[Devel] Re: [PATCH v6 06/10] tcp buffer limitation: per-cgroup limit

[KAMEZAWA Hiroyuki]

some comments.

On Fri, 25 Nov 2011 15:38:12 -0200
Glauber Costa <glommer at parallels.com> wrote:

> This patch uses the "tcp.limit_in_bytes" field of the kmem_cgroup to
> effectively control the amount of kernel memory pinned by a cgroup.
> 
> This value is ignored in the root cgroup, and in all others,
> caps the value specified by the admin in the net namespaces'
> view of tcp_sysctl_mem.
> 
> If namespaces are being used, the admin is allowed to set a
> value bigger than cgroup's maximum, the same way it is allowed
> to set pretty much unlimited values in a real box.
> 
> Signed-off-by: Glauber Costa <glommer at parallels.com>
> CC: David S. Miller <davem at davemloft.net>
> CC: Hiroyouki Kamezawa <kamezawa.hiroyu at jp.fujitsu.com>
> CC: Eric W. Biederman <ebiederm at xmission.com>

<snip>

>  EXPORT_SYMBOL(tcp_destroy_cgroup);
> +
> +int tcp_update_limit(struct mem_cgroup *memcg, u64 val)
> +{
> +	struct net *net = current->nsproxy->net_ns;
> +	struct tcp_memcontrol *tcp;
> +	struct cg_proto *cg_proto;
> +	int i;
> +	int ret;
> +
> +	cg_proto = tcp_prot.proto_cgroup(memcg);
> +	if (!cg_proto)
> +		return -EINVAL;
> +
> +	tcp = tcp_from_cgproto(cg_proto);
> +
> +	ret = res_counter_set_limit(&tcp->tcp_memory_allocated, val);

Here, you changed the limit.

> +	if (ret)
> +		return ret;
> +
> +	val >>= PAGE_SHIFT;

Here, you modifies 'val'

> +
> +	for (i = 0; i < 3; i++)
> +		tcp->tcp_prot_mem[i] = min_t(long, val,
> +					     net->ipv4.sysctl_tcp_mem[i]);
> +
> +	if (val == RESOURCE_MAX)
> +		jump_label_dec(&memcg_socket_limit_enabled);

the 'val' never be RESOUECE_MAX.


> +	else {
> +		u64 old_lim;
> +		old_lim = res_counter_read_u64(&tcp->tcp_memory_allocated,
> +					       RES_LIMIT);

old_lim is not already overwritten ?

> +		if (old_lim == RESOURCE_MAX)
> +			jump_label_inc(&memcg_socket_limit_enabled);
> +	}
> +	return 0;
> +}
> +

Thanks,
-Kame