RFR: 8264411: serviceability/jvmti/HeapMonitor tests intermittently fail due to large TLAB size [v3]

[Chris Plummer]

On Sat, 3 Apr 2021 04:09:53 GMT, Hui Shi <hshi at openjdk.org> wrote:

>> …ue to large TLAB size
>> 
>> serviceability/jvmti/HeapMonitor tests intermittently fail when using PS/Serial GC, original test has implicit assumptions on TLAB size and depends on allocate fix amount of objects to consume TLAB and trigger object sampling. These tests will fail if TLAB is above 20M (this can easily happen when using PS/Serial GC and heap is large), when allocation can not consume current TLAB and _byte_until_sample.
>> 
>> Fix in tests is adding an explicit GC to consume current TLAB.
>> Running on 256G memory machine, make run-test CONF=release TEST="test/hotspot/jtreg/serviceability/jvmti/HeapMonitor/MyPackage/" 'JTREG=JOBS=12;VM_OPTIONS=-XX:ActiveProcessorCount=1'
>> 
>> before fix: 6 or 7 tests in 20 tests intermittently fail
>> after fix: no failure in 100 runs release/fastdebug
>> 
>> This might also fix https://bugs.openjdk.java.net/browse/JDK-8225313
>
> Hui Shi has updated the pull request incrementally with one additional commit since the last revision:
> 
>   clarify comments

Changes requested by cjplummer (Reviewer).

test/hotspot/jtreg/serviceability/jvmti/HeapMonitor/MyPackage/HeapMonitor.java line 169:

> 167:     // Trigger GC then loop around an allocation loop and wait until Object Sampling
> 168:     // is enabled for every later allocation. It takes two steps:
> 169:     // 1. Consume current TLAB, whose size can be varies with heap/GC configuration

"whose size can vary"

test/hotspot/jtreg/serviceability/jvmti/HeapMonitor/MyPackage/HeapMonitor.java line 175:

> 173:     System.gc();
> 174:     // Step2 loop allocation consume "bytes until sample", each iteration allocate
> 175:     // about 1600KB, 10 iterations can definitly consume initial "bytes until sample"

// Step2 loop allocation consumes "bytes until sample". Each iteration allocates
    // about 1600KB, so 10 iterations will definitely consume initial "bytes until sample"

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PR: https://git.openjdk.java.net/jdk/pull/3265