I am on PC and I am trying to allocate 4G. I altered the JVM arguments like most videos and sites say to by changing -Xmx2G to -Xmx4G however when I check f3 it says mem 512mb. I reinstalled minecraft and the problem persists. game doesn't crash but lags bad when the small amount of memory fills up. I uninstalled twitch before I reinstalled Minecraft to see if that would help and it did not. I have up to date Java and I just installed optifine but I think that was after the problem started. I have 8G of ram available. If you need more info I will try my best to provided it and I would be overjoyed with any help with this.