linux-kernel - Re: [Feature] x86_64 page tracking for Stratus servers

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Message-Id: <200609060936.19268.ak@suse.de>
Date:	Wed, 6 Sep 2006 09:36:19 +0200
From:	Andi Kleen <ak@...e.de>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Kimball Murray <kimball.murray@...il.com>,
	linux-kernel@...r.kernel.org, akpm@...eo.com
Subject: Re: [Feature] x86_64 page tracking for Stratus servers

> 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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