RFR: 8274178: Occupancy value in logging and JFR event is inaccurate in G1IHOPControl

[Thomas Schatzl]

On Wed, 29 Sep 2021 20:03:03 GMT, Man Cao <manc at openjdk.org> wrote:

> Hi all,
> 
> Could we have reviews for this minor fix for logging and JFR event occupancy number for G1? See https://bugs.openjdk.java.net/browse/JDK-8274178 for more details.
> 
> This fix is contributed by colleague Jonathan Joo <jonathanjoo at google.com>.

I am not completely sure this change is correct: the target occupancy is the occupancy we want to reach, which is 


void G1Policy::record_new_heap_size(uint new_number_of_regions) {
[...]
  _ihop_control->update_target_occupancy(new_number_of_regions * HeapRegion::GrainBytes);
}

i.e. the current committed amount of regions.

I think it is interesting for the user to see what the current usage (fraction of target occupancy, i.e. committed regions) is when marking starts.

The change has a valid point though: since `get_conc_mark_start_threshold` is compared towards the non-young occupancy. What about providing that information additionally instead of replacing the existing info?

Or alternatively only provide information compared against non young capacity (i.e. the `_target_occupancy` is, as mentioned, against the whole committed memory, not just non-young).

Thanks,
  Thomas

-------------

PR: https://git.openjdk.java.net/jdk/pull/5762