RFR: 8342927: GenShen: Guarantee slices of time for coalesce and filling [v2]

[William Kemper]

> By design, young collections may preempt old collections. However, in some cases, this leads to starvation of old collection cycles. When old generation collections cannot make progress, the system continues to get "backed up" until an eventual degenerated or full GC cleans out the old generation. Genshen already has a mechanism to guarantee progress for old marking. It should be extended to also provide for coalescing and filling.

William Kemper has updated the pull request incrementally with one additional commit since the last revision:

  Update description of ShenandoahMinimumOldTimeMs

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Changes:
  - all: https://git.openjdk.org/shenandoah/pull/526/files
  - new: https://git.openjdk.org/shenandoah/pull/526/files/e3ee59ba..a0aac0b6

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=shenandoah&pr=526&range=01
 - incr: https://webrevs.openjdk.org/?repo=shenandoah&pr=526&range=00-01

  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/shenandoah/pull/526.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/526/head:pull/526

PR: https://git.openjdk.org/shenandoah/pull/526