Java，JVM和OS以及交换

Question

I wonder if i start a java virtual machine with:

-Xms2048m -Xmx2048m -XX:PermSize=256m -XX:MaxPermSize=256m 
-XX:+UseParallelGC -XX:ParallelGCThreads=4 -XX:+UseParallelOldGC 
-XX:LargePageSizeInBytes=4m -XX:-BindGCTaskThreadsToCPUs 

So I start the server with -Xms equal to -Xmx I the java OS process will "hold" the memory from the OS for good ? So this JVM will have 2GB for it and if the OS has it then it will allow the process to start otherwise no.

Is there a possibility that after the JVM start with 2GB to use the swap memory of the os ?

(so if it starts initially without using the swap memory)

Answer 1

This will use about 2400 MB of virtual memory on start up. It never gives back the virtual memory. It can give back the main memory but rarely does.

Is there a possibility that after the JVM start with 2GB to use the swap memory of the os ?

Technical yes, but in practice this is a very bad idea. The GC when it is performed assumes it has random access to all the memory. If you JVM starts to swap it can halt for long periods of time (many minutes) and even hang the machine.

Given you can buy 32 GB for about $200, it's usually simpler to buy enough memory for your needs.