RFR: 8228991: Obsolete -XX:UseAdaptiveGCBoundary

[Kim Barrett]

> On Apr 15, 2020, at 4:49 AM, Thomas Schatzl <thomas.schatzl at oracle.com> wrote:
> 
> Hi,
> 
> On 15.04.20 00:23, Kim Barrett wrote:
>> Please review this change which obsoletes the boolean product flag
>> -XX:UseAdaptiveGCBoundary and removed the supporting code.
>> […]
>> CR:
>> https://bugs.openjdk.java.net/browse/JDK-8228991
>> https://bugs.openjdk.java.net/browse/JDK-8242164 (CSR)
>> Webrev:
>> https://cr.openjdk.java.net/~kbarrett/8228991/open.00/
>> Testing:
>> mach5 tier1-5.
> 
>  thanks for tackling this.
> 
> Found some outdated comments:

StefanK found some more unnecessary stuff that I’d missed.  In particular, AdjoiningGenerations
and AdjoiningVirtualSpaces can be removed with a small amount of additional changes.

> - maybe add a release note for this to get some more publicity of that change (if we want it)

OK.  I’m not familiar with the release note process, so may need some pointers.

> - adjoiningenerations.hpp:36: s/down/done (pre-existing)
> 
> - in the same paragraph, I think the last sentence referes to moving the boundary and should be removed.
> 
> - adjoiningVirtualSpaces.hpp: the comment at the beginning of the file also refers to moving the boundary.

These are all things that get removed as part of the additional cleanup found by Stefan,
so I’m not going to do anything with them.

> - PSGCAdaptivePolicyCounters::_boundary_moved and related code is obsolete now

Removed.

> - outdated comment for PSScavenge::set_young_generation_boundary (both in hpp and cpp file)

Done.

> - comment in psYoungGen::gen_size_limit() outdated

Looking at this and similar function in PSOldGen, I think they are now duplicative of other functions
in the corresponding APIs (PSYoungGen::max_size() and PSOldGen::Max_gen_size()).  More stuff
I missed.  Stefen didn’t do anything with these in his proposed followup cleanup either.   In order to
minimize the risk of causing merge collisions with his existing webrev, I think I want to avoid doing
anything significant in this area with this change. I’ve changed the description though, which now
matches that of PSYoungGen::max_size().

> > Note: Unable to test nvdimm usage since we don't have any machines
> > with that configuration.
> 
> The only related option Parallel GC supports is AllocateHeapAt, and you can pass it any arbitrary file name. I.e. you could test it by specifying a file name in a memory backed directory.
> 
> Since the impact is only memory reservation, I do not expect a difference though.

OK, I’ll figure out how to run them that way.

New webrevs:
full: https://cr.openjdk.java.net/~kbarrett/8228991/open.01/
incr: https://cr.openjdk.java.net/~kbarrett/8228991/open.01.inc/