How to determine the optimal size of a resource group in a GFS2 filesystem

Issue

• Analysis of glocktop and GFS2 lockdumps shows glock contention over glock type 3 (rgrp, or GFS2 resource group).
• We found out that the default size of resource group of our GFS2 filesystem causes glock contention, and want to change the resource group size
• We were asked to reformat our GFS2 filesystem to use different size of resource group by Red Hat Support, and we are not sure what size we should use