linux-kernel - Re: What can OpenVZ do?

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Date:	Thu, 19 Feb 2009 00:15:45 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	Alexey Dobriyan <adobriyan@...il.com>,
	Nathan Lynch <nathanl@...tin.ibm.com>,
	linux-api@...r.kernel.org, containers@...ts.linux-foundation.org,
	mpm@...enic.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	viro@...iv.linux.org.uk, hpa@...or.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	torvalds@...ux-foundation.org, tglx@...utronix.de, xemul@...nvz.org
Subject: Re: What can OpenVZ do?


* Dave Hansen <dave@...ux.vnet.ibm.com> wrote:

> On Wed, 2009-02-18 at 19:16 +0100, Ingo Molnar wrote:
> > Nothing motivates more than app designers complaining about the 
> > one-way flag.
> > 
> > Furthermore, it's _far_ easier to make a one-way flag SMP-safe. 
> > We just set it and that's it. When we unset it, what do we about 
> > SMP races with other threads in the same MM installing another 
> > non-linear vma, etc.
> 
> After looking at this for file descriptors, I have to really 
> agree with Ingo on this one, at least as far as the flag is 
> concerned.  I want to propose one teeny change, though: I 
> think the flag should be per-resource.
> 
> We should have one flag in mm_struct, one in files_struct, 
> etc...  The task_is_checkpointable() function can just query 
> task->mm, task->files, etc...  This gives us nice behavior at 
> clone() *and* fork that just works.
> 
> I'll do this for files_struct and see how it comes out so you 
> can take a peek.

Yeah, per resource it should be. That's per task in the normal 
case - except for threaded workloads where it's shared by 
threads.

	Ingo
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