RFR: 8199927: Make WhiteBox more GC agnostic

[Aleksey Shipilev]

On 03/22/2018 10:04 AM, Per Liden wrote:
> On 03/21/2018 04:03 PM, Aleksey Shipilev wrote:
>> This is a little dizzy, because I would have expected gc.isSelected() would tell me exactly what GC
>> was being selected:
>>
>>   isAcceptable = gc.isSupported() && (gc.isSelected() || GC.isSelectedErgonomically());
>>
>> ...so it should be just:
>>
>>   for (GC gc : GC.values()) {
>>     map.put("vm.gc." + gc.name(), "" + gc.isSelected());
>>   }
>>
> 
> The way VMProps works and how the properties are set up can indeed make you a little dizzy. For
> example, vm.gc.Parallel=true doesn't necessarily mean that ParallelGC was "selected", just that it's
> an "acceptable" configuration.
> 
> A test running with an explicit -XX:UseG1GC flag will get:
> vm.gc.Serial=false
> vm.gc.Parallel=false
> vm.gc.CMS=false
> vm.gc.G1=true
> 
> And a test running with no explicit GC flag (which selects G1 ergonomically), will get:
> vm.gc.Serial=true
> vm.gc.Parallel=true
> vm.gc.CMS=true
> vm.gc.G1=true

Ewww, messy. I naively thought vm.gc.* filters for jtregs are filtering based on what GC was
actually running. But this is another thing to follow-up on. The patch itself looks good then.

-Aleksey

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