java process memory usage is higher than Xmx

[yao]

Hi Thomas,

Possibly remembered set size.
>
> Can you enable -XX:+UnlockDiagnosticVMOptions and -XX:
> +G1SummarizeRSetStats?
>
> The line
>
>   Total heap region rem set sizes = 5256086K.  Max = 8640K.
>
> gives you a good idea about remembered set size memory usage.
>

You are right, rem set occupies ~7GB

 Concurrent RS processed -1863202596 cards
  Of 12780432 completed buffers:
     12611979 ( 98.7%) by conc RS threads.
       168453 (  1.3%) by mutator threads.
  Conc RS threads times(s)
          0.00     0.00     0.00     0.00     0.00     0.00     0.00
0.00     0.00     0.00     0.00     0.00     0.00     0.00     0.00
0.00     0.00     0.00    \
 0.00
  Total heap region rem set sizes = 7520648K.  Max = 13256K.
  Static structures = 347K, free_lists = 28814K.
    141012349 occupied cards represented.
    Max size region =
93:(O)[0x00007fcb48000000,0x00007fcb4a000000,0x00007fcb4a000000], size =
13257K, occupied = 2639K.
    Did 0 coarsenings.

I copied above line from one of your responses to the "G1 GC clean up
> time is too long" thread, and it seems the remembered set takes ~5GB
> there.
>

I did set -XX:G1RSetRegionEntries=4096 to avoid coarsenings; however, the
cleanup time seems not being reduced, it is still around 700 milliseconds,
althrough there is no coarsenings.

Any hint for tuning ? Because I want process with G1 use the same heap as
CMS to compare the performance. But I cannot do so if rem set is that
large, the process will be likely killed by OOM killed if I gave more
memory.

-Shengzhe


On Mon, Jan 6, 2014 at 1:43 PM, Thomas Schatzl <thomas.schatzl at oracle.com>wrote:

> Hi,
>
> On Mon, 2014-01-06 at 12:03 -0800, yao wrote:
> > Hi All,
> >
> > I have a java process (HBase region server process ) running under
> > Java 7 (1.7.0_40-b43) with G1 enabled. Both Xms and Xmx are the same.
> > After running process for a few hours, I see the actual memory used by
> > the process is about 10 percent higher than given Xmx. Has anyone
> > experienced the similar when use Java 7 or G1 ? Is there useful tools
> > to diagnose the cause ?
> >
> >
> > I've tried jmap but the output doesn't say anything about high memory
> > usage. FYI, the java process use a large heap (90GB), but the actual
> > memory usage ($ top) is about 99GB.
> >
> Possibly remembered set size.
>
> Can you enable -XX:+UnlockDiagnosticVMOptions and -XX:
> +G1SummarizeRSetStats?
>
> The line
>
>   Total heap region rem set sizes = 5256086K.  Max = 8640K.
>
> gives you a good idea about remembered set size memory usage.
>
> I copied above line from one of your responses to the "G1 GC clean up
> time is too long" thread, and it seems the remembered set takes ~5GB
> there.
>
> Hth,
> Thomas
>
>
>
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