RFR: [XS] 8229284: [TESTBUG] jdk/internal/platform/cgroup/TestCgroupMetrics.java fails for - memory:getMemoryUsage

[Severin Gehwolf]

On Thu, 2019-08-15 at 16:08 +0000, Baesken, Matthias wrote:
> https://bugs.openjdk.java.net/browse/JDK-8229284
> 
> http://cr.openjdk.java.net/~mbaesken/webrevs/8229284.3/

Hmm, unrelated to this bug, but still an issue:

It appears the failure message is bogus when the test fails. It should
be:

java.lang.RuntimeException: Test failed for - memory:getMemoryUsage, expected [56200986624], got [56019386368]

I.e. the old/new values need to be swapped here:

 597             fail(SubSystem.MEMORY, "getMemoryUsage", newMemoryUsage, memoryUsage);

Same for the getMemoryMaxUsage() fail:

 592             fail(SubSystem.MEMORY, "getMemoryMaxUsage", newMemoryMaxUsage,
 593                     memoryMaxUsage);

As to the bug. It suggests the memoryUsage code causes problems, not
memoryMaxUsage.

 587         // allocate memory in a loop and check more than once for new values
 588         // otherwise we might see seldom the effect of decreasing new memory values
 589         // e.g. because the system could free up memory
 590         byte[][] bytes = new byte[32][];
 591         for (int i = 0; i < 32; i++) {
 592             bytes[i] = new byte[8*1024*1024];
 593             newMemoryMaxUsage = metrics.getMemoryMaxUsage();
 594             newMemoryUsage = metrics.getMemoryUsage();
 595             if (newMemoryMaxUsage > memoryMaxUsage && newMemoryUsage > memoryUsage) {
 596                 break;
 597             }

Do we really need to call metrics.getMemoryMaxUsage() in that loop? I'd
expect for the following code to work more reliably as the max usage is
supposed to capture the high water mark. If memoryMaxUsage ever
decreases, it's a bug in the cgroups accounting system right?

byte[][] bytes = new byte[32][];
for (int i = 0; i < 32; i++) {
    bytes[i] = new byte[8*1024*1024];
    newMemoryUsage = metrics.getMemoryUsage();
    if (newMemoryUsage > memoryUsage) {
        break;
    }
}
newMemoryMaxUsage = metrics.getMemoryMaxUsage();

// assert things

Perhaps even assert prior the loop:

if (memoryMaxUsage < memoryUsage) {
    throw new RuntimeException("cgroup accounting bug?");
}

Thanks,
Severin