Re: [Xen-users] can Xen use swap instead or RAM?

[Martinx - ジェームズ <thiagocmartinsc@xxxxxxxxx>]

Okay, I understand... And what about the Linux Kernel Samepage Merging feature?

http://www.linux-kvm.com/content/using-ksm-kernel-samepage-merging-kvm

 But I don't know if Xen can take advantage of it...

 I my Ubuntu 10.04 Desktop, I have 4G of RAM and I can bootup ~6 clone VMs with 1024M of RAM for each...

On 24 September 2010 18:53, George Shuklin <george.shuklin@xxxxxxxxx> wrote:

Nope.

Ballooning is cool mechanism, but it is not overcommitment. We can say
'theoretical overcommitment' - if we starting few machines with mem=1GiB
maxmem=10GiB, we (theoretically) give every machine 10G, but this is not
overcommitment, it just limits, raised up beyond host memory.

Actual overcommitment/oversell is when sum of actually allocated memory
(as displayed by 'free' in every guest) is more then memory on host.

Xen lack of this feature and I believe this make it more pricey in term
of VPS/VDS hosting, but much better quality for end-users (domUs),
compare to OpenVZ overcommitment.


В Птн, 24/09/2010 в 16:24 -0300, Martinx - ジェームズ пишет:

> Mmm... You mean this:
>
>
> http://blog.xen.org/index.php/2008/08/27/xen-33-feature-memory-overcommit/
>
>
> ?
>
> On 24 September 2010 15:49, George Shuklin <george.shuklin@xxxxxxxxx>
> wrote:
>         Yes, It is nice technology, but it still do not allow
>         hypervisor
>         swapping or overselling. :)
>
>         В Птн, 24/09/2010 в 14:57 -0300, Martinx - ジェームズ пишет:
>         > Hi!
>
>         >  The Xen 4.0 introduces the TMEM project, take a look at it:
>
>         >  http://wiki.xensource.com/xenwiki/Xen4.0
>
>         >  TMEM allows improved utilization of unused (for example
>         page cache)
>         > PV guest memory. more
>         > information: http://oss.oracle.com/projects/tmem/
>         >
>
>
>         > On 24 September 2010 14:46, George Shuklin
>         <george.shuklin@xxxxxxxxx>
>         > wrote:
>         >         You can use swap of any size at VM level (every VM
>         will have
>         >         it own
>         >         swap).
>         >
>         >         Right now there is no way to do hypervisor swap or
>         oversell
>         >         memory.
>         >
>         >         В Птн, 24/09/2010 в 13:14 -0400, Boris Epstein
>         пишет:
>         >
>         >         > Hello listmates,
>         >         >
>         >         > Let's say I've got a machine with 1 GB of RAM and
>         I want to
>         >         host 3 512
>         >         > MB virtual machines on it? Is that possible -
>         i.e., is it
>         >         possible to
>         >         > force Xen to use swap and pass it off as RAM to
>         the VM's? I
>         >         know it is
>         >         > slow and inefficient but for the purposes of
>         testing - is
>         >         that
>         >         > possible?
>         >         >
>
>
>
>
>
>
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>
>
>



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