Re: Balloon driver.

["Cherry G. Mathew" <cherry.g.mathew%gmail.com@localhost>]

On 7 July 2010 00:02, Thor Lancelot Simon <tls%panix.com@localhost> wrote:
> On Tue, Jul 06, 2010 at 10:56:22PM +0530, Cherry G. Mathew wrote:
>>
>> Briefly, there are two methods to play with this now.
>>
>> >From dom0:
>>
>> # xm mem-set $domid $newmemsz
>>
>> or, from within the domU
>>
>> # sysctl -w kern.xen.balloon.target=$newtargetinpages
>
> How does one control, from the dom0, how much memory a domU may use?
>

Hi Thor,

use 'xm mem-set' command as mentioned above.

# xm mem-set $domid $newmemsz

The driver tries to honour this (asynchronously - there's a kernel
thread which polls for these requests) within reasonable limits
defined by:

- domU memory pressure ( ie;, UVM can't hand out any more wired frames
== balloon driver gives up after BALLOON_RETRIES)
- Absolute minimum and maximum, defined as  XEN_RESERVATION_ and
XEN_RESERVATION_MAX in the source. These values definitely need more
tweaking ( for eg: its perfectly possible to panic()/DOS a domU by
over-expanding the balloon. The min limit needs to co-operate with UVM
to prevent this from happening.

I hope this helps,
-- 
~Cherry