JEP 248: Make G1 the Default Garbage Collector

Yu Zhang yu.zhang at oracle.com
Tue Jun 2 18:33:07 UTC 2015


sorry if this is a duplicate message. I had some problems sending it 
earlier.

The correlation between young gc pause and occupancy in tenure, might be 
related to Remember Set operations. Do you see ScanRS/UpdateRS goes up 
with the tenure occupancy is high?

If the occupancy of a region in old gen is higher than 
G1MixedLiveThresholdPercent(default 65 before 8u40, 85 8u40 and later), 
then it is not considered as a candidate for cset.

Thanks,
Jenny

On 6/2/2015 5:19 AM, Kirk Pepperdine wrote:
> Hi,
>
> I can show you a direct correlation between young gen pauses and 
> occupancy of Tenured. In fact please find attached graphs from work I 
> did on Monday. What I do know is that under normal operations there 
> are regions that I wished could be collected that can’t be collected. 
> I say this because they don’t meet the thresholds to be included in 
> the CSet. That said, the amount of dead in each of the tenured regions 
> is enough that overall there is a visible negative effect on GC pause 
> times. So, I think I'd like a continuous concurrent cleaning of 
> tenured regions or something else that I’ve not quite thought through 
> just yet. What I do know is that if I run a full gc, the pause time 
> picture clears up because the regions that wouldn’t get collected do 
> and that reduces the “live set”. Some where tucked away I’ve got 
> others logs that demonstrate this effect. I’ll see if I can dig it up.
>
> Regards,
> Kirk
> PS, once we’re finished with this conversation I’d like to tackle 
> safe-pointing behavior. I think Charlie knows what I’m talking about.

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