G1GC and Permgen

Question

I'm having doubts regarding which metrics I should follow to allocate memory for the permgen. I'm having crashing problems and that permgen is full, my server has 32gb of memory for the heap and 512m for permgen, would you have any metrics or recommendations to follow to configure Permgen? Another doubt would be related to the GC, the G1GC was configured because from what I had researched it was one of the best options, but I noticed that it demands more of the heap memory, would there be a better gc for a server with a lot of demand and that needs a precise collection or would it just be the same? CentOS operating system Java 7 tomcat 7