My jvm options:
-verbose:gc -Xmx200M -Xmn40M -XX:+PrintTenuringDistribution -XX:+PrintGCDetails -XX:+PrintGCDateStamps -XX:+UseG1GC -XX:NewSize=40m -XX:MaxTenuringThreshold=1 -XX:-UseAdaptiveSizePolicy
The following is gc log:
Desired survivor size 2621440 bytes, new threshold 1 (max 1)
- age 1: 792 bytes, 792 total
, 0.0012861 secs]
[Parallel Time: 0.4 ms, GC Workers: 8]
[GC Worker Start (ms): Min: 120214.2, Avg: 120214.3, Max: 120214.3, Diff: 0.2]
[Ext Root Scanning (ms): Min: 0.1, Avg: 0.2, Max: 0.3, Diff: 0.2, Sum: 1.3]
[Update RS (ms): Min: 0.0, Avg: 0.0, Max: 0.1, Diff: 0.1, Sum: 0.3]
[Processed Buffers: Min: 0, Avg: 0.6, Max: 1, Diff: 1, Sum: 5]
[Scan RS (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
[Code Root Scanning (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
[Object Copy (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1]
[Termination (ms): Min: 0.0, Avg: 0.0, Max: 0.1, Diff: 0.1, Sum: 0.4]
[Termination Attempts: Min: 1, Avg: 1.0, Max: 1, Diff: 0, Sum: 8]
[GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1]
[GC Worker Total (ms): Min: 0.2, Avg: 0.3, Max: 0.4, Diff: 0.2, Sum: 2.2]
[GC Worker End (ms): Min: 120214.5, Avg: 120214.5, Max: 120214.6, Diff: 0.0]
[Code Root Fixup: 0.0 ms]
[Code Root Purge: 0.0 ms]
[Clear CT: 0.1 ms]
[Other: 0.7 ms]
[Choose CSet: 0.0 ms]
[Ref Proc: 0.4 ms]
[Ref Enq: 0.0 ms]
[Redirty Cards: 0.2 ms]
[Humongous Register: 0.0 ms]
[Humongous Reclaim: 0.0 ms]
[Free CSet: 0.0 ms]
[Eden: 39.0M(39.0M)->0.0B(39.0M) Survivors: 1024.0K->1024.0K Heap: 39.9M(200.0M)->670.6K(200.0M)]
[Times: user=0.00 sys=0.01, real=0.00 secs]
My question is why heap space(670.6K) is smaller than sum of(0+1024=1024) eden and survivors from the gc log [Eden: 39.0M(39.0M)->0.0B(39.0M) Survivors: 1024.0K->1024.0K Heap: 39.9M(200.0M)->670.6K(200.0M)]
