Re: Virtual address space exhaustion (was Discontigmem virt_to_page() )

From: Tony Luck (
Date: Fri May 03 2002 - 13:37:01 EST

Richard B. Johnson wrote:
> One of the Unix characteristics is that the kernel
> address space is shared with each of the process
> address space.

This hasn't been an absolute requirement. There have
been 32-bit Unix implementations that gave separate
4G address spaces to the kernel and to each user
process. The only real downside to this is that
copyin()/copyout() are more complex. Some processors
provided special instructions to access user-mode
addresses from kernel to mitigate this complexity.


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