Re: [Qemu-devel] [PATCH v7 0/1] balloon: add a feature bit to let Guest OS deflate

["Denis V. Lunev" <den@openvz.org>]

On 15/06/15 13:52, Denis V. Lunev wrote:
> Excessive virtio_balloon inflation can cause invocation of OOM-killer,
> when Linux is under severe memory pressure. Various mechanisms are
> responsible for correct virtio_balloon memory management. Nevertheless it
> is often the case that these control tools does not have enough time to
> react on fast changing memory load. As a result OS runs out of memory and
> invokes OOM-killer. The balancing of memory by use of the virtio balloon
> should not cause the termination of processes while there are pages in the
> balloon. Now there is no way for virtio balloon driver to free memory at
> the last moment before some process get killed by OOM-killer.
>
> This does not provide a security breach as balloon itself is running
> inside Guest OS and is working in the cooperation with the host. Thus
> some improvements from Guest side should be considered as normal.
>
> To solve the problem, introduce a virtio_balloon callback which is
> expected to be called from the oom notifier call chain in out_of_memory()
> function. If virtio balloon could release some memory, it will make the
> system to return and retry the allocation that forced the out of memory
> killer to run.
>
> This behavior should be enabled if and only if appropriate feature bit
> is set on the device. It is off by default.
>
> This functionality was recently merged into vanilla Linux (actually in
> linux-next at the moment)
>
>    commit 5a10b7dbf904bfe01bb9fcc6298f7df09eed77d5
>    Author: Raushaniya Maksudova <rmaksudova@parallels.com>
>    Date:   Mon Nov 10 09:36:29 2014 +1030
>
> This patch adds respective control bits into QEMU. It introduces
> deflate-on-oom option for baloon device which do the trick.
>
> Changes from v6:
> - ported to virtio_add_feature
>
> Changes from v5:
> - ported to QEMU current
>
> Changes from v4:
> - spelling corrected according to suggestions from Eric Blake
>
> Changes from v3:
> - ported to git://git.kernel.org/pub/scm/virt/kvm/mst/qemu.git tags/for_upstream_rebased
>
> Changes from v2:
> - fixed mistake with bit number in virtio_balloon_get_features
>
> Changes from v1:
> - From: in patch 1 according to the original ownership
> - feature processing in patch 2 as suggested by Michael. It could be done
>    without additional field, but this will require to move the property
>    level up, i.e. to PCI & CCW level.
>
> Signed-off-by: Raushaniya Maksudova <rmaksudova@virtuozzo.com>
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> CC: Anthony Liguori <aliguori@amazon.com>
> CC: Michael S. Tsirkin <mst@redhat.com>
>
> P.S. Sorry for resend (if you have caught additional patch), I have
>       expirienced some troubles in the process
>
ping