Re: [Feature] x86_64 page tracking for Stratus servers

[Andi Kleen]

> Silly question, why can't you do all this from stop_machine_run context (or
> your SMI) that doesn't have to worry about other CPUs dirtying memory?

Because that would be too slow for continuous mirroring.

You can't go through 10+GB of virtual memory (or more with shared 
memory because the scan has to be virtual) in an interrupt.

The only sane way is to do it continuously.

> [*] Though if it gets included, it would not stop me lamenting the
> proliferation of complexities to support *tiny* obscure userbases. Can
> we wait until your hardware is smart enough to snoop the cc? :)


My guess is that if we had a generic memory mirror subsystem other people would
find uses for it too. e.g. a lot of systems support spare DIMMs these days and mirroring
some memory to it seems like a smart idea. That means normally the hardware
does it, but perhaps some stuff can be done better by doing it in software.

Or it is also a bit similar to the algorithms Xen uses for live migration.
If that was implemented on the kernel level something like this might 
be useful too. I think OpenVZ has some kind of migration support, but it's
currently not live.

-andi

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