linux-kernel - Re: How much of a mess does OpenVZ make? ;) Was: What can OpenVZ do?

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Message-ID: <49BA8FA5.5030003@free.fr>
Date:	Fri, 13 Mar 2009 17:53:57 +0100
From:	Cedric Le Goater <legoater@...e.fr>
To:	"Serge E. Hallyn" <serue@...ibm.com>
CC:	Alexey Dobriyan <adobriyan@...il.com>, linux-api@...r.kernel.org,
	containers@...ts.linux-foundation.org, hpa@...or.com,
	linux-kernel@...r.kernel.org,
	Dave Hansen <dave@...ux.vnet.ibm.com>, linux-mm@...ck.org,
	viro@...iv.linux.org.uk, mingo@...e.hu, mpm@...enic.com,
	tglx@...utronix.de, torvalds@...ux-foundation.org,
	Andrew Morton <akpm@...ux-foundation.org>, xemul@...nvz.org
Subject: Re: How much of a mess does OpenVZ make? ;) Was: What can OpenVZ
 do?

Serge E. Hallyn wrote:
> Quoting Cedric Le Goater (legoater@...e.fr):
>>> No, what you're suggesting does not suffice.
>> probably. I'm still trying to understand what you mean below :)
>>
>> Man, I hate these hierarchicals pid_ns. one level would have been enough, 
>> just one vpid attribute in 'struct pid*'
> 
> Well I don't mind - temporarily - saying that nested pid namespaces
> are not checkpointable.  It's just that if we're going to need a new
> syscall anyway, then why not go ahead and address the whole problem?
> It's not hugely more complicated, and seems worth it.

yes. agree. there's a thread going on that topic. i'm following it.

[ ... ] 

>> anyway, I think that some CLONE_NEW* should be forbidden. Daniel should
>> send soon a little patch for the ns_cgroup restricting the clone flags
>> being used in a container.
> 
> Uh, that feels a bit over the top.  We want to make this
> uncheckpointable (if it remains so), not prevent the whole action.
> After all I may be running a container which I don't plan on ever
> checkpointing, and inside that container running a job which i do
> want to migrate.

ok. i've been scanning the emails a bit fast. that would be fine 
and useful.

> So depending on if we're doing the Dave or the rest-of-the-world
> way :), we either clear_bit(pidns->may_checkpoint) on the parent
> pid_ns when a child is created, or we walk every task being
> checkpointed and make sure they each are in the same pid_ns.  
> Doesn't that suffice?

yes. this 'may_checkpoint' is a container level info so I wonder 
where you store it. in a cgroup_checkpoint ? sorry for jumping in 
and may be restarting some old topics of discussion.

C.
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