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  1. JDK
  2. JDK-8025813

G1: Code root marking unbalanced

    Details

    • Type: Enhancement
    • Status: Closed
    • Priority: P3
    • Resolution: Won't Fix
    • Affects Version/s: hs25
    • Fix Version/s: 9
    • Component/s: hotspot
    • Subcomponent:
      gc

      Backports

        Description

        The fix for JDK-7145569 introduced work distribution of nmethod scanning on a per region basis: nmethods are "attached" to the regions they have references into.

        While the fix helps lowering the maximum scan time, in large applications code root marking is very unbalanced: a few regions contain most of the nmethods that need to be scanned (see nmethod_distribution.png), and as the work is distributed on a per-region basis typically one or two threads take much longer than the others.

        See maximum/avg times for code root marking in the attached figure (code_root_marking_avg_max.png).

        This still negatively impacts overall gc pause times significantly.

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                • Assignee:
                  tschatzl Thomas Schatzl
                  Reporter:
                  tschatzl Thomas Schatzl
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                    Updated:
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