Re: [Xen-users] xenballooning

[George Shuklin <george.shuklin@xxxxxxxxx>]

Ð ÐÑÐ, 29/07/2010 Ð 22:52 +0700, Fajar A. Nugraha ÐÐÑÐÑ: 
> On Thu, Jul 29, 2010 at 9:58 PM, Simon Hobson <linux@xxxxxxxxxxxxxxxx> wrote:
> > George Shuklin wrote:
> >> Can we somehow make balloon inflated at start time? (F.e. VM starts with
> >> memory = 512Mb and balloon inflating to +512Mb).
> >
> > Yes, you can do that, and it took me a while to find out how. In your config
> > file put something like this :
> > memory  = '512'
> > maxmem  = '1024'
> >
> > As I understnad it, it will start the guest with (in this example) 512M of
> > RAM, but you can use "xm mem-set nnn" to increase that within the bounds of
> > the maxmem setting. If increasing, the extra memory is hotplugged into the
> > client. When decreasing, I assume there is a process for getting the client
> > to free up the memory before it is hotplug removed.
> 
> Note two caveats:
> (1) In order to allow the additional memory to be hot-add later, some
> memory needs to be allocated to maintain the maximum amount of memory
> address that will be available. And that can be a waste. So while the
> above (memory=512/maxmem=1024) is a good example, it wouldn't make
> sense to have something like maxmem having 10 times the amount of
> memory, cause the overhead will be too big (from my test, the overhead
> was about 4.8M or 16% of the original memory with memory=30/maxmem=300
> setup)
> (2) Last time I check, it didn't work with Ubuntu Lucid stock pv_ops
> kernel (linux-image-server or linux-image-virtual). It simply use the
> value in "maxmem" from the start. It works great with RHEL-5's
> kernel-xen or novell's xenified kernel though.


Thank you.

Some more information about reserved memory (in our work we call it
'stealed').

This memory depends on max_memory (in term of xen cloud platform -
memory-static-max), and (in %) become lower, as max-mem raising.

In range 4-8-16Gb it is about 1-10% of memory (so we can use range
320-3Gb without any problems).

here my experimental data (both in Mb):

MAXMEM  STEAL
256     8,0
320     8,9
512     10,9
1024    16,2
2048    25,2
3072    34,3
4096    43,3
5120    52,3
6144    61,3

As you can see, 61Mb for 300Mb minimum with 6Gb maximum is not so bad...




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