selftests/damon: add tests for DAMON_LRU_SORT's enabled parameter

Add simple test cases for DAMON_LRU_SORT's 'enabled' parameter.  Those
tests are focusing on the synchronous behavior of DAMON_RECLAIM enabling
and disabling.

Link: https://lkml.kernel.org/r/20221025173650.90624-5-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>

tools/testing/selftests/damon/Makefile

@@ -8,6 +8,6 @@ TEST_PROGS = debugfs_attrs.sh debugfs_schemes.sh debugfs_target_ids.sh
 TEST_PROGS += debugfs_empty_targets.sh debugfs_huge_count_read_write.sh
 TEST_PROGS += debugfs_duplicate_context_creation.sh
 TEST_PROGS += sysfs.sh
-TEST_PROGS += reclaim.sh
+TEST_PROGS += reclaim.sh lru_sort.sh
 
 include ../lib.mk

tools/testing/selftests/damon/lru_sort.sh

@@ -0,0 +1,41 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+# Kselftest framework requirement - SKIP code is 4.
+ksft_skip=4
+
+if [ $EUID -ne 0 ]
+then
+	echo "Run as root"
+	exit $ksft_skip
+fi
+
+damon_lru_sort_enabled="/sys/module/damon_lru_sort/parameters/enabled"
+if [ ! -f "$damon_lru_sort_enabled" ]
+then
+	echo "No 'enabled' file.  Maybe DAMON_LRU_SORT not built"
+	exit $ksft_skip
+fi
+
+nr_kdamonds=$(pgrep kdamond | wc -l)
+if [ "$nr_kdamonds" -ne 0 ]
+then
+	echo "Another kdamond is running"
+	exit $ksft_skip
+fi
+
+echo Y > "$damon_lru_sort_enabled"
+nr_kdamonds=$(pgrep kdamond | wc -l)
+if [ "$nr_kdamonds" -ne 1 ]
+then
+	echo "kdamond is not turned on"
+	exit 1
+fi
+
+echo N > "$damon_lru_sort_enabled"
+nr_kdamonds=$(pgrep kdamond | wc -l)
+if [ "$nr_kdamonds" -ne 0 ]
+then
+	echo "kdamond is not turned off"
+	exit 1
+fi