Running Java progams and Java overhead about isolate HOT 2 CLOSED

Basically, the JVM is going to eat lots of memory whatever you do. The size of the VM can be controlled by the -Xmx option of the JVM and the memory limit given to Isolate must be large enough to accomodate this amount of memory and probably a bit more. However, if you restrict VM size too much, the JVM will run its garbage collector frequently, which leads to significant slowdown (sometimes by an order of magnitude).

At the IOI, it ended up with raising all memory limits to a couple of gigabites, so that all reasonable Java programs fit in the memory limit without triggering garbage collection. If anybody has a better idea, please let me know.

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@gollux I am sorry for such a delay about this discussion.

Think I know why there is an error when I try to run it like:

$ isolate -p -m 256000 --cg -i input.txt --run /usr/local/jdk1.8.0_91/bin/java Main

Option -m indicates per process, but what if JVM is creating a process that needs more than 256MB. I found that instead of using -m and rather --cg-mem it works as expected. But now I have another question.

What is the difference between setting the memory limit given to Isolate and setting the JVM memory limit?

$ isolate -p --cg-mem 256000 --cg -i input.txt --run /usr/local/jdk1.8.0_91/bin/java Main
$ isolate -p --cg -i input.txt --run -- /usr/lib/jvm/java-8-oracle/bin/java -Xmx256m Main

Also, a question. At the IOI, are you raising all memory limits only for Java? If you raise a memory limit only for Java (because of GC) to lets say 4GB, how would you then check if contestant allocated more memory than allowed, let's say 512MB. Am I missing something out here? 😄 Thanks!

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