Re: [Xen-users] setting max memory

[Danilo Godec <danilo.godec@xxxxxxxxx>]

On 07/21/2011 10:30 AM, Jonathan Tripathy wrote:
> On 21/07/2011 09:26, Jonathan Tripathy wrote:
> > > > If you are going to be using these DomUs for anything even remotely
> > > > serious, then I would strongly advise against dynamically resizing a
> > > > Linux environment's available memory. Form personal experience, I can
> > > > categorically say that this leads to a very unstable system.
> > > >
> > > > Just my 2 pence
> > > Even without keeping beside the memory-max? I remember Having done it
> > > too but it did not turn the system unstable AFAICT.
> > >
> > > Does anybody have similar feelings about playing with meme making Linux
> > > domU unstable?
Not really.

My Xen servers have 32GB of memory. I limit Dom0 memory to 2GB.

I start all my DomU's with 'maxmem=xxxx' (where xxxx is what I consider 
to be 'enough' in every possible scenario for that particular host). I 
also use 'mem=xxxxM' kernel parameter for DomU kernels - maybe that's 
deprecated now but in the past it was required for the DomU kernel to 
properly allocate memory.
> > http://wiki.xensource.com/xenwiki/XenBestPractices
> >
> > Read the section "http://wiki.xensource.com/xenwiki/XenBestPractices";.
> > Even though that talks about Dom0, the same still applys for DomU as
> > they run Linux too.
> That should be "read section "Why should I dedicate fixed amount of 
> memory for Xen dom0""
To me the ability to dynamically reduce or increase DomU memory is one 
of the essentials of virtualization. Besides - I've been doing it for 
about 4-5 years now and wouldn't say I noticed any related stability issues.
IMHO the section of the XenBestPractices you mention it's applicable to 
Dom0 only (as in you start with huge amount of memory, but eventually 
end up with just 'a bit' anyway. It's usually a different story with 
DomU's - I like to start with not-so-much memory and add it when needed.
   D.


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--
Danilo Godec, sistemska podpora / system administration

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