just mine

ram is controlled by JRE start commandline.  here are minecraft people on that

https://forum.feed-the-beast.com/threads/jvm-arguments-for-modded-minecraft-updated-12-30-13.28994/

here is a less technical

https://docs.google.com/document/d/1iHwZUjPFGSbeo8qPVbsefMLPKOeuOscQP1_a09rKI1k/edit