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    SubjectRe: hammer: MAP_32BIT
    Hash: SHA1

    Andi Kleen wrote:

    > That's just an inadequate data structure. It does an linear search of the
    > VMAs and you probably have a lot of them. Before you add kludges like this
    > better fix the data structure for fast free space lookup.

    If you mean the code in arch_get_unmapped_area(), yes, this needs
    fixing. In fact, Ingo has already a patch which brings back the
    performance of thread creation to what we had back in September/October.

    > In some vendor kernels it's already in /proc/pid/mapped_base, but that is
    > quite costly to change. That would probably give you the best of both, Just
    > set it to a low value for the thread stacks and then reset it to the default.
    > I guess that would be the better solution for your stacks.

    Are you sure this is the best solution? It means the mmap regions for
    restricted 31/32 bit addresses and that for the normal, unrestricted
    mapping is continuous. This removes a lot of freedom in deciding where
    the unrestricted mappings are best located and it would make programs
    using threads have a very different memory layout. Not that it should
    make any difference; but I can here /them/ already scream that this
    breaks applications.

    My kernel-uninformed opinion would be to keep the settings separate.

    Oh, and please rename MAP_32BIT to MAP_31BIT. This will save nerves on
    all sides.

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