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

[Rui Li]

On Thu, 6 Nov 2025 00:21:55 GMT, Rui Li <duke at openjdk.org> wrote:

> 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;
>     }
> 
> }

Will set Xmx to 3g instead and add `@requires os.maxMemory > 3g`

Initially set Xms to 3g was purely to satisfy the "minimal heap size needed" condition for the test. `@requires os.maxMemory` is apparently more close to what I was thinking and I didn't think about reproducibility. Thanks for the suggestions!

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PR Comment: https://git.openjdk.org/jdk/pull/28167#issuecomment-3499525127