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Re: [Qemu-devel] [PATCH 2/2] balloon: add a feature bit to let Guest OS
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCH 2/2] balloon: add a feature bit to let Guest OS deflate balloon on oom |
Date: |
Thu, 26 Feb 2015 13:39:27 -0700 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0 |
On 02/26/2015 10:39 AM, 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
s/to return/return/
> 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 <address@hidden>
> 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.
s/baloon/balloon/
s/do/does/
I'll leave the content review to someone more familiar with the code.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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