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  1. JDK
  2. JDK-8054326

Confusing message in "Current rem set statistics"

    Details

    • Subcomponent:
      gc
    • Resolved In Build:
      b120

      Backports

        Description


         
        "Max = 0K" in the following "Current rem set statistics" is confusing.

          Total heap region code root sets sizes = 98K. Max = 0K.
                   0K ( 0.7%) by 93 Young regions
                   0K ( 0.0%) by 4 Humonguous regions
                   0K ( 0.6%) by 79 Free regions
                  96K ( 98.6%) by 336 Old regions
            79865 code roots represented.
                    0 ( 0.0%) elements by 93 Young regions
                    0 ( 0.0%) elements by 4 Humonguous regions
                    0 ( 0.0%) elements by 79 Free regions
                79865 (100.0%) elements by 336 Old regions
            Region with largest amount of code roots =
        511:(E)[0x00000000ffc00000,0x0000000100000000,0x0000000100000000], size = 0K,
        num_elems = 0.

        The size (i.e., in "Max" and "size") reported seems to be limited to
        "strongly" reachable.

        If the the max of code root sets size is 0K. The total should be 0K too.
        Hence the confusing part.

        The following flags have been used for the summary report:

        -XX:+UnlockDiagnosticVMOptions -XX:+G1SummarizeRSetStats
        -XX:G1SummarizeRSetStatsPeriod=10
         

          Activity

          Hide
          tschatzl Thomas Schatzl added a comment -
          The problem is caused by rounding. The result is as it is because taking the maximum of a region's code root size and individually rounding it down results to 0k, but the sum of the code root sizes (79k of them, taking 98k of space, for 512 regions) simply is not only 0k.

          Show
          tschatzl Thomas Schatzl added a comment - The problem is caused by rounding. The result is as it is because taking the maximum of a region's code root size and individually rounding it down results to 0k, but the sum of the code root sizes (79k of them, taking 98k of space, for 512 regions) simply is not only 0k.
          Hide
          ehelin Erik Helin added a comment -
          Impact: Low, wrong ouput but no impact on correctness of product
          Likelihood: High, will happen every time
          Workaround: High, there is no workaround

          ILW = LHH => P4
          Show
          ehelin Erik Helin added a comment - Impact: Low, wrong ouput but no impact on correctness of product Likelihood: High, will happen every time Workaround: High, there is no workaround ILW = LHH => P4
          Hide
          hgupdate HG Updates added a comment -
          URL: http://hg.openjdk.java.net/jdk9/hs/hotspot/rev/32379cd4f38b
          User: kevinw
          Date: 2016-05-06 11:27:56 +0000
          Show
          hgupdate HG Updates added a comment - URL: http://hg.openjdk.java.net/jdk9/hs/hotspot/rev/32379cd4f38b User: kevinw Date: 2016-05-06 11:27:56 +0000
          Hide
          hgupdate HG Updates added a comment -
          URL: http://hg.openjdk.java.net/jdk9/jdk9/hotspot/rev/32379cd4f38b
          User: lana
          Date: 2016-05-25 17:36:48 +0000
          Show
          hgupdate HG Updates added a comment - URL: http://hg.openjdk.java.net/jdk9/jdk9/hotspot/rev/32379cd4f38b User: lana Date: 2016-05-25 17:36:48 +0000

            People

            • Assignee:
              csahu Cheleswer Sahu (Inactive)
              Reporter:
              shadowbug Shadow Bug
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              Watchers:
              6 Start watching this issue

              Dates

              • Created:
                Updated:
                Resolved: