RFR: JDK-8148736: Let the G1 heap transition log regions instead of bytes

kirk.pepperdine at gmail.com kirk.pepperdine at gmail.com
Mon Feb 1 13:13:54 UTC 2016


Hi Bengt,

>> 
>> 
>> Sorry but I hit the send too quickly. The occupancy numbers before and after the collection are the numbers that I’m not so happy losing. It is true that they never did add up but it was never more than what would be normal rounding error given that things are reported in K and M and not bytes. Even with the small errors, the numbers are incredibly useful.
> 
> 
> If  you multiply the region numbers that are now logged with the region size you get the same occupancy numbers as before. It is hard to say if the difference is small or not. It depends on the fragmentation and the region size. In Jenny's example for JDK-8147976 the difference was > 1G for a 50G heap. I find that too much of a difference to make the numbers feel reliable. The proposed change makes it clearer what is going on and why the difference is there.

Sorry to be repetitive here but I can’t get pass being feeling that this move represents a loss of information. If there is an inaccuracy in the measures I would be more comfortable finding out why the values are inaccurate rather than throwing the baby out with the bath water.

Kind regards,
Kirk



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