Java eden space is not 8 times larger than s0 space

Question

according to oracle's doc default parameter values for SurvivorRatio is 8, that means each survivor space will be one-eighth the size of eden space. but in my application it don't work

$ jmap -heap 48865
Attaching to process ID 48865, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.45-b02

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

Heap Configuration:
   MinHeapFreeRatio         = 0
   MaxHeapFreeRatio         = 100
   MaxHeapSize              = 4294967296 (4096.0MB)
   NewSize                  = 89128960 (85.0MB)
   MaxNewSize               = 1431306240 (1365.0MB)
   OldSize                  = 179306496 (171.0MB)
   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 = 67108864 (64.0MB)
   used     = 64519920 (61.53099060058594MB)
   free     = 2588944 (2.4690093994140625MB)
   96.14217281341553% used
From Space:
   capacity = 11010048 (10.5MB)
   used     = 0 (0.0MB)
   free     = 11010048 (10.5MB)
   0.0% used
To Space:
   capacity = 11010048 (10.5MB)
   used     = 0 (0.0MB)
   free     = 11010048 (10.5MB)
   0.0% used
PS Old Generation
   capacity = 179306496 (171.0MB)
   used     = 0 (0.0MB)
   free     = 179306496 (171.0MB)
   0.0% used

7552 interned Strings occupying 605288 bytes.

but in VisualVM eden space is 1.332G and S0 is 455M, eden is only 3 times larger than S0 not the 8

score 0 · Accepted Answer · answered Dec 08 '18 at 14:57

You have neither disabled -XX:-UseAdaptiveSizePolicy, nor set -Xms equal to -Xmx, so JVM is free to resize heap generations (and survivor spaces) in runtime. In this case the estimated maximum Survior size is

MaxSurvivor = NewGen / MinSurvivorRatio

where -XX:MinSurvivorRatio=3 by default. Note: this is an estimated maximum, not the actual size.

Java eden space is not 8 times larger than s0 space

1 Answers1