RFR: 8335126: Shenandoah: Improve OOM handling

[Y. Srinivas Ramakrishna]

On Wed, 26 Jun 2024 17:51:36 GMT, Kelvin Nilsen <kdnilsen at openjdk.org> wrote:

> 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.

Reviewed. The code changes look good to me, so I am approving this.

Will discuss the terminology questions I raised earlier in our discussion tomorrow.

I think we want to move some of the big comments out of line and into a block comment at the start of this method. We also want to clearly document the intent of the terms "good_progress", "no_progress", etc. somewhere in the code, probably in the header files for the methods that are named `*_progress_*`.

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Marked as reviewed by ysr (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/19912#pullrequestreview-2143124067