Question

我有一个Netty进程，它使用具有4个线程的并行GC运行8 GB的堆。我正在尝试分析堆，并观察到jmap中显示的所有容量的总和甚至不接近8 GB，Old Gen仅1.5 GB，Young Gen 750 MB。

下面是 jmap -heap 7595

的输出

Attaching to process ID 7595, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.131-b11

using thread-local object allocation.
Parallel GC with 4 thread(s)

Heap Configuration:
   MinHeapFreeRatio         = 30
   MaxHeapFreeRatio         = 70
   MaxHeapSize              = 8589934592 (8192.0MB)
   NewSize                  = 88080384 (84.0MB)
   MaxNewSize               = 2863136768 (2730.5MB)
   OldSize                  = 176160768 (168.0MB)
   NewRatio                 = 2
   SurvivorRatio            = 8
   MetaspaceSize            = 21807104 (20.796875MB)
   CompressedClassSpaceSize = 1073741824 (1024.0MB)
   MaxMetaspaceSize         = 17592186044415 MB
   G1HeapRegionSize         = 0 (0.0MB)

Heap Usage:
PS Young Generation
Eden Space:
   capacity = 763363328 (728.0MB)
   used     = 418551600 (399.1619110107422MB)
   free     = 344811728 (328.8380889892578MB)
   54.8299328311459% used
From Space:
   capacity = 1048576 (1.0MB)
   used     = 458752 (0.4375MB)
   free     = 589824 (0.5625MB)
   43.75% used
To Space:
   capacity = 1048576 (1.0MB)
   used     = 0 (0.0MB)
   free     = 1048576 (1.0MB)
   0.0% used
PS Old Generation
   capacity = 1530396672 (1459.5MB)
   used     = 1196099760 (1140.6896209716797MB)
   free     = 334296912 (318.8103790283203MB)
   78.15619191309898% used

27146 interned Strings occupying 3164408 bytes.

[年轻一代（728）+老一代（1459）= 2187 MB] << 8GB

Answer 1

默认情况下，JVM在启动后不会分配最大堆，而是在JVM需要时分配并扩展较小的初始堆。您可以使用-Xms标志，例如将初始堆大小强制为8GB。 docs中的-Xms8g：

-Xmssize

设置堆的初始大小（以字节为单位）。此值必须是1024的倍数且大于1 MB。字母k或K表示千字节，m或M表示兆字节，g或G表示千兆字节。

Java堆分解总和不等于总堆容量

1 个答案: