RFR 8015391: NPG: With -XX:+UseCompressedKlassPointers OOME due to exhausted metadat, a space could occur when metaspace is almost empty

[Jon Masamitsu]

http://cr.openjdk.java.net/~coleenp/8015391/src/share/vm/memory/metaspace.cpp.frames.html

> 2673   size_t specialized_count = 0, small_count = 0, medium_count = 0, large_count = 0;
> 2675   size_t cls_specialized_count = 0, cls_small_count = 0, cls_medium_count = 0, cls_large_count = 0;

Not introduced by your change but

humongous_count instead of large_count
and
cls_humongous_count instead of cls_large_count

would be more consistent.

http://cr.openjdk.java.net/~coleenp/8015391/src/share/vm/classfile/classLoaderData.cpp.frames.html

I'd suggest adding Metaspace::AppClassMetaspaceType
>   385     } else if (SystemDictionary::is_app_class_loader(class_loader())) {
>   386       if (TraceClassLoaderData && Verbose && class_loader() != NULL) {
>   387         tty->print_cr("sun/misc/Launcher$AppClassLoader class loader");
>   388       }
>   389       set_metaspace(new Metaspace(_metaspace_lock, Metaspace::BootMetaspaceType));
and adding a flag InitialAppClassLoaderMetaspaceSize.  It's not obvious 
to me
that we should always be reserving  the same amount of space for the 
AppClassLoader
as the BootClassLoader.   The same default is OK with me.

Rest looks good.

Jon


On 6/20/13 9:26 AM, Coleen Phillimore wrote:
> Summary: Allocate medium chunks for class metaspace when class loader 
> has lots of classes
>
> I originally made class metaspace keep small chunks and not start 
> allocating from medium chunks, because I thought with only Klass 
> objects, small chunks is enough.  This test has a large set of class 
> loaders who have a lot of classes, so allocated thousands of small 
> chunks each.  Class loaders with that many classes should start 
> allocating from medium chunks, for class metaspace.
>
> I also increased the ClassMediumChunk size to 4k and measured a lot 
> less fragmentation waste than 1K or 2K for this test.  Lastly, the 
> AppClassLoader instance should have as large of an initial metaspace 
> as the bootclass loader.
>
> Tested with vm.quick.testlist and the failing test.
>
> open webrev at http://cr.openjdk.java.net/~coleenp/8015391/
> bug link at http://bugs.sun.com/view_bug.do?bug_id=8015391
> local bug link https://jbs.oracle.com/bugs/browse/JDK-8015391
>
> Thanks,
> Coleen
>