The builds (particularly of the j2se) use various -Xmx and -Xms settings when running the boot javac and the built javac. Some of these settings of -Xms are as low as 32Mb, and the settings are not consolidated in one place. Some time needs to be spent to find a more optimum settings to improve overall build time, within the limits of the build machine being used perhaps. Use of -Xms256m and -Xmx512m may make sense, but needs some experimentation. Also, there may be places in the build process that are not setting these options and this could be an opportunity to improve the build time for everyone.