Buldbot profiler file size increasing cumulatively

Buildbot profiler recently had a nice addition of service mode in https://github.com/tardyp/buildbot_profiler#usage, which continuously profiles buildbot and dumps data every 30 minutes.

However, the file size seems to increase cumulatively in this mode. After a while, files are so huge that they are difficult to analyze. For example here are file sizes on a test instance:

-rw-r--r-- 1 buildbot buildbot 480K Aug 7 20:16 profile_2017-08-07T20:16:48.797626.json
-rw-r--r-- 1 buildbot buildbot 3.0M Aug 7 20:46 profile_2017-08-07T20:46:52.201871.json
-rw-r--r-- 1 buildbot buildbot 3.0M Aug 7 21:17 profile_2017-08-07T21:17:07.408111.json
-rw-r--r-- 1 buildbot buildbot 3.1M Aug 7 21:47 profile_2017-08-07T21:47:48.798623.json
-rw-r--r-- 1 buildbot buildbot 3.1M Aug 7 22:18 profile_2017-08-07T22:18:13.870010.json
-rw-r--r-- 1 buildbot buildbot 3.2M Aug 7 22:48 profile_2017-08-07T22:48:32.444599.json
-rw-r--r-- 1 buildbot buildbot 7.1M Aug 7 23:18 profile_2017-08-07T23:18:33.621863.json
-rw-r--r-- 1 buildbot buildbot 9.4M Aug 7 23:48 profile_2017-08-07T23:48:48.800888.json
-rw-r--r-- 1 buildbot buildbot 12M Aug 8 00:19 profile_2017-08-08T00:19:16.148646.json
-rw-r--r-- 1 buildbot buildbot 12M Aug 8 00:49 profile_2017-08-08T00:49:32.322790.json
-rw-r--r-- 1 buildbot buildbot 12M Aug 8 01:19 profile_2017-08-08T01:19:51.523342.json
-rw-r--r-- 1 buildbot buildbot 14M Aug 8 01:50 profile_2017-08-08T01:50:53.907013.json
-rw-r--r-- 1 buildbot buildbot 14M Aug 8 02:21 profile_2017-08-08T02:21:48.794229.json
-rw-r--r-- 1 buildbot buildbot 14M Aug 8 02:52 profile_2017-08-08T02:52:48.804969.json
-rw-r--r-- 1 buildbot buildbot 14M Aug 8 03:22 profile_2017-08-08T03:22:48.802061.json
-rw-r--r-- 1 buildbot buildbot 14M Aug 8 03:52 profile_2017-08-08T03:52:54.566964.json
-rw-r--r-- 1 buildbot buildbot 14M Aug 8 04:23 profile_2017-08-08T04:23:12.820794.json
-rw-r--r-- 1 buildbot buildbot 16M Aug 8 04:53 profile_2017-08-08T04:53:13.869574.json
-rw-r--r-- 1 buildbot buildbot 16M Aug 8 05:23 profile_2017-08-08T05:23:48.797043.json
-rw-r--r-- 1 buildbot buildbot 16M Aug 8 05:54 profile_2017-08-08T05:54:48.798552.json
-rw-r--r-- 1 buildbot buildbot 16M Aug 8 06:25 profile_2017-08-08T06:25:48.798690.json
-rw-r--r-- 1 buildbot buildbot 16M Aug 8 06:56 profile_2017-08-08T06:56:48.796558.json
-rw-r--r-- 1 buildbot buildbot 16M Aug 8 07:26 profile_2017-08-08T07:26:48.797046.json
-rw-r--r-- 1 buildbot buildbot 16M Aug 8 07:56 profile_2017-08-08T07:56:55.585291.json
-rw-r--r-- 1 buildbot buildbot 17M Aug 8 08:27 profile_2017-08-08T08:27:48.794022.json
-rw-r--r-- 1 buildbot buildbot 17M Aug 8 08:57 profile_2017-08-08T08:57:48.796139.json
-rw-r--r-- 1 buildbot buildbot 17M Aug 8 09:28 profile_2017-08-08T09:28:47.895713.json
-rw-r--r-- 1 buildbot buildbot 18M Aug 8 09:58 profile_2017-08-08T09:58:47.906966.json
-rw-r--r-- 1 buildbot buildbot 21M Aug 8 10:28 profile_2017-08-08T10:28:48.797822.json
-rw-r--r-- 1 buildbot buildbot 25M Aug 8 10:58 profile_2017-08-08T10:58:48.794560.json
-rw-r--r-- 1 buildbot buildbot 35M Aug 8 11:28 profile_2017-08-08T11:28:49.849422.json
-rw-r--r-- 1 buildbot buildbot 47M Aug 8 11:58 profile_2017-08-08T11:58:50.459862.json
-rw-r--r-- 1 buildbot buildbot 58M Aug 8 12:28 profile_2017-08-08T12:28:52.024912.json
-rw-r--r-- 1 buildbot buildbot 64M Aug 8 12:58 profile_2017-08-08T12:58:52.249505.json

Seems like instead of dumping just last 30 minutes of data, profiler is dumping cumulative data from beginning.