On Mon, 2015-05-04 at 12:47 +0300, Denis V. Lunev wrote: > On 01/04/15 13:18, Michael S. Tsirkin wrote: > > On Wed, Apr 01, 2015 at 12:51:42PM +0300, James Bottomley wrote: > >> On Wed, 2015-04-01 at 11:50 +0200, Michael S. Tsirkin wrote: > >>> On Wed, Apr 01, 2015 at 12:44:28PM +0300, James Bottomley wrote: > >>>> On Fri, 2015-02-27 at 09:57 +0300, 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 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. > >>>>> > >>>>> commit 5a10b7dbf904bfe01bb9fcc6298f7df09eed77d5 > >>>>> Author: Raushaniya Maksudova <rmaksud...@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 balloon device which does the trick. > >>>> What's the status on this, please? It's been over a month since this > >>>> was posted with no further review feedback, so I think it's ready. > >>>> Getting this into qemu is blocking our next step which would be adding > >>>> the feature bit to the virtio spec. > >>>> > >>>> James > >>> This was posted after soft feature freeze for 2.3, so it'll have to go > >>> into 2.4. I don't see why would this block your work on the spec: you > >>> should make progress on this meanwhile. > >> I can do that ... I just thought the spec was trailing edge, so I was > >> waiting to have the patch accepted, which confirms the implementation. > >> I didn't want to write it into the spec and have the actual > >> implementation changed by review later. > >> > >> James > >> > > It's up to you really, I would just like to point out two things: > > - spec process is a long one, assuming we accept a spec change, > > we go though a public review period, multiple votes etc. > > About half a year to release a spec revision with > > new features. > > So time enough to make minor changes. > > - oasis process works like this (roughly): > > spec is written > > spec goes through a public review process > > community standard is published > > 3 implementations are reported > > spec becomes an oasis standard > > so implementations aren't required at early stages > 2.3 is done, 2.4 window is opened.... > > The patch is applicable for both > git://git.kernel.org/pub/scm/virt/kvm/mst/qemu.git > and vanilla qemu. > > How can we proceed?
The spec update supporting this feature is published for review: https://www.oasis-open.org/committees/download.php/55709/virtio-v1.0-csprd04.zip It's probably a good idea to have the implementation there as well. Do we need to resend these patches? James
