RFR: 8361339: Test gc/shenandoah/TestLargeObjectAlignment.java#generational fails on macOS aarch64 with OOM: Java heap space [v4]

[Rui Li]

> Sporadic failures were observed for TestLargeObjectAlignment.java#generational. The current theory is that jtreg deafult heap size on the reporter's machines is too small, and the randomness in test just sometimes created a huge heap larger than what the test had. 
> 
> Did a calculation for the worst case (see the code snippet at the end - it removes the Random in the original test and always allocates the array to full) and the test needs at least 2g. Initiating 3g heap for safety to reduce the noise.
> 
> Also use the test to compare between Shenandoah vs GenShen: on my laptop (Mac M3), Shen failed at 2150m Xmx, GenShen could pass Xmx2150m and failed at Xmx2050m (step: 50m), so GenShen isn't worse, it's actually better. The reported GenShen failure observation probably came from the Random.
> 
> 
> 
> public class TestLargeObjectAlignmentDeterministic {
> 
>     static final int SLABS_COUNT = Integer.getInteger("slabs", 10000);
>     static final int NODE_COUNT = Integer.getInteger("nodes", 10000);
>     static final long TIME_NS = 1000L * 1000L * Integer.getInteger("timeMs", 5000);
> 
>     static Object[] objects;
> 
>     public static void main(String[] args) throws Exception {
>         objects = new Object[SLABS_COUNT];
> 
>         for (int i = 0; i < SLABS_COUNT; i++) {
>             objects[i] = createSome();
>         }
>     }
> 
>     public static Object createSome() {
>         List<Integer> result = new ArrayList<Integer>();
>         for (int c = 0; c < NODE_COUNT; c++) {
>             result.add(new Integer(c));
>         }
>         return result;
>     }
> 
> }

Rui Li has updated the pull request incrementally with one additional commit since the last revision:

  Bump maxMem to 4g

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/28167/files
  - new: https://git.openjdk.org/jdk/pull/28167/files/3dbe9a10..142d00e2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28167&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28167&range=02-03

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/28167.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28167/head:pull/28167

PR: https://git.openjdk.org/jdk/pull/28167