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

[Zoltán Majó]

Hi,



On 01/11/2016 02:11 PM, Zoltán Majó wrote:
> [...]
> 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 test contains and unnecessary @library tag and package import. The 
year in the copyright statement must be changed as well (to 2016).

Here is the webrev with those changes:
http://cr.openjdk.java.net/~zmajo/8086053/webrev.02/

Sorry for the noise.

Thank you and best regards,


Zoltan


>
> 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
>>>
>