外部碎片如何发生? [英] How does external fragmentation happen?

问题描述

随着进程从内存中加载和删除，可用内存空间被分解成小块，导致碎片化……但是这是怎么发生的呢? 外部碎片的最佳解决方案是什么?

As processes are loaded and removed from memory , the free memory space is broken into little pieces ,causing fragmentation ... but how does this happen ? And what is the best solution to external fragmentation ?

推荐答案

外部碎片

当动态内存分配算法分配了一些内存，而剩下的一小块无法有效使用时，就会发生外部碎片.如果发生过多的外部碎片，则可用内存量将大大减少.存在总内存空间可以满足请求，但是不连续. 参见以下示例

External Fragmentation

External fragmentation happens when a dynamic memory allocation algorithm allocates some memory and a small piece is left over that cannot be effectively used. If too much external fragmentation occurs, the amount of usable memory is drastically reduced. Total memory space exists to satisfy a request, but it is not contiguous. see following example

 0x0000 0x1000  0x2000  
   A    B     C               //Allocated three blocks A, B, and C, of size 0x1000.
   A          C         //Freed block B

现在请注意，对于大于B大小的分配，不能包含B使用的内存

Now Notice that the memory that B used cannot be included for an allocation larger than B's size

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