[9] RFR (M): 8086053: Address inconsistencies regarding ZeroTLAB

[Tobias Hartmann]

Hi Zoltan,

looks good to me!

Best,
Tobias

On 11.01.2016 14:11, Zoltán Majó wrote:
> Hi Tobias,
> 
> 
> On 01/11/2016 09:48 AM, Tobias Hartmann wrote:
>> Hi Zoltan,
>>
>> looks good to me.
> 
> thank you for the feedback!
> 
>> Do you think it would make sense to add a regression test running with flag combinations like -XX:-UseTLAB and -XX:+ZeroTLAB to catch the missing initialization?
> 
> Yes, that is a good idea. I added a test that launches the VM with all flag combinations and also with different GCs. I did the same what the test does to reproduce the original failure.
> 
> Here is the updated webrev:
> http://cr.openjdk.java.net/~zmajo/8086053/webrev.01/
> 
> The newly added test passes on all supported platforms.
> 
> Thank you and best regards,
> 
> 
> Zoltan
> 
>>
>> Best,
>> Tobias
>>
>>
>> On 08.01.2016 12:06, Zoltán Majó wrote:
>>> Hi,
>>>
>>>
>>> please review the patch for 8086053.
>>>
>>> https://bugs.openjdk.java.net/browse/JDK-8086053
>>>
>>> Problem: With ZeroTLAB enabled, the GC is supposed to zero-fill newly allocated TLAB regions. With ZeroTLAB disabled, the interpreter and compiled code should assume the responsibility to zero-fill newly allocated regions.
>>> Currently, the handling of the ZeroTLAB flag shows some inconsistencies between the GC and the compilers. These inconsistencies lead to newly allocated regions not being filled with zeros.
>>>
>>> Solution: Address the following:
>>> - With -XX:+FastTLABRefill, C1-compiled code refills the TLAB without notifying the GC. As a result, the newly allocated TLAB is not initialized with zero. Add TLAB initialization code to C1.
>>> - With -XX:+ZeroTLAB, the C2 compiler skips zero-initialization of newly allocated objects/arrays even if TLAB allocation is disabled. Add stricter conditions to C2 on when to skip filling objects/arrays with zero.
>>>
>>> Webrev:
>>> http://cr.openjdk.java.net/~zmajo/8086053/webrev.00/
>>>
>>> Testing:
>>> - local testing (linux_x86_64) of failing test case with -XX:+UseG1GC and -XX:+UseSerialGC;
>>> - JPRT;
>>> - all hotspot tests on all platforms affected by the change using all combinations of +/-UseTLAB and +/-ZeroTLAB.
>>>
>>> Thank you and best regards,
>>>
>>>
>>> Zoltan
>>>
>