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    SubjectRe: locking question: do_mmap(), do_munmap()


    On Mon, 11 Oct 1999, Stephen C. Tweedie wrote:

    > Hi,
    >
    > On Sun, 10 Oct 1999 15:03:45 -0400 (EDT), Alexander Viro
    > <viro@math.psu.edu> said:
    >
    > > Hold on. In swap_out_mm() you have to protect find_vma() (OK, it doesn't
    > > block, but we'll have to take care of mm->mmap_cache) _and_ you'll have to
    > > protect vma from destruction all way down to try_to_swap_out(). And to
    > > vma->swapout(). Which can sleep, so spinlocks are out of question
    > > here.
    >
    > No, spinlocks would be ideal. The vma swapout codes _have_ to be
    > prepared for the vma to be destroyed as soon as we sleep. In fact, the
    > entire mm may disappear if the process happens to exit. Once we know
    > which page to write where, the swapout operation becomes a per-page
    > operation, not per-vma.

    Aha, so you propose to drop it in ->swapout(), right? (after get_file() in
    filemap_write_page()... Ouch. Probably we'ld better lambda-expand the call
    in filemap_swapout() - the thing is called from other places too)...


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