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:
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. This is the mode you might prefer if you know that on this host only Zing java processes are used and their -Xmx settings are not changed often. It is also the preferred mode on large machines in the range of hundreds of GBytes for the -Xmx setting.
Selecting reserve-at-launch will preallocate all the Zing memory when the Zing java process starts, and releases it when the process ends. This is the mode you might prefer if Zing java is not always used on this host, like on developer machines, or if you have a mixed environment with other processes running.
When doing new installation of Zing, the memory allocation policy is set to reserve-at-launch by default to simplify the installation and to avoid to preallocate too much memory for Zing.
For further details about the Zing memory configuration using sudo system-config-zing-memory, please go to the following documentation page: http://docs.azul.com/zing/index.htm#ModZingMemConfig.htm