G1: higher perm gen footprint or a possible perm gen leak?

[Thomas Schatzl]

Hi,

On Fri, 2014-01-03 at 11:30 -0800, Srinivas Ramakrishna wrote:
> Thanks everyone for sharing yr experiences. As I indicated, I do
> realize that G1 does not collect perm gen concurrently.
> What was surprising was that G1's use of perm gen was much higher
> following its stop-world full gc's
> which would have collected the perm gen. As a result, G1 needed a perm
> gen quite a bit more than twice that
> given to parallel gc to be able to run an application for a certain
> length of time.

Maybe explained by different soft reference policies? I.e. maybe the
input for the soft reference processing is different in both collectors,
making it behave differently, possibly keeping alive more
objects/classes for longer.

> I'll provide more data on perm gen dynamics when I have it. My guess
> would be that somehow G1's use of
> regions in the perm gen is causing a dilation of perm gen footprint on
> account of fragmentation in the G1 perm
> gen regions. If that were the case, I would expect a modest increase
> in the perm gen footprint, but it seemed the increase in
> footprint was much higher. I'll collect and post more concrete numbers
> when I get a chance.

(G1) Perm gen is never region based.

Thomas