Hi, this is a little misleading. I am sorry for it, but I can not see any other option. Job Disk-usage directory are here to compare how much disk usage is taken by builds itself and how much other stuffs. It can not remember state of job directory since it is not calculated after build, but only recalculation task. I thought that I should include it into calculation of build, but some job directory can be large even without builds (some plugins save their information into job directory not into build directory) and it can stuck build for long time.
Attaching a screen shot of the trend graph from 0.24-SNAPSHOT of the plugin. As you can see the job directory (green area) is drawn at 590KB for all builds. This cannot be correct, but it should have started at somewhere around 200KB for hte first build and then grown.
Checking the code also confirms that it is the current job directory size that is used for all graph plots.