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  1. JDK
  2. JDK-8177044

Remove _scan_top from HeapRegion

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    Details

    • Type: Enhancement
    • Status: Resolved
    • Priority: P4
    • Resolution: Fixed
    • Affects Version/s: 9, 10
    • Fix Version/s: 10
    • Component/s: hotspot
    • Labels:
    • Subcomponent:
      gc
    • Resolved In Build:
      b21

      Description

      HeapRegion's _scan_top serves the single purpose that during garbage collection we do not try to scan areas that are potentially being allocated into at the moment.

      This enhancement suggests to remove _scan_top from HeapRegion and take a snapshot of top() values at start of GC.

      This removes potentially slow access to top/scan_top during GC as we need to serialize using a loadload barrier.

      Additionally, the "new" scan_top information can be subsumed with the cascade of if's that refinement during GC needs to do otherwise.

      Incidentally doing all that improves update rs/scan rs times in benchmarks.

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              Assignee:
              tschatzl Thomas Schatzl
              Reporter:
              tschatzl Thomas Schatzl
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