Kernel address space is the portion of the virtual address space marked supervisor-mode-only. In many systems, it includes the first 700+ MB of RAM, mapped to virtual address 0xC0000000.
The split is usually referred to as 3G/1G. There have been experiments with the organization you suggest, 4G/4G. The problem with it is that switching between the user-mode and supervisor-mode address maps takes a lot of time because the poorly-designed Intel MMU requires that the TLBs be flushed. The PowerPC MMU, by contrast, includes the supervisor/user attribute in each TLB entry and so does not require this flush.
By dedicating the first 3G of a 32-bit virtual address space to user mode and the last 1G to kernel mode, the Intel MMU can describe both user and kernel spaces simultaneously.
answers
Kernel address space is the portion of the virtual address space marked supervisor-mode-only. In many systems, it includes the first 700+ MB of RAM, mapped to virtual address 0xC0000000.
The split is usually referred to as 3G/1G. There have been experiments with the organization you suggest, 4G/4G. The problem with it is that switching between the user-mode and supervisor-mode address maps takes a lot of time because the poorly-designed Intel MMU requires that the TLBs be flushed. The PowerPC MMU, by contrast, includes the supervisor/user attribute in each TLB entry and so does not require this flush.
By dedicating the first 3G of a 32-bit virtual address space to user mode and the last 1G to kernel mode, the Intel MMU can describe both user and kernel spaces simultaneously.