Optimistic memory allocation strategy in Linux

If you know C programming language, you must know what is malloc. malloc is for dynamic memory allocation. In colleges, we learned that malloc should return NULL in case of out-of-memory. However, it is not the case in Linux. By default, Linux uses optimistic memory allocation strategy. Under this strategy, Linux assumes there always exists free memory. The memory region returns by malloc is not actually allocated until the process touches the memory region. This means the memory region returns by malloc may not be available. In case of out-of-memory, the OOM Killer in Linux will pick up one or more process to kill. This sounds strange!

Reference:
man malloc
http://linux-mm.org/OOM_Killer