> But all physical memory/frames are eventually controlled by > kernel , then how can there ever exist a frame which doesn't > have mapping with kernel or kernel virtual address ? The key point is that frames are in physical memory while pages are in virtual memory. For a 4G Linux system, low 896M physical memory (low memory) is mapped directly into kernel space(virtual), and the rest is high memory at all (initally not mapped into any virtual space). If kernel needs more frames other than those directly mapped, it can map frames from high memory into its 128M virtaul space. If a user task needs frames, these frames might be from low memory or from high memory. In the former case, kernel shares these frames with user task. While in the latter case, these frames are only used by the user task. Therefore, some frames in high memory might not be mapped into kernel space at all. In addition, 896M low memory(physical) can be used directly by kernel, while all physical memory frames are allocated and mapped by kernel. _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
