Re: [PATCH 2/2] Make res_counter hierarchical

[yamamoto-jCdQPDEk3idL9jVzuh4AOg@public.gmane.org (YAMAMOTO Takashi)]

> > @@ -36,10 +37,26 @@ int res_counter_charge(struct res_counter *counter, unsigned long val)
> >  {
> >  	int ret;
> >  	unsigned long flags;
> > +	struct res_counter *c, *unroll_c;
> > +
> > +	local_irq_save(flags);
> > +	for (c = counter; c != NULL; c = c->parent) {
> > +		spin_lock(&c->lock);
> > +		ret = res_counter_charge_locked(c, val);
> > +		spin_unlock(&c->lock);
> > +		if (ret < 0)
> > +			goto unroll;
> > +	}
> > +	local_irq_restore(flags);
> > +	return 0;
> >  
> > -	spin_lock_irqsave(&counter->lock, flags);
> > -	ret = res_counter_charge_locked(counter, val);
> > -	spin_unlock_irqrestore(&counter->lock, flags);
> > +unroll:
> > +	for (unroll_c = counter; unroll_c != c; unroll_c = unroll_c->parent) {
> > +		spin_lock(&unroll_c->lock);
> > +		res_counter_uncharge_locked(unroll_c, val);
> > +		spin_unlock(&unroll_c->lock);
> > +	}
> > +	local_irq_restore(flags);
> >  	return ret;
> >  }
> 
> what prevents the topology (in particular, ->parent pointers) from
> changing behind us?
> 
> YAMAMOTO Takashi

to answer myself: cgroupfs rename doesn't allow topological changes
in the first place.

btw, i think you need to do the same for res_counter_limit_check_locked
as well.  i'm skeptical about doing these complicated stuffs in kernel,
esp. in this potentially performance critical code.

YAMAMOTO Takashi