How to config gc policy when server machine memory is greater than 64G

[xiujin yang]

Hi all
 
Backgrand:
Hadoop : CDH3u0
HBase : CDH3u0
ZK : CDH3u0
Servers: 30
 
Now our hbase server is more than 64G.  and we want to use hbase on online 
projects. 
 
Does any body have GC config policy? Or some advice on how to use these memory.
Java Heap ? Old generation? New generation? and or so. 
 
thank you.
 
 
Yang