JDK-8049421 : G1 Class Unloading after completing a concurrent mark cycle
  • Type: Enhancement
  • Component: hotspot
  • Sub-Component: gc
  • Affected Version: 9
  • Priority: P2
  • Status: Resolved
  • Resolution: Fixed
  • Submitted: 2014-07-07
  • Updated: 2017-11-19
  • Resolved: 2014-07-07
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JDK 8 JDK 9
8u40Fixed 9 b24Fixed
Related Reports
Cloners :  
JDK-8048248 - [Backed out] G1 Class Unloading after completing a concurrent mark cycle
Duplicate :  
JDK-8015332 - G1: Interned strings with no references only garbage collected upon full GC.
Relates :  
JDK-8048269 - Add flag to turn off class unloading after G1 concurrent mark
Relates :  
JDK-8048268 - G1 Code Root Migration performs poorly
Relates :  
JDK-8015332 - G1: Interned strings with no references only garbage collected upon full GC.
Relates :  
JDK-8058563 - InstanceKlass::_dependencies list isn't cleared from empty nmethodBucket entries
Relates :  
JDK-8056240 - Investigate increased GC remark time after class unloading changes in CRM Fuse
Relates :  
JDK-8136973 - Unreachable classes are not deleted after the end of Conc Mark Cycle
Relates :  
JDK-8046146 - JEP 156: G1 GC: Reduce need for full GCs
Relates :  
JDK-8051611 - Implement Class Unloading after completing a concurrent mark cycle
Relates :  
JDK-8049420 - Backout 8048248 to correct attribution
Relates :  
JDK-8166277 - SIGSEGV in Dependencies::DepStream::argument(int)
Description
Currently G1 treats all classes as live except for during full gcs.

Modify the concurrent marking code to keep track of liveness of classes in order to be able to unload unreachable classes at the remark pause.
This involves reusing the infrastructure used by CMS to follow the object headers to find live classes.