RFR: JDK-8312018: Improve reservation of class space and CDS [v4]

[Thomas Stuefe]

On Tue, 15 Aug 2023 04:20:17 GMT, Ioi Lam <iklam at openjdk.org> wrote:

>> Thomas Stuefe has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   fix windows
>
> I think the API looks OK. I need to spend more time looking at the algorithm itself.

@iklam @rkennke thanks for the reviews so far.

Changes to os::vm_min_address
- I encoded the a default value for os::vm_min_address() (16 MB) centrally
- I changes the linux implementation to actually read vm.mmap_min_address.
- I changed the interface to return size_t since char* seemed weird
Other changes:
- tried to come up with a better comment for the cds_runtime path in MetaspaceShared. I somewhat regret now not staying with strict_base, since in hindsight that describes behavior much better; but cds_runtime is fine and we hopefully will remove this code path soon when we recalc nKlass IDs on archive load.

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PR Comment: https://git.openjdk.org/jdk/pull/15041#issuecomment-1680039598