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

[Jon Masamitsu]

Looks good.

On 6/28/2013 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
>