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Date: Thu, 7 Jun 2007 19:39:17 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: balbir@linux.vnet.ibm.com
Cc: menage@google.com, dev@sw.ru, xemul@sw.ru, serue@us.ibm.com,
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Subject: Re: Per container statistics (containerstats)
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On Fri, 08 Jun 2007 07:51:12 +0530 Balbir Singh <balbir@linux.vnet.ibm.com> wrote:

> Andrew Morton wrote:
> > 
> > I'd have hoped to see containerstats.c in here.
> > 
> 
> The current statistics code is really small, so it fit into taskstats.c.
> May be in the future, we could re-factor it and move it out.

I was referring to your userspace tool which reads this stuff.  The one
which you described in the changelog.

> >> +	rcu_read_lock();
> >> +
> >> +	for_each_root(root) {
> >> +		if (!root->subsys_bits)
> >> +			continue;
> >> +		root_cont = &root->top_container;
> >> +		get_first_subsys(root_cont, NULL, &subsys_id);
> >> +		do_each_thread(g, p) {
> > 
> > this needs tasklist_lock?
> > 
> 
> rcu_read_lock() should be fine. From Eric's patch at
> 
> 2.6.17-mm2 - proc-remove-tasklist_lock-from-proc_pid_readdir.patch
> 
> The patch mentions that "We don't need the tasklist_lock to safely
> iterate through processes anymore."
> 

oh, OK.  rcu_read_lock() is the new lock_kernel() - always hard to tell
what it's locking.