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 withj9vm_minNewSpace
andj9vm_maxNewSpace
j9vm_oldSpaceFixed
is mutually exclusive withj9vm_minOldSpace
andj9vm_maxOldSpace
the sum of
j9vm_minNewSpace
andj9vm_minOldSpace
must be equal toj9vm_minHeapSize
, so it's useless to tune all of them together. Max values seem to be more complex.
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