MetaSpace and StackMapTable

[David Holmes]

Hi John,

Re-directing to hotspot-runtime-dev. Please drop the discuss mailing 
list in replies.

Thanks,
David

On 11/06/2020 6:03 am, john bergin wrote:
> Hi all.
> 
> I'm generating a bunch of classes at run-time with ASM (which automatically
> generates StackMapTable attributes) and when all the classes are
> loaded the *MethodAll
> *(bytecodes, StackMapTable, ...) column from *jmap -clstats *tells me that
> all classes account for about 100MB. When I generate the same classes with
> ASM but tell it *not* to compute the StackMapTable attributes and I switch
> class verification off (-noverify) *MethodAll* reduces to 55MB.
> 
> I'm interested to know:
>   - does the JVM free memory held in MetaSpace by StackMapTable attributes
> after class verification and a full GC? My testing shows it doesn't.
>   - is it possible to generate one StackMapTable entry for each method that
> would satisfy the verifier? I had a quick look at the code and it doesn't
> seem possible *ClassVerifier::verify_stackmap_table *
> http://hg.openjdk.java.net/jdk8/jdk8/hotspot/file/87ee5ee27509/src/share/vm/classfile/verifier.cpp
> 
> 
> Thanks,
> John.
>