Re: [Xen-users] xenballooning

["Fajar A. Nugraha" <fajar@xxxxxxxxx>]

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.

-- 
Fajar

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