RFR: 8335126: Shenandoah: Improve OOM handling [v2]

[Kelvin Nilsen]

> 1. Throw OOM after failed allocation request following a Full GC (rather
>    than retrying as long as Full GC makes good progress because
>    repeatedly retrying the allocation request creates brown-out behavior
>    with no identified benefits on real-world workloads)
> 
> 2. Count a successful allocation following a blocking
>    handle_allocation_failure() request to be good GC progress.
>    Otherwise, we increment gc_no_progress_count in full GCs that
>    have bad progress but successful allocations, and this causes
>    unwanted failure to even try a full GC in a different thread after
>    an out-of-memory condition might have been resolved in this thread.
> 
> 3. Count a completed concurrent GC cycle as good progress, regardless
>    of how much memory it might have been able to reclaim.  The fact that
>    concurrent GC succeeded without allocation failure and without
>    degeneration is considered good progress.  Successful concurrent
>    GCs between Full GCs will reset the gc_no_progress_count to zero.
> 
> 4. Do not count degenerated cycles as having no-progress.  If a
>    degenerated cycle has no progress, it will upgrade to full GC.
>    The upgraded full GC will evaluate its own progress.  We don't
>    want to count this "same [upgraded] cycle" twice.
> 
> These changes have been tested over a variety of workloads and standard tests.  These changes have also been tested with the generational mode of Shenandoah.  It appears these changes provide more robust and consistent handling across a diversity of scenarios than the original implementation.

Kelvin Nilsen has updated the pull request incrementally with one additional commit since the last revision:

  Change TODO comment to reference JBS issue

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/19912/files
  - new: https://git.openjdk.org/jdk/pull/19912/files/439d394c..24cd0fa6

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19912&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19912&range=00-01

  Stats: 15 lines in 1 file changed: 0 ins; 14 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/19912.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19912/head:pull/19912

PR: https://git.openjdk.org/jdk/pull/19912