How to minimize (unshareable) memory usage?

Mon Jan 18 09:50:00 GMT 2010

On 01/18/2010 09:40 AM, Justin Santa Barbara wrote:
> I have some simple Java utilities that I've written that need to run
> on machines with limited free memory, and I'm looking at GCJ for this.
> Using the full Sun JVM we run into problems with memory usage - we're
> able to limit the heap to 8MB, but we need to allow at least 16MB for
> PermGen (despite not really having much application code), and at
> least 8MB for ReservedCodeCacheSize; even a simple utility therefore
> needs at least 32MB of unshareable memory.
>> Running under GCJ the results are encouraging, but still not as good
> as I'd hope. The output from pmap is included below. The interesting
> ones are these four:
> 00010000 10404K rw--- [ anon ]
> b4125000 8192K rw--- [ anon ]
> b49d2000 8192K rw--- [ anon ]
> b7096000 6324K rw--- /usr/lib/libgcj.so.10.0.0
>> I've limited GCJ to 10MB of heap (it seems to need a little more than
> the Sun JVM for some reason), so that's the first entry. But what are
> the two 8MB anonymous allocations that aren't the 10MB heap? What is
> the 6MB of read/write libgcj mappings?

Hard to be sure, but propbably more heap. To find out for sure I'd put
a breakpoint on mmap().
Andrew.