JDK-8225406 : Account for hot card cache cards in distributing heap root scan times
  • Type: Bug
  • Component: hotspot
  • Sub-Component: gc
  • Affected Version: 13
  • Priority: P4
  • Status: Closed
  • Resolution: Duplicate
  • Submitted: 2019-06-06
  • Updated: 2019-12-03
  • Resolved: 2019-12-03
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JDK 14
14Resolved
Related Reports
Duplicate :  
JDK-8227739 - Merge cost predictions for scanning cards and log buffer entries
Relates :  
JDK-8213108 - Improve work distribution during remembered set scan
Relates :  
JDK-8225409 - Investigate removal of the Hot Card Cache
Description
For ergonomics decisions (young gen size) we need a fairly accurate measure of how the various sources of heap roots contribute to garbage collection time.

With JDK-8213108 the method to distribute card scanning costs radically changed as scanning the heap roots is a single pass. It distributed the total time according to the number of cards the various roots contribute.

Since the hot card cache is small and either completely unused (not doing lots of refinement) or if there is lots of refinement, the cards in there are dwarfed by the other sources of heap roots, the change did not incorporate this count in the calculation.

Fix this and investigate impact.
Comments
JDK-8227739 updated cost prediction accounting to what is actually being done now during card scanning. This included the hot card cache times.
03-12-2019