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    SubjectRe: [RFC] simple_lmk: Introduce Simple Low Memory Killer for Android
    On Tue, Mar 12, 2019 at 1:05 AM Michal Hocko <mhocko@kernel.org> wrote:
    >
    > On Mon 11-03-19 15:15:35, Suren Baghdasaryan wrote:
    > > On Mon, Mar 11, 2019 at 1:46 PM Sultan Alsawaf <sultan@kerneltoast.com> wrote:
    > > >
    > > > On Mon, Mar 11, 2019 at 01:10:36PM -0700, Suren Baghdasaryan wrote:
    > > > > The idea seems interesting although I need to think about this a bit
    > > > > more. Killing processes based on failed page allocation might backfire
    > > > > during transient spikes in memory usage.
    > > >
    > > > This issue could be alleviated if tasks could be killed and have their pages
    > > > reaped faster. Currently, Linux takes a _very_ long time to free a task's memory
    > > > after an initial privileged SIGKILL is sent to a task, even with the task's
    > > > priority being set to the highest possible (so unwanted scheduler preemption
    > > > starving dying tasks of CPU time is not the issue at play here). I've
    > > > frequently measured the difference in time between when a SIGKILL is sent for a
    > > > task and when free_task() is called for that task to be hundreds of
    > > > milliseconds, which is incredibly long. AFAIK, this is a problem that LMKD
    > > > suffers from as well, and perhaps any OOM killer implementation in Linux, since
    > > > you cannot evaluate effect you've had on memory pressure by killing a process
    > > > for at least several tens of milliseconds.
    > >
    > > Yeah, killing speed is a well-known problem which we are considering
    > > in LMKD. For example the recent LMKD change to assign process being
    > > killed to a cpuset cgroup containing big cores cuts the kill time
    > > considerably. This is not ideal and we are thinking about better ways
    > > to expedite the cleanup process.
    >
    > If you design is relies on the speed of killing then it is fundamentally
    > flawed AFAICT. You cannot assume anything about how quickly a task dies.
    > It might be blocked in an uninterruptible sleep or performin an
    > operation which takes some time. Sure, oom_reaper might help here but
    > still.

    That's what I was considering. This is not a silver bullet but
    increased speed would not hurt.

    > The only way to control the OOM behavior pro-actively is to throttle
    > allocation speed. We have memcg high limit for that purpose. Along with
    > PSI, I can imagine a reasonably working user space early oom
    > notifications and reasonable acting upon that.

    That makes sense and we are working in this direction.

    > --
    > Michal Hocko
    > SUSE Labs

    Thanks,
    Suren.

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