[Virtual-pkg-base-maintainers] Bug#825211: OOM in Debian guests on balloon overinflation

[Anna Melekhova (Vorobyova)]

Package: base
Version: Debian 7, Debian 8

There is QEMU/KVM and a Linux OS running inside the guest. 
Inside the Linux guest a balloon consumes memory in accordance with 
commands performed on the host side in QEMU. Rapid increases of memory consumption
inside the guest may end up with guest OOMs 
since memory locked by balloon couldn’t be returned to the guest OS/vm in time. 

The problem is addressed in mainstream Linux with the following patchset:

commit 5a10b7dbf904bfe01bb9fcc6298f7df09eed77d5
Author: Raushaniya Maksudova <rmaksudova at parallels.com>
Date:   Mon Nov 10 09:36:29 2014 +1030
virtio_balloon: free some memory from balloon on OOM

   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 some memory at the last moment before some process will be 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.

   Allocate virtio  feature bit for this: it is not set by default,
   the the guest will not deflate virtio balloon on OOM without explicit
   permission from host.

   Signed-off-by: Raushaniya Maksudova <rmaksudova at parallels.com>
   Signed-off-by: Denis V. Lunev <den at openvz.org>
   Acked-by: Michael S. Tsirkin <mst at redhat.com>
   Signed-off-by: Rusty Russell <rusty at rustcorp.com.au>

commit 1fd9c67203af91977bf3b964ff3744cf74fc6f3f
Author: Raushaniya Maksudova <rmaksudova at parallels.com>
Date:   Mon Nov 10 09:35:29 2014 +1030

   virtio_balloon: return the amount of freed memory from leak_balloon()

   This value would be useful in the next patch to provide the amount of
   the freed memory for OOM killer.

   Signed-off-by: Raushaniya Maksudova <rmaksudova at parallels.com>
   Signed-off-by: Denis V. Lunev <den at openvz.org>
   CC: Rusty Russell <rusty at rustcorp.com.au>
   CC: Michael S. Tsirkin <mst at redhat.com>
   Signed-off-by: Rusty Russell <rusty at rustcorp.com.au>