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    SubjectRe: The 3G (or nG) Kernel Memory Space Offset
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    On Wed, 2006-08-30 at 00:01 +0800, Dong Feng wrote:
    > 2006/8/29, Jan Engelhardt <jengelh@linux01.gwdg.de>:
    > >
    > > "0-4G physical memory space" denotes RAM. Since kernelspace is resident, it
    > > only seems logical to map it to 0G (that is, the start of RAM), because the
    > > end of RAM can be flexible.
    > >
    > > IOW, you cannot map kernelspace to the physical location 0xc0000000 because
    > > there might not be that much RAM.
    > >
    > > (Also note the PCI memory hole which is near the end of the 4G range.)
    > >
    > >
    > > Jan Engelhardt
    > > --
    > >
    >
    >
    > Sorry for my typo. I actually means "0-1G physical memory space." My
    > question is actually why there is a 3G offset from linear kernel to
    > physical kernel. Why not simply have kernel memory linear space
    > located on 0-1G linear address, and therefore the physical kernel and
    > linear kernel just coincide?


    the price for that would be that you would have to flush all the tlb's
    on each syscall. That's seen as a quite hefty price by many kernel
    developers.


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