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

[Erik Österlund]

Hi Stefan,

Looks... even better!

Thanks,
/Erik

> On 9 Dec 2019, at 22:29, Stefan Karlsson <stefan.karlsson at oracle.com> 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
>>>> 
>