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Date:	Mon, 20 Oct 2014 09:55:41 +0300
From:	"Michael S. Tsirkin" <>
To:	"Denis V. Lunev" <>
	Raushaniya Maksudova <>,
	Rusty Russell <>
Subject: Re: [PATCH v3 0/2] shrink virtio baloon on OOM in guest

On Wed, Oct 15, 2014 at 07:47:42PM +0400, 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 baloon 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.
> Patch 1 of this series adds support for implementation of virtio_balloon
> callback, so now leak_balloon() function returns number of freed pages.
> Patch 2 implements virtio_balloon callback itself.
> Changes from v2:
> - added feature bit to control OOM baloon behavior from host
> Changes from v1:
> - minor cosmetic tweaks suggested by rusty@
> Signed-off-by: Raushaniya Maksudova <>
> Signed-off-by: Denis V. Lunev <>
> CC: Rusty Russell <>
> CC: Michael S. Tsirkin <>

With the feature bit, I think it's fine.

Acked-by: Michael S. Tsirkin <>

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