RFR (S): Update ShenandoahHeapRegionSampling protocol

[Aleksey Shipilev]

I haven't seen the sampling in profiles. And it does not seem to affect phase
times in a noticeable way.

Thanks,
-Aleksey

On 02/01/2017 12:43 PM, Roman Kennke wrote:
> Yes!
> 
> Does the sampling affect performance in any measurable way?
> 
> Roman
> 
> Am Mittwoch, den 01.02.2017, 11:56 +0100 schrieb Aleksey Shipilev:
>> Hi,
>>
>> I would like to update the ShenandoahHeapRegionSampling a bit:
>>   http://cr.openjdk.java.net/~shade/shenandoah/sampling-update/webrev
>> .01/
>>
>> Changes:
>>   *) Record and maintain "recently allocated" region flag
>>   *) Steal more bits for region flags
>>   *) Rehash the flags order
>>   *) Coarsen region_size and used/live data to KB to make up for
>> stolen bits
>>   *) Update the sampling frequency to 40ms (25 FPS)
>>   *) ShenandoahHR:is_pinned enabled to be read outside the safepoint
>>
>> Testing: hotspot_gc_shenandoah
>>
>> Thanks,
>> -Aleksey
>>