Re: What can OpenVZ do?

[Dave Hansen <dave-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>]

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