Set MaxDirectMemorySize to some reasonable value

[stas-sbi]

MaxDirectMemorySize should be set to some reasonable value instead of relying on the default which equals max memory limit. Let's say if max memory is set to 75% total may exceed 150% without this option. Setting this option would help us detecting software or configuration issues easier as Java would complain on not being able to allocate more memory by some routing explicitly instead of being killed by OOM Killer provided by the OS.