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

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Date:	Tue, 29 Jul 2014 11:43:25 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Christoph Lameter <cl@...two.org>, Tejun Heo <tj@...nel.org>
CC:	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 07/29/2014 11:22 AM, Christoph Lameter wrote:
> On Tue, 29 Jul 2014, Tejun Heo wrote:
> 
>> I'm not sure that's a viable way forward.  It's not like we can
>> readily trigger the problematic cases which can lead to long pauses
>> during cpu down.  Besides, we need the distinction at the API level,
>> which is the whole point of this.  The best way probably is converting
>> all the correctness ones (these are the minorities) over to
>> queue_work_on() so that the per-cpu requirement is explicit.
> 
> Ok so we would need this fix to avoid the message:
> 
> 
> Subject: vmstat: use schedule_delayed_work_on to avoid false positives
> 
> It seems that schedule_delayed_work_on will check for preemption even
> though none can occur. schedule_delayed_work_on will not do that. So
> use that function to suppress false positives.
> 
> Signed-off-by: Christoph Lameter <cl@...ux.com>
> 
> Index: linux/mm/vmstat.c
> ===================================================================
> --- linux.orig/mm/vmstat.c	2014-07-29 10:14:42.356988271 -0500
> +++ linux/mm/vmstat.c	2014-07-29 10:18:28.205920997 -0500
> @@ -1255,7 +1255,8 @@ static void vmstat_update(struct work_st
>  		 * to occur in the future. Keep on running the
>  		 * update worker thread.
>  		 */
> -		schedule_delayed_work(this_cpu_ptr(&vmstat_work),
> +		schedule_delayed_work_on(smp_processor_id(),
> +			this_cpu_ptr(&vmstat_work),
>  			round_jiffies_relative(sysctl_stat_interval));
>  	else {
>  		/*
> 

I've tested, and this patch doesn't fix neither of the bugs reported.


Thanks,
Sasha
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