[9] RFR(S): 8134493: Cleaning inline caches of unloaded nmethods should be done in sweeper

[Tobias Hartmann]

Thanks, Vladimir!

Best,
Tobias

On 28.08.2015 18:28, Vladimir Kozlov wrote:
> Nice! Looks good.
> 
> Thanks,
> Vladimir
> 
> On 8/28/15 2:47 AM, Tobias Hartmann wrote:
>> Thanks, Vladimir.
>>
>> On 28.08.2015 04:51, Vladimir Kozlov wrote:
>>> CodeCache::gc_epilogue() could be optimized more. When needs_cache_clean() is false we need to execute loop only in debug VM.
>>
>> Right, I changed the implementation to only execute the loop in the product VM if needs_cache_clean() is set and always execute it in the debug VM. Like this we also save the needs_cache_clean() checks in each loop iteration in the product VM.
>>
>> I changed nmethod::can_not_entrant_be_converted() to can_convert_to_zombie() because the name was misleading and caused some misconceptions in the past.
>>
>> http://cr.openjdk.java.net/~thartmann/8134493/webrev.01/
>>
>> Best,
>> Tobias
>>
>>>
>>> Otherwise it looks good.
>>>
>>> Thanks,
>>> Vladimir
>>>
>>> On 8/27/15 12:10 AM, Tobias Hartmann wrote:
>>>> Hi,
>>>>
>>>> please review the following patch.
>>>>
>>>> https://bugs.openjdk.java.net/browse/JDK-8134493
>>>> http://cr.openjdk.java.net/~thartmann/8134493/webrev.00/
>>>>
>>>> Problem:
>>>> This is a follow up on JDK-8075805 [1] which modified CodeCache::gc_epilogue() to clean the ICs of unloaded nmethods as well. The problem is that this code is executed at a safepoint and may affect safepoint duration. The other changes of JDK-8134493 are fine.
>>>>
>>>> Solution:
>>>> We do the cleaning of unloaded nmethods at the unloaded -> zombie transition in the sweeper. I also modified nmethod::cleanup_inline_caches() to not emit any transition stubs if the nmethod is already dead.
>>>>
>>>> As Martin Doerr pointed out in another thread, we have to be careful with accessing CompiledIC::cached_metadata() of unloaded nmethods. For example, the following scenario may happen (IC of A references B):
>>>>
>>>>       state of A       state of B
>>>> -------------------------------
>>>>       not-entrant
>>>> S   [not-on-stack]
>>>> S   zombie
>>>>                   unloaded
>>>>
>>>> Now the IC of A still references the unloaded nmethod B and is_call_to_compiled() will access the unloaded metadata. I fixed this by checking caller->is_alive().
>>>>
>>>> Thanks,
>>>> Tobias
>>>>
>>>> [1] https://bugs.openjdk.java.net/browse/JDK-8075805
>>>>
>>>>