On 04.10.21 11:14, Marek Marczykowski-Górecki wrote:
> On Mon, Oct 04, 2021 at 07:31:40AM +0200, Juergen Gross wrote:
>> On 03.10.21 06:47, Marek Marczykowski-Górecki wrote:
>>> Hi,
>>>
>>> After updating a PVH domU to 5.4.150, I see xen-balloon thread using
>>> 100% CPU (one thread).
>>> This is a domain started with memory=maxmem=716800KiB (via libvirt). Then,
>>> inside, I see:
>>>
>>> # cat /sys/devices/system/xen_memory/xen_memory0/target_kb
>>> 716924
>>> # cat /sys/devices/system/xen_memory/xen_memory0/info/current_kb
>>> 716400
>>>
>>> Doing `cat info/current_kb > target_kb` "fixes" the issue. But still,
>>> something is wrong - on earlier kernel (5.4.143 to be precise), it
>>> wasn't spinning, with exactly the same values reported in sysfs. It
>>> shouldn't run in circles if it can't get that much memory it wants. I
>>> strongly suspect "xen/balloon: use a kernel thread instead a workqueue"
>>> or related commit being responsible, but I haven't verified it.
>>
>> I think you are right. I need to handle the BP_ECANCELED case similar to
>> BP_EAGAIN in the kernel thread (wait until target size changes again).
>>
>> One further question: do you see any kernel message in the guest related
>> to the looping balloon thread?
> 
> Nothing, only the usual "xen:balloon: Initialising balloon driver", and
> nothing related to balloon after that.

Could you try the attached patch, please? I've tested it briefly with
PV and PVH guests.


Juergen