Hi, I'm currently studying the memory management subsystem. When I read the code of x86_64 memory mapping initialization, I encounter a problem and can't find answers on Google. I wonder why the kernel needs `split_mem_range()`[0] to split physical address range. To make this question clear, I find an example from dmesg. The arguments of `split_mem_range` are start=0x00100000, end=0x80000000. The splitting result is: [mem 0x00100000-0x001FFFFF] page 4k [mem 0x00200000-0x7FFFFFFF] page 2M I don't know why the first 1MiB range is separated out to use 4k page frame. I think these two ranges can be merged and let the range [0x00100000-0x7FFFFFFF] use 2M page frame completely. I can't understand the purpose of this range splitting. Could someone please explain this function to me? Many Thanks! [0] https://github.com/torvalds/linux/blob/10b84daddbec72c6b440216a69de9a9605127f7a/arch/x86/mm/init.c#L325 Regards, Hao Lee
