linux-kernel - Re: [PATCHv1 3/6] rdmacg: implements rdma cgroup

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Message-ID: <20160105220128.GJ5995@mtj.duckdns.org>
Date:	Tue, 5 Jan 2016 17:01:28 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Parav Pandit <pandit.parav@...il.com>
Cc:	cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org,
	lizefan@...wei.com, hannes@...xchg.org, dledford@...hat.com,
	liranl@...lanox.com, sean.hefty@...el.com,
	jgunthorpe@...idianresearch.com, haggaie@...lanox.com,
	corbet@....net, james.l.morris@...cle.com, serge@...lyn.com,
	ogerlitz@...lanox.com, matanb@...lanox.com, raindel@...lanox.com,
	akpm@...ux-foundation.org, linux-security-module@...r.kernel.org
Subject: Re: [PATCHv1 3/6] rdmacg: implements rdma cgroup

Hello,

On Wed, Jan 06, 2016 at 12:28:03AM +0530, Parav Pandit wrote:
> +/* hash table to keep map of tgid to owner cgroup */
> +DEFINE_HASHTABLE(pid_cg_map_tbl, 7);
> +DEFINE_SPINLOCK(pid_cg_map_lock);	/* lock to protect hash table access */
> +
> +/* Keeps mapping of pid to its owning cgroup at rdma level,
> + * This mapping doesn't change, even if process migrates from one to other
> + * rdma cgroup.
> + */
> +struct pid_cg_map {
> +	struct pid *pid;		/* hash key */
> +	struct rdma_cgroup *cg;
> +
> +	struct hlist_node hlist;	/* pid to cgroup hash table link */
> +	atomic_t refcnt;		/* count active user tasks to figure out
> +					 * when to free the memory
> +					 */
> +};

Ugh, there's something clearly wrong here.  Why does the rdma
controller need to keep track of pid cgroup membership?

> +static void _dealloc_cg_rpool(struct rdma_cgroup *cg,
> +			      struct cg_resource_pool *rpool)
> +{
> +	spin_lock(&cg->cg_list_lock);
> +
> +	/* if its started getting used by other task,
> +	 * before we take the spin lock, then skip,
> +	 * freeing it.
> +	 */

Please follow CodingStyle.

> +	if (atomic_read(&rpool->refcnt) == 0) {
> +		list_del_init(&rpool->cg_list);
> +		spin_unlock(&cg->cg_list_lock);
> +
> +		_free_cg_rpool(rpool);
> +		return;
> +	}
> +	spin_unlock(&cg->cg_list_lock);
> +}
> +
> +static void dealloc_cg_rpool(struct rdma_cgroup *cg,
> +			     struct cg_resource_pool *rpool)
> +{
> +	/* Don't free the resource pool which is created by the
> +	 * user, otherwise we miss the configured limits. We don't
> +	 * gain much either by splitting storage of limit and usage.
> +	 * So keep it around until user deletes the limits.
> +	 */
> +	if (atomic_read(&rpool->creator) == RDMACG_RPOOL_CREATOR_DEFAULT)
> +		_dealloc_cg_rpool(cg, rpool);

I'm pretty sure you can get away with an fixed length array of
counters.  Please keep it simple.  It's a simple hard limit enforcer.
There's no need to create a massive dynamic infrastrucure.

Thanks.

-- 
tejun
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