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Re: [Xen-users] How to know if the balloon driver is running

Hi Ian,

So let me see if I understand you correctly. If the CONFIG_XEN_BALLOON is enabled (as in my case),
root@xxxx# grep CONFIG_XEN_BALLOON /boot/config-3.8.0-35-generic
then the balloon driver is automatically started at boot time by the domU.

Finally, regarding the files in /sys/devices/system/xen_memory/xen_memory0/selfballoon (inside the domU), are they used by the balloon driver or the selfballoon daemon?


On Thu, 2014-01-23 at 09:11 +0100, napster wrote:
> > But there is some files in the /sys file system which refers to the
> > selfballooning. Does that mean that the balloon driver is running? If
> > it is the case, how is about /proc/xen/balloon? Else, how to activate
> > the balloon driver?

> IIRC the core balloon driver is always present when Xen is enabled and
> so the kernel will respond to requests from the host/toolstack to change
> the amount of RAM (e.g "xm/xl mem-set foo" in dom0, which would result
> in changes to /proc/meminfo).

> In order to get in-guest access to control ballooning you need to
> CONFIG_XEN_BALLOON enable and load the xen-balloon.ko module. I'm not
> sure but I think with modern kernels this will appear in /sys and
> not /proc.

> It seems like the docs might be out of date and/or incomplete here. If
> you would be so kind as to produce a docs patch against xen.git (see [0]
> for tips) or create/update a page on the wiki once you've figured this
> out then we would be very grateful -- conveniently there is a document
> day[1] on Monday.

> The selfballoon stuff is a separate thing (although related), it's
> something to do with tmem AFAIUI.

> Ian.

> [0] http://wiki.xen.org/wiki/Submitting_Xen_Patches
> [1] http://wiki.xen.org/wiki/Xen_Document_Days

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