RFR(S) 8153843: G1CardLiveDataHelper incorrectly sets next_live_bytes on dead humongous regions

Derek White derek.white at oracle.com
Tue Apr 12 17:27:13 UTC 2016

On 4/12/16 12:40 PM, Derek White wrote:
> On 4/12/16 8:57 AM, Mikael Gerdin wrote:
>> Hi Derek, Tom
>> Are you planning to re-review webrev.1 or can I push this?
>> http://cr.openjdk.java.net/~mgerdin/8153843/webrev.1/
>> /Mikael
> Hi Mikael,
> My only question is about the issue Thomas pointed out and you fixed:
> g1CollectedHeap.cpp, Line 2946.
> I am surprised that "Dead objects cannot be eager reclaim candidates" 
> -  I thought they were the perfect eager reclaim candidates. Should it 
> be that we simply declare victory and return true at line 2951 
> (bypassing the unsafe stuff)?

OK, answering my own question :-)
  - Derek, please read the big block comment. If the object is dead we 
can't prove all of the constraints listed are satisfied.

But it might be a good idea to tag humongous regions that don't contain 
references at humongous object allocation time. Then we should be able 
to do eager reclaim without looking at the Klass.


  - Derek
> Otherwise everything looks fine to me.
> Thanks,
>  - Derek

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