RFR: 8324995: Shenandoah: Skip to full gc for humongous allocation failures [v3]

[Y. Srinivas Ramakrishna]

On Wed, 31 Jan 2024 21:50:06 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> Shenandoah degenerated cycles do not compact regions. When a humongous allocation fails, it is likely due to fragmentation which is better addressed by a full gc.
>
> William Kemper has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix typo in comment

In regards to:

> ... that the space will reappear in contiguous form as soon as the ongoing concurrent gc (albeit degenerated now?) completes without taking recourse to a full gc.

I may be misunderstanding here, but what if the failure to honor the request doesn't cause degeneration but is held up while the concurrent cycle completes, after which said space may become available, albeit penalizing this allocation request with a much longer stall, while not subjecting other threads to the pause. May be that isn't worthwhile, or would require a bigger change.

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PR Comment: https://git.openjdk.org/jdk/pull/17638#issuecomment-1935038610