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    SubjectRe: [bisected] pre-3.16 regression on open() scalability
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    On Wed, 2014-06-18 at 20:38 -0700, Andi Kleen wrote:
    > On Wed, Jun 18, 2014 at 07:13:37PM -0700, Paul E. McKenney wrote:
    > > On Wed, Jun 18, 2014 at 06:42:00PM -0700, Andi Kleen wrote:
    > > >
    > > > I still think it's totally the wrong direction to pollute so
    > > > many fast paths with this obscure debugging check workaround
    > > > unconditionally.
    > >
    > > OOM prevention should count for something, I would hope.
    >
    > OOM in what scenario? This is getting bizarre.
    >
    > If something keeps looping forever in the kernel creating
    > RCU callbacks without any real quiescent states it's simply broken.

    Typical problem we faced in the past is in exit() path when multi
    thousands of files/sockets are rcu-freed, and qhimark is hit.

    Huge latency alerts, as freeing 10000+ items takes a while (about 70 ns
    per item...)

    Maybe close_files() should use a
    cond_resched_and_keep_rcu_queues_small_please() ;)





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