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    SubjectRe: Bug: Discontigmem virt_to_page() [Alpha,ARM,Mips64?]
    On Wed, May 01, 2002 at 03:35:20AM +0200, Daniel Phillips wrote:
    > On Thursday 02 May 2002 02:20, Anton Blanchard wrote:
    > > > 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:
    > >
    > > * The iSeries may have very large memories ( > 128 GB ) and a partition
    > > * may get memory in "chunks" that may be anywhere in the 2**52 real
    > > * address space. The chunks are 256K in size.
    > >
    > > Also check out CONFIG_MSCHUNKS code and see why I'd love to see a generic
    > > solution to this problem.
    > Using the config_nonlinear model, you'd change the four mapping functions:
    > logical_to_phys
    > phys_to_logical
    > pagenum_to_phys
    > phys_to_pagenum
    > to use a hash table instead of a table lookup. Bill Irwin suggested a btree
    > would work here as well.

    btree? btree is not an interesting in core data structure. Anyways you
    can use a btree with discontigmem too for the lookup. nonlinear will pay
    off if you've something of the order of 256 discontigmem chunks with
    significant holes in between like origin 2k, and I think it should be
    resolved internally to the arch without exposing it to the common code.

    > (Note I'm trying out the term 'pagenum' instead of 'ordinal' here, following
    > comments on lse-tech.)
    > --
    > Daniel

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