netdev - Re: [PATCH v9 3/9] socket: initial cgroup code.

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Date:	Thu, 22 Dec 2011 16:10:29 -0500
From:	Jason Baron <jbaron@...hat.com>
To:	Glauber Costa <glommer@...allels.com>
Cc:	davem@...emloft.net, linux-kernel@...r.kernel.org,
	paul@...lmenage.org, lizf@...fujitsu.com,
	kamezawa.hiroyu@...fujitsu.com, ebiederm@...ssion.com,
	gthelen@...gle.com, netdev@...r.kernel.org, linux-mm@...ck.org,
	kirill@...temov.name, avagin@...allels.com, devel@...nvz.org,
	eric.dumazet@...il.com, cgroups@...r.kernel.org
Subject: Re: [PATCH v9 3/9] socket: initial cgroup code.

On Mon, Dec 12, 2011 at 11:47:03AM +0400, Glauber Costa wrote:
> +
> +static bool mem_cgroup_is_root(struct mem_cgroup *memcg);
> +void sock_update_memcg(struct sock *sk)
> +{
> +	/* A socket spends its whole life in the same cgroup */
> +	if (sk->sk_cgrp) {
> +		WARN_ON(1);
> +		return;
> +	}
> +	if (static_branch(&memcg_socket_limit_enabled)) {
> +		struct mem_cgroup *memcg;
> +
> +		BUG_ON(!sk->sk_prot->proto_cgroup);
> +
> +		rcu_read_lock();
> +		memcg = mem_cgroup_from_task(current);
> +		if (!mem_cgroup_is_root(memcg)) {
> +			mem_cgroup_get(memcg);
> +			sk->sk_cgrp = sk->sk_prot->proto_cgroup(memcg);
> +		}
> +		rcu_read_unlock();
> +	}
> +}
> +EXPORT_SYMBOL(sock_update_memcg);
> +
> +void sock_release_memcg(struct sock *sk)
> +{
> +	if (static_branch(&memcg_socket_limit_enabled) && sk->sk_cgrp) {
> +		struct mem_cgroup *memcg;
> +		WARN_ON(!sk->sk_cgrp->memcg);
> +		memcg = sk->sk_cgrp->memcg;
> +		mem_cgroup_put(memcg);
> +	}
> +}

Hi Glauber,

I think for 'sock_release_memcg()', you want:

static inline sock_release_memcg(sk)
{
	if (static_branch())
		__sock_release_memcg();
}

And then re-define the current sock_release_memcg -> __sock_release_memcg().
In that way the straight line path is a single no-op. As currently
written, there is function call and then an immediate return.

Thanks,

-Jason



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