RFR(S) 8142436: [JVMCI] fix management of nmethod::_installed_code field

[Mikael Gerdin]

On 2015-11-11 17:19, Tom Rodriguez wrote:
>> Additionally, you can run with +G1VerifyHeapRegionCodeRoots to enable
>> verification of the heap region to nmethod mapping in order to detect
>> other issues which don't cause a crash right away.
>
> I didn’t know that existed.  That probably would have told me exactly
> what I wanted to know.  Why isn’t that on by default?  Too expensive?  I
> was getting crashes and VerifyBeforeGC didn’t find anything so I added
> verify logic that checked that no zombie methods are in the code root
> set, which helped me track down the bug.
> http://hg.openjdk.java.net/graal/graal-jvmci-8/rev/2d21c13d7829 Having
> at least minimal verification enabled all the time would be nicer, at
> least it would have been for me.  Failing this verify could suggest
> enabling G1VerifyHeapRegionCodeRoots.

I don't know why it's disabled by default, G1's verification is 
expensive enough that enabling it should not make a large impact I 
think. It's probably just a case of "if I don't enable it by default I 
don't have to measure its impact"

/Mikael

>
> tom
>
>>
>> /Mikael
>>
>>>
>>> tom
>>
>