Java使用的内存远远多于使用-Xmx分配的内存 [英] Java using up far more memory than allocated with -Xmx

问题描述

我正在编写一个项目（用Java编写），其中教授说我们不允许使用超过200m
我将堆栈内存限制为50m（只是为了绝对肯定）使用-Xmx50m，但根据顶部，它仍然使用300m

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

我试过运行 Eclipse内存分析器它只报告26m

I tried running Eclipse Memory Analyzer and it reports only 26m

这可能都是堆栈中的内存吗？我很确定我再也不会超过大约300个方法调用深度（是的，它是一个递归DFS搜索），所以这将意味着每个堆栈帧使用几乎一兆字节似乎很难相信。

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.

该程序是单线程的。有谁知道我可能减少内存使用的任何其他地方？另外，我如何检查/限制堆栈使用的内存量？

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?

更新：我现在使用以下JVM选项但没有效果（仍然约300米）到顶部）： -Xss104k -Xms40m -Xmx40m -XX：MaxPermSize = 1k

UPDATE: I'm using the following JVM options now with no effect (still about 300m according to top): -Xss104k -Xms40m -Xmx40m -XX:MaxPermSize=1k

另一个更新：实际上，如果我让它运行一点点（带有所有这些选项）大约一半的时间它在4或5秒后突然下降到150米（另一半不会下降）。这真的很奇怪的是我的程序没有随机（正如我所说的那样是单线程）所以没有理由它在不同的运行中表现不同

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

可能吗与我正在使用的JVM有关？

Could it have something to do with the JVM I'm using?

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)

根据java -h，默认的JVM是-server。我尝试添加-cacao和现在（所有其他选项）它只有59米。所以我想这解决了我的问题。谁能解释为什么这是必要的？另外，我应该知道有什么缺点吗？

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?

还有一个更新：与服务器相比，可可真的很慢。这是一个糟糕的选择

One more update: cacao is really really slow compared to server. This is an awful option

推荐答案

Top命令反映了Java应用程序使用的总内存量。其中包括：

Top command reflects the total amount of memory used by the Java application. This includes among other things:

• JVM本身的基本内存开销


• 堆空间（以-Xmx为界）


• 永久生成空间（-XX：MaxPermSize - 并非所有JVM中的标准）


• 线程堆栈空间（-Xss）每个堆栈）可能会根据线程数量显着增长


• 本机分配使用的空间（使用ByteBufer类或JNI）

• A basic memory overhead of the JVM itself
• the heap space (bounded with -Xmx)
• The permanent generation space (-XX:MaxPermSize - not standard in all JVMs)
• threads stack space (-Xss per stack) which may grow significantly depending on the number of threads
• Space used by native allocations (using ByteBufer class, or JNI)

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