Reading @
How to know if the balloon driver is running
http://www.gossamer-threads.com/lists/xen/users/315064#315064
"...
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.
...
AFAIK the balloon driver is started if you just have CONFIG_XEN.
LIke I said before CONFIG_XEN_BALLOON enables additional support for
controlling the balloon driver from within the guest (as opposed to from
the host toolstack).
..."
in the Guest,
grep -i config_xen= /boot/*config*
/boot/config-4.4.0-28-generic:CONFIG_XEN=y
grep -i xen /boot/*config* | grep -i balloon
/boot/config-4.4.0-28-generic:CONFIG_XEN_BALLOON=y
/boot/config-4.4.0-28-generic:CONFIG_XEN_SELFBALLOONING=y
/boot/config-4.4.0-28-generic:CONFIG_XEN_BALLOON_MEMORY_HOTPLUG=y
/boot/config-4.4.0-28-generic:CONFIG_XEN_BALLOON_MEMORY_HOTPLUG_LIMIT=512
find /sys /proc -type d | grep -i balloon | grep xen
/sys/devices/system/xen_memory/xen_memory0/selfballoon
/proc/sys/xen/balloon
ls -al /proc/sys/xen/balloon
hotplug_unpopulated
How do you blacklist the Guest ballooning?
Perhaps related? Not clear 2 me that it's the same issue,
xen/balloon: cancel ballooning if adding new memory failed
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=3dcf63677d4eb7fdfc13290c8558c301d2588fe8
There's also balloon-related comments at
http://wiki.xenproject.org/wiki/XenParavirtOps
although they now look somewhat out of date w.r.t. current 4x kernel
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