RFR: 8340166: [REDO] CDS: Trim down minimum GC region alignment

[Ioi Lam]

On Mon, 16 Sep 2024 09:10:45 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> Now that [JDK-8338912](https://bugs.openjdk.org/browse/JDK-8338912) is in, we can try to redo [JDK-8337828](https://bugs.openjdk.org/browse/JDK-8337828). See the rationale for this change in [JDK-8337828](https://bugs.openjdk.org/browse/JDK-8337828) PR: https://github.com/openjdk/jdk/pull/20469. This change is identical to that PR.
> 
> Additional testing:
>  - [x] Linux x86_64 server fastdebug, `runtime/cds`
>  - [x] Linux x86_64 server fastdebug, `runtime/cds` `-XX:-UseCompressedOops` (failed during the original attempt to do this)
>  - [x] Linux x86_64 server fastdebug, `runtime/cds` `-XX:+UseShenandoahGC`
>  - [x] Linux x86_64 server fastdebug, `runtime/cds` `-XX:+UseShenandoahGC -XX:-UseCompressedOops`

For sanity, we will run test tiers 5-7 as well. I'll post an update once we have the results.

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PR Review: https://git.openjdk.org/jdk/pull/21011#pullrequestreview-2313142502