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    SubjectRe: [RFC PATCH 10/10] psi: aggregate ongoing stall events when somebody reads pressure
    On Thu, Jul 12, 2018 at 04:45:37PM -0700, Andrew Morton wrote:
    > On Thu, 12 Jul 2018 13:29:42 -0400 Johannes Weiner <hannes@cmpxchg.org> wrote:
    >
    > > Right now, psi reports pressure and stall times of already concluded
    > > stall events. For most use cases this is current enough, but certain
    > > highly latency-sensitive applications, like the Android OOM killer,
    > > might want to know about and react to stall states before they have
    > > even concluded (e.g. a prolonged reclaim cycle).
    > >
    > > This patches the procfs/cgroupfs interface such that when the pressure
    > > metrics are read, the current per-cpu states, if any, are taken into
    > > account as well.
    > >
    > > Any ongoing states are concluded, their time snapshotted, and then
    > > restarted. This requires holding the rq lock to avoid corruption. It
    > > could use some form of rq lock ratelimiting or avoidance.
    > >
    > > Requested-by: Suren Baghdasaryan <surenb@google.com>
    > > Not-yet-signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
    >
    > What-does-that-mean:?

    I didn't think this patch was ready for upstream yet, hence the RFC
    and the lack of a proper sign-off.

    But Suren has been testing this and found it useful in his specific
    low-latency application, so I included it for completeness, for other
    testers to find, and for possible suggestions on how to improve it.
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