PermGen problem jmap/jhat leads to dead end
Y. Srinivas Ramakrishna
Y.S.Ramakrishna at Sun.COM
Mon Dec 14 14:04:24 PST 2009
Could you try the latest hs17 from OpenJDK 7 and
see if 4957990 fixes your problem?
On 12/14/09 14:01, Keith McNeill wrote:
> java version "1.6.0_16"
> Java(TM) SE Runtime Environment (build 1.6.0_16-b01)
> Java HotSpot(TM) Server VM (build 14.2-b01, mixed mode)
> Y. Srinivas Ramakrishna wrote:
>> What's the version of the HotSpot JVM you are running with? (See
>> -- ramki
>> On 12/14/09 13:54, Keith McNeill wrote:
>>> We're having a perm gen problem (maybe also code cache). Our product
>>> generates bytecodes and then loads and optionally unloads them.
>>> Running stability tests where we repeatably load & unload our
>>> generated applications we have encountered problems running out of
>>> perm gen space. A few years ago we had similar problems but by using
>>> jmap/jhat we were able to debug and fix this.
>>> This time using jmap/jhat to analyze the problem has lead to a dead end.
>>> In particular we see:
>>> 1) There are no instances left of the classes that we load/unload
>>> 2) The class objects of the classes that we load/unload hang around,
>>> they don't seem to get GC'ed
>>> 3) The ClassLoader of the loaded classes is hanging around. Doing a
>>> "Reference Chains from Rootset" in jhat results in 0 chains. Unless
>>> jhat is lying then the classes/classloader should be able to be
>>> GC'ed. Right?
>>> 4) Using jmap -permstat I see the classloaders in question are marked
>>> as 'dead'. This means that it should be able to be GC'ed
>>> 5) Tried Current GC, default GC, G1 GC and basically get the same
>>> errors. The G1 GC might error out with code cache problems instead.
>>> 6) The IBM JVM in the same scenario seems to be happy
>>> 7) If we load the classes (Class.forName()) but don't instantiate
>>> them, PermGen seems happier but we then run out of Code Cache. I'm
>>> not sure if the problems are related.
>>> The tests are run on linux & linux64. We are using:
>>> -XX:MaxPermSize=128m -Xms800m -Xmx1500m -XX:+CMSClassUnloadingEnabled
>>> and appropriate JVM args for the different GC's
>>> Given #3,4 & #6 above I'm thinking that it maybe a hotspot problem.
>>> What should I try next to track this problem down?
>>> Keith McNeill
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