RFR (S): 8023021: Unnecessary clearing of the card table introduced by the fix for JDK-8023013

Bengt Rutisson bengt.rutisson at oracle.com
Thu Aug 15 01:04:45 PDT 2013


Thanks, Stefan!

Bengt


On 8/15/13 10:03 AM, Stefan Karlsson wrote:
> On 8/14/13 4:04 PM, Bengt Rutisson wrote:
>>
>> Hi all,
>>
>> Erik discovered a bug with the change for JDK-8023013 that I just 
>> pushed. With my change we will do some unnecessary clearing of the 
>> card table.
>>
>> Here's a webrev to fix that:
>> http://cr.openjdk.java.net/~brutisso/8023021/webrev.00/
>
> Looks good to me.
>
> StefanK
>>
>> Thanks Erik for finding this!
>>
>> From the bug report:
>>
>> The fix for JDK-8023013 "Use specific generations rather than 
>> generation iteration" introduced unnecessary clearing of the card table.
>>
>> This loop (which existed both in CardTableRS::clear_into_younger() 
>> and CardTableRS::invalidate_or_clear()):
>>
>>   Generation* g = gen;
>>   for(Generation* prev_gen = gch->prev_gen(g); prev_gen != NULL;
>>       g = prev_gen, prev_gen = gch->prev_gen(g)) {
>>     ...
>>   }
>>
>> was translated in to one call for the old generation and one for the 
>> young generation. But this is wrong. The loop is actually not a loop 
>> when we only have two generations. These methods are only called with 
>> gen being the old generation, so the translation should be to only do 
>> one call to the old generation. No work should be done for the young 
>> generation.
>>
>>
>> Thanks,
>> Bengt
>
>



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