Re: [rvm-research] Runtime Exception when running JMX

On 17/06/18 03:26, Khaled Z Mahmoud wrote:
> Hi,
>
> Thanks. That now works and the exception is gone.
> I realized that JMX operations in Jikes are very slow. Sometimes they 
> take 45 or 50 milliseconds and sometimes more.
>
> Are there any synchronized variables shared with the Jikes run-time 
> that could potentially slowdown jikes if I read JMX frequently ?
> I have experience 10 fold increase in application execution time when 
> reading JMX information.
>
No mystery here, just read through the code
> MemoryMXBean memMx = ManagementFactory.getMemoryMXBean();
>         memMx.getHeapMemoryUsage().getCommitted();
>         memMx.getHeapMemoryUsage().getUsed();

You can halve the runtime of this by saying

MemoryMXBean memMx = ManagementFactory.getMemoryMXBean();
MemoryUsage usage = memMx.getHeapMemoryUsage();
usage.getCommitted();
usage.getUsed();

getHeapMemoryUsage() iterates over all the spaces in the heap adding up 
the memory usage, then allocates a MemoryUsage instance to hold the 
result.  Not something I'd use for high frequency instrumentation.

Take a look at the methods of org.mmtk.plan.Plan that are listed under 
'VM Accounting'.  These are the methods MMTk uses in its slow-path to 
decide whether a GC is required, so they should be several orders of 
magnitude faster than the JMX interface.

You'll probably take a little time to adjust to how MMTk views memory 
usage: eg, used memory isn't exactly the sum of the sizes of the live 
objects, it's more complicated than that.

cheers

>
>
>
> Regards,
> Khaed Mahmoud
>
> On Sat, Jun 16, 2018 at 7:29 AM, Erik Brangs <[email protected] 
> <mailto:[email protected]>> wrote:
>
>     Hi,
>
>     On 16.06.2018 03:28, Khaled Z Mahmoud wrote:
>     > *I get the below exception:*
>     > Unexpected exception thrown in timer thread: java.lang.IllegalArgumentException: Maximum value of 0 is
>     below 42733568, the amount committed.
>     > java.lang.IllegalArgumentException: Maximum value of 0 is below
>     42733568, the amount committed.
>     >    at java.lang.management.MemoryUsage.<init>(MemoryUsage.java:141)
>     >    at
>     org.jikesrvm.mm.mminterface.JMXSupport.getUsage(JMXSupport.java:159)
>     >    at
>     gnu.java.lang.management.VMMemoryMXBeanImpl.getUsage(VMMemoryMXBeanImpl.java:79)
>     >    at
>     gnu.java.lang.management.VMMemoryMXBeanImpl.getHeapMemoryUsage(VMMemoryMXBeanImpl.java:28)
>     >    at
>     gnu.java.lang.management.MemoryMXBeanImpl.getHeapMemoryUsage(MemoryMXBeanImpl.java:149)
>     >    at org.jikesrvm.scheduler.TimerThread.run(TimerThread.java:97)
>     >
>     > Any ideas ??
>
>     this was a bug in the Jikes RVM JMX implementation. It didn't
>     handle discontiguous spaces correctly. I've changed the
>     implementation to set the maximum value to undefined when
>     discontiguous spaces are used. The git commit id of the commit
>     with the fix is c065b7379b1db7c15e75b452b634ee0199ff7ce5 .
>
>
>     Kind regards,
>
>     Erik Brangs
>
>
>     >
>     > --
>     > Regards,
>     > Khaled Mahmoud
>     >
>     >
>     >
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> -- 
> Regards,
> Khaled Mahmoud
>
>
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