Re: What can OpenVZ do?

* Dave Hansen [off-list ref] wrote:

On Wed, 2009-02-18 at 19:16 +0100, Ingo Molnar wrote:

quoted

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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