Descriptions of JVM flags for BEA JRockit P27.1.0

-Xms
The -Xms option sets the initial and minimum Java heap size. The Java heap (the "heap") is the part of the memory where blocks of memory are allocated to objects and freed during garbage collection.

-Xmx
This option sets the maximum Java heap size. The Java heap (the "heap") is the part of the memory where blocks of memory are allocated to objects and freed during garbage collection. Depending upon the kind of operating system you are running, the maximum value you can set for the Java heap can vary.

-Xns
This option sets the nursery size. BEA JRockit uses a nursery when the generational garbage collection model is used, that is, when the dynamic garbage collector has determined that the generational garbage collection model should be used or when the static generational concurrent garbage collector ( -Xgc : gencon) has been selected. You can also use -Xns to set a static nursery size when running the dynamic garbage collector.


-XXaggressive 
This option has a collection of configurations that make the JVM perform at a high speed and reach a stable state as soon as possible. To achieve this goal, the JVM uses more internal resources at startup; however, it requires less adaptive optimization once the goal is reached. We recommend that you use this option for long-running, memory-intensive applications that work alone or is carefully sized.

-Xlargepages 
This option tells BEA JRockit to use large pages, if they are available, for the Java heap and other areas in the JVM. Large pages allow your application to more effectively use the translation look-aside buffer (TLB) in the processor.

-XXlazyunlocking 
When -XXlazyUnlocking is set, locks will not be released when a critical section is exited. Instead, once a lock is acquired, the next thread that tries to acquire such a lock will have to ensure that the lock is or can be released. It does this by determining if the initial thread still uses the lock. A shared lock will convert to a normal lock and not stay in lazy mode.

-Xgc:genpar 
Use -Xgc to set a static garbage collector. Static garbage collector are classified as follows:
genpar  Generational Parallel

-XXgcthreads
This option specifies how many garbage collection threads the garbage collector will use. This applies both to parallel nursery and parallel old space collectors as well as the concurrent and deterministic collector.

-XXtlasize:min=16k,preferred=64k
Sets the thread-local area size. To increase performance JRockit uses thread-local areas for allocation of small objects. This option can be used to tune the size of the thread-local areas, which may affect performance.


Other flags and more information is available at:
http://e-docs.bea.com/jrockit/jrdocs/refman/intro.html