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

[David Holmes]

On Mon, 17 Jun 2024 16:09:48 GMT, Sonia Zaldana Calles <szaldana at openjdk.org> wrote:

>> Hi all, 
>> 
>> This PR addresses [8333769](https://bugs.openjdk.org/browse/JDK-8333769).
>> 
>> We already have a test for  parallel GC that makes sure pretouching behaviour is correct ([test/hotspot/jtreg/gc/parallel/TestAlwaysPreTouchBehavior.java](https://github.com/openjdk/jdk/blob/master/test/hotspot/jtreg/gc/parallel/TestAlwaysPreTouchBehavior.java)). 
>> 
>> Unfortunately this test is limited to linux because of the scanning of `/proc/pid/status`. With this patch I propose two changes: 
>> 
>> - Adding a function to the os namespace `os::rss` and exposing this API via WhiteBox. This in turn allows us to generalize the above test to be used across all platforms. 
>> - Running the modified test with all collectors. 
>> 
>> Additionally, I considered removing other pre-existing pretouch tests (for example, this [z test](https://github.com/openjdk/jdk/blob/master/test/hotspot/jtreg/gc/z/TestAlwaysPreTouch.java)), as this new test is a bit more thorough. However, I noticed that some of these tests run alongside other configurables such as varying numbers of parallel GC threads, varying heap sizes, etc. Therefore, there might not be any harm in running these tests as well. 
>> 
>> Looking forward to your comments, 
>> Sonia
>
> Sonia Zaldana Calles has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains four commits:
> 
>  - Fixing comment from KB to bytes
>  - Merge master
>  - Changes based on feedback and also adding test for serial collector
>  - 8333769: Pretouching tests dont test pretouching

The new test is failing in our CI. I have filed [JDK-8334513](https://bugs.openjdk.org/browse/JDK-8334513)

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PR Comment: https://git.openjdk.org/jdk/pull/19699#issuecomment-2177895033