JDK-6543076 : CMS: Adaptive collection of perm gen
  • Type: Enhancement
  • Component: hotspot
  • Sub-Component: gc
  • Affected Version: 7
  • Priority: P3
  • Status: Closed
  • Resolution: Won't Fix
  • OS: generic
  • CPU: generic
  • Submitted: 2007-04-05
  • Updated: 2014-02-12
  • Resolved: 2014-02-12
Related Reports
Relates :  
JDK-6329603 - CMS: +CMSClassUnloadingEnabled and +CMSPermGenSweepingEnabled by default
Relates :  
JDK-6541037 - Ability to unload classes upon an explicit concurrent gc request
Relates :  
JDK-6634032 - CMS: Need CMSInitiatingPermOccupancyFraction for perm, divorcing from CMSInitiatingOccupancyFraction
Description
If this RFE pans out in practice, it might make 6329603 moot.
As noted in 6541037, ergonomic adaptation of perm gen collection may
be tricky because of the more bursty nature of allocation therein,
which might generally defeat predictive models based on smoother
statistics. Nevertheless, it would be an improvement over the
current state of affairs in the case of non-terminating
applications that do not have a bound on their perm gen
allocation volume.
Comments
Perm gen has been replace by native memory (metaspace); a new bug should be filed if adaptive collection of metaspace is needed.
12-02-2014
WORK AROUND -XX:+CMSClassUnloadingEnabled -XX:+CMSPermGenSweepingEnabled, but that can increase remark pauses; see also 6541037 for another approach.
05-04-2007
EVALUATION The basic functionality is straightforward, especially in light of the modifications for 6541037. The tricky part would be tuning the filters to perform well in the face of what is expected to be very bursty allocation behaviour in the perm gen. We are currently targeting this RFE to the 7.0 time-frame.
05-04-2007