JDK-8073146 : G1 merges thread local age tables too early with global age table
  • Type: Bug
  • Component: hotspot
  • Sub-Component: gc
  • Affected Version: 9
  • Priority: P4
  • Status: Resolved
  • Resolution: Fixed
  • Submitted: 2015-02-13
  • Updated: 2015-11-09
  • Resolved: 2015-08-20
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JDK 9
9 b81Fixed
Related Reports
Blocks :  
JDK-8040162 - Avoid reallocating PLABs between GC phases in G1
Relates :  
JDK-8030849 - Investigate high fragmentation/waste in some situations during allocation during GC in G1
Description
In G1ParTask::do_work() G1 merges the thread local age tables with the global one.

However, in later phases G1 continues to evacuate objects into the survivor spaces during java.lang.Reference processing (and CM reference processing).

This means that the age information to determine survivor size is incomplete. Both CMS and Serial GC count them.
Comments
Same problem with counting the number of surviving young words which is used to estimate the number of survivors per eden region age.
16-02-2015
ILW: I -> L: unknown, but most likely mild performance problem since survivor space may be sized too small L -> H: happens always W -> H: none
13-02-2015
JDK-8040162 revises the way the thread state is managed to fix that issue. It would be prudent to wait until that is completed.
13-02-2015