Re: xen-balloon thread using 100% of CPU, regression in 5.4.150

[Juergen Gross <jgross@xxxxxxxx>]

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

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