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

[Albert Mingkun Yang]

On Tue, 18 Jun 2024 13:58:16 GMT, Sonia Zaldana Calles <szaldana 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".

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PR Comment: https://git.openjdk.org/jdk/pull/19699#issuecomment-2176232104