linux-kernel - Re: vmstat: make vmstat_updater deferrable again and shut down on idle

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Date:	Thu, 10 Dec 2015 19:41:08 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Michal Hocko <mhocko@...nel.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, hannes@...xchg.org,
	penguin-kernel@...ove.SAKURA.ne.jp
Subject: Re: vmstat: make vmstat_updater deferrable again and shut down on
 idle

On Thu, 10 Dec 2015, Andrew Morton wrote:

> >  /*
> > + * Switch off vmstat processing and then fold all the remaining differentials
> > + * until the diffs stay at zero. The function is used by NOHZ and can only be
> > + * invoked when tick processing is not active.
> > + */
> > +void quiet_vmstat(void)
> > +{
> > +	do {
> > +		if (!cpumask_test_and_set_cpu(smp_processor_id(), cpu_stat_off))
> > +			cancel_delayed_work(this_cpu_ptr(&vmstat_work));
> > +
> > +	} while (refresh_cpu_vm_stats(false));
> > +}
>
> How do we know this will terminate in a reasonable amount of time if
> other CPUs are pounding away?

This is only dealing with the differentials of the local cpu. Other cpus
do not matter.

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