IBM J9 VM 6

This page describes the Optimization Pack for Eclipse OpenJ9 (formerly known as IBM J9) Virtual Machine version 6.

Metrics

All metrics

Parameters

Heap

Garbage Collection

JIT

Other parameters

Domains

The following parameters require their ranges or default values to be updated according to the described rules:

Memory

Notice that the value nocompressedreferences for j9vm_compressedReferences can only be specified for JVMs compiled with the proper --with-noncompressedrefs flag. If this is not the case you cannot actively disable compressed references, meaning:

• for Xmx <= 57GB is useless to tune this parameter since compressed references are active by default and it is not possible to explicitly disable it

• for Xmx > 57GB, since the by default (blank value) compressed references are disabled, Akamas can try to enable it. This requires removing the nocompressedreferences from the domain

Constraints

The following tables show a list of constraints that may be required in the definition of the study, depending on the tuned parameters:

Memory

Notice that

• j9vm_newSpaceFixed is mutually exclusive with j9vm_minNewSpace and j9vm_maxNewSpace

• j9vm_oldSpaceFixed is mutually exclusive with j9vm_minOldSpace and j9vm_maxOldSpace

• the sum of j9vm_minNewSpace and j9vm_minOldSpace must be equal to j9vm_minHeapSize, so it's useless to tune all of them together. Max values seem to be more complex.