linux-kernel - Re: [PATCH -V3 7/8] memcg: move HugeTLB resource count to parent cgroup on memcg removal

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Date:	Wed, 14 Mar 2012 17:52:28 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-mm@...ck.org, mgorman@...e.de,
	kamezawa.hiroyu@...fujitsu.com, dhillf@...il.com,
	aarcange@...hat.com, mhocko@...e.cz, hannes@...xchg.org,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [PATCH -V3 7/8] memcg: move HugeTLB resource count to parent cgroup on memcg removal

On Tue, 13 Mar 2012 14:47:05 -0700, Andrew Morton <akpm@...ux-foundation.org> wrote:
> On Tue, 13 Mar 2012 12:37:11 +0530
> "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> wrote:
> 
> > From: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
> > 
> > This add support for memcg removal with HugeTLB resource usage.
> > 
> > ...
> >
> > +int hugetlb_force_memcg_empty(struct cgroup *cgroup)
> 
> It's useful to document things, you know.  For a major function like
> this, a nice little description of why it exists, what its role is,
> etc.  Programming is not just an act of telling a computer what to do:
> it is also an act of telling other programmers what you wished the
> computer to do.  Both are important, and the latter deserves care.
> 


Will do.

> > +{
> > +	struct hstate *h;
> > +	struct page *page;
> > +	int ret = 0, idx = 0;
> > +
> > +	do {
> > +		if (cgroup_task_count(cgroup) || !list_empty(&cgroup->children))
> > +			goto out;
> > +		if (signal_pending(current)) {
> > +			ret = -EINTR;
> > +			goto out;
> > +		}
> 
> Why is its behaviour altered by signal_pending()?  This seems broken.

If the task that is doing a cgroup_rmdir got a signal we don't really
need to loop till the hugetlb resource usage become zero. 


> 
> > +		for_each_hstate(h) {
> > +			spin_lock(&hugetlb_lock);
> > +			list_for_each_entry(page, &h->hugepage_activelist, lru) {
> > +				ret = mem_cgroup_move_hugetlb_parent(idx, cgroup, page);
> > +				if (ret) {
> > +					spin_unlock(&hugetlb_lock);
> > +					goto out;
> > +				}
> > +			}
> > +			spin_unlock(&hugetlb_lock);
> > +			idx++;
> > +		}
> > +		cond_resched();
> > +	} while (mem_cgroup_hugetlb_usage(cgroup) > 0);
> > +out:
> > +	return ret;
> > +}

-aneesh

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