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Subject: Re: [ckrm-tech] [RFC] Resource Management - Infrastructure choices
From: Matt Helsley <matthltc@us.ibm.com>
To: vatsa@in.ibm.com
Cc: Pavel Emelianov <xemul@openvz.org>, dev@openvz.org, sekharan@us.ibm.com,
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Organization: IBM Linux Technology Center
Date: Wed, 01 Nov 2006 14:19:25 -0800
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On Wed, 2006-11-01 at 23:42 +0530, Srivatsa Vaddagiri wrote:
> On Wed, Nov 01, 2006 at 12:30:13PM +0300, Pavel Emelianov wrote:

<snip>

> > > 	- Support movement of all threads of a process from one group
> > > 	  to another atomically?
> > 
> > I propose such a solution: if a user asks to move /proc/<pid>
> > then move the whole task with threads.
> > If user asks to move /proc/<pid>/task/<tid> then move just
> > a single thread.
> > 
> > What do you think?
> 
> Isnt /proc/<pid> listed also in /proc/<pid>/task/<tid>?
> 
> For ex:
> 
> 	# ls /proc/2906/task
> 	2906  2907  2908  2909
> 
> 2906 is the main thread which created the remaining threads.
> 
> This would lead to an ambiguity when user does something like below:
> 
> 	echo 2906 > /some_res_file_system/some_new_group
> 
> Is he intending to move just the main thread, 2906, to the new group or
> all the threads? It could be either.
> 
> This needs some more thought ...

	I thought the idea was to take in a proc path instead of a single
number. You could then distinguish between the whole thread group and
individual threads by parsing the string. You'd move a single thread if
you find both the tgid and the tid. If you only get a tgid you'd move
the whole thread group. So:

<pid>                   -> if it's a thread group leader move the whole
			   thread group, otherwise just move the thread
/proc/<tgid>            -> move the whole thread group
/proc/<tgid>/task/<tid> -> move the thread


	Alternatives that come to mind are:

1. Read a flag with the pid
2. Use a special file which expects only thread groups as input 

Cheers,
	-Matt Helsley

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