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    SubjectRe: Deadlock possibly caused by too_many_isolated.
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    On Tue, Oct 19, 2010 at 11:03 AM, KOSAKI Motohiro
    <kosaki.motohiro@jp.fujitsu.com> wrote:
    >> On Tue, Oct 19, 2010 at 10:21 AM, KOSAKI Motohiro
    >> <kosaki.motohiro@jp.fujitsu.com> wrote:
    >> >> On Tue, Oct 19, 2010 at 9:57 AM, KOSAKI Motohiro
    >> >> <kosaki.motohiro@jp.fujitsu.com> wrote:
    >> >> >> > I think there are two bugs here.
    >> >> >> > The raid1 bug that Torsten mentions is certainly real (and has been around
    >> >> >> > for an embarrassingly long time).
    >> >> >> > The bug that I identified in too_many_isolated is also a real bug and can be
    >> >> >> > triggered without md/raid1 in the mix.
    >> >> >> > So this is not a 'full fix' for every bug in the kernel :-), but it could
    >> >> >> > well be a full fix for this particular bug.
    >> >> >> >
    >> >> >>
    >> >> >> Can we just delete the too_many_isolated() logic?  (Crappy comment
    >> >> >> describes what the code does but not why it does it).
    >> >> >
    >> >> > if my remember is correct, we got bug report that LTP may makes misterious
    >> >> > OOM killer invocation about 1-2 years ago. because, if too many parocess are in
    >> >> > reclaim path, all of reclaimable pages can be isolated and last reclaimer found
    >> >> > the system don't have any reclaimable pages and lead to invoke OOM killer.
    >> >> > We have strong motivation to avoid false positive oom. then, some discusstion
    >> >> > made this patch.
    >> >> >
    >> >> > if my remember is incorrect, I hope Wu or Rik fix me.
    >> >>
    >> >> AFAIR, it's right.
    >> >>
    >> >> How about this?
    >> >>
    >> >> It's rather aggressive throttling than old(ie, it considers not lru
    >> >> type granularity but zone )
    >> >> But I think it can prevent unnecessary OOM problem and solve deadlock problem.
    >> >
    >> > Can you please elaborate your intention? Do you think Wu's approach is wrong?
    >>
    >> No. I think Wu's patch may work well. But I agree Andrew.
    >> Couldn't we remove the too_many_isolated logic? If it is, we can solve
    >> the problem simply.
    >> But If we remove the logic, we will meet long time ago problem, again.
    >> So my patch's intention is to prevent OOM and deadlock problem with
    >> simple patch without adding new heuristic in too_many_isolated.
    >
    > But your patch is much false positive/negative chance because isolated pages timing
    > and too_many_isolated_zone() call site are in far distance place.

    Yes.
    How about the returning *did_some_progress can imply too_many_isolated
    fail by using MSB or new variable?
    Then, page_allocator can check it whether it causes read reclaim fail
    or parallel reclaim.
    The point is let's throttle without holding FS/IO lock.

    > So, if anyone don't say Wu's one is wrong, I like his one.
    >

    I am not against it and just want to solve the problem without adding new logic.



    --
    Kind regards,
    Minchan Kim
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