Default for XX:MaxDirectMemorySize

Question

What is the default value for XX:MaxDirectMemorySize?

Answer 1

From sun.misc.VM, it's Runtime.getRuntime.maxMemory(), that's what is configured with -Xmx. E. g. if you don't configure -XX:MaxDirectMemorySize and do configure -Xmx5g, the "default" MaxDirectMemorySize will also be 5 Gb, and the total heap+direct memory usage of the app may grow up to 5 + 5 = 10 Gb.

Answer 2

From http://www.docjar.com/html/api/sun/misc/VM.java.html

i see:

 163       // A user-settable upper limit on the maximum amount of allocatable direct  164       // buffer memory.  This value may be changed during VM initialization if  165       // "java" is launched with "-XX:MaxDirectMemorySize=<size>".  166       //  167       // The initial value of this field is arbitrary; during JRE initialization  168       // it will be reset to the value specified on the command line, if any,  169       // otherwise to Runtime.getRuntime.maxDirectMemory().  170       //  171       private static long directMemory = 64 * 1024 * 1024; 

so it appears to default to 64 megs.