Re: [patch 6/7] cpusets: per cpuset dirty ratios

[David Rientjes <rientjes@google.com>]

On Thu, 30 Oct 2008, Peter Zijlstra wrote:

> 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.
> 

As far as I know, task_lock(current) is required to dereference 
task_cs(current) and callback_mutex is required to ensure its the same 
cpuset.