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    SubjectRe: MM deadlock [was: Re: arca-vm-8...]
    Hi!

    > In fact, to make it really safe we'd need to avoid synchronous swapout
    > altogether: otherwise we can have
    >
    > A kswiod nbd server process
    > lock_super();
    > bread(ndb device);
    > try_to_free_page();
    > rw_swap_page_async();
    > filemap_write_page();
    > lock_super();
    > wait_on_buffer();
    > try_to_free_page();
    > rw_swap_page_sync();
    > Oops, kswiod is stalled.
    >
    > Can we get away without synchronous swapout? Notice that in this case,
    > kswiod may be blocked but kswapd itself will not be. As long as the nbd
    > server does not try to do a synchronous swap, it won't deadlock on
    > kswiod. In other words, it is safe to wait for avaibility of
    > another

    Is this only matter of nbd? If so, maybe the best solution is to start
    claiming: "don't swap over nbd, don't mount localhost drives read
    write". [It is bad, but it is probably better than polluting rest of
    kernel with nbd workarounds...]

    Pavel
    --
    The best software in life is free (not shareware)! Pavel
    GCM d? s-: !g p?:+ au- a--@ w+ v- C++@ UL+++ L++ N++ E++ W--- M- Y- R+

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