RFR: 8264008: Incorrect metaspace statistics after JEP 387 when UseCompressedClassPointers is off

[Jie Fu]

Hi all,

Metaspace statistics is incorrect after JEP 387 when UseCompressedClassPointers is off.

For example, here is the incorrect metaspace statistics before the fix:
Event:jdk.MetaspaceSummary {
  startTime = 10:35:24.762
  gcId = 3
  when = "Before GC"
  gcThreshold = 21.0 MB
  metaspace = {
    committed = 10.3 MB
    used = 10.2 MB
    reserved = 16.0 MB
  }
  dataSpace = {
    committed = 10.3 MB
    used = 10.2 MB
    reserved = 16.0 MB
  }
  classSpace = {
    committed = 10.3 MB
    used = 10.2 MB
    reserved = 16.0 MB
  }
}

This bug can be reproduced by running the following tests with `-XX:-UseCompressedClassPointers`, which would pass before JEP 387.
jdk/jfr/event/gc/heapsummary/TestHeapSummaryEventDefNewSerial.java
jdk/jfr/event/gc/heapsummary/TestHeapSummaryEventG1.java
jdk/jfr/event/gc/heapsummary/TestHeapSummaryEventPSParOld.java

The failing reason is that `Metaspace::is_class_space_allocation(mdtype)` [1] will always return false when `UseCompressedClassPointers` is off.
So `RunningCounters::committed_words_nonclass()` will be returned even called with `Metaspace::is_class_space_allocation(Metaspace::ClassType)`, which is unreasonable.
And `MetaspaceUtils::reserved_words(Metaspace::MetadataType mdtype)`/`MetaspaceUtils::used_words(Metaspace::MetadataType mdtype)` also suffer from the same bug.

Thanks.
Best regards,
Jie

[1] https://github.com/openjdk/jdk/blob/master/src/hotspot/share/memory/metaspace.cpp#L90


Metaspace statistics after the fix:
Event:jdk.MetaspaceSummary {
  startTime = 10:44:38.230
  gcId = 1
  when = "After GC"
  gcThreshold = 21.0 MB
  metaspace = {
    committed = 10.3 MB
    used = 10.2 MB
    reserved = 16.0 MB
  }
  dataSpace = {
    committed = 10.3 MB
    used = 10.2 MB
    reserved = 16.0 MB
  }
  classSpace = {
    committed = 0 bytes
    used = 0 bytes
    reserved = 0 bytes
  }
}

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

Commit messages:
 - 8264008: Incorrect metaspace statistics after JEP 387 when UseCompressedClassPointers is off

Changes: https://git.openjdk.java.net/jdk/pull/3142/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3142&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8264008
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3142.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3142/head:pull/3142

PR: https://git.openjdk.java.net/jdk/pull/3142