G1 GC heap size is not bounded ?

[YU ZHANG]

Shengzhe,

All gcs have some memory overhead.  G1 might have more compared to other 
gcs.

Can you share your data about what have increased?

Thanks,
Jenny

On 2/18/2014 11:41 AM, yao wrote:
> Hi All,
>
> We've tracked our system memory usage for a week and found it seems 
> stop increasing when reaching 100G. Besides RSet, it looks like G1 
> also allocates other data structure in off-heap manner. I have a 
> follow up question, could we restrict the application memory usage 
> equal to what we set in -Xmx when G1 is enabled ? Assume application 
> itself doesn't allocate data in off-heap manner, that will make 
> application memory usage more predictable.
>
> Thanks
> Shengzhe
>
>
> On Mon, Feb 10, 2014 at 2:06 PM, yao <yaoshengzhe at gmail.com 
> <mailto:yaoshengzhe at gmail.com>> wrote:
>
>     Hi Ramki,
>
>     JDK version is  1.7.0_40
>
>     -Shengzhe
>
>
>     On Mon, Feb 10, 2014 at 1:36 PM, Srinivas Ramakrishna
>     <ysr1729 at gmail.com <mailto:ysr1729 at gmail.com>> wrote:
>
>         Hi Shengzhe --
>
>         What's the version of JDK where you're running into this
>         issue, and has the JVM had any STW full gc's because of mixed
>         gc's not keeping up?
>
>         -- ramki
>
>
>         On Mon, Feb 10, 2014 at 11:39 AM, yao <yaoshengzhe at gmail.com
>         <mailto:yaoshengzhe at gmail.com>> wrote:
>
>             Hi All,
>
>             We've enabled G1 GC on our cluster for about 1 month and
>             recently we observed the heap size keeps growing (via RES
>             column in top), though very slowly. My question is, is
>             there a way to bound heap size for G1 GC ?
>
>             We set heap size to 82G
>
>             /-Xms83868m -Xmx83868m -XX:+UnlockExperimentalVMOptions
>             -XX:+UseG1GC
>             /
>             We found RES column is about 100G, (a few days ago it was
>             about 93G)
>
>             *$ top*
>             PID USER      PR  NI  VIRT  RES SHR S %CPU %MEM    TIME+ 
>             COMMAND
>             5757 hbase     20   0  104g *100g* 5240 S 271.3 79.6
>             177771:41 java
>
>             From previous discussion, Thomas Schatzl pointed out this
>             might be due to large RSet. From below lines in gc log, we
>             found RSet size is about 10.5G. So we get Xmx + RSet = 82G
>             + 10.5G = 92.5G, here you can see there are still
>             unexplained 7.5G data occupied our off-heap.
>
>             RSet log:
>
>             / Concurrent RS processed -1601420092 cards
>               Of 651507426 completed buffers:
>                  634241940 ( 97.3%) by conc RS threads.
>                  17265486 (  2.7%) 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     0.00     0.00 0.00     0.00     0.00
>               Total heap region rem set sizes = 10980692K.  Max = 16182K.
>               Static structures = 563K, free_lists = 78882K.
>                 197990656 occupied cards represented.
>                 Max size region =
>             165:(O)[0x00007f0ce0000000,0x00007f0ce2000000,0x00007f0ce2000000],
>             size = 16183K, occupied = 3474K.
>                 Did 0 coarsenings./
>
>             Thanks
>             -Shengzhe
>
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