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    SubjectRe: bigphysarea in 2.2

    I deal with some high-performance image processing hardware. I work in
    gray a lot, and a 200DPI high-speed color scanner is soon to come to
    reality. That said... said:
    > With the new kernel memory manager, and if the defragmenting code
    > which is under development works, wouldn't it be more useful to use
    > standard kernel memory allocation. Static allocation like in
    > bigphysarea is more a work-around that a real solution.

    It is common for me to need many megabytes per board. In most cases
    they are perfectly capable of scatter-gather, but the huge volume, even
    broken into 4K pages, is usually hard to get, especially after the system
    has been running for a while. (Think loadable modules.)

    I do occasionally run into boards that do *not* do scatter-gather, and
    they require lots of contiguous memory. These are typically not high
    quantity, and so not worth the effort of fancy DMA controllers.

    It actually strikes me as a bad idea to try to make a memory manager
    that handles these extreme cases at the expense of the normal case. The
    bigphysarea patch offers a different memory allocator intended for doing
    only a few allocations in a big space. This way it doesn't get in the
    way or needlessly complicate the normal allocator. It can also be
    practically turned off without recompiling the kernel.

    I think it is reasonable to expect my customers of such extreme hardware
    to set aside memory specifically for the board so that such allocation
    doesn't over-tax the normal allocation mechanism. Putting bigphysarea=foo
    in /etc/lilo.conf is not too much to ask, patching the kernel source or
    restricting them to a specific kernel version, well...

    I believe that the bigphysarea patch is worth making a part of the kernel
    as a whole because the Linux kernel is very well suited to these extreme
    tasks that occasionally have special memory requirements. The bigphysarea
    support is simple, yes, and it helps *a lot*.

    (The patch can also be modified to put to good use that non-cached memory
    that some computers seem to have.)

    Steve Williams "The woods are lovely, dark and deep. But I have promises to keep, and lines to code before I sleep, And lines to code before I sleep."

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