RFR: 8332514: Allow class space size to be larger than 3GB

[Thomas Stuefe]

On Wed, 22 May 2024 12:05:28 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

> Class space size is capped at 3GB. Technically, the Klass encoding range is 4GB.
> 
> We cap class space at 3GB to leave breathing room for CDS. However, CDS needs a lot less, so we waste address space. In addition, class space is unnecessarily capped at 3GB even if we run without CDS, which is unnecessary.
> 
> What we should do instead:
> - if CDS is off, use the full 4GB
> - if CDS is on, use as much memory as we can after accommodating the archive
> 
> This patch implements that new behavior. 
> 
> Now, we can have 4GB class space without CDS; with CDS, a bit less (depends on the CDS archive size; by default, on MacOS, we reach about 3.98GB).

Pinging @iklam. And @coleenp, maybe?

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PR Comment: https://git.openjdk.org/jdk/pull/19347#issuecomment-2127446538