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

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Date:	Mon, 26 Sep 2011 20:02:47 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Glauber Costa <glommer@...allels.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 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

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