RFR: 8236847: CDS archive with 4K alignment unusable on machines with 64k pages

[Thomas Stuefe]

On Tue, 23 Feb 2021 07:27:54 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>> Changes requested by iklam (Reviewer).
>
> Should we only use this on platforms where one can have different base page sizes *on the same platform*? Since the only one of our platforms I know where this could even be an issue are aarch, and possibly AIX.

> @tstuefe @theRealAph @iklam
> Thanks for review! Currently linux-aarch64, macos-aarch64(I don't know AIX) can be configured with 4K/64K page size. To make one build compatible with both, this change takes the 64K (or bigger) as the default region alignment. It is hard to make it optional I think. Will check the possibility of more options.

Hi Yumin,

What I meant was to leave `_core_region_alignment` at allocation granularity for all platforms but aarch64. Since we do not move the archive across platforms, and all other platforms only have one base page size, so on those platforms you never run into build page size being different than runtime page size. Or am I overlooking something?

Wrt to AIX, I looked at it, I think you can disregard it for now.

Thanks, Thomas

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PR: https://git.openjdk.java.net/jdk/pull/2651