Re: [Xen-devel] [PATCH 6 of 8 [RFC]] libxc: introduce xc_domain_move_memory

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On mar, 2013-04-09 at 09:13 +0100, Juergen Gross wrote:
> What about the following approach:
> 
In general, I like it... More details below.

> - do the migration in chunks (like 1GB, may be configurable)
>
Yes, provided these chunks are big enough, I think the overhead of is
acceptable.

> - don't move pages which are already on one of the target nodes
>
Yep, that is definitely sane, and was already on my TODO list (although,
you're right, I forgot to mention it in the cover or in the various
changelogs). It's not there yet because I'm missing a way of knowing on
what node a page is, but I'm already working of putting it together.

Anyway, I agree on this too, and thanks for pointing that out. :-)

> - try to allocate memory on the target node while the domain is still running.
>    If this fails, there is no need to move that chunk. Depending on the page
>    size requirements (huge pages) decide whether the move is aborted or done
>    partially.
> - in case of successful allocation suspend the domain, do the copy and update
>    page tables for the copied pages, then resume the domain
>
This is also fine, the only issue being that I'd probably need to fiddle
with the domain max_mem, and stuff like that, wouldn't I? I'm saying
this because, when testing the few that I sent already, I run right into
this when I was trying to do it in the allocate-copy-deallocate order
(of course, depending on how big a chunk is, but this is going to be
much less than 1GB!).

Do you see what I mean? Do you think it would be nice to increase the
domain's "memory allowance" (temporarily, of course) for this to be
possible?

> - free the memory chunk on the old node(s)
> - repeat until either no memory obtained or move is finished
> 
> This will have higher overhead, but the domain will be suspended for only
> short periods of time. The memory requirements don't matter, as the additional
> memory will be allocated only for a short period of time. 
>
Yep, this all makes sense, with the only nit being the max_mem issue
above.

Thanks again and Regards,
Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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