JFR: YoungGenerationConfiguration event

[tajila]

The YoungGenerationConfig event contains the following fields:

minSize - j9gc_get_minimum_young_generation_size()
maxSize - j9gc_get_maximum_young_generation_size()
newRatio - New ratio=N, where Young gen = (1/(1 + N)) * total Heap size

//total heap size - j9gc_get_maximum_heap_size()

The GCHeapConfig event only needs to be written in the initial chunk. In JFRChunkWriter::writeJFRChunk this event can be added along the other 1 time events if (0 == _vm->jfrState.jfrChunkCount) {.

Note, not all J9 GC policies have a nursery/tenure (AKA young/old generation), in these cases the answer for all fields is zero.

[tajila]

@adpopescu Please take a look at this issue

[adpopescu]

@tajila I assume where it says GCHeapConfig in the description, it's meant to be YoungGenerationConfig?

[tajila]

@tajila I assume where it says GCHeapConfig in the description, it's meant to be YoungGenerationConfig?

Yes

[adpopescu]

@tajila in the case where it's using another gc heap configuration, will it fill those values with zeroes? Or will they be populated with default values?

[tajila]

@tajila in the case where it's using another gc heap configuration, will it fill those values with zeroes? Or will they be populated with default values?

This event is only emitted once, in the first chunk.

[adpopescu]

I was referring to this comment you made:

Note, not all J9 GC policies have a nursery/tenure (AKA young/old generation), in these cases the answer for all fields is zero.

I checked the j9gc_get_maximum_young_generation_size and j9gc_get_minimum_young_generation_size functions and they return the value based on the GC scheme. So I don't need to worry about it on my end.

[adpopescu]

PR #21840

[tajila]

I was referring to this comment you made:

Okay, I understand now. I thought you were talking about something else. Please run with -Xgcpolicy:optavgpause, -Xgcpolicy:optthruput and -Xgcpolicy:balanced just to make sure everything is sane.