Understanding Zing's memory model is a bit involved, because it differs from other JVMs like Oracle HotSpot or IBM J9. Zing preallocates a chunk of memory to hold the entire Xmx value setting to house regular Java objects that get allocated on the heap, plus additional spaces for other data types.
The first choices you make in reserving memory in Zing are how much memory to reserve and when in the JVM process life cycle you want it allocated. Use the utility system-config-zing-memory in the Zing Systems Tools set to make your choices.
The two available policies for determining when to preallocate Zing memory are:
reserve-at-config or reserve-at-launch
Selecting reserve-at-config will preallocate all the Zing memory at once. Memory stays allocated, no matter how many times the ZVM starts or stops.
Selecting reserve-at-launch will preallocate all the Zing memory when the ZVM process starts, and releases it when the ZVM process ends.
When doing installation of Zing from the trial downloads package, memory allocation policy is set to reserve-at-launch by default. That means your existing Xmx value will set the reserved memory size and preallocate space on the fly when the ZVM starts.
When you want instead to refine and fix your memory configuration for live workloads, you typically reconfigure Zing to instead use reserve-at-config with your precisely determined Xmx level.
For the complete story on how Zing uses system memory and how to configure it, review the Understanding Memory Use chapter in the Zing User's Guide.