[ale] Memory and virtualization

Fri Jul 12 10:35:02 EDT 2013

The blog I mentioned does mention the page size issue a bit:

"Also, despite claims by our competitors, Transparent Page Sharing will in
fact work with large memory pages in guests by breaking those pages into
smaller sizes to enable page sharing when the host is under memory
pressure."

On Fri, Jul 12, 2013 at 9:31 AM, Jim Kinney <jim.kinney at gmail.com> wrote:

> 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
> *
> *Every time you stop a school, you will have to build a jail. What you
> gain at one end you lose at the other. It's like feeding a dog on his own
> tail. It won't fatten the dog.
> - Speech 11/23/1900 Mark Twain
> *
> http://electjimkinney.org
> http://heretothereideas.blogspot.com/
> *
>
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-- 
  Ed Cashin <ecashin at noserose.net>
  http://noserose.net/e/
  http://www.coraid.com/
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