RFR: 8333769: Pretouching tests dont test pretouching [v3]

[Sonia Zaldana Calles]

On Tue, 18 Jun 2024 14:22:29 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> > yes I broke os::pretouch_memory and confirmed the tests fail.
> 
> I just tried using `return` to impl `os::pretouch_memory` and `test/hotspot/jtreg/gc/TestAlwaysPreTouchBehavior.java` still passes for Serial in debug-build.
> 
> > I thought ZapUnusedHeapArea is only for clearing after evacuation.
> 
> Any unused mem will be written with this value; can be mistaken as "pretoucing".

I had tried it out with the release build previously.
Just tried it with the debug build and I observe the following: 
4 pass and 3 fail (ZGenerational, ZSingleGen and G1). 

Would it be worthwhile to open a follow-up issue to disable these tests for the debug build for the passing tests and/or all of them? 
@albertnetymk @tstuefe

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PR Comment: https://git.openjdk.org/jdk/pull/19699#issuecomment-2176376454