selftests/damon: implement test for min/max_nr_regions

Implement a kselftest for DAMON's {min,max}_nr_regions' parameters.  The
test ensures both the minimum and the maximum number of regions limit is
respected even if the workload's real number of regions is less than the
minimum or larger than the maximum limits.

Link: https://lkml.kernel.org/r/20240625180538.73134-7-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

@@ -13,7 +13,7 @@ TEST_PROGS = debugfs_attrs.sh debugfs_schemes.sh debugfs_target_ids.sh
 TEST_PROGS += sysfs.sh
 TEST_PROGS += sysfs_update_schemes_tried_regions_wss_estimation.py
 TEST_PROGS += damos_quota.py damos_quota_goal.py damos_apply_interval.py
-TEST_PROGS += damos_tried_regions.py
+TEST_PROGS += damos_tried_regions.py damon_nr_regions.py
 TEST_PROGS += reclaim.sh lru_sort.sh
 
 # regression tests (reproducers of previously found bugs)

tools/testing/selftests/damon/damon_nr_regions.py

@@ -0,0 +1,85 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0
+
+import subprocess
+import time
+
+import _damon_sysfs
+
+def test_nr_regions(real_nr_regions, min_nr_regions, max_nr_regions):
+    '''
+    Create process of the given 'real_nr_regions' regions, monitor it using
+    DAMON with given '{min,max}_nr_regions' monitoring parameter.
+
+    Exit with non-zero return code if the given {min,max}_nr_regions is not
+    kept.
+    '''
+    sz_region = 10 * 1024 * 1024
+    proc = subprocess.Popen(['./access_memory_even', '%d' % real_nr_regions,
+                             '%d' % sz_region])
+
+    # stat every monitored regions
+    kdamonds = _damon_sysfs.Kdamonds([_damon_sysfs.Kdamond(
+            contexts=[_damon_sysfs.DamonCtx(
+                monitoring_attrs=_damon_sysfs.DamonAttrs(
+                    min_nr_regions=min_nr_regions,
+                    max_nr_regions=max_nr_regions),
+                ops='vaddr',
+                targets=[_damon_sysfs.DamonTarget(pid=proc.pid)],
+                schemes=[_damon_sysfs.Damos(action='stat',
+                    )] # schemes
+                )] # contexts
+            )]) # kdamonds
+
+    err = kdamonds.start()
+    if err is not None:
+        proc.terminate()
+        print('kdamond start failed: %s' % err)
+        exit(1)
+
+    collected_nr_regions = []
+    while proc.poll() is None:
+        time.sleep(0.1)
+        err = kdamonds.kdamonds[0].update_schemes_tried_regions()
+        if err is not None:
+            proc.terminate()
+            print('tried regions update failed: %s' % err)
+            exit(1)
+
+        scheme = kdamonds.kdamonds[0].contexts[0].schemes[0]
+        if scheme.tried_regions is None:
+            proc.terminate()
+            print('tried regions is not collected')
+            exit(1)
+
+        nr_tried_regions = len(scheme.tried_regions)
+        if nr_tried_regions <= 0:
+            proc.terminate()
+            print('tried regions is not created')
+            exit(1)
+        collected_nr_regions.append(nr_tried_regions)
+        if len(collected_nr_regions) > 10:
+            break
+    proc.terminate()
+    kdamonds.stop()
+
+    test_name = 'nr_regions test with %d/%d/%d real/min/max nr_regions' % (
+            real_nr_regions, min_nr_regions, max_nr_regions)
+    if (collected_nr_regions[0] < min_nr_regions or
+        collected_nr_regions[-1] > max_nr_regions):
+        print('fail %s' % test_name)
+        print('number of regions that collected are:')
+        for nr in collected_nr_regions:
+            print(nr)
+        exit(1)
+    print('pass %s ' % test_name)
+
+def main():
+    # test min_nr_regions larger than real nr regions
+    test_nr_regions(10, 20, 100)
+
+    # test max_nr_regions smaller than real nr regions
+    test_nr_regions(15, 3, 10)
+
+if __name__ == '__main__':
+    main()