RFR: 8338526: Don't store abstract and interface Klasses in class metaspace [v4]

[Coleen Phillimore]

On Thu, 29 Aug 2024 13:17:50 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>> Is this right?  If UseCompressedClassPointers is off, then the shared metaspace isn't in compressed space?
>
> If UseCompressedClassPointers is off, we don't have a compressed class space. If its on, Klass from CDS and from class space are compressable. With your patch, interfaces will live in normal metaspace, not int class space, so those are excluded now.
> 
> TBH, I am not really sure what this code here does, but I assume it tries to reduce the size of a JFR recording by using a compressed identifier for X if X can be expressed by such. Maybe a JFR person should look at this.

With UseCompressedClassPointers off, I think Metaspace::is_in_shared_metaspace() would still return true but I don't think he compression base is the bottom of the CDS archive.  I asked Markus to have a look.

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PR Review Comment: https://git.openjdk.org/jdk/pull/19157#discussion_r1736538545