Java : how to check current Perm / PermGen Size?

Question

Yesterday when I was running the WebLogic Application Server 11g installer, I encountered a OutOfMemory error, so I Googled for the answer:

java -Xms256m -Xmx512m -XX:PermSize=128m -XX:MaxPermSize=256m -jar wls1032_generic.jar

Everything worked :)

However, when I think twice about the solution, I might have made a mistake: How could I know the current settings of those? I certainly need to check their values before overriding them, right?

Any thoughts?

Related link: People in another thread on SO suggested trial and error approach, which is not ideal.

Many thanks in advance.

Answer 1

You can check the values of any JVM flags of a running JVM by using the jinfo.exe utility.

%JAVA_HOME%\bin\jinfo.exe -flag <flagName> <pid>

so to check the value of -XX:PermSize JVM option you can run

%JAVA_HOME%\bin\jinfo.exe -flag PermSize <pid>

Answer 2

You can use jmap at here, it's JVM Heap Dump Tool.

for example:

jmap -heap 5900

It will print:

Heap Configuration:
   MinHeapFreeRatio = 40
   MaxHeapFreeRatio = 70
   MaxHeapSize      = 989855744 (944.0MB)
   NewSize          = 1310720 (1.25MB)
   MaxNewSize       = 17592186044415 MB
   OldSize          = 5439488 (5.1875MB)
   NewRatio         = 2
   SurvivorRatio    = 8
   PermSize         = 21757952 (20.75MB)
   MaxPermSize      = 85983232 (82.0MB)

Heap Usage:
PS Young Generation
Eden Space:
   capacity = 242352128 (231.125MB)
   used     = 9196056 (8.770042419433594MB)
   free     = 233156072 (222.3549575805664MB)
   3.79450185805672% used
From Space:
   capacity = 41877504 (39.9375MB)
   used     = 0 (0.0MB)
   free     = 41877504 (39.9375MB)
   0.0% used
To Space:
   capacity = 42663936 (40.6875MB)
   used     = 0 (0.0MB)
   free     = 42663936 (40.6875MB)
   0.0% used
PS Old Generation
   capacity = 80609280 (76.875MB)
   used     = 34187936 (32.604156494140625MB)
   free     = 46421344 (44.270843505859375MB)
   42.41191088668699% used
PS Perm Generation
   capacity = 85393408 (81.4375MB)
   used     = 63472624 (60.53221130371094MB)
   free     = 21920784 (20.905288696289062MB)
   74.32965317416539% used

It gets memory information (including PermGen).5900 is the process id of Java.