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POJava using up far more memory than allocated with -Xmx
 

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    <p>I have a project I'm writing (in Java) for a class where the prof says we're not allowed to use more than 200m I limit the stack memory to 50m (just to be absolutely sure) with -Xmx50m but according to top, it's still using 300m</p> <p>I tried running <a href="http://www.eclipse.org/mat/" rel="noreferrer">Eclipse Memory Analyzer</a> and it reports only 26m</p> <p>Could this all be memory on the stack?, I'm pretty sure I never go further than about 300 method calls deep (yes, it is a recursive DFS search), so that would have to mean every stack frame is using up almost a megabyte which seems hard to believe.</p> <p>The program is single-threaded. Does anyone know any other places in which I might reduce memory usage? Also, how can I check/limit how much memory the stack is using?</p> <p>UPDATE: I'm using the following JVM options now with no effect (still about 300m according to top): <code>-Xss104k -Xms40m -Xmx40m -XX:MaxPermSize=1k</code></p> <p>Another UPDATE: Actually, if I let it run a little bit longer (with all these options) about half the time it suddenly drops to 150m after 4 or 5 seconds (the other half it doesn't drop). What makes this really strange is that my program has no stochastic (and as I said it's single-threaded) so there's no reason it should behave differently on different runs</p> <p>Could it have something to do with the JVM I'm using?</p> <pre><code>java version "1.6.0_27" OpenJDK Runtime Environment (IcedTea6 1.12.3) (6b27-1.12.3-0ubuntu1~10.04) OpenJDK 64-Bit Server VM (build 20.0-b12, mixed mode) </code></pre> <p>According to java -h, the default JVM is -server. I tried adding -cacao and now (with all the other options) it's only 59m. So I suppose this solves my problem. Can anyone explain why this was necessary? Also, are there any drawbacks I should know about?</p> <p>One more update: cacao is really really slow compared to server. This is an awful option</p>
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    1. COHeap memory and stack memory are configured separately. The memory you're seeing in top includes both.
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    2. COI realize that, but I don't think it's stack memory. I'm not using that much. So where else could the memory be coming from
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    3. COAre you setting the minimum heap size as well? If `-Xms` is larger than `-Xmx`, I think it uses up to `-Xms`
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      1. USSotirios Delimanolis
 

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