HEADS UP Re: cvs commit: src/sys/conf options.i386 src/sys/i386/i386 bios.c locore.s machdep.c mpboot.s pmap.c vm86bios.s vm_machdep.c src/sys/i386/include _types.h bus_at386.h param.h pmap.

Mike Silbersack silby at silby.com
Sun Mar 30 15:34:14 PST 2003

On Sun, 30 Mar 2003, Jake Burkholder wrote:

> I'm not sure I understand the question, you mean is it possible to use
> separate address spaces for the kernel and userland, giving a full 4G each?
> Yes it is possible, but it is not practical.  It would be prohibitively
> expensive and ugly.  For example you would need to use task gates for
> system calls, and copyin or copyout would need to look up the user pages
> and map them temporarily, something like that.
> Keep in mind that the restriction is what can be mapped.  It is still
> possible to keep around huge amounts of memory as long as its not all
> mapped all the time.  For example many device drivers just do dma and
> don't need a virtual mapping for every chunk of memory they see, avoiding
> mapping and unmapping it would save a lot of KVA.
> Jake

Yes, 4G/4G is what I was asking about.  The reason I'm confused is that I
don't understand how copies from the upper 2G of a 6G box work any better
than copies from overlapping user memory with < 4G addresses.  Are we
using 64 pointers throughout the kernel while in PAE mode?  (I didn't
think i386 supported that, which is why I'm asking.)

Sorry if these are "dumb" questions, but I'm quite green when it comes to
address space mapping.


Mike "Silby" Silbersack

More information about the cvs-src mailing list