JVM memory allocation - xms128m - xmx512m - XX: permsize = 128M - XX: maxpermsize = 512M

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stay linux When configuring the project running environment under the environment , The deployment personnel will allocate memory , To ensure the normal operation of the program . In fact, during the development （window System ）, Memory allocation is already involved , It's just that these parameters have default values , So I didn't pay attention to it .
With Myeclipse For example , stay Preferences->Java->Installed JREs below , There are settings jvm Memory allocation .

Here we can configure memory , Generally, what we see is

-Xms128m -Xmx512m -XX:PermSize=128m -XX:MaxPermSize=512m

linux In general, it is ：
-vmargs -Xms128m -Xmx512m -XX:PermSize=128m -XX:MaxPermSize=512m

But what exactly does this string mean , Here's to explain .
According to the official statement ：Java The virtual machine has a heap (Heap), The heap is the runtime data area , Memory for all class instances and arrays is allocated from here . The pile is in Java Created when the virtual machine starts , stay JVM Memory outside the heap is called non heap memory (Non-heap memory).

Simply put ： The pile is java Code accessible memory , What developers write is heap allocated memory （ Except for the underlying implementation ）. And non heap memory is JVM For your own use , such as JVM Internal processing or optimization , Garbage disposal , Constant pool, etc .

Memory allocation for heap -Xms and -Xmx

-Xms Allocate heap minimum memory , Default to physical memory 1/64;-Xmx Allocate maximum memory , Default to physical memory 1/4.

Heap is not used to allocate memory -XX:PermSize and -XX:MaxPermSize

-XX:PermSize Allocate non heap minimum memory , Default to physical memory 1/64;-XX:MaxPermSize Allocate non heap maximum memory , Default to physical memory 1/4.

therefore , Reasonable memory allocation is the basis of normal and stable operation of the program . Otherwise, the memory overflow will be troublesome .