netdev - Re: [PATCH v7 02/10] foundations of per-cgroup memory pressure controlling.

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Date:	Fri, 2 Dec 2011 15:46:46 -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>
Subject: Re: [PATCH v7 02/10] foundations of per-cgroup memory pressure controlling.


>>   static void proto_seq_printf(struct seq_file *seq, struct proto *proto)
>>   {
>> +	struct mem_cgroup *memcg = mem_cgroup_from_task(current);
>> +
>>   	seq_printf(seq, "%-9s %4u %6d  %6ld   %-3s %6u   %-3s  %-10s "
>>   			"%2c %2c %2c %2c %2c %2c %2c %2c %2c %2c %2c %2c %2c %2c %2c %2c %2c %2c %2c\n",
>>   		   proto->name,
>>   		   proto->obj_size,
>>   		   sock_prot_inuse_get(seq_file_net(seq), proto),
>> -		   proto->memory_allocated != NULL ? atomic_long_read(proto->memory_allocated) : -1L,
>> -		   proto->memory_pressure != NULL ? *proto->memory_pressure ? "yes" : "no" : "NI",
>> +		   sock_prot_memory_allocated(proto, memcg),
>> +		   sock_prot_memory_pressure(proto, memcg),
>
> I wonder I should say NO, here. (Networking guys are ok ??)
>
> IIUC, this means there is no way to see aggregated sockstat of all system.
> And the result depends on the cgroup which the caller is under control.
>
> I think you should show aggregated sockstat(global + per-memcg) here and
> show per-memcg ones via /cgroup interface or add private_sockstat to show
> per cgroup summary.
>

Hi Kame,

Yes, the statistics displayed depends on which cgroup you live.
Also, note that the parent cgroup here is always updated (even when 
use_hierarchy is set to 0). So it is always possible to grab global 
statistics, by being in the root cgroup.

For the others, I believe it to be a question of naturalization. Any 
tool that is fetching these values is likely interested in the amount of 
resources available/used. When you are on a cgroup, the amount of 
resources available/used changes, so that's what you should see.

Also brings the point of resource isolation: if you shouldn't interfere 
with other set of process' resources, there is no reason for you to see 
them in the first place.

So given all that, I believe that whenever we talk about resources in a 
cgroup, we should talk about cgroup-local ones.
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