RFR: 8264008: Incorrect metaspace statistics after JEP 387 when UseCompressedClassPointers is off [v2]

[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
>   }
> }

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

  Add a test run to reproduce the bug

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3142/files
  - new: https://git.openjdk.java.net/jdk/pull/3142/files/137b9267..c72e91ec

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3142&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3142&range=00-01

  Stats: 12 lines in 1 file changed: 11 ins; 0 del; 1 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