linux-kernel - Re: [PATCH 1/5] vmstat: Implement refresh_vm

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Date:	Tue, 5 Jun 2012 09:30:26 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Anton Vorontsov <anton.vorontsov@...aro.org>
cc:	Pekka Enberg <penberg@...nel.org>,
	Leonid Moiseichuk <leonid.moiseichuk@...ia.com>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Minchan Kim <minchan@...nel.org>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	John Stultz <john.stultz@...aro.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linaro-kernel@...ts.linaro.org,
	patches@...aro.org, kernel-team@...roid.com
Subject: Re: [PATCH 1/5] vmstat: Implement refresh_vm_stats()

On Fri, 1 Jun 2012, Anton Vorontsov wrote:

> This function forcibly flushes per-cpu vmstat diff counters to the
> global counters.

Why is it necessary to have a function that does not expire the pcps? Is
that side effect important? We use refresh_vm_cpu_stats(cpu) in
page_alloc.c already to flush the vmstat counters. Is the flushing of the
pcps in 2 seconds insteads of 3 once really that important?

Also if we do this

Can we therefore also name the function in a different way like

	flush_vmstats()


> @@ -456,11 +457,15 @@ void refresh_cpu_vm_stats(int cpu)
>  				local_irq_restore(flags);
>  				atomic_long_add(v, &zone->vm_stat[i]);
>  				global_diff[i] += v;
> +				if (!drain_pcp)
> +					continue;
>  #ifdef CONFIG_NUMA
>  				/* 3 seconds idle till flush */
>  				p->expire = 3;
>  #endif

Erm. This should be

#ifdef CONFIG_NUMA
	if (drain_pcp)
		p->expire = 3;
#endif

The construct using "continue" is weird.


>  			}
> +		if (!drain_pcp)
> +			continue;
>  		cond_resched();
>  #ifdef CONFIG_NUMA
>  		/*
> @@ -495,6 +500,21 @@ void refresh_cpu_vm_stats(int cpu)
>  			atomic_long_add(global_diff[i], &vm_stat[i]);
>  }
>
> +void refresh_cpu_vm_stats(int cpu)
> +{
> +	__refresh_cpu_vm_stats(cpu, 1);
> +}

Fold __refresh_cpu_vm_stats into this function and modify the caller
of refresh_cpu_vm_stats instead.

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