JIT stops compiling after a while (java 7)

[Martin Traverso]

We're seeing some strange behavior with the JIT compiler in jdk7. As far as
we can tell, at some point in the lifetime of the process the vm decides to
stop generating native code.

I wrote a simple program that reproduces the behavior. It generates classes
dynamically, with a method that loops and performs some computation. It
does this over and over and it calls the method each time to make the vm
optimize and generate native code. Separately, it gathers and prints the
following stats: cumulative compilation time, code cache size, perm gen
size and invocations per second.

You can take a look at the code here: http://github.com/martint/jittest.
Here's a chart that shows how those stats behave over time:
https://raw.github.com/martint/jittest/master/stats-7u40.png.

As you can see in the chart, the code cache grows steadily in the
beginning. So does the cumulative compilation time. At some point, the
cache fills up and the vm stops compiling (my interpretation) and
invocation throughput drops significantly. Nothing much happens for a while
after that, until the perm gen fills up and goes through a GC cycle. Some
time after (not sure if related to the perm gen GC), the code cache flushes
and the vm starts compiling again. Eventually, the code cache fills up
again, but at a lower level that the first time. The vm stops compiling
once again and performance drops to an even lower level that before. I
haven't seen it recover from this condition, which is consistent with what
we see in our production system.

I've been able to reproduce it in both 7u10 and the 7u40 early access
that's available in the openjdk site. Interestingly, java 8 does not
exhibit this issue.

Is this a known problem? Is there any way around it (other than restarting
the vm) or things to try out while we wait for java 8 to come out?

Thanks!

Martin
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