[ale] Memory and virtualization

[Jim Kinney]

The ballooning process works pretty well to share memory chunks across VMs.
I've used it in KVM. The chunks are all supposedly read-only with copy on
write the same as a thin allocation vm clone. So the caching works in your
favor.

Here's the kicker for running Linux vm on a Linux host: that caching also
works in your favor! For windows vm, not at all. But between windows vms it
does work.

What I have not seen is how to specify/change page size for
allocation/sharing. Is it always a fixed size? Can I get more efficiency
from a variable page size? I would think so. a host has glibc in ram as do
all VMs using glibc. That save one or more pointers for each vm if all of
glibc is a single page.


On Fri, Jul 12, 2013 at 9:07 AM, Ed Cashin <ecashin at noserose.net> wrote:

> One early technique (I saw a presentation on it at OSDI 2003, I think) for
> reclaiming memory from guests was memory ballooning.  You can Google for,
> e.g.,
>
>   vmware ballooning
>
> ... to learn more about it.  This blog post talks about some of the other
> techniques.
>
>
> http://blogs.vmware.com/virtualreality/2011/02/hypervisor-memory-management-done-right.html
>
> I have no idea, really, about Hyper-V, but these are the most obvious
> techniques to use, so I assume Hyper-V has to use the same kinds of
> techniques.  I'd be interested to hear about anything original they've come
> up with.
>
> On Fri, Jul 12, 2013 at 8:15 AM, Lightner, Jeff <JLightner at water.com>wrote:
>
>>   Given that Linux pre-caches/pre-buffers most memory presented to it
>> what impact if any does this have to memory allocation to a virtual guest
>> for the virtual platform itself?    That is to say if one has a mix of
>> Linux and Windows virtual machines on say Hyper-V or MWare does the memory
>> allocated to each Linux guest become totally unavailable to other guest
>> machines because of this pre-allocation or is oversubscription possible
>> without impacting the guest machines?****
>>
>> ** **
>>
>> P.S. Don’t tell me not to use Hyper-V unless you can provide
>> documentation it absolutely won’t work for RHELinux guests – I didn’t make
>> the choice and won’t be able to undo it    My question is NOT asking which
>> virtualization platform to use.****
>>
>> ** **
>>
>> ** **
>>
>>
>>
>>
>>
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>
> --
>   Ed Cashin <ecashin at noserose.net>
>   http://noserose.net/e/
>   http://www.coraid.com/
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-- 
-- 
James P. Kinney III
*
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