RFR: 8234654: ZGC: Only disarm NMethods when marking/relocating code roots

[Per Liden]

Thanks for reviewing. I'll fold the suggested changes into the patch.

/Per

On 12/9/19 10:29 PM, Stefan Karlsson wrote:
> Reworked the patch a bit, because I wanted to move _disarm_nmethod out 
> from the iterator and into the closures:
> 
> https://cr.openjdk.java.net/~stefank/8234654/webrev.01.delta/
> https://cr.openjdk.java.net/~stefank/8234654/webrev.01/
> 
> - Ripped out _disarm_nmethod from the ZRootsIterator.
> 
> - Added a should_disarm_nmethod() virtual function to the closure. The 
> mark and relocation closures return true. Had a version that introduced 
> a ZRootsIterator::do_code_blob analogous to ZRootsIterator::do_thread, 
> but we don't need that flexibility right now, so backed away from that 
> in favor of more straight forward code.
> 
> - Removed closure indirection in ZRootsIteratorCodeBlobClosure.
> 
> - Changed to use ZNMethod::nmethod_oops_do instead of nm->oops_do and 
> nm->fix_oop_relocations, since it's faster .
> 
> - Changed to use ZNMethod::disarm(nm) instead of _bs->disarm(nm), since 
> it hides the _bs retrieval.
> 
> - Added armed state assert.
> 
> This passes tier1-7 of ZGC testing.
> 
> Sat down with Per for the final version of this. Either we fold this 
> patch into his change, or I'll add this as a patch afterwards.
> 
> Thanks,
> StefanK
> 
> 
> On 2019-12-09 10:17, Per Liden wrote:
>> Here's an updated webrev, which removes the "assert(is_armed, ...)" 
>> BarrierSetNMethod::disarm(), as it's a bit too strict. Also, added the 
>> "if (ZNMethod::is_armed(nm))" to the ZNMethodUnlinkClosure, so avoid 
>> walking to oops if it's already disarmed.
>>
>> http://cr.openjdk.java.net/~pliden/8234654/webrev.1
>>
>> /Per
>>
>> On 11/22/19 3:38 PM, Per Liden wrote:
>>> Thanks Erik!
>>>
>>> /Per
>>>
>>> On 11/22/19 3:35 PM, erik.osterlund at oracle.com wrote:
>>>> Hi Per,
>>>>
>>>> Looks good.
>>>>
>>>> Thanks,
>>>> /Erik
>>>>
>>>> On 11/22/19 3:03 PM, Per Liden wrote:
>>>>> ZRootIterator will currently always try to disarm on-stack 
>>>>> NMethods. Strictly speaking, we should only do this when 
>>>>> marking/relocating code roots, not when e.g. iterating the heap.
>>>>>
>>>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8234654
>>>>> Webrev: http://cr.openjdk.java.net/~pliden/8234654/webrev.0
>>>>>
>>>>> /Per
>>>>
>