Poison

OperatingSystemMXBean

发表于

OperatingSystemMXBean 中的 getFreePhysicalMemorySize() 方法返回的值为不含缓存的可用物理内存，该指标不能很好的反应 Linux 中实际可用的物理内存，因为 Linux 会尽量将物理内存用作 page cache，该指标返回的值（等价于 /proc/meminfo 的 MemFree）在长期运行的机器上通常接近 0，远小于实际可用的物理内存，我们根据 /proc/meminfo 中返回的数据采集出类似 free 命令中 available 列的值以便更好的监测可用物理内存。

部分代码如下：

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/**
 * Metrics collection similar to the free command.
 * <p>See also the <a href='https://man7.org/linux/man-pages/man1/free.1.html'>free(1) — Linux manual page</a>.
 *
 */
 public interface OperatingSystemMemoryMXBean {

     /**
      * Returns the amount of used physical memory in bytes.
      * Used memory (calculated as MemTotal - MemAvailable in /proc/meminfo)
      *
      * @return the amount of used physical memory in bytes.
      */
     long getUsedPhysicalMemorySize();

     /**
      * Returns the total amount of physical memory in bytes.
      * Total memory (MemTotal in /proc/meminfo)
      *
      * @return the total amount of physical memory in bytes.
      */
     long getTotalPhysicalMemorySize();

 }
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public class OperatingSystemMemoryImpl implements OperatingSystemMemoryMXBean {

    private static final String METRICS_MEM_TOTAL = "MemTotal";
    private static final String METRICS_MEM_AVAILABLE = "MemAvailable";

    @Override
    public long getUsedPhysicalMemorySize() {
        Map<String, Long> metricsToValueMap = getMetricsToValueMapFromMemInfo();
        return metricsToValueMap.getOrDefault(METRICS_MEM_TOTAL, 0L) - metricsToValueMap.getOrDefault(METRICS_MEM_AVAILABLE, 0L);
    }

    @Override
    public long getTotalPhysicalMemorySize() {
        Map<String, Long> metricsToValueMap = getMetricsToValueMapFromMemInfo();
        return metricsToValueMap.getOrDefault(METRICS_MEM_TOTAL, 0L);
    }

    private Map<String, Long> getMetricsToValueMapFromMemInfo() {
        Map<String, Long> metricsToValueMap = new HashMap<>(); // value unit: byte

        try (BufferedReader reader = new BufferedReader(new FileReader("/proc/meminfo"))) {
            String line;
            while ((line = reader.readLine()) != null) {
                if (!line.endsWith("kB")) {
                    continue;
                }

                int colonIndex = line.indexOf(':');
                int lastSpaceIndex = line.lastIndexOf(' ');
                if (colonIndex != -1 && lastSpaceIndex != -1) {
                    String metrics = line.substring(0, colonIndex);
                    int firstDigitIndex = colonIndex;
                    while (!Character.isDigit(line.charAt(firstDigitIndex))) {
                        firstDigitIndex++;
                    }
                    long valueInKB = Long.parseLong(line.substring(firstDigitIndex, lastSpaceIndex));

                    metricsToValueMap.put(metrics, valueInKB * 1024);
                }
            }

            return metricsToValueMap;
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

}
References

How to monitor free memory ( including buffers and cache) in java? - Stack Overflow
jdk/OperatingSystemMXBean.java at jdk8-b120 · openjdk/jdk · GitHub
free(1) - Linux manual page
proc(5) - Linux manual page
extras-memory-monitor/ProcMemInfo.java at master · jenkinsci/extras-memory-monitor · GitHub
How to calculate system memory usage from /proc/meminfo (like htop) - Stack Overflow
/proc/meminfo: provide estimated available memory - Linux kernel source tree