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Date: Fri, 9 Jan 2009 16:22:55 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
To: Li Zefan <lizf@cn.fujitsu.com>
Cc: Paul Menage <menage@google.com>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       "akpm@linux-foundation.org" <akpm@linux-foundation.org>
Subject: Re: [RFC][PATCH] NOOP cgroup subsystem
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On Fri, 09 Jan 2009 14:44:00 +0800
Li Zefan <lizf@cn.fujitsu.com> wrote:

> Paul Menage wrote:
> > On Thu, Jan 8, 2009 at 10:29 PM, Li Zefan <lizf@cn.fujitsu.com> wrote:
> >> Agreed, but it can't work by just removing the checking in cgroup mount option,
> > 
> > Right - it's more complicated than that. There are some places in the
> > code that rely on the fact that every hierarchy currently has at least
> > one subsystem (anything that uses find_first_subsystem() for example)
> > and we'd need to work around that.
> > 
> 
> And some other problems, like what's the semantic of /proc/<pid>/cgroup when
> using none subsys.
> 
> I'm afraid even if it's do-able it might require a lot of changes in cgroup.
> 
After quick look,
it seems that css_set->subsys==empty case cannot be handled and need much
changes. Maintaining hierarchy tree itself seems difficult.

I think cgroup is being stable day by day. So, I don't like to crash it
by big hummer for this tiny feature.

How about adding "none" subsys  ? (I'd like to set default=y ;)

As Paul said, "Show multiple hierarchy view for each mount point"
seems attractive but it's not very fundametal, IMHO.
If we can increase subsys_id dynamically or subsys can have
multiple root node, the situation will change.

Thanks,
-Kame

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