8369013: Shenandoah: passive mode should support enabling ShenandoahCardBarrier

[rgithubli]

WIP. Add card barriers to passive mode to test out the price of card barriers.

How this change is implemented is to instantiate the old region in passive mode - old region owns the card table so this would minimize the code change with a bit price of native memory. It does sound weird to have old gen in passive mode, but since passive mode is a just diagnostic mode, we'll go with it for the cleanliness of the change.

Pending tests. Probably also good to have a perf test to test card barrier cost?

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Issue

• JDK-8369013: Shenandoah: passive mode should support enabling ShenandoahCardBarrier (Enhancement - P4)

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[earthling-amzn]

This turned out to be simpler than expected. Nice work. I suggest some small changes.

[earthling-amzn]

I think we could simplify here by not using the _generation_sizer. It should be fine to pass max_capacity() instead of max_capacity_old here.

[rgithubli]

Yeah that'd be simpler. Updating. Thanks.

[earthling-amzn]

Can we assert that ShenandoahCardBarrier is on instead of removing this assertion?

[rgithubli]

Sure

[earthling-amzn]

I don't think we need this here.

[earthling-amzn]

Can we put these assertions back? I don't see any code in the PR that would invalidate these assertions. I also don't see any changes that would instantiate the generational heap for non generational mode, so if there is code trying to use the generational heap, its behavior will be undefined.

[rgithubli]

It would crash at here with the assertion: code. Provided some of the stacktrace below. It's mostly because we enabled card barrier flag and the code just fell through and assumes it's generational.

Would it be more appropriate to change this line to be ShenandoahHeap* heap = ShenandoahHeap::heap();?

Stack: [0x00007f1082bd2000,0x00007f1082cd2000],  sp=0x00007f1082cce370,  free space=1008k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V  [libjvm.so+0x13e0e90]  NativeStackPrinter::print_stack(outputStream*, char*, int, unsigned char*&, bool
, int)+0x70  (shenandoahGenerationalHeap.hpp:47)
V  [libjvm.so+0x18fd2e9]  VMError::report(outputStream*, bool)+0x1bff  (vmError.cpp:979)
V  [libjvm.so+0x1900d01]  VMError::report_and_die(int, char const*, char const*, __va_list_tag*, Thread*, 
unsigned char*, void const*, void const*, char const*, int, unsigned long)+0x8b1  (vmError.cpp:1887)
V  [libjvm.so+0xacf5ca]  report_vm_status_error(char const*, int, char const*, int, char const*)+0x0  (deb
ug.cpp:196)
V  [libjvm.so+0xacf33b]  print_error_for_unit_test(char const*, char const*, __va_list_tag*)+0x0  (debug.c
pp:149)
V  [libjvm.so+0x15bbec1]  ShenandoahAsserts::assert_generational(char const*, int)+0x8b  (shenandoahAssert
s.cpp:532)
V  [libjvm.so+0x15be196]  ShenandoahGenerationalHeap::heap()+0x19  (shenandoahGenerationalHeap.hpp:47)
V  [libjvm.so+0x16993bc]  void card_mark_barrier<narrowOop>(narrowOop*, oopDesc*)+0x73  (shenandoahReferenceProcessor.cpp:65)
V  [libjvm.so+0x169a2ac]  bool ShenandoahReferenceProcessor::discover<narrowOop>(oopDesc*, ReferenceType, unsigned int)+0x1da  (shenandoahReferenceProcessor.cpp:409)
V  [libjvm.so+0x1698a5d]  ShenandoahReferenceProcessor::discover_reference(oopDesc*, ReferenceType)+0xed  (shenandoahReferenceProcessor.cpp:433)
V  [libjvm.so+0x1684aeb]  bool InstanceRefKlass::try_discover<narrowOop, ShenandoahMarkRefsClosure<(ShenandoahGenerationType)0> >(oopDesc*, ReferenceType, ShenandoahMarkRefsClosure<(ShenandoahGenerationType)0>*)+0x77  (instanceRefKlass.inline.hpp:74)
V  [libjvm.so+0x1682bfc]  void InstanceRefKlass::oop_oop_iterate_discovery<narrowOop, ShenandoahMarkRefsClosure<(ShenandoahGenerationType)0>, AlwaysContains>(oopDesc*, ReferenceType, ShenandoahMarkRefsClosure<(ShenandoahGenerationType)0>*, AlwaysContains&)+0x2c  (instanceRefKlass.inline.hpp:84)
V  [libjvm.so+0x1680acc]  void InstanceRefKlass::oop_oop_iterate_ref_processing<narrowOop, ShenandoahMarkRefsClosure<(ShenandoahGenerationType)0>, AlwaysContains>(oopDesc*, ShenandoahMarkRefsClosure<(ShenandoahGenerationType)0>*, AlwaysContains&)+0x80  (instanceRefKlass.inline.hpp:111)
V  [libjvm.so+0x167ec2e]  void InstanceRefKlass::oop_oop_iterate_ref_processing<narrowOop, ShenandoahMarkRefsClosure<(ShenandoahGenerationType)0> >(oopDesc*, ShenandoahMarkRefsClosure<(ShenandoahGenerationType)0>*)+0x2c  (instanceRefKlass.inline.hpp:134)
V  [libjvm.so+0x167ba88]  void InstanceRefKlass::oop_oop_iterate<narrowOop, ShenandoahMarkRefsClosure<(ShenandoahGenerationType)0> >(oopDesc*, ShenandoahMarkRefsClosure<(ShenandoahGenerationType)0>*)+0x16c  (instanceRefKlass.inline.hpp:154)