RFR: 8370732: vmTestbase/nsk/jvmti/AttachOnDemand/attach020/TestDescription.java intermittent fails [v4]

[SendaoYan]

> Hi all,
> 
> We observed the test vmTestbase/nsk/jvmti/AttachOnDemand/attach020/TestDescription.java intermittent fails. since the target application intermittent OOM. The target application will try to exhaust the heap memory and then trigger garbage collection by `ClassUnloader.eatMemory()` in file test/hotspot/jtreg/vmTestbase/nsk/jvmti/AttachOnDemand/attach020/attach020Target.java.
> 
> So I think it's better to limited the max heap usage of target application. Before this PR, the physical memory usage is about 30.7GB(this depends the total free memory on the test machine), and the jtreg main action take about 11 seconds to finish; After this PR, the physical memory usage is about 126MB, and the jtreg main action take about 0.7 senonds to finish. I use below command to get the usage of physical memory.
> 
> Change has been verified locally, test-fix only, no risk.
> 
> 
> grep VmRSS /proc/`ps -ef | grep -w java | grep vmsqe.aod.AppId | awk '{print $2}'`/status

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

  Use WhiteBox.getWhiteBox().fullGC() instead of ClassUnloader.eatMemory()

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/28011/files
  - new: https://git.openjdk.org/jdk/pull/28011/files/e69a794a..9d2ae419

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28011&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28011&range=02-03

  Stats: 56 lines in 19 files changed: 33 ins; 1 del; 22 mod
  Patch: https://git.openjdk.org/jdk/pull/28011.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28011/head:pull/28011

PR: https://git.openjdk.org/jdk/pull/28011