linux-kernel - Re: vmstat: On demand vmstat workers V8

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Message-ID: <alpine.DEB.2.11.1407291057410.21390@gentwo.org>
Date:	Tue, 29 Jul 2014 10:59:46 -0500 (CDT)
From:	Christoph Lameter <cl@...two.org>
To:	Sasha Levin <sasha.levin@...cle.com>
cc:	Tejun Heo <tj@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
	akpm@...ux-foundation.org, Gilad Ben-Yossef <gilad@...yossef.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <johnstul@...ibm.com>,
	Mike Frysinger <vapier@...too.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	Max Krasnyansky <maxk@...lcomm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, hughd@...gle.com,
	viresh.kumar@...aro.org, hpa@...or.com, mingo@...nel.org,
	Lai Jiangshan <laijs@...fujitsu.com>
Subject: Re: vmstat: On demand vmstat workers V8

On Tue, 29 Jul 2014, Sasha Levin wrote:

> > Index: linux/mm/vmstat.c
> > ===================================================================
> > --- linux.orig/mm/vmstat.c	2014-07-29 10:22:45.073884943 -0500
> > +++ linux/mm/vmstat.c	2014-07-29 10:34:45.083369228 -0500
> > @@ -1277,8 +1277,8 @@ static int vmstat_cpuup_callback(struct
> >  		break;
> >  	case CPU_DOWN_PREPARE:
> >  	case CPU_DOWN_PREPARE_FROZEN:
> > -		cancel_delayed_work_sync(&per_cpu(vmstat_work, cpu));
> >  		per_cpu(vmstat_work, cpu).work.func = NULL;
> > +		cancel_delayed_work_sync(&per_cpu(vmstat_work, cpu));
> >  		break;
> >  	case CPU_DOWN_FAILED:
> >  	case CPU_DOWN_FAILED_FROZEN:
> >
>
> I'm slightly confused here. The on demand vmstat workers patch did this:
>
>         case CPU_DOWN_PREPARE_FROZEN:
> -               cancel_delayed_work_sync(&per_cpu(vmstat_work, cpu));
> -               per_cpu(vmstat_work, cpu).work.func = NULL;
> +               if (!cpumask_test_and_set_cpu(cpu, cpu_stat_off))
> +                       cancel_delayed_work_sync(&per_cpu(vmstat_work, cpu));
>
> So your new patch doesn't apply on top of it, and doesn't make sense before it.

Tejun was looking at upsteram and so I fixed upstream ;-)

Is it really necessary to set the work.func to NULL? If so then the
work.func will have to be initialized when a processor is brought online.

Canceling the work should be enough to disable the execution of the
function.

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