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    SubjectRe: System freezes after OOM
    On Fri 15-07-16 13:02:17, Mikulas Patocka wrote:
    >
    >
    > On Fri, 15 Jul 2016, Michal Hocko wrote:
    >
    > > On Fri 15-07-16 08:11:22, Mikulas Patocka wrote:
    > > >
    > > > The stacktraces showed that the kcryptd process was throttled when it
    > > > tried to do mempool allocation. Mempool adds the __GFP_NORETRY flag to the
    > > > allocation, but unfortunatelly, this flag doesn't prevent the allocator
    > > > from throttling.
    > >
    > > Yes and in fact it shouldn't prevent any throttling. The flag merely
    > > says that the allocation should give up rather than retry
    > > reclaim/compaction again and again.
    > >
    > > > I say that the process doing mempool allocation shouldn't ever be
    > > > throttled. Maybe add __GFP_NOTHROTTLE?
    > >
    > > A specific gfp flag would be an option but we are slowly running out of
    > > bit space there and I am not yet convinced PF_LESS_THROTTLE is
    > > unsuitable.
    >
    > PF_LESS_THROTTLE will make it throttle less, but it doesn't eliminate
    > throttling entirely. So, maybe add PF_NO_THROTTLE? But PF_* flags are also
    > almost exhausted.

    I am not really sure we can make anybody so special to not throttle at all.
    Seeing a congested backig device sounds like a reasonable compromise.
    Besides that it seems that we do not really need to eliminate
    wait_iff_congested for dm to work properly again AFAIU. I plan to repost
    both patch today after some more internal review. If we need to do more
    changes I would suggest making them in separet patches.
    --
    Michal Hocko
    SUSE Labs

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