netdev - Re: [PATCH v3 6/7] tcp buffer limitation: per-cgroup limit

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Date:	Mon, 26 Sep 2011 19:49:43 -0300
From:	Glauber Costa <glommer@...allels.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC:	Greg Thelen <gthelen@...gle.com>, <linux-kernel@...r.kernel.org>,
	<paul@...lmenage.org>, <lizf@...fujitsu.com>,
	<ebiederm@...ssion.com>, <davem@...emloft.net>,
	<netdev@...r.kernel.org>, <linux-mm@...ck.org>,
	<kirill@...temov.name>
Subject: Re: [PATCH v3 6/7] tcp buffer limitation: per-cgroup limit

On 09/26/2011 08:02 AM, KAMEZAWA Hiroyuki wrote:
> On Sat, 24 Sep 2011 10:30:42 -0300
> Glauber Costa<glommer@...allels.com>  wrote:
>
>> On 09/22/2011 03:01 AM, Greg Thelen wrote:
>>> On Sun, Sep 18, 2011 at 5:56 PM, Glauber Costa<glommer@...allels.com>   wrote:
>>>> +static inline bool mem_cgroup_is_root(struct mem_cgroup *mem)
>>>> +{
>>>> +       return (mem == root_mem_cgroup);
>>>> +}
>>>> +
>>>
>>> Why are you adding a copy of mem_cgroup_is_root().  I see one already
>>> in v3.0.  Was it deleted in a previous patch?
>>
>> Already answered by another good samaritan.
>>
>>>> +static int tcp_write_maxmem(struct cgroup *cgrp, struct cftype *cft, u64 val)
>>>> +{
>>>> +       struct mem_cgroup *sg = mem_cgroup_from_cont(cgrp);
>>>> +       struct mem_cgroup *parent = parent_mem_cgroup(sg);
>>>> +       struct net *net = current->nsproxy->net_ns;
>>>> +       int i;
>>>> +
>>>> +       if (!cgroup_lock_live_group(cgrp))
>>>> +               return -ENODEV;
>>>
>>> Why is cgroup_lock_live_cgroup() needed here?  Does it protect updates
>>> to sg->tcp_prot_mem[*]?
>>>
>>>> +static u64 tcp_read_maxmem(struct cgroup *cgrp, struct cftype *cft)
>>>> +{
>>>> +       struct mem_cgroup *sg = mem_cgroup_from_cont(cgrp);
>>>> +       u64 ret;
>>>> +
>>>> +       if (!cgroup_lock_live_group(cgrp))
>>>> +               return -ENODEV;
>>>
>>> Why is cgroup_lock_live_cgroup() needed here?  Does it protect updates
>>> to sg->tcp_max_memory?
>>
>> No, that is not my understanding. My understanding is this lock is
>> needed to protect against the cgroup just disappearing under our nose.
>>
>
> Hm. reference count of dentry for cgroup isn't enough ?
>
> Thanks,
> -Kame
>
think think think think think think...
Yeah, I guess it is.

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