Strage jmap heap output for G1 on 32bit JVM

Jakub Kubryński jk at codearte.io
Wed May 20 20:46:10 UTC 2015


I've checked with latest JDK 9 and it's OK. However 8u60 still reports
incorrect number of regions for Xmx2g. For -Xmx2046m it's OK and for
-Xmx2047m there are 14336 regions reported and eden capacity is 15032385536
(14336.0MB).

I don't know PrintHeapAtExit flag but I've added PrintHeapAtGC and it
reported:

Heap
 garbage-first heap   total 125952K, used 99580K [0x66600000, 0x667001ec,
0xe6600000)
  region size 1024K, 62 young (63488K), 7 survivors (7168K)
 Metaspace       used 29856K, capacity 30136K, committed 30208K, reserved
31024K

Cheers,
Kuba


2015-05-20 17:48 GMT+02:00 Jesper Wilhelmsson <jesper.wilhelmsson at oracle.com
>:

> FYI, I filed JDK-8080784 to cover this issue.
>
> https://bugs.openjdk.java.net/browse/JDK-8080784
>
> /Jesper
>
>
> Jakub Kubryński skrev den 20/5/15 16:50:
>
>> Yes,  I'll check it on latest Jdk9 and let you know.
>>
>> Best,
>> Jakub
>>
>> 20 maj 2015 16:35 "Jesper Wilhelmsson" <jesper.wilhelmsson at oracle.com
>> <mailto:jesper.wilhelmsson at oracle.com>> napisał(a):
>>
>>     Ok. I tried that as well but it didn't reproduce.
>>
>>     After a closer look it seems as if it is the number of regions that
>> is wrong
>>     and causes the huge free size reported. There have been a few changes
>> in
>>     this area recently which may have fixed this issue.
>>
>>     Is it possible to try your reproducer with a recent build of JDK 9 or
>> the
>>     latest version of 8u from the OpenJDK source repositories?
>>     /Jesper
>>
>>
>>     Jakub Kubryński skrev den 20/5/15 15:23:
>>
>>         64 bit Linux with 32bit JVM.
>>
>>         Cheers,
>>         Jakub
>>
>>         20 maj 2015 15:18 "Jesper Wilhelmsson" <
>> jesper.wilhelmsson at oracle.com
>>         <mailto:jesper.wilhelmsson at oracle.com>
>>         <mailto:jesper.wilhelmsson at oracle.com
>>         <mailto:jesper.wilhelmsson at oracle.com>>> napisał(a):
>>
>>              Hi,
>>
>>              Does this reproduce every time?
>>              What platform is it?
>>
>>              I have tried to reproduce this on 32bit linux but can't see
>>         anything weird
>>              there. It seems likely that there is a variable with the
>> wrong type
>>              somewhere on the way. I'll see if I can find something.
>>              /Jesper
>>
>>
>>              Jakub Kubryński skrev den 15/5/15 17:22:
>>
>>                  Hi,
>>
>>                  I've just checked that on 32bit JVM (HotSpot 8u45) jmap
>> reports
>>         strange
>>                  region
>>                  information for G1 collector. As you can see Xmx is set
>> to 2G
>>         (which fits
>>                  MaxHeapSize) but regions count (almost 15k) and capacity
>> is
>>         incorrect.
>>                  Any ideas
>>                  why?
>>
>>                  Heap Configuration:
>>                       MinHeapFreeRatio         = 40
>>                       MaxHeapFreeRatio         = 70
>>                       MaxHeapSize              = 2147483648 <tel:
>> 2147483648>
>>         <tel:2147483648 <tel:2147483648>> (2048.0MB)
>>                       NewSize                  = 1048576 (1.0MB)
>>                       MaxNewSize               = 428867584 (409.0MB)
>>                       OldSize                  = 4194304 (4.0MB)
>>                       NewRatio                 = 2
>>                       SurvivorRatio            = 8
>>                       MetaspaceSize            = 16777216 (16.0MB)
>>                       CompressedClassSpaceSize = 1073741824 (1024.0MB)
>>                       MaxMetaspaceSize         = 4294963200
>> (4095.99609375MB)
>>                       G1HeapRegionSize         = 1048576 (1.0MB)
>>
>>                  Heap Usage:
>>                  G1 Heap:
>>                       regions  = 14336
>>                       capacity = 15032385536 <tel:15032385536> <tel:
>> 15032385536
>>         <tel:15032385536>> (14336.0MB)
>>                       used     = 76347888 (72.81101989746094MB)
>>                       free     = 14956037648 (14263.188980102539MB)
>>                       0.5078893687043872% used
>>
>>                  --
>>                  Best regards,
>>                  Jakub Kubrynski
>>
>>


-- 
Best regards,
Jakub Kubrynski
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