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    SubjectRe: Current mainline git (24e700e291d52bd2) hangs when building e.g. perf

    * Andy Lutomirski <luto@kernel.org> wrote:

    > PeterZ and Ingo, would you be okay with adding a define so arches can
    > opt out of the task_struct::active_mm field entirely? That is, with
    > the option set, task_struct wouldn't have an active_mm field, the core
    > wouldn't call mmgrab and mmdrop, and the arch would be responsible for
    > that bookkeeping instead? x86, and presumably all arches without
    > cross-core invalidation, would probably prefer to just shoot down the
    > old mm entirely in __mmput() rather than trying to figure out when do
    > finish freeing old mms. After all, exit_mmap() is going to send an
    > IPI regardless, so I see no reason to have the scheduler core pin an
    > old dead mm just because some random kernel thread's active_mm field
    > points to it.
    >
    > IOW, if I'm going to reintroduce something like what the old lazy mode
    > did on x86, I'd rather do it right.

    How realistic would it be to get rid of ::active_mm on all architectures
    at once?

    Thanks,

    Ingo

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