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

[Arno Zeller]

On Thu, 6 Nov 2025 11:17:01 GMT, SendaoYan <syan 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;
>>     }
>> 
>> }
>
> test/hotspot/jtreg/gc/shenandoah/TestLargeObjectAlignment.java line 34:
> 
>> 32:  * @library /test/lib
>> 33:  *
>> 34:  * @run main/othervm -Xms3g -XX:+UnlockExperimentalVMOptions -XX:+UseShenandoahGC -XX:ObjectAlignmentInBytes=16 -Xint                   TestLargeObjectAlignment
> 
> Since the initial heap memory set to 3G,  maybe we should add '@requires os.maxMemory > 4g' to skip this test when the physical memory of test machine is less than 4g.

I suggest to  also set -Xmx3g - otherwise the test will fail in case an -Xmx value of less than 3GB is set by a jtreg -vmoption.

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PR Review Comment: https://git.openjdk.org/jdk/pull/28167#discussion_r2500542446