netdev - Re: [PATCH v7 04/10] tcp memory pressure controls

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Date:	Fri, 2 Dec 2011 15:57:28 -0200
From:	Glauber Costa <glommer@...allels.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC:	<linux-kernel@...r.kernel.org>, <paul@...lmenage.org>,
	<lizf@...fujitsu.com>, <ebiederm@...ssion.com>,
	<davem@...emloft.net>, <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>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujtisu.com>
Subject: Re: [PATCH v7 04/10] tcp memory pressure controls

On 11/29/2011 11:49 PM, KAMEZAWA Hiroyuki wrote:
>
>> -static struct mem_cgroup *mem_cgroup_from_cont(struct cgroup *cont)
>> +struct mem_cgroup *mem_cgroup_from_cont(struct cgroup *cont)
>>   {
>>   	return container_of(cgroup_subsys_state(cont,
>>   				mem_cgroup_subsys_id), struct mem_cgroup,
>> @@ -4717,14 +4732,27 @@ static int register_kmem_files(struct cgroup *cont, struct cgroup_subsys *ss)
>>
>>   	ret = cgroup_add_files(cont, ss, kmem_cgroup_files,
>>   			       ARRAY_SIZE(kmem_cgroup_files));
>> +
>> +	if (!ret)
>> +		ret = mem_cgroup_sockets_init(cont, ss);
>>   	return ret;
>>   };
>
> You does initizalication here. The reason what I think is
> 1. 'proto_list' is not available at createion of root cgroup and
>      you need to delay set up until mounting.
>
> If so, please add comment or find another way.
> This seems not very clean to me.

Yes, we do can run into some ordering issues. A part of the 
initialization can be done earlier. But I preferred to move it all later
instead of creating two functions for it. But I can change that if you 
want, no big deal.

>
>
>
>
>> +static DEFINE_RWLOCK(proto_list_lock);
>> +static LIST_HEAD(proto_list);
>> +
>> +#ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
>> +int mem_cgroup_sockets_init(struct cgroup *cgrp, struct cgroup_subsys *ss)
>> +{
>> +	struct proto *proto;
>> +	int ret = 0;
>> +
>> +	read_lock(&proto_list_lock);
>> +	list_for_each_entry(proto,&proto_list, node) {
>> +		if (proto->init_cgroup)
>> +			ret = proto->init_cgroup(cgrp, ss);
>> +			if (ret)
>> +				goto out;
>> +	}
>
> seems indent is bad or {} is missing.
>
Thanks. I'll rewrite it, since I did miss {} around the first if. But no 
test could possibly catch it, since what I wanted to write, and what I 
wrote by mistake end up being equivalent.

>> +EXPORT_SYMBOL(memcg_tcp_enter_memory_pressure);
>> +
>> +int tcp_init_cgroup(struct cgroup *cgrp, struct cgroup_subsys *ss)
>> +{
>> +	/*
>> +	 * The root cgroup does not use res_counters, but rather,
>> +	 * rely on the data already collected by the network
>> +	 * subsystem
>> +	 */
>> +	struct res_counter *res_parent = NULL;
>> +	struct cg_proto *cg_proto;
>> +	struct tcp_memcontrol *tcp;
>> +	struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
>> +	struct mem_cgroup *parent = parent_mem_cgroup(memcg);
>> +
>> +	cg_proto = tcp_prot.proto_cgroup(memcg);
>> +	if (!cg_proto)
>> +		return 0;
>> +
>> +	tcp = tcp_from_cgproto(cg_proto);
>> +	cg_proto->parent = tcp_prot.proto_cgroup(parent);
>> +
>> +	tcp->tcp_prot_mem[0] = sysctl_tcp_mem[0];
>> +	tcp->tcp_prot_mem[1] = sysctl_tcp_mem[1];
>> +	tcp->tcp_prot_mem[2] = sysctl_tcp_mem[2];
>> +	tcp->tcp_memory_pressure = 0;
>
> Question:
>
> Is this value will be updated when an admin chages sysctl ?

yes.

> I guess, this value is set at system init script or some which may
> happen later than mounting cgroup.
> I don't like to write a guideline 'please set sysctl val before
> mounting cgroup'

Agreed.

This code is in patch 6 (together with the limiting):

+#ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
+       rcu_read_lock();
+       memcg = mem_cgroup_from_task(current);
+
+       tcp_prot_mem(memcg, vec[0], 0);
+       tcp_prot_mem(memcg, vec[1], 1);
+       tcp_prot_mem(memcg, vec[2], 2);
+       rcu_read_unlock();
+#endif

tcp_prot_mem is just a wrapper around the assignment so we can access 
memcg's inner fields.

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