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  1. JDK
  2. JDK-8177044

Remove _scan_top from HeapRegion

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    • Icon: Enhancement Enhancement
    • Resolution: Fixed
    • Icon: P4 P4
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    • gc
    • b21

      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.

            tschatzl Thomas Schatzl
            tschatzl Thomas Schatzl
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