RFR: Improve evacuation instrumentation

[Kelvin Nilsen]

On Fri, 4 Nov 2022 21:24:21 GMT, William Kemper <wkemper at openjdk.org> wrote:

> This change adds instrumentation to reveal the following:
> * How many bytes were evacuated by gc workers and mutators
> * How many bytes were abandoned due to evacuation races
> * The age of survivors
> * The break down of targets for evacuation in the collection set
> 
> The implementation is based on a new thread local structure to track and aggregate these statistics.

Marked as reviewed by kdnilsen (Committer).

src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp line 858:

> 856:   // We squelch excessive reports to reduce noise in logs.  Squelch enforcement is not "perfect" because
> 857:   // this same code can be in-lined in multiple contexts, and each context will have its own copy of the static
> 858:   // last_report_epoch and this_epoch_report_count variables.

Is this comment still relevant.  Maybe not since the code is no longer in-lined in multiple contexts.

Thanks for this improvement to the code structure.  This should be relatively rare, so we don't want to in-line it everywhere.

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PR: https://git.openjdk.org/shenandoah/pull/167