Re: [PATCH] hotplug: Optimize {get,put}_online_cpus()

[Oleg Nesterov]

On 10/01, Paul E. McKenney wrote:
>
> On Tue, Oct 01, 2013 at 04:48:20PM +0200, Peter Zijlstra wrote:
> > On Tue, Oct 01, 2013 at 07:45:37AM -0700, Paul E. McKenney wrote:
> > > If you don't have cpuhp_seq, you need some other way to avoid
> > > counter overflow.  Which might be provided by limited number of
> > > tasks, or, on 64-bit systems, 64-bit counters.
> >
> > How so? PID space is basically limited to 30 bits, so how could we
> > overflow a 32bit reference counter?
>
> Nesting.

Still it seems that UINT_MAX / PID_MAX_LIMIT has enough room.

But again, OK lets make it ulong. The question is, how cpuhp_seq can
help and why we can't kill it.

Oleg.

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