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  1. JDK
  2. JDK-8027761

Investigate fast-path for scanning only objects with references during gc

    Details

    • Type: Enhancement
    • Status: Closed
    • Priority: P3
    • Resolution: Fixed
    • Affects Version/s: hs25, 8
    • Fix Version/s: 16
    • Component/s: hotspot
    • Subcomponent:
      gc
    • Resolved In Build:
      b16
    • Verification:
      Fix failed

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        Description

        During evacuation, after copying an object to survivor space, it is scanned for further references that may need to be fixed up. This scanning involves calling oop_iterate() on the object.

        We noticed that in many benchmarks (dacapo, specjbb) a large part of the copied objects do not contain any references.

        I.e. across all dacapo benchmarks, over all gcs, on average only 63% of objects contain references, on Specjbb2005 only 60% (looking at instanceOops, typeArrayOops and objArrayOops which make up >97% of the objects copied).

        Investigate if it is possible to have a very fast check whether the copied object potentially contains references or not, skipping the oop iteration call otherwise (and hopefully improving performance in the process).

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                • Assignee:
                  kbarrett Kim Barrett
                  Reporter:
                  tschatzl Thomas Schatzl
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                    Updated:
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