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Thank you for your reply but I mean is "KVM is also the better option for memory ballooning according to most users who accuse XEN of not returning unused RAM that has been previously shared with other VMs. KVM, unlike XEN is close to dedicated servers and users claim that KVM is way faster. Many users also admire the fact that KVM is more frequently updated which in turn leads to firmer security."

Please see "https://cloudcone.com/blog/kvm-vs-xen-knowing-the-differences-and-picking-the-best/".

On Tuesday, December 19, 2017, 2:04:58 AM PST, James Dingwall <james-xen@xxxxxxxxxxxxxx> wrote:

Hi Jason,

On Fri, Dec 15, 2017 at 09:18:14PM +0000, Jason Long wrote:
> Can it work well? I mean is release the memory and back it to host.

If I understand correctly you want to take memory from one running guest and then assign it to another? Yes, this is works. The tmem module helps you do this
automatically but as an example you can also do:

You want to start guest 3 but you only have 512M free memory, you are happy to take 256M from guests 1 & 2:

guest 1: memory = 1024
guest 2: memory = 1024
guest 3: memory = 1024

xl mem-set guest1 768
xl mem-set guest2 768
xl create guest3

James

> --------------------------------------------
> On Fri, 12/15/17, James Dingwall <james@xxxxxxxxxxxxxx> wrote:
>
> Subject: Re: [Xen-users] Xen ballooning problem.
> To: "Jason Long" <hack3rcon@xxxxxxxxx>
> Cc: xen-users@xxxxxxxxxxxxx
> Date: Friday, December 15, 2017, 5:29 PM
>
> Hi,
>
> On Fri, Dec 15, 2017 at
> 01:28:22PM +0000, Jason Long wrote:
> >
> Hello.
> > Is it true that "Xen
> ballooning" has some problems? For example, when it
> dedicate memory to VMs then it can't release it and back
> it to the host and it is a reason for migrate from Xen to
> KVM.
> >
> > Thank
> you.
>
> I have found a
> few combinations of xen/kernel which don't work well but
> otherwise I find it works for my case.
> Currently xen 4.9.1, 4.1.47 dom0 kernel, mix of
> Ubuntu 16.04 4.4 and 4.14 kernels in pv guests. I use the
> tmem
> module to automatically balloon the
> guest up/down as memory pressure changes.
>
> James
>
> -----Inline Attachment Follows-----

>
>
>
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