Generally, you want to leave some memory available to other things, like the OS, buffers in the network stack, etc. Having a limit for the VM is helpful. Also,

Generally, you want to leave some memory available to other things, like the OS, buffers in the network stack, etc. Having a limit for the VM is helpful. Also, by default it is automatically 20% of available memory. Personally, I've had to tune this kind of stuff with every VM I worked with (JVM, Node, PHP). :)