out-of-memory error — why not paging?

Question

Out-of-memory error occurs frequently in the java programs. My question is simple: when exceeding the memory limitation, why java directly kill the program rather than swap it out to the disk? I think memory paging/swapping strategy is frequently used in the modern operating system and programming languages like c++ definitely supports swapping. Thanks.

Answer 1

@Pimgd is sorta on track: but @Kayaman is right. Java doesn't handle memory besides requesting it from the system. C++ doesn't support swapping, it requests memory from the OS and the OS will do the swapping. If you request enough memory for your application with -Xmx , it might start swapping because the OS thinks it can.

Answer 2

Because Java is cross-platform. There might not be a disk.

Other reasons could be that such a thing would affect performance and the developers didn't want that to happen (because Java already carries a performance overhead?).

Answer 3

A few words about paging. Virtual memory using paging - storing 4K (or similar) chunks of any program that runs on a system - is something an operating system can or cannot do. The promise of an address space only limited by the capacity of a machine word used to store an address sounds great, but there's a severe downside, which is called thrashing . This happens when the number of page (re)loads exceeds a certain frequency, which in turn is due of too many processes requesting too much memory in combination with non-locality of memory accesses of those processes. (A process has a good locality if it can execute long stretches of code while accessing only a small percentage of its pages.)

Paging also requires (fast) secondary storage.

The ability to limit your program's memory resources (as in Java) is not only a burden; it must also be seen as a blessing when some overall plan for resource usage needs to be devised for a, say, server system.