Java Maven Tomcat7：为jvm运行Java内存选项

Question

my question is right complicated for me. I am running a server for a game and i have some problems setting up the java settings for memory correctly.

I am running Ubuntu 12.10 64bit with 32 gb ram.

The java task should take up to 20 gb of real memory. Instead of doing it it uses virtual memory all the time.

top - 19:51:44 up 15 min,  1 user,  load average: 0.29, 0.30, 0.19
Tasks: 120 total,   2 running, 118 sleeping,   0 stopped,   0 zombie
Cpu(s):  0.9%us,  0.3%sy,  0.0%ni, 98.5%id,  0.2%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:  32809368k total,  2237888k used, 30571480k free,    28092k buffers
Swap: 16776116k total,        0k used, 16776116k free,   411660k cached

PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
1876 test      20   0 46.1g 1.2g  15m S    8  3.7   1:37.17 java

currently i am running it with this command: MAVEN_OPTS="-Xnoagent -Xrunjdwp:transport=dt_socket,server=y,suspend=n,address=8000 -Xmx20480M" screen -S Test -d -m mvn -o tomcat7:run

I also tried to add it to the pom.xml (build selection):

    <plugin>
            <groupId>org.codehaus.mojo</groupId>
            <artifactId>exec-maven-plugin</artifactId>
            <version>1.2.1</version>
            <executions>
                <execution>
                    <goals>
                        <goal>exec</goal>
                    </goals>
                </execution>
            </executions>
            <configuration>
                <argLine>-Xmx20480m</argLine>
                <mainClass>org.server.Server</mainClass>
                <arguments>
                </arguments>
            </configuration>
        </plugin>

Would be very nice if anyone knows a solution for this.

Thank you very much.

Edit: /proc/{pid}/ ls -l I cant answer to your comment directly but i dont understand where this mmap is exactly. Thats what i get when i switch into the folder you wrote:

    root@testserver /proc/1876 # ls -l
    total 0
    dr-xr-xr-x   2 root root 0 Nov 10 20:15 attr
    -rw-r--r--   1 root root 0 Nov 10 20:15 autogroup
    -r--------   1 root root 0 Nov 10 20:15 auxv
    -r--r--r--   1 root root 0 Nov 10 20:15 cgroup
    --w-------   1 root root 0 Nov 10 20:15 clear_refs
    -r--r--r--   1 root root 0 Nov 10 20:15 cmdline
    -rw-r--r--   1 root root 0 Nov 10 20:15 comm
    -rw-r--r--   1 root root 0 Nov 10 19:37 coredump_filter
    -r--r--r--   1 root root 0 Nov 10 20:15 cpuset
    lrwxrwxrwx   1 root root 0 Nov 10 19:39 cwd -> /srv/main
    -r--------   1 root root 0 Nov 10 20:15 environ
    lrwxrwxrwx   1 root root 0 Nov 10 19:37 exe -> /usr/lib/jvm/java-7-oracle/bin/java
    dr-x------   2 root root 0 Nov 10 19:39 fd
    dr-x------   2 root root 0 Nov 10 20:15 fdinfo
    -r--------   1 root root 0 Nov 10 20:15 io
    -r--r--r--   1 root root 0 Nov 10 20:15 latency
    -r--r--r--   1 root root 0 Nov 10 20:15 limits
    -rw-r--r--   1 root root 0 Nov 10 20:15 loginuid
    dr-x------   2 root root 0 Nov 10 20:15 map_files
    -r--r--r--   1 root root 0 Nov 10 19:37 maps
    -rw-------   1 root root 0 Nov 10 20:15 mem
    -r--r--r--   1 root root 0 Nov 10 20:15 mountinfo
    -r--r--r--   1 root root 0 Nov 10 20:15 mounts
    -r--------   1 root root 0 Nov 10 20:15 mountstats
    dr-xr-xr-x   5 root root 0 Nov 10 19:37 net
    dr-x--x--x   2 root root 0 Nov 10 20:15 ns
    -r--r--r--   1 root root 0 Nov 10 20:15 numa_maps
    -rw-r--r--   1 root root 0 Nov 10 20:15 oom_adj
    -r--r--r--   1 root root 0 Nov 10 20:15 oom_score
    -rw-r--r--   1 root root 0 Nov 10 20:15 oom_score_adj
    -r--r--r--   1 root root 0 Nov 10 20:15 pagemap
    -r--r--r--   1 root root 0 Nov 10 20:15 personality
    lrwxrwxrwx   1 root root 0 Nov 10 19:39 root -> /
    -rw-r--r--   1 root root 0 Nov 10 20:15 sched
    -r--r--r--   1 root root 0 Nov 10 20:15 schedstat
    -r--r--r--   1 root root 0 Nov 10 20:15 sessionid
    -r--r--r--   1 root root 0 Nov 10 20:15 smaps
    -r--r--r--   1 root root 0 Nov 10 20:15 stack
    -r--r--r--   1 root root 0 Nov 10 19:37 stat
    -r--r--r--   1 root root 0 Nov 10 19:37 statm
    -r--r--r--   1 root root 0 Nov 10 20:15 status
    -r--r--r--   1 root root 0 Nov 10 20:15 syscall
    dr-xr-xr-x 627 root root 0 Nov 10 20:15 task
    -r--r--r--   1 root root 0 Nov 10 20:15 wchan

Edit 2: Maps file: https://drive.google.com/file/d/0BxN3fm0mPOMUMVF1X0VEc2NSWVU/edit?usp=sharing

Answer 1

You need to work out where the extra virtual memory is coming from. The heap is not the only memory used but the JVM or your application.

I suggest you look at /proc/{pid}/maps to see if the virtual memory is coming from memory mapped files, thread stacks or native memory.

How many threads do you have as these can contribute a lot (if you have thousands)

If you have memory mapped files, this could easily be hundreds of GB of virtual memory. Given your entire system is actually using 2 GB of memory, I would suspect large memory mappings as these often use a lot of virtual memory without using read memory. You should be able to see this in maps easily as it includes the path to each memory mapped file.

Here is a program you can use to decode the mapping. Run this with

java -cp . Main /proc/{pid}/maps

---

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.math.BigInteger;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new FileReader(args[0]));
        List<Mapping> mappings = new ArrayList<>();
        for (String line; (line = br.readLine()) != null; ) {
            mappings.add(new Mapping(line));
        }
        Collections.sort(mappings);
        for (Mapping mapping : mappings) {
            System.out.println(mapping);
        }
    }

    static class Mapping implements Comparable<Mapping> {
        final String details;
        final long size;

        Mapping(String details) {
            this.details = details;
            String[] words = details.split("[- ]");
            long size = 0;
            try {
                if (words.length > 2)
                size = new BigInteger(words[1], 16).longValue() - new BigInteger(words[0], 16).longValue();
            } catch (NumberFormatException e) {
                // ignored.
            }
            this.size = size;
        }

        @Override
        public int compareTo(Mapping o) {
            // reverse order.
            return -Long.compare(size, o.size);
        }

        @Override
        public String toString() {
            return String.format("%.3f %s", size / 1024.0 / 1024, details);
        }
    }
}