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Subject: Re: [patch 6/7] cpusets: per cpuset dirty ratios
From: Peter Zijlstra <peterz@infradead.org>
To: David Rientjes <rientjes@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
       Christoph Lameter <cl@linux-foundation.org>,
       Nick Piggin <npiggin@suse.de>, Paul Menage <menage@google.com>,
       Derek Fults <dfults@sgi.com>, linux-kernel@vger.kernel.org
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Date: Thu, 30 Oct 2008 09:44:45 +0100
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On Tue, 2008-10-28 at 09:08 -0700, David Rientjes wrote:

> +/*
> + * Determine the dirty ratios for the currently active cpuset
> + */
> +void cpuset_get_current_dirty_ratios(int *background, int *throttle)
> +{
> +	mutex_lock(&callback_mutex);
> +	task_lock(current);
> +	*background = task_cs(current)->dirty_background_ratio;
> +	*throttle = task_cs(current)->cpuset_dirty_ratio;
> +	task_unlock(current);
> +	mutex_unlock(&callback_mutex);
> +
> +	if (*background == -1)
> +		*background = dirty_background_ratio;
> +	if (*throttle == -1)
> +		*throttle = vm_dirty_ratio;
> +}

That's rather an awful lot of locking to read just two integers.