1. Various GC combinations have now been removed

The GC combinations that were deprecated in JDK 8 have now been removed. This means that the following GC combinations no longer exist:

DefNew + CMS

ParNew + SerialOld

Incremental CMS The "foreground" mode for CMS has also been removed.

The command line flags that were removed are:

-Xincgc

-XX:+CMSIncrementalMode

-XX:+UseCMSCompactAtFullCollection

-XX:+CMSFullGCsBeforeCompaction

-XX:+UseCMSCollectionPassing

The command line flag -XX:+UseParNewGC no longer has any effect. ParNew can only be used with CMS and CMS requires ParNew. Thus, the -XX:+UseParNewGC flag has been deprecated and will likely be removed in a future release.

See JDK-8044022

hotspot/gc

2. Remove deprecated command line flags

These internal command line flags, which have been deprecated or aliased since JDK 6, have been removed:

CMSParPromoteBlocksToClaim

ParCMSPromoteBlocksToClaim

ParallelGCOldGenAllocBufferSize

ParallelGCToSpaceAllocBufferSize

UseGCTimeLimit

CMSPermGenSweepingEnabled

ResizeTLE

PrintTLE

TLESize

UseTLE

MaxTLERatio

TLEFragmentationRatio

TLEThreadRatio

In addition, these internal flags have been deprecated:

CMSMarkStackSizeMax

ParallelMarkingThreads

ParallelCMSThreads

CMSMarkStackSize

G1MarkStackSize

See JDK-8061611

hotspot/runtime

3. VM Options AdjustConcurrency and PrintJVMWarnings are removed

The VM Options -XX:AdjustConcurrency and -XX:PrintJVMWarnings are removed from JDK 9.

The VM option -XX:AdjustConcurrency was only needed on Solaris 8/9 (when using the T1 threading library).

The VM option -XX:PrintJVMWarnings was a development option only used by unimplemented VM functions that have themselves been removed in JDK 9.

See JDK-8073861