什么是本机内存跟踪的“可维护性内存类别”？
2022-09-03 13:50:06
我有一个在 docker 容器中运行的 java 应用程序 （JDK13）。最近，我将应用程序移动到JDK17（OpenJDK17），发现Docker容器的内存使用量逐渐增加。
在调查过程中，我发现“可维护性内存类别”NMT不断增长（每小时15mb）。我检查了页面 https://docs.oracle.com/en/java/javase/17/troubleshoot/diagnostic-tools.html#GUID-5EF7BB07-C903-4EBD-A9C2-EC0E44048D37 但那里没有提到这个类别。
谁能解释一下这个可维护性类别意味着什么，以及什么会导致这种逐渐增加？此外，与 JDK13 相比，还有一些额外的新内存类别。也许有人知道我在哪里可以阅读有关他们的详细信息。
这是命令的结果jcmd 1 VM.native_memory summary
Native Memory Tracking:
(Omitting categories weighting less than 1KB)
Total: reserved=4431401KB, committed=1191617KB
- Java Heap (reserved=2097152KB, committed=479232KB)
(mmap: reserved=2097152KB, committed=479232KB)
- Class (reserved=1052227KB, committed=22403KB)
(classes #29547)
( instance classes #27790, array classes #1757)
(malloc=3651KB #79345)
(mmap: reserved=1048576KB, committed=18752KB)
( Metadata: )
( reserved=139264KB, committed=130816KB)
( used=130309KB)
( waste=507KB =0.39%)
( Class space:)
( reserved=1048576KB, committed=18752KB)
( used=18149KB)
( waste=603KB =3.21%)
- Thread (reserved=387638KB, committed=40694KB)
(thread #378)
(stack: reserved=386548KB, committed=39604KB)
(malloc=650KB #2271)
(arena=440KB #752)
- Code (reserved=253202KB, committed=76734KB)
(malloc=5518KB #23715)
(mmap: reserved=247684KB, committed=71216KB)
- GC (reserved=152419KB, committed=92391KB)
(malloc=40783KB #34817)
(mmap: reserved=111636KB, committed=51608KB)
- Compiler (reserved=1506KB, committed=1506KB)
(malloc=1342KB #2557)
(arena=165KB #5)
- Internal (reserved=5579KB, committed=5579KB)
(malloc=5543KB #33822)
(mmap: reserved=36KB, committed=36KB)
- Other (reserved=231161KB, committed=231161KB)
(malloc=231161KB #347)
- Symbol (reserved=30558KB, committed=30558KB)
(malloc=28887KB #769230)
(arena=1670KB #1)
- Native Memory Tracking (reserved=16412KB, committed=16412KB)
(malloc=575KB #8281)
(tracking overhead=15837KB)
- Shared class space (reserved=12288KB, committed=12136KB)
(mmap: reserved=12288KB, committed=12136KB)
- Arena Chunk (reserved=18743KB, committed=18743KB)
(malloc=18743KB)
- Tracing (reserved=32KB, committed=32KB)
(arena=32KB #1)
- Logging (reserved=7KB, committed=7KB)
(malloc=7KB #289)
- Arguments (reserved=1KB, committed=1KB)
(malloc=1KB #53)
- Module (reserved=1045KB, committed=1045KB)
(malloc=1045KB #5026)
- Safepoint (reserved=8KB, committed=8KB)
(mmap: reserved=8KB, committed=8KB)
- Synchronization (reserved=204KB, committed=204KB)
(malloc=204KB #2026)
- Serviceability (reserved=31187KB, committed=31187KB)
(malloc=31187KB #49714)
- Metaspace (reserved=140032KB, committed=131584KB)
(malloc=768KB #622)
(mmap: reserved=139264KB, committed=130816KB)
- String Deduplication (reserved=1KB, committed=1KB)
(malloc=1KB #8)
有关增加部分内存的详细信息如下：
[0x00007f6ccb970cbe] OopStorage::try_add_block()+0x2e
[0x00007f6ccb97132d] OopStorage::allocate()+0x3d
[0x00007f6ccbb34ee8] StackFrameInfo::StackFrameInfo(javaVFrame*, bool)+0x68
[0x00007f6ccbb35a64] ThreadStackTrace::dump_stack_at_safepoint(int)+0xe4
(malloc=6755KB type=Serviceability #10944)
2022-01-17更新#1：
感谢@Aleksey Shipilev的帮助！我们能够找到一个导致问题的地方，与许多ThreadMXBean#.dumpAllThreads调用有关。以下是 MCVE、Test.java：
运行方式：
java -Xmx512M -XX:NativeMemoryTracking=detail Test.java
并定期检查可维护性类别的结果
jcmd YOUR_PID VM.native_memory summary
测试 java：
import java.lang.management.ManagementFactory;
import java.lang.management.ThreadInfo;
import java.lang.management.ThreadMXBean;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
public class Test {
private static final int RUNNING = 40;
private static final int WAITING = 460;
private final Object monitor = new Object();
private final ThreadMXBean threadMxBean = ManagementFactory.getThreadMXBean();
private final ExecutorService executorService = Executors.newFixedThreadPool(RUNNING + WAITING);
void startRunningThread() {
executorService.submit(() -> {
while (true) {
}
});
}
void startWaitingThread() {
executorService.submit(() -> {
try {
monitor.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
});
}
void startThreads() {
for (int i = 0; i < RUNNING; i++) {
startRunningThread();
}
for (int i = 0; i < WAITING; i++) {
startWaitingThread();
}
}
void shutdown() {
executorService.shutdown();
try {
executorService.awaitTermination(5, TimeUnit.SECONDS);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
public static void main(String[] args) throws InterruptedException {
Test test = new Test();
Runtime.getRuntime().addShutdownHook(new Thread(test::shutdown));
test.startThreads();
for (int i = 0; i < 12000; i++) {
ThreadInfo[] threadInfos = test.threadMxBean.dumpAllThreads(false, false);
System.out.println("ThreadInfos: " + threadInfos.length);
Thread.sleep(100);
}
test.shutdown();
}
}
