linux-kernel - Re: [PATCH] mm, vmstat: make quiet_vmstat lighter (was: Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable) again and shut down on idle)

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Date:	Thu, 28 Jan 2016 10:40:10 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Michal Hocko <mhocko@...nel.org>
cc:	Mike Galbraith <umgwanakikbuti@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm, vmstat: make quiet_vmstat lighter (was: Re: fast
 path cycle muncher (vmstat: make vmstat_updater deferrable) again and shut
 down on idle)

On Thu, 28 Jan 2016, Michal Hocko wrote:

> +void quiet_vmstat(void)
> +{
> +	if (system_state != SYSTEM_RUNNING)
> +		return;
> +
> +	/*
> +	 * If we are already in hands of the shepherd then there
> +	 * is nothing for us to do here.
> +	 */
> +	if (cpumask_test_and_set_cpu(smp_processor_id(), cpu_stat_off))
> +		return;
> +
> +	if (!need_update(smp_processor_id()))
> +		return;
> +

You can drop the need_update check. refresh_cpu_vm_stats() does the same
checks in a more efficient way. If you keep this the checks will
performed twice.

> +	/*
> +	 * Just refresh counters and do not care about the pending delayed
> +	 * vmstat_update. It doesn't fire that often to matter and canceling
> +	 * it would be too expensive from this path.
> +	 * vmstat_shepherd will take care about that for us.
> +	 */
> +	refresh_cpu_vm_stats(false);
> +}
> +
>