xen-devel
[Xen-devel] Re: [Xen-users] (xen) Possible bug: Memory squeeze in netbac
On 7 Jun 2006, at 21:43, Anthony Liguori wrote:
I suspected it would but I was hoping it wouldn't. Do this mean that
the netback driver needs to be able to increase it's reservation? If
so, should we be enforcing (in the tools) that memory < maxmem? Any
thoughts Keir?
The kernel should be able to do it for itself. Drivers inform how much
'headroom' they need via balloon_update_driver_allowance(). Balloon
driver then strives to keep its memory allocation below maxmem by that
amount. Possibly the balloon driver needs a kick when allocation fails
in teh driver, to expand the balloon a little. Another alternative is
for drivers to incr/decr reservation via another balloon driver
interface, giving another hook point for the balloon driver to do
something sensible.
So, in short, tools may be able to screw things for a short while (and
maybe crash things entirely, if maxmem is reduced drastically with no
prior warning (update of memory target)). But the balloon driver is
expected to recover except in that kind of unreasonable circumstance.
-- Keir
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