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    SubjectRe: [Lse-tech] Re: 10.31 second kernel compile

    On Sat, 16 Mar 2002 yodaiken@fsmlabs.com wrote:

    > On Sat, Mar 16, 2002 at 10:06:06AM -0800, Linus Torvalds wrote:
    > > We'll end up (probably five years from now) re-doing the thing to allow
    > > four levels (so a tired old x86 would fold _two_ levels instead of just
    > > one, but I bet they'll still be the majority), simply because with three
    > > levels you reasonably reach only about 41 bits of VM space.
    >
    > Why so few bits per level? Don't you want bigger pages or page clusters?

    Simply because I want to be able to share the software page tables with
    the hardware page tables.

    Not sharing the page tables implies that you have to have two copies and
    keep them in sync, which is almost certainly going to make fork/exec just
    suck badly.

    Now I agree with you that in the long range all the hardware will just use
    a 64k pagesize or we'll have extents or whatever. I'm not saying that
    trees are the only good way to populate a VM, it's just the currently
    dominant way, and as long as it's the dominant way I want to have the
    common mapping be the 1:1 mapping.

    Linus

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