linux-kernel - Re: [PATCH v3 1/5] cpusets, hotplug: Implement cpuset tree traversal in a helper function

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Date:	Tue, 15 May 2012 11:04:54 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
cc:	a.p.zijlstra@...llo.nl, mingo@...nel.org, pjt@...gle.com,
	paul@...lmenage.org, akpm@...ux-foundation.org, rjw@...k.pl,
	nacc@...ibm.com, paulmck@...ux.vnet.ibm.com, tglx@...utronix.de,
	seto.hidetoshi@...fujitsu.com, tj@...nel.org, mschmidt@...hat.com,
	berrange@...hat.com, nikunj@...ux.vnet.ibm.com,
	vatsa@...ux.vnet.ibm.com, liuj97@...il.com,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH v3 1/5] cpusets, hotplug: Implement cpuset tree traversal
 in a helper function

On Tue, 15 May 2012, Srivatsa S. Bhat wrote:

> >> diff --git a/kernel/cpuset.c b/kernel/cpuset.c
> >> index 14f7070..23e5da6 100644
> >> --- a/kernel/cpuset.c
> >> +++ b/kernel/cpuset.c
> >> @@ -2000,6 +2000,23 @@ static void remove_tasks_in_empty_cpuset(struct cpuset *cs)
> >>  	move_member_tasks_to_cpuset(cs, parent);
> >>  }
> >>  
> >> +static struct cpuset *traverse_cpusets(struct list_head *queue)
> > 
> > I suggest a different name for this, traverse_cpusets() doesn't imply that 
> > it will be returning struct cpuset *.
> 
> 
> OK, I guess something like cpuset_next() or next_cpuset() should be fine?
> 

The generic cgroup code seems to prefer cgroup_iter_next(), so 
cpuset_next() sounds appropriate.

> >> +{
> >> +	struct cpuset *cp;
> >> +	struct cpuset *child;	/* scans child cpusets of cp */
> >> +	struct cgroup *cont;
> >> +
> >> +	cp = list_first_entry(queue, struct cpuset, stack_list);
> >> +	list_del(queue->next);
> >> +	list_for_each_entry(cont, &cp->css.cgroup->children, sibling) {
> >> +		child = cgroup_cs(cont);
> >> +		list_add_tail(&child->stack_list, queue);
> >> +	}
> >> +
> >> +	return cp;
> > 
> > Eek, what happens if queue is empty?  It can't happen with only this 
> > patch applied, but since you're doing this to be used in other places then 
> > you'd need to check for list_empty().
> > 
> 
> 
> Actually, I didn't intend this to be used in other places because their
> traversals are a little bit different anyway.. But yes, having a check for
> list_empty() would be good. I'll add it and change the loop to something like:
> 
> while (cpuset_next(&queue) {
> 	...
> }
> 
> Thanks for pointing this out!
> 

Sounds good if cpuset_next() returns NULL for list_empty().
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