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  1. JDK
  2. JDK-8177044

Remove _scan_top from HeapRegion

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    • Enhancement
    • Resolution: Fixed
    • P4
    • 10
    • 9, 10
    • hotspot
    • gc
    • 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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              tschatzl Thomas Schatzl
              tschatzl Thomas Schatzl
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                Updated:
                Resolved: