RFR: 8261029: Code heap page sizes not traced correctly using os::trace_page_sizes

[Stefan Johansson]

On Wed, 10 Feb 2021 14:45:55 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

> 
> ```
> void* os::reserve_xxx(size, ... blabla..., reservation_info_t* info = NULL);
> ```
> 
> with reservation_info_t being a holder for information both "public" and opaque: e.g. whether this is executable memory (e.g. for MacOS MAP_JIT issue on committiong), the page size of course, as well as a way for platforms to piggyback internal information (eg. memory type used on AIX).
> 
> But your solution sounds simpler, and its sufficient at least for now. So I don't think we work at cross purposes.
> 

Yes, we'll see who gets around to making it happen first :)

> > > There is also another possible simplification I was thinking about, which is to remove the "UseSHM" feature from Linux. I honestly do not know why we still need it. That would simplify rework of large page handling on Linux a lot. I did ask around in December: https://mail.openjdk.java.net/pipermail/hotspot-dev/2020-December/046885.html , but did not get many answers.
> > 
> > 
> > I know and I've been digging around in this area and agree even more now that it would be great to get rid of `UseSHM`. Not sure how if everybody agrees though and I'm currently working on small fix for `UseSHM` so that at least we don't leave it enabled everytime someone sets `+UseLargePages` without having any explicit large pages enabled ([PR#2488](https://github.com/openjdk/jdk/pull/2488)).
> 
> Nice that you think the same. I am not sure many people are around which know the history. Maybe we should ask Andrew Haley, I believe he wrote some of that coding.
> 
> I commented on your PR in your PR.

Thanks for all your input, very helpful =)

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PR: https://git.openjdk.java.net/jdk/pull/2481