Originally Posted by
Dannerick
I recognize the JVM argument list as coming from the FTB formus. I tried that JVM set and found it generated way too much CPU overhead and backed down to a simpler set arguments. If you are using the machine for only Minecraft when you are running Minecraft (not doing a lot of multi-tasking), you could try something like: -XX:PermSize=256m -Xmn1G -Xms2G -Xmx2G -XX:TargetSurvivorRatio=80 -XX:SurvivorRatio=3 -XX:ParallelGCThreads=2 -XX:+CMSIncrementalMode -XX:+DisableExplicitGC -XX:+UseConcMarkSweepGC -XX:MaxGCPauseMillis=20 -XX:GCPauseIntervalMillis=250 -XX:+AggressiveOpts -XX:+UseCodeCacheFlushing
I would agree with Adarcer that the mod set is a bit heavy for the machine you are using. I might try to reduce down the list by 10 or 15 mods. However, raw count of mods can be misleading. You could run 120+ light-weight mods with little problems, but choke on 70 heavy-weight ones. First, review your list of mods and remove any that you are not using and don't really expect to use at all. Then, look at the ones that add a huge amount of content, especially heavy world gen, examples are Thaumcraft and Ars Magica; do you need all of those. Another thing to do is check to see if some specific entities in your world are causing significant lag; use the Opis mod to help track down lag issues even with SSP.
Even after all that, you are probably seeing some issue dealing with a memory leak in some mod. I have issues jumping between dimensions frequently chewing up all the available memory and the only solution is to close Minecraft and restart.