RFR(XXS): 8017070: G1: assert(_card_counts[card_num] <= G1ConcRSHotCardLimit) failed

John Cuthbertson john.cuthbertson at oracle.com
Fri Jun 28 20:54:06 UTC 2013

Hi Tao,

Thanks for the review.


On 6/28/2013 12:35 PM, Tao Mao wrote:
> looks good to me.
> Tao
> On 6/28/13 12:01 PM, John Cuthbertson wrote:
>> Hi All,
>> Can I couple of volunteers review this extremely small change? The 
>> webrev can be found at: 
>> http://cr.openjdk.java.net/~johnc/8017070/webrev.0/
>> Summary:
>> The assert that fired is invalid. A card can be added to more than 
>> one update buffer since reads and writes to the card table are not 
>> atomic. If two threads end up refining the card at the same time then 
>> the count for that card can be incremented twice. If count is just 
>> below the hot threshold, the double increment will trip the assert. 
>> Since the card was enqueued by two different threads we do want the 
>> the double increment to more accurately reflect how hot the card is. 
>> I have removed the invalid assert and use a bounding expression to 
>> assign the new count value.
>> Testing:
>> Weblogic+medrec on the failing SQE machine (though I couldn't 
>> reproduce the original problem)
>> Weblogic+medrec on an Intel Haswell machine
>> GC test suite
>> jprt.
>> Thanks,
>> JohnC

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