Excessive memory uses

On start up the java process allocates a massive amount of memory (during the Mojang screen), it's not the Java heap because my JVM arguments are
-Xmx512M -Xms256M -XX:+TieredCompilation -dsa -da -XX:+AggressiveOpts -XX:+UseFastAccessorMethods -XX:MaxGCPauseMillis=2 -XX:GCPauseIntervalMillis=16

the virtual memory of the process rapidly went up to 2GB before the menu even shows, and since I only have 2GB of memory everything went very slow and Minecraft continued to allocate more and more memory, it was over 4GB before the menu showed. It normal only ends up with about 300MB RSS at the main menu, The snapshot the RSS rapidly shoots up to about 1.4GB and stays there while the system thrashes.