Trying to allocate more RAM for Minecraft to run a little better. When I go to the JVM Arguments this is whats already in there:

-Xmx1G -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode -XX:-UseAdaptiveSizePolicy -Xmn128M  

If I try to change anything minecraft wont start and in game it shows it only has 462MB now

1 Answer 1


The argument at the beginning: -xmx1G defines the maximum ram usage. Try changing the 1G to 3500M for 3.5GB Maximum usage. Also if that doesn't work change it to1500M Also get 64-Bit Java or else the steps above might not work.

  • Anything other then 1G pulls up this message "Error occurred during initialization of VM Could not reserve enough space for 1536000KB object heap Java HotSpot(TM) Client VM warning: Using incremental CMS is deprecated and will likely be removed in a future release" Mar 16, 2016 at 1:10
  • Figured it out! When upgraded my java it installed 32 bit instead of keeping 64 bit got it to 64 bit and it works great now. Thanks for the help Mar 16, 2016 at 1:21
  • @Baggiergorgon41 of course! 32 bit only allows less then 2 GB. I forgot about that
    – MadMrCrazy
    Mar 16, 2016 at 7:43
  • @MadMrCrazy 32bit java allows only 1GB RAM, not 2GB ;-) Mar 16, 2016 at 15:45
  • @AntoineHejlík I feel stupid now...
    – MadMrCrazy
    Mar 21, 2016 at 5:55

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