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.
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