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

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Date:	Tue, 13 Mar 2012 14:47:05 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
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 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.

> +{
> +	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.

> +		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;
> +}

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