RFR: Abandon mixed collections if all candidates are pinned

[Kelvin Nilsen]

On Wed, 29 Mar 2023 21:57:43 GMT, William Kemper <wkemper at openjdk.org> wrote:

> A new `WAITING_FOR_FILL` state has been added to the old generation. This state is now entered when all the candidates for a mixed collection cycle are found to be pinned (which should be quite rare). This state permits a new old generation collection cycle to begin (which itself begins with making these regions parseable).
> 
> This change also adds a new diagnostic flag `ShenandoahCoalesceChance` which is the probability (expressed as a percentage) of abandoning all the candidates of a mixed collection. Any abandoned candidate regions will be made parseable.

this is nice.  thanks.

src/hotspot/share/gc/shenandoah/shenandoah_globals.hpp line 454:

> 452:           "Testing: make lots of artificial allocation failures.")          \
> 453:                                                                             \
> 454:   product(uintx, ShenandoahCoalesceChance, 0, DIAGNOSTIC,                   \

Should this read: "Abandon remaining mixed collections with this likelihood.  Following each mixed collection, we abandon all remaining mixed collection candidate regions with likelihood ShenandoahCoalesceChance." ?  (I don't think this is precisely abandon this percentage of mixed collections".)

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Marked as reviewed by kdnilsen (Committer).

PR Review: https://git.openjdk.org/shenandoah/pull/236#pullrequestreview-1364120423
PR Review Comment: https://git.openjdk.org/shenandoah/pull/236#discussion_r1152593828