* Called before init function.  The function will handle this. */
+	if (!ctx)
+		goto set_param_out;
+
+	err = damon_reclaim_turn(enable);
+	if (err)
+		return err;
+
+set_param_out:
+	enabled = enable;
+	return err;
 }
 
 static const struct kernel_param_ops enabled_param_ops = {
@@ -262,10 +254,11 @@ static int __init damon_reclaim_init(void)
 	ctx->callback.after_wmarks_check = damon_reclaim_after_wmarks_check;
 	ctx->callback.after_aggregation = damon_reclaim_after_aggregation;
 
-	schedule_delayed_work(&damon_reclaim_timer, 0);
+	/* 'enabled' has set before this function, probably via command line */
+	if (enabled)
+		err = damon_reclaim_turn(true);
 
-	damon_reclaim_initialized = true;
-	return 0;
+	return err;
 }
 
 module_init(damon_reclaim_init);