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    <p>Memory allocated by the native code wrapped by JNI is allocated to the JVM process, but is not under the control of your Java code. It is not part of the heap, and is not tunable via JVM parameters. Basically, anything allocated with a native malloc must be managed by that native code. If you are in control of the libraries you are using, its imperative that you go through it and check for resource leaks. This is especially important if this is being used in a long lived process.</p> <p>In my experience the best approach would be to examine your actual memory use by pulling the JMX stats exposed by the JVM. Once you have an idea about how much memory your Java app consumes You'll have a better idea about where to set your max heap settings. Permgen space is used for class definitions and such, so you really shouldn't need much memory there unless you are doing a bunch of dynamic class loading.</p> <p>While you cannot tune the memory available for the JNI library, tuning the memory reserved for your heap and such will potentially free up resources for use by the library.</p> <p>As would be expected, adding the heap memory peaks together it comes out to about 1022.19 (the max size of your heap). When the heap is exhausted a full GC run is kicked off and dirty heap is reclaimed. Based on the numbers that you have provided, I'd suggest starting with a Xmx512m. This will give your JNI code room to breath. </p> <p>If you find that the JVM is thrashing due to excessive garbage collection, meaning that you're running out of Java heap too quickly, you could grow that allocation. However, if it is eating up 512mb rapidly enough to cause a noticeable performance impact, its unlikely that anything short of a significant increase will have much effect. This all depends heavily on your program, how quickly it eats the Java heap, and how effective the full GC run is.</p>
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    1. POJava app calls C++ DLL via JNI; how best to allocate memory?
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    1. POJava app calls C++ DLL via JNI; how best to allocate memory?
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    1. COIn case I haven't stated this specifically enough. You really have no way of setting a maximum limit on the amount of memory that your JNI library can request.
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    2. COSo are you saying to minimize overall memory allocated to the JVM process? Should I be able to subtract the total memory value given by JMX from the value consumed by /allocated to the JVM process to determine the amount used by the DLL?
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    3. COYes, approximately. The process heap (which contains the Java heap plus everything else) is restricted to approximately 2GB on a 32 bit architecture. The limit is much larger on a 64 bit arch. If you are allocating gigs of memory specifically to the Java heap and other Java specific components of your programs memory, that doesn't leave much room for the JNI memory allocation (which is allocated against the process heap).
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