序
本文主要研究一下jvm的mapped buffer的统计
示例
private void writeDirectBuffer() {
// 分配一个256MB的直接缓冲区
ByteBuffer buffer = ByteBuffer.allocateDirect(256 * 1024 * 1024);
// 填充数据
Random random = new Random();
while (buffer.remaining() >= 4) {
buffer.putInt(random.nextInt());
}
System.out.println("Allocated direct buffer with capacity " + buffer.capacity());
}
private void writeMappedBuffer() throws IOException {
RandomAccessFile file = new RandomAccessFile("/tmp/test.txt", "rw");
FileChannel channel = file.getChannel();
MappedByteBuffer buffer = channel.map(FileChannel.MapMode.READ_WRITE, 0, 128 * 1024 * 1024); // 映射128MB的空间
// 随机写入数据
for (int i = 0; i < buffer.capacity(); i++) {
buffer.put((byte) i);
}
}
jvm.buffer.memory.used
http://localhost:8080/actuator/metrics/jvm.buffer.memory.used
{
"name": "jvm.buffer.memory.used",
"description": "An estimate of the memory that the Java virtual machine is using for this buffer pool",
"baseUnit": "bytes",
"measurements": [
{
"statistic": "VALUE",
"value": 402685952
}
],
"availableTags": [
{
"tag": "id",
"values": [
"direct",
"mapped"
]
}
]
}
jvm.buffer.memory.used分了direct和mapped两大类,一共用了384MB
mapped
http://localhost:8080/actuator/metrics/jvm.buffer.memory.used...
{
"name": "jvm.buffer.memory.used",
"description": "An estimate of the memory that the Java virtual machine is using for this buffer pool",
"baseUnit": "bytes",
"measurements": [
{
"statistic": "VALUE",
"value": 134217728
}
],
"availableTags": []
}
可以看到这里mapped用了128MB
direct
http://localhost:8080/actuator/metrics/jvm.buffer.memory.used...
{
"name": "jvm.buffer.memory.used",
"description": "An estimate of the memory that the Java virtual machine is using for this buffer pool",
"baseUnit": "bytes",
"measurements": [
{
"statistic": "VALUE",
"value": 268500992
}
],
"availableTags": []
}
可以看到这里direct用了256MB
Native Memory Tracking
开启
java -XX:+UnlockDiagnosticVMOptions -XX:NativeMemoryTracking=summary -jar target/app.jar
监控
jcmd 2315 VM.native_memory summary scale=MB
2315:
Native Memory Tracking:
Total: reserved=5882MB, committed=1100MB
- Java Heap (reserved=4096MB, committed=577MB)
(mmap: reserved=4096MB, committed=577MB)
- Class (reserved=1066MB, committed=46MB)
(classes #7035)
(malloc=10MB #10793)
(mmap: reserved=1056MB, committed=37MB)
- Thread (reserved=36MB, committed=36MB)
(thread #37)
(stack: reserved=36MB, committed=36MB)
- Code (reserved=246MB, committed=16MB)
(malloc=2MB #3971)
(mmap: reserved=244MB, committed=13MB)
- GC (reserved=160MB, committed=148MB)
(malloc=10MB #219)
(mmap: reserved=150MB, committed=138MB)
- Internal (reserved=266MB, committed=266MB)
(malloc=266MB #10067)
- Symbol (reserved=9MB, committed=9MB)
(malloc=8MB #74334)
(arena=2MB #1)
- Native Memory Tracking (reserved=2MB, committed=2MB)
(tracking overhead=2MB)
NTM的Internal包含了direct buffer的统计,不包含mapped buffer的占用,而BufferPoolMXBean包含了direct和mapped。
另外通过调用System.loadLibrary()加载的共享库分配的内存NTM没办法追踪到,MXBean貌似也没办法统计到。
小结
- 聊聊jvm的direct buffer统计
- Memory Types in JVM
- Native Memory Tracking in JVM
- How to monitor JVM native memory usage by enabling native memory tracking
- Troubleshooting Problems With Native (Off-Heap) Memory in Java Applications
- Can a Java Application Use More Memory Than the Heap Size?
- java-non-heap-memory-analyzes
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