From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp•fujitsu.com>
To: Glauber Costa <glommer@parallels•com>
Cc: netdev@vger•kernel.org, David Miller <davem@davemloft•net>,
Andrew Morton <akpm@linux-foundation•org>
Subject: Re: [PATCH] memcg/tcp: fix warning caused b res->usage go to negative.
Date: Tue, 10 Apr 2012 13:15:57 +0900 [thread overview]
Message-ID: <4F83B3FD.4010107@jp.fujitsu.com> (raw)
In-Reply-To: <4F83A29D.1060402@parallels.com>
(2012/04/10 12:01), Glauber Costa wrote:
> On 04/09/2012 11:51 PM, Glauber Costa wrote:
>> On 04/09/2012 11:37 PM, KAMEZAWA Hiroyuki wrote:
>>> Hm. What happens in following sequence ?
>>>
>>> 1. a memcg is created
>>> 2. put a task into the memcg, start tcp steam
>>> 3. set tcp memory limit
>>>
>>> The resource used between 2 and 3 will cause the problem finally.
>>
>> I don't get it. if a task is in memcg, but no limit is set,
>> that socket will be assigned null memcg, and will stay like that
>> forever. Only new sockets will have the new memcg pointer.
>>
>> And previously, we could have the memcg pointer alive, but the jump
>> labels to be disabled. With the patch I posted, this can't happen
>> anymore, since the jump labels are guaranteed to live throughout the
>> whole socket life.
>>
>>> Then, Dave's request
>>> ==
>>> You must either:
>>>
>>> 1) Integrate the socket's existing usage when the limit is set.
>>>
>>> 2) Avoid accounting completely for a socket that started before
>>> the limit was set.
>>> ==
>>> are not satisfied. So, we need to have a state per sockets, it's accounted
>>> or not. I'll look into this problem again, today.
>>>
>>
>> Of course they are.
>>
>> Every socket created before we set the limit is not accounted.
>> This is 2) that Dave mentioned, and it was *always* this way.
>>
>> The problem here was the opposite: You could disable the jump labels
>> with sockets still in flight, because we were disabling it based on
>> the limit being set back to unlimited.
>>
>> What this patch does, is defer that until the last socket limited dies.
>>
>
> Okay, there is an additional thing to be considered here:
>
> Due to the nature of how jump label works, once they are enabled for one
> of the cgroups, they will be enabled for all of them. So the patch I
> sent may still break in some scenarios because of the way we record that
> the limit was set.
>
> However, if my theory behind what is causing the problem is correct,
> this patch should fix the issue for you.
Now, our issue is leak of accounting, regardless of warning.
> Let me know if it does, and
> I'll work on the final solution.
>
The problem is that jump_label updating is not atomic_ops.
I'm _not_ sure the update order of the jump_label in sock_update_memcg()
and other jump instructions inserted at accounting.
For example, if the jump instruction in sock_update_memcg() is updated 1st
and others are updated later, it's unclear whether sockets which has _valid_
sock->sk_cgrp will be accounted or not because accounting jump instruction
may not be updated yet.
Hopefully, label in sock_update_memcg should be updated last...
Hm. If I do, I'll add one more key as:
atomic_t sock_should_memcg_aware;
And update 2 keys in following order.
At enable
static_key_slow_inc(&memcg_socket_limit_enabled)
atomic_inc(&sock_should_memcg_aware);
At disable
atomic_dec(&sock_should_memcg_aware);
static_key_slow_dec(&memcg_socket_limit_enabled)
And
==
void sock_update_memcg(struct sock *sk)
{
if (atomic_read(&sock_should_memcg_aware)) {
==
Thanks,
-Kame
next prev parent reply other threads:[~2012-04-10 4:17 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-03-29 7:01 [BUGFIX][PATCH 0/3] memcg: tcp memcontrol fixes KAMEZAWA Hiroyuki
2012-03-29 7:03 ` [PATCH 1/3] [BUGFIX] memcg/tcp : fix to see use_hierarchy in tcp memcontrol cgroup KAMEZAWA Hiroyuki
2012-03-29 9:14 ` Glauber Costa
2012-03-29 9:16 ` KAMEZAWA Hiroyuki
2012-03-29 7:07 ` [BUGFIX][PATCH 2/3] memcg/tcp: remove static_branch_slow_dec() at changing limit KAMEZAWA Hiroyuki
2012-03-29 10:58 ` Glauber Costa
2012-03-29 23:51 ` KAMEZAWA Hiroyuki
2012-03-30 6:18 ` Glauber Costa
2012-03-29 7:10 ` [BUGFIX][PATCH 3/3] memcg/tcp: ignore tcp usage before accounting started KAMEZAWA Hiroyuki
2012-03-29 9:21 ` Glauber Costa
2012-03-30 1:44 ` [PATCH] memcg/tcp: fix warning caused b res->usage go to negative KAMEZAWA Hiroyuki
2012-04-06 15:49 ` Glauber Costa
2012-04-10 2:37 ` KAMEZAWA Hiroyuki
2012-04-10 2:51 ` Glauber Costa
2012-04-10 3:01 ` Glauber Costa
2012-04-10 4:15 ` KAMEZAWA Hiroyuki [this message]
2012-04-11 2:22 ` Glauber Costa
2012-04-10 3:21 ` KAMEZAWA Hiroyuki
2012-04-13 17:33 ` Glauber Costa
2012-04-18 8:02 ` KAMEZAWA Hiroyuki
2012-04-18 16:32 ` Glauber Costa
2012-04-02 3:41 ` [BUGFIX][PATCH 3/3] memcg/tcp: ignore tcp usage before accounting started David Miller
2012-04-03 22:31 ` Glauber Costa
2012-04-09 0:58 ` KAMEZAWA Hiroyuki
2012-04-09 1:44 ` Glauber Costa
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