Re: What can OpenVZ do?

From: Dave Hansen
Date: Wed Feb 18 2009 - 16:27:44 EST


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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