After JDK-8373246 I see a large increase of used disk space in tier2 and tier3 test runs when running with concurrency in fastdebug/debug builds.

JDK-8373246 adds debuginfo files to JDK images that are produced by builds with debug settings (e.g. fastdebug or slowdebug). This could add up to 1GB of additional debuginfo to the JDK image.
Now jpackage calls jlink with default options and then jlink includes the debuginfo files in the image it outputs.
This could be avoided when jlink is called with the "--strip-debug" option.
As the tests do not need the debug information that would save a lot of diskspace (I have seen a usage of up to 22 GB in /tmp during concurrent tools/jpackage/linux test execution) and should also reduce the runtime of jpackage tests by factor 2-4.