RFR: Evacuate thread stack code oops

[Aleksey Shipilev]

Let me think more about this.

The reason to process them during STW is not because we want nmethod scan, but
because we are walking the thread stack for that closure. But you are right, it
should be the subset of all code roots.

That said, there are also suspicious CodeCacheSweeper field accepted by that
closure:
   CompiledMethod*       _scanned_compiled_method; // nmethod being scanned by
the sweeper

...

-Aleksey

On 06/30/2017 09:44 PM, Roman Kennke wrote:
> I am not sure I understand. I thought we want to evac them concurrently?
> Now you're moving them back to evacuating code roots at STW?
> 
> The thread stack code roots are oops in nmethods of methods currently on
> the stack, i.e. a subset of all code roots.
> 
> Do we understand why it's crashing there?
> Why do we have to evac thread stack code roots at stw, but the others
> concurrently? By the time we evac the others, they could have become on
> stack too?
> 
> Roman
> 
> Am 30.06.2017 um 21:37 schrieb Aleksey Shipilev:
>> I have seen crashes in here:
>>
>> V  [libjvm.so+0xc9b5a4]  SCMUpdateRefsClosure::do_oop(oopDesc**)+0x74
>> V  [libjvm.so+0xb05324]  nmethod::oops_do(OopClosure*, bool)+0x224
>> V  [libjvm.so+0x83813f]  CodeBlobToOopClosure::do_code_blob(CodeBlob*)+0x2f
>> V  [libjvm.so+0xd5adbe]  JavaThread::oops_do(OopClosure*, CodeBlobClosure*)+0x1ce
>> V  [libjvm.so+0xd5fe87]  Threads::possibly_parallel_oops_do(bool, OopClosure*,
>> CodeBlobClosure*, CodeBlobClosure*)+0x57
>> V  [libjvm.so+0xcad10c]
>> ShenandoahRootProcessor::process_java_roots(OopClosure*, CLDClosure*,
>> CLDClosure*, CodeBlobClosure*, CodeBlobClosure*, unsigned int)+0xdc
>>
>> There is a closure for walking thread stack code roots in
>> Threads::possibly_parallel_oops_do, but our evacuator passes NULL there. I think
>> it should pass our usual code roots closure. For concurrent code cache scan, we
>> want to evac those during STW while threads are not moving.
>>
>> See:
>>
>> http://cr.openjdk.java.net/~shade/shenandoah/codecache-conc-evac-threadroots/webrev.01
>>
>> Testing: hotspot_gc_shenandoah
>>
>> Thanks,
>> -Aleksey
>>
>