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jvm memory usage on Linux

 
 
tlo
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      07-17-2007
Hi,

I have a program where the main program runs a TimerTask every 10 sec. I have
observed that the memory usage when running the commands " top" and "ps -aux"
on the Linux box slowly increases. Over the time span of 3 hours Linux reports
that the java process has grown approx 30kb. I have started the java process
with the options -Xmx32M and -Xms32M (as it is running on a small hardware
platfrom) and I can see that by using the Runtime.getRuntime() the jvm's memory
usage looks fine:

Total : 33357824
Max : 33357824
Free : 24832448
Used : 8525376

When looking at the top command following is displayed:
PID USER STATUS RSS PPID %CPU %MEM COMMAND
1544 root S 38180 1 0.0 32.2 java

And the ps command:
1544 root 38180 S java -Xmx32m -Xms32m main

There are a couple of things that I don't understand:

1. Why the Java process seems to increase in memory usage and it doesn't ever
decrease again. The program needs to run 24/7 and I'm not sure if it will do
this at the moment. Could this have something to do with Java program or could
it be related to the JVM. I have tried it with Java 1.5 and Java 1.6 on Debain
and another Linux distro with the same result.

2. Why Linux reports the java process uses 38180kb, when I have limited the
java heap to 32Mb.

3. Why it increaes the memory when Java clealy have enough, is this maybe
related to os resoures like files, sockets, etc?

Any Help would be greatly appriciated.

Thanks

TLO







 
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