You can put that in the javaopts
javaopts: [
"-Dfile.encoding=UTF-8", "-XX:MaxPermSize=128M", "-Xmx512M", "-Xms512M",
"-Djava.io.tmpdir=/srv/mendix/data/tmp"
]
https://docs.mendix.com/howto8/monitoring-troubleshooting/manage-app-performance-with-new-relic/