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    SubjectRe: Bug: Discontigmem virt_to_page() [Alpha,ARM,Mips64?]
    [Looks like this buffer was laying dormant in my Emacs and never sent.
    Hence the delay... ;-) ]

    >>>>> On Thu, 2 May 2002 10:20:11 +1000, Anton Blanchard <anton@samba.org> said:

    >> so ia64 is one of those archs with a ram layout with huge holes
    >> in the middle of the ram of the nodes? I'd be curious to know
    >> what's the hardware advantage of designing the ram layout in such
    >> a way, compared to all other numa archs that I deal with. Also if
    >> you know other archs with huge holes in the middle of the ram of
    >> the nodes I'd be curious to know about them too. thanks for the
    >> interesting info!

    >> From arch/ppc64/kernel/iSeries_setup.c:

    Anton> * The iSeries may have very large memories ( > 128 GB ) and
    Anton> a partition * may get memory in "chunks" that may be anywhere
    Anton> in the 2**52 real * address space. The chunks are 256K in
    Anton> size.

    Anton> Also check out CONFIG_MSCHUNKS code and see why I'd love to
    Anton> see a generic solution to this problem.

    Me too. HP's zx1 platform also has a rather giant hole above the 1GB
    boundary. I don't know the exact reasons for this hole, but it's
    related to the fact that (many) PCI devices need <4GB memory.

    The current solution for zx1 is to place the mem_map in virtual
    memory. This obviously increases TLB pressure when touching lots of
    mem_map[] entries randomly, but I haven't really seen any benchmarks
    so far (real or artificial) where this has a signifcant performance
    effect. The nice part of this approach is that it is a rather general
    solution, provided the kernel's page-table mapped address space is
    sufficiently big.

    --david
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