selftests/damon/damon_nr_regions: test online-tuned max_nr_regions

User could update max_nr_regions parameter while DAMON is running to a
value that smaller than the current number of regions that DAMON is
seeing.  Such update could be done for reducing the monitoring overhead. 
In the case, DAMON should merge regions aggressively more than normal
situation to ensure the new limit is successfully applied.  Implement a
kselftest to ensure that.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: SeongJae Park <[email protected]>
Cc: Shuah Khan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: sjp38

tools/testing/selftests/damon/damon_nr_regions.py

@@ -81,5 +81,65 @@ def main():
     # test max_nr_regions smaller than real nr regions
     test_nr_regions(15, 3, 10)
 
+    # test online-tuned max_nr_regions that smaller than real nr regions
+    sz_region = 10 * 1024 * 1024
+    proc = subprocess.Popen(['./access_memory_even', '14', '%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=10, max_nr_regions=1000),
+                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)
+
+    # wait until the real regions are found
+    time.sleep(3)
+
+    attrs = kdamonds.kdamonds[0].contexts[0].monitoring_attrs
+    attrs.min_nr_regions = 3
+    attrs.max_nr_regions = 7
+    err = kdamonds.kdamonds[0].commit()
+    if err is not None:
+        proc.terminate()
+        print('commit failed: %s' % err)
+        exit(1)
+    # wait for next merge operation is executed
+    time.sleep(0.3)
+
+    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)
+    proc.terminate()
+
+    if nr_tried_regions > 7:
+        print('fail online-tuned max_nr_regions: %d > 7' % nr_tried_regions)
+        exit(1)
+    print('pass online-tuned max_nr_regions')
+
 if __name__ == '__main__':
     main()