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I find everywhere how to implement dynamic memory management an stuffs like that.

But no where it is given where to keep the base address for the allocation.
In the wiki, it is given " But it is not alone: BIOS data structures, memory-mapped hardware registers etc. populate the address space.". But EXACTLY how much space? Which addresses should be skipped?
Which address will be the best address to start allocation from?

You have to get a memory map to be able to find memory holes to map around... On the wiki it gives you methods to do this, or you could have a multiboot-compliant bootloader(GRUB, syslinux, etc) pass you the memory map.