Set MaxDirectMemorySize to some reasonable value

[giner]

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 70% total may exceed 140% without this option set. Setting this option would help to detect software or configuration issues easier as Java would complain on not being able to allocate more memory explicitly instead of being killed by OOM Killer provided by the OS.

Additionally adding option -Dio.netty.noPreferDirect=true could be considered for netty/grpc apps to make them use heap instead of direct memory for buffers.