linux-kernel - Re: What can OpenVZ do?

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Date:	Wed, 18 Feb 2009 13:27:27 -0800
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	Ingo Molnar <mingo@...e.hu>
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?

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.

-- Dave

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