RFR (S): [9+8u] Min region size should be 256K to allow small heaps

[Aleksey Shipilev]

On 03/03/2017 01:26 PM, Roman Kennke wrote:
> Am 03.03.2017 um 13:23 schrieb Aleksey Shipilev:
>> Hi,
>>
>> Turns out, some JDK tool launchers set -Xms8M. Shenandoah fails cryptically then:
>>
>> Error occurred during initialization of VM
>> Invalid -XX:ShenandoahMinRegionSize option
>>
>> While those tools configs are the actual culprit, we might want to bite the
>> bullet and afford those smaller heaps. And turns out, we supposed to! Because
>> the failure is due to requesting 10 regions, with SHR::MIN_REGION_SIZE being
>> 256K. But that ShenandoahMinRegionSize default is 1M, oops. I suggest we change
>> ShenandoahMinRegionSize to match MIN_REGION_SIZE:
>>   http://cr.openjdk.java.net/~shade/shenandoah/regionsizes-match/webrev.01/
>>
>> I don't want to depend on ShenandoahHeapRegion in *globals.hpp. Tests should
>> cover future discrepancies.
>>
>> The patch applies to 8u with some fuzz, and I will push it there simultaneously
>> with 9.
>>
>> Testing: hotspot_gc_shenandoah
> 
> Ok!
> 

Pushed:
  http://hg.openjdk.java.net/shenandoah/jdk9/hotspot/rev/710d02eae915
  http://hg.openjdk.java.net/shenandoah/jdk8u/hotspot/rev/fa1071cc5aee

-Aleksey