jmap output with Garbage-First (G1) GC

2817636

The output of jmap command is shown below.

I wonder why the used value highlighted in red in Heap usage G1 Heap section is not the sum of the three values highlighted in blu (used in Eden Space, in Survivor Space and in Old Generation Space).

Have I misunderstood the output of jmap command? Or is there any error in calculation.

Can anyone help on this topic?

opt/jdk/bin/jmap -J-d64 -heap 9537

Attaching to process ID 9537, please wait...

Debugger attached successfully.

Server compiler detected.

JVM version is 25.102-b14

using thread-local object allocation.

Garbage-First (G1) GC with 4 thread(s)

Heap Configuration:

MinHeapFreeRatio         = 40

MaxHeapFreeRatio         = 70

MaxHeapSize = 268435456 (256.0MB)

NewSize = 1363144 (1.2999954223632812MB)

MaxNewSize = 160432128 (153.0MB)

OldSize = 5452592 (5.1999969482421875MB)

NewRatio = 2

SurvivorRatio = 8

   MetaspaceSize = 21807104 (20.796875MB)

   CompressedClassSpaceSize = 1073741824 (1024.0MB)

MaxMetaspaceSize         = 17592186044415 MB

G1HeapRegionSize         = 1048576 (1.0MB)

Heap Usage:

G1 Heap:

   regions  = 256

   capacity = 268435456 (256.0MB)

  used     = 212237728 (202.40567016601562MB)

   free     = 56197728 (53.594329833984375MB)

   79.06471490859985% used

G1 Young Generation:

Eden Space:

   regions  = 145

   capacity = 167772160 (160.0MB)

  used     = 152043520 (145.0MB)

   free     = 15728640 (15.0MB)

   90.625% used

Survivor Space:

   regions  = 1

   capacity = 1048576 (1.0MB)

   used     = 1048576 (1.0MB)

   free     = 0 (0.0MB)

   100.0% used

G1 Old Generation:

   regions  = 58

   capacity = 99614720 (95.0MB)

   used     = 58097056 (55.405670166015625MB)

   free = 41517664 (39.594329833984375MB)

58.32175806949013% used