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

[Jie Fu]

On Tue, 23 Mar 2021 03:50:36 GMT, Jie Fu <jiefu at openjdk.org> wrote:

> 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
>   }
> }

This pull request has now been integrated.

Changeset: 06d46d6c
Author:    Jie Fu <jiefu at openjdk.org>
URL:       https://git.openjdk.java.net/jdk/commit/06d46d6c
Stats:     15 lines in 2 files changed: 11 ins; 0 del; 4 mod

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

Reviewed-by: stuefe

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

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