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  1. JDK
  2. JDK-8196522

The Default JVM Config Does Not Properly Configure Eden/Survivor Spaces

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    • Subcomponent:
      gc

      Description

      The default JVM 1.8 configuration does not properly configure Eden/Survivor spaces.

      While the JVM default is SurvivorRatio=8 and it says so, the actual sizes of
      Eden and Survivor areas are the same (which mean that SurvivorRatio=1) .

      $ ./jmap -heap 25879
      Attaching to process ID 25879, please wait...
      Debugger attached successfully.
      Server compiler detected.
      JVM version is 25.151-b12

      using thread-local object allocation.
      Parallel GC with 8 thread(s)

      Heap Configuration:
         MinHeapFreeRatio = 0
         MaxHeapFreeRatio = 100
         MaxHeapSize = 12884901888 (12288.0MB)
         NewSize = 536870912 (512.0MB)
         MaxNewSize = 4294967296 (4096.0MB)
         OldSize = 1073741824 (1024.0MB)
         NewRatio = 2
         SurvivorRatio = 8
         MetaspaceSize = 21807104 (20.796875MB)
         CompressedClassSpaceSize = 1073741824 (1024.0MB)
         MaxMetaspaceSize = 17592186044415 MB
         G1HeapRegionSize = 0 (0.0MB)

      Heap Usage:
      PS Young Generation
      Eden Space:
         capacity = 1390411776 (1326.0MB)
         used = 1390411776 (1326.0MB)
         free = 0 (0.0MB)
         100.0% used
      From Space:
         capacity = 1278738432 (1219.5MB)
         used = 0 (0.0MB)
         free = 1278738432 (1219.5MB)
         0.0% used
      To Space:
         capacity = 1431306240 (1365.0MB)
         used = 0 (0.0MB)
         free = 1431306240 (1365.0MB)
         0.0% used
      PS Old Generation
         capacity = 8589934592 (8192.0MB)
         used = 8499819848 (8106.059883117676MB)
         free = 90114744 (85.94011688232422MB)
         98.95092630758882% used

      If we explicitly add -XX:SurvivorRatio=8, it restores what it should be.

      $ ./jmap -heap 7764
      Attaching to process ID 7764, please wait...
      Debugger attached successfully.
      Server compiler detected.
      JVM version is 25.151-b12

      using thread-local object allocation.
      Parallel GC with 8 thread(s)

      Heap Configuration:
         MinHeapFreeRatio = 0
         MaxHeapFreeRatio = 100
         MaxHeapSize = 12884901888 (12288.0MB)
         NewSize = 536870912 (512.0MB)
         MaxNewSize = 4294967296 (4096.0MB)
         OldSize = 1073741824 (1024.0MB)
         NewRatio = 2
         SurvivorRatio = 8
         MetaspaceSize = 21807104 (20.796875MB)
         CompressedClassSpaceSize = 1073741824 (1024.0MB)
         MaxMetaspaceSize = 17592186044415 MB
         G1HeapRegionSize = 0 (0.0MB)

      Heap Usage:
      PS Young Generation
      Eden Space:
         capacity = 3666345984 (3496.5MB)
         used = 2636838920 (2514.6855545043945MB)
         free = 1029507064 (981.8144454956055MB)
         71.92007877890447% used
      From Space:
         capacity = 157810688 (150.5MB)
         used = 114371680 (109.07333374023438MB)
         free = 43439008 (41.426666259765625MB)
         72.47397590713247% used
      To Space:
         capacity = 159383552 (152.0MB)
         used = 0 (0.0MB)
         free = 159383552 (152.0MB)
         0.0% used
      PS Old Generation
         capacity = 8589934592 (8192.0MB)
         used = 6882442576 (6563.60871887207MB)
         free = 1707492016 (1628.3912811279297MB)
         80.12217674404383% used

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            • Assignee:
              poonam Poonam Bajaj Parhar
              Reporter:
              shadowbug Shadow Bug
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              • Created:
                Updated:
                Resolved: