MaxMetaspaceSize and CompressedClassSpaceSize

[Yasumasa Suenaga]

Hi Jon,

> Please send the hs_err log.  It will have a better description of the heap.

This is not crash (OutOfMemoryError). So I do not have hs_err log.


> The CompressedClassSpaceSize is the size reserved for the Class space.  The
> size of the compressed-class-space is included in the comparison with
> MaxMetaspaceSize
> only when the space is committed.  So no, it should not be compared to the
> MaxMetaspaceSize at initialization.

Reserved memory will affect overcommit memory in OS.
In case of Linux, it may cause of OOM-killer.
So I want to check CompressedClassSpaceSize before initialization.


> I would fix this in share/vm/memory/metaspace.cpp
> 
> Metaspace::global_initialize()
> 
> in the calculation of _first_chunk_word_size.
> 
>       _first_chunk_word_size = MIN2(InitialBootClassLoaderMetaspaceSize,
> MaxMetaspaceSize) / BytesPerWord;

Thank you for your suggestion.
May I file it to JBS?


Thanks,

Yasumasa


On 2015/06/12 4:01, Jon Masamitsu wrote:
> On 06/11/2015 03:52 AM, Yasumasa Suenaga wrote:
>> Hi all,
>>
>> I booted Tomcat 8 with "-XX:MaxMetaspaceSize=5m -XX:+PrintGCDetails",
>> but it failed.
>> I checked GC log, Java heap and Metaspace was NOT exhausted.
> 
> Please send the hs_err log.  It will have a better description of the heap.
> 
>> ------------
>> [Full GC (Last ditch collection) [Tenured: 1049K->1049K(10944K), 0.0050992 secs] 1049K->1049K(15936K), [Metaspace: 4871K->4871K(1056768K)], 0.0051411 secs] [Times: user=0.01 sys=0.00, real=0.00 secs]
>> [Full GC (Metadata GC Threshold) [Tenured: 1049K->1049K(10944K), 0.0050587 secs] 1049K->1049K(15936K), [Metaspace: 4871K->4871K(1056768K)], 0.0051023 secs] [Times: user=0.00 sys=0.00, real=0.01 secs]
>> [Full GC (Last ditch collection) [Tenured: 1049K->1049K(10944K), 0.0050200 secs] 1049K->1049K(15936K), [Metaspace: 4871K->4871K(1056768K)], 0.0050613 secs] [Times: user=0.01 sys=0.00, real=0.00 secs]
>>
>> Exception: java.lang.OutOfMemoryError thrown from the UncaughtExceptionHandler in thread "main"
>> ------------
>>
>> My environment:
>>     Fedora22 x86_64
>>      - kernel-4.0.4-303.fc22.x86_64
>>      - glibc-2.21-5.fc22.x86_64
>>      - java-1.8.0-openjdk-1.8.0.45-39.b14.fc22.x86_64
>>      - apache-tomcat-8.0.23
>>
>> This java process is enabled CompressedClassSpace (as default).
>> Metaspace size in GC log seems to be contained it (1GB).
>>
>> I checked arguments.cpp and metaspace.cpp, CompressedClassSpaceSize
>> does not seem to be checked consistent with MaxMetaspaceSize.
>>
>> Does JVM have to check CompressedClassSpaceSize and InitialBootClassLoaderMetaspaceSize
>> which are consistent with MaxMetaspaceSize?
> 
> The CompressedClassSpaceSize is the size reserved for the Class space.  The
> size of the compressed-class-space is included in the comparison with
> MaxMetaspaceSize
> only when the space is committed.  So no, it should not be compared to the
> MaxMetaspaceSize at initialization.
> 
>>
>> I think we can fix as below:
>> ------------
>> diff -r 85e2c3553384 src/share/vm/runtime/arguments.cpp
>> --- a/src/share/vm/runtime/arguments.cpp        Wed Jun 03 08:49:34 2015 +0900
>> +++ b/src/share/vm/runtime/arguments.cpp        Thu Jun 11 19:50:11 2015 +0900
>> @@ -2333,6 +2333,15 @@
>>      status = status && verify_interval(CompressedClassSpaceSize, 1*M, 3*G,
>>                                          "CompressedClassSpaceSize");
>>
>> +  if (UseCompressedClassPointers) {
>> +    status = status &&
>> +         ((CompressedClassSpaceSize + InitialBootClassLoaderMetaspaceSize)
>> +                                                           <= MaxMetaspaceSize);
>> +  } else {
>> +    status = status &&
>> +                (InitialBootClassLoaderMetaspaceSize <= MaxMetaspaceSize);
> 
> I would fix this in share/vm/memory/metaspace.cpp
> 
> Metaspace::global_initialize()
> 
> in the calculation of _first_chunk_word_size.
> 
>       _first_chunk_word_size = MIN2(InitialBootClassLoaderMetaspaceSize,
> MaxMetaspaceSize) / BytesPerWord;
> 
> 
> Jon
> 
> 
> 
>> +  }
>> +
>>      status = status && verify_interval(MarkStackSizeMax,
>>                                      1, (max_jint - 1), "MarkStackSizeMax");
>>      status = status && verify_interval(NUMAChunkResizeWeight, 0, 100, "NUMAChunkResizeWeight");
>> ------------
>>
>>
>> If it is accepted as a bug, I will file it to JBS and upload webrev.
>>
>>
>> Thanks,
>>
>> Yasumasa
>>