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  1. JDK
  2. JDK-8152724

Sum of Eden, survivor and old capacity may be larger than heap size

    Details

    • Type: Bug
    • Status: Open
    • Priority: P4
    • Resolution: Unresolved
    • Affects Version/s: 8u74, 9
    • Fix Version/s: tbd_major
    • Component/s: hotspot
    • Labels:
    • Subcomponent:
      gc

      Description

      G1 calculates survivor capacity based on eden capacity and SurvivorRatio (literally current_eden_capacity / SurvivorRatio).

      If eden capacity is very large, e.g. set by limiting min young gen size by G1NewSizePercent to something > 50%, and SurvivorRatio=1, the total of eden, survivor and old gen capacities will exceed total heap size.

      This is just an issue with logging, e.g. on a 256M heap it is possible that the following log output is given:

      [2.335s][info ][gc,heap ] GC(0) Eden regions: 153->0(133)
      [2.335s][info ][gc,heap ] GC(0) Survivor regions: 0->20(133)

      I.e. eden + survivor capacity = 266 regions, which is more regionas than are available.

      The problem is that in the calculation of the next survivor capacity in G1CollectorPolicy::update_survivors_policy() does not guarantee consistency.

      This seems to only be a printing issue.

      This is a day one G1 bug.

        Issue Links

          Activity

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          tschatzl Thomas Schatzl added a comment -
          Potential fix attached. This simply bounds survivor to current heap size regions - (eden + old + humongous).

          However, some tests seem to expect the old behavior, so they need to be fixed too.
          Show
          tschatzl Thomas Schatzl added a comment - Potential fix attached. This simply bounds survivor to current heap size regions - (eden + old + humongous). However, some tests seem to expect the old behavior, so they need to be fixed too.

            People

            • Assignee:
              Unassigned
              Reporter:
              tschatzl Thomas Schatzl
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              Dates

              • Created:
                Updated: