Dockerfile

#FROM openjdk:11.0-jre
FROM openjdk:16-alpine3.13

COPY web/target/graphhopper*.jar ./graphhopper.jar

ENTRYPOINT [ "java -Xmx1g -Xms1g -jar graphhopper.jar", "10" ]

MMapTest.java

import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.util.ArrayList;
import java.util.Date;
import java.util.EnumSet;
import java.util.List;

public class Main {
  public static void main(String[] args) throws Exception {
        RandomAccessFile raFile = new RandomAccessFile("test.data", "rw");

        System.out.println("START MMAP " + new Date());

        int count = args.length > 0 ? Integer.parseInt(args[0]) : 1;
        List<MappedByteBuffer> segments = new ArrayList<>();

        long offset = 0;
        int size = 1024 * 1024 * 1024;

        for (int i = 0; i < count; i++) {
            MappedByteBuffer buf = raFile.getChannel().map(FileChannel.MapMode.READ_WRITE, offset, size);
            offset += size;
            buf.position(0);
            buf.putChar('A');
            buf.position(size / 2);
            buf.putChar('B');
            buf.position(size - 100);
            buf.putChar('C');

            buf.force();
            segments.add(buf);
            System.out.println("loaded MMAP " + i + " " + new Date());
        }
        raFile.getFD().sync();
        raFile.close();
        System.out.println("END MMAP " + new Date() + " " + segments.size());

        System.out.println("START' memory " + new Date());

        List<byte[]> ints = new ArrayList<>();
        for (int i = 0; i < count; i++) {
            ints.add(new byte[size]);
            System.out.println("loaded memory " + i + " " + new Date());
        }
        System.out.println("END memory " + new Date() + " " + ints.size());
    }
}

start.sh

sudo docker run --rm -it --memory 2g --memory-swap=0g --entrypoint /bin/sh test/test -c "java -Xmx2000m -Xms2000m -jar graphhopper.jar 50"