RFR: JDK-8297796 GenShen: instrument the remembered set scan [v12]

[William Kemper]

On Thu, 22 Dec 2022 04:00:10 GMT, Y. Srinivas Ramakrishna <ysr at openjdk.org> wrote:

>> Maybe "Log cumulative card stats every so many scans of the remembered set"? "Cycle" is a bit overloaded. If I read this, I would expect to see a log message every 50 GC cycles, but with (probably) two rset scans per GC cycle, it would be closer to every 25 GC cycles.
>
> I reworded along the lines of your suggestion.
> 
> For the specific example you gave, we will in fact see one cumulative RS log message every 50 RS scans, and one cumulative UR log message every 50 UR scans, thus roughly one each every 50 GC cycles, if you will. The case when they may not be in lockstep might be if there were full gc's or degenerated cycles that did one (e.g. RS) but skipped the other (e.g. UR -- can this happen?), because we maintain two independent counters one for RS scans and one for UR scans.

Okay - thank you. Yes, Shenandoah will skip evacuation (and update references) if it finds a sufficient number of regions with no live objects after final mark.

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

PR: https://git.openjdk.org/shenandoah/pull/176