MaxMetaspaceSize and CompressedClassSpaceSize

[Jon Masamitsu]

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
>