RFR: JDK-8328272: [AIX] Use flag kind "diagnostic" for platform specific flags

[Thomas Stuefe]

On Mon, 18 Mar 2024 12:29:56 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

> I think this is acceptable for a new Java release. We just shouldn't backport it. Do you really think anybody sets one of these flags in production? Are you aware of any `MaxExpectedDataSegmentSize` user other than in SAP JVM 8? I leave it up to you guys to decide if you prefer keeping that one a regular product flag.

`MaxExpectedDataSegmentSize` is needed because of the implicit problem with AIX that libc only allocates in sbrk. So, like on Solaris, this will always be an issue where we need a flag in case the breathing room for the libc is not large enough. Either that, or we need to completely avoid allocating at arbitrary wish addresses, which makes coops friendly heap and class space less coops friendly.


> @tstuefe I'm fine with keeping `MaxExpectedDataSegmentSize` The one I'm most interested to get rid of is `Use64KPages`. And I think you too, because then we can eliminate the 4K Pages support. What about making the remaining 4 flags diagnostic in jdk23 and removing at least `Use64KPages` in jdk24?

Sounds good to me.

-------------

PR Comment: https://git.openjdk.org/jdk/pull/18337#issuecomment-2004029044