JDK-8043574 : Investigate decreasing the RS scrubbing work in the GC cleanup pause
  • Type: Enhancement
  • Component: hotspot
  • Sub-Component: gc
  • Affected Version: 8u20,9
  • Priority: P4
  • Status: Closed
  • Resolution: Duplicate
  • Submitted: 2014-05-20
  • Updated: 2016-11-24
  • Resolved: 2014-11-03
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JDK 9
9Resolved
Related Reports
Duplicate :  
JDK-7187490 - G1: Limit the amount of remembered set scrubbing
Relates :  
JDK-8017163 - G1: Refactor remembered sets
Description
During GC cleanup G1 scrubs the entire remembered set, i.e. removes stale remembered set entries.

This can take a while for large remembered sets, and lengthens the GC cleanup pause a lot.

Conceptually it is not necessary to do this RSet scrubbing in the GC cleanup pause - presumably it is currently done there because after marking completed, you get the most gain out of this.

It could be done concurrently to the mutator or incrementally in other pauses.

Think of ways to distribute this work across mutator or gc time.
Comments
Concurrent scrubbing could be done by: 1) during gc pause, disconnect the remembered set of the target region(s) from these regions, and empty it 2) a concurrent thread iterate over the cards of the remembered sets one by one and if a cross-region reference is found, add an entry to the corresponding remembered set.
05-08-2014
Linked to JDK-7187490: the linked issue is about delaying RSet scrubbing
22-05-2014