Buddy System

1、什么是Buddy System：    

      The buddy memory allocation technique is a memory allocation algorithm that divides memory into partitions to try to satisfy a memory request as suitably as possible.

2、辅助理解的例子：

       The following is an example of what happens when a program makes requests for memory. Let's say in this system, the smallest possible block is 64 kb in size, and the upper limit for the order is 4, which results in a largest possible allocatable block, 24 times 64 K = 1024 K in size. The following shows a possible state of the system after various memory requests.

     

           However, there still exists the problem of internal fragmentation – memory wasted because the memory requested is a little larger than a small block, but a lot smaller than a large block. Because of the way the buddy memory allocation technique works, a program that requests 66 K of memory would be allocated 128 K, which results in a waste of 62 K of memory. This problem can be solved by slab allocation, which may be layered on top of the more coarse buddy allocator to provide more fine-grained allocation.