There are many reasons that could cause OOM:permgen error; some of them are:

- permgen settings are not being applied as expected

- application requires more than defined permgen

- classloader leak

- frequent hot deployment or redployment.

If increasing the permgen do not resolve oom:perm, then you can use jmap java utility to check what classe are consuming perm space:

jmap -permstat $pid >& jmap.out