RFR: 8364183: Shenandoah: Improve commit/uncommit handling

[William Kemper]

On Mon, 28 Jul 2025 10:34:25 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> While working on related bug, I found that Shenandoah commit/uncommit code has a few issues:
>  1. It throws Java OOME on commit/uncommit failures. These should actually be VM-level out of memory errors, so they are properly fatal.
>  2. Throwing OOME on uncommit looks fairly weird.
>  3. We are not zapping on the newly committed regions. 
> 
> Additional testing:
>  - [x] Linux x86_64 server fastdebug, `hotspot_gc_shenandoah`
>  - [ ] Linux x86_64 server fastdebug, `all`  + `-XX:+UseShenandoahGC`

LGTM

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Marked as reviewed by wkemper (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/26502#pullrequestreview-3064858769