So, I was downloading and playing the newest MInecraft snapshot, 15w51b. By default, Xmx and Xms have 3 gigabytes of RAM allocated, and this worked on all releases. However, upon pressing Play, I got an error message, saying:
'Error: Could not find or load main class net.minecraft.client.main.Main
Java HotSpot(TM) 64-Bit Server VM warning: Using incremental CMS is deprecated and will likely be removed in a future release
Java HotSpot(TM) 64-Bit Server VM warning: MaxNewSize (3145728k) is equal to or greater than the entire heap (3145728k). A new max generation size of 3145664k will be used.'. Now obviously, 3145728k is equal to itself, but a) Presuming MaxNewSize is equal to the entire heap, what's the problem, since the heap obviously is it's own size, and b) If MaxNewSize is greater than the heap size, so what?
Reprodcution methodology:
Open Minecraft Launcher 1.6.48. Select your profile. Click the Edit Profile button. Make sure you have JVM Arguments checked, then have the following text in the arguments box: -Xmx3G -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode -XX:-UseAdaptiveSizePolicy -Xmn3G. If this doesn't reproduce the bug, it's possibly a problem with my computer.
This may be a bug in the JVM but not in Minecraft.