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    SubjectRe: Linux and physical memory
    >Why can't the kernel just map in its address space the pieces of RAM it needs
    >for kernel code/data, and unmap them when done with them?
    >Maybe that mapping/unmapping of memory in kernel address space is expensive,
    >but I don't know. So I posted the question.

    Yes, the mapping/unmapping can be expensive, depending upon
    the underlying hardware architecture. The code to implement it adds
    complexity to kernel services and device drivers. It also introduces
    another set of potential deadlocks and resource mismanagements.

    There is a question of strategy in managing the kernel's
    evolution in a changing world. The limitations of the kernel's
    physical memory map vanish on a properly implemented 64-bit
    architecture. *If* you believe that 64-bit machines are now (or are
    soon to be) more cost-effective than 32-bit ones, and if the memory
    problem is one that affects only top-end machines, then is it worth
    putting a lot of effort into fixing top-end performance on 32-bit
    machines, when the same effort can yield greater results on 64-bit

    Craig Milo Rogers

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