Modify scavenger GC count

[adpopescu]

Currently, scavengerStats is used to count increments and incrementScavengerStats is not used to count anything. This change aligns scavengerStats with cycles and incrementScavengerStats with increments.

[adpopescu]

@amicic

[amicic]

this can be simplified away, so that we have only the else clause

bool
MM_ScavengerStats::isAvailable(MM_EnvironmentBase *env) {
	if (env->getExtensions()->isConcurrentScavengerEnabled()) {
		/* with CS, we count STW increments (2 per each cycle) */
		return (_gcCount > 1);
	} else {
		return (_gcCount > 0);
	}
}

[adpopescu]

I've made the change to isAvailable as well @amicic

[amicic]

I've made the change to isAvailable as well @amicic

Thanks. While this is a good simplification, looking more deeply we may have a problem....

MM_ScavengerStats::isAvailable() is used by Concurrent Global GC to determine that ScavengerStats have been gathered, which means that a full cycle has to complete.

So, the original spot where we moved gcCount++ is too early. There is a spot later in MM_Scavenger::mainThreadGarbageCollect that checks if it's the last increment that should be better. Let's put it first thing in that block.

[adpopescu]

I moved it to after it reports the cycle end.

[amicic]

Let's try to piggyback one more thing to this:

let's introduce a clone of j9gc_get_unique_GC_count, but have it based on OMR/GC (nothing J9 specific):

GCExtensions::getUniqueGCCycleCount()

which will then be called by j9gc_get_unique_GC_count (updated later in a J9 PR) and potentially used elsewhere in OMR/GC

[amicic]

argh, reopening

[adpopescu]

I've added the get function as well.

[amicic]

I've added the get function as well.

there is a spot you originally updated (but reverted) in Collector.cpp where you can use it

[amicic]

@dsouzai please, reivew/merge

[amicic]

jenkins build all

[amicic]

@babsingh please, review/merge

[dsouzai]

I'm ok to step aside to let Babneet be committer for this PR since it involves changes outside the compiler; however, this PR is still in draft state, so it will need to be marked Ready for review before it can be merged.

[babsingh]

minor nits

[babsingh]

jenkins build all