On Wed, Nov 26, 2014 at 01:11:25PM +0300, Denis V. Lunev wrote:
> From: Raushaniya Maksudova <rmaksud...@parallels.com>
>
> 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 <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 baloon device which do the trick.
>
> Signed-off-by: Raushaniya Maksudova <rmaksud...@parallels.com>
> Signed-off-by: Denis V. Lunev <d...@openvz.org>
> CC: Anthony Liguori <aligu...@amazon.com>
> CC: Michael S. Tsirkin <m...@redhat.com>
> ---
> hw/virtio/virtio-balloon.c | 7 +++++++
> include/hw/virtio/virtio-balloon.h | 2 ++
> qemu-options.hx | 6 +++++-
> 3 files changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
> index 7bfbb75..9d145fa 100644
> --- a/hw/virtio/virtio-balloon.c
> +++ b/hw/virtio/virtio-balloon.c
> @@ -305,7 +305,12 @@ static void virtio_balloon_set_config(VirtIODevice *vdev,
>
> static uint32_t virtio_balloon_get_features(VirtIODevice *vdev, uint32_t f)
> {
> + VirtIOBalloon *dev = VIRTIO_BALLOON(vdev);
> f |= (1 << VIRTIO_BALLOON_F_STATS_VQ);
> + if (dev->deflate_on_oom) {
> + f |= (1 << VIRTIO_BALLOON_F_DEFLATE_ON_OOM);
> + }
> +
> return f;
> }
>
> @@ -409,6 +414,7 @@ static void virtio_balloon_device_unrealize(DeviceState
> *dev, Error **errp)
> }
>
> static Property virtio_balloon_properties[] = {
> + DEFINE_PROP_BOOL("deflate-on-oom", VirtIOBalloon, deflate_on_oom, false),
> DEFINE_PROP_END_OF_LIST(),
> };
>
> diff --git a/include/hw/virtio/virtio-balloon.h
> b/include/hw/virtio/virtio-balloon.h
> index f863bfe..45cc55a 100644
> --- a/include/hw/virtio/virtio-balloon.h
> +++ b/include/hw/virtio/virtio-balloon.h
> @@ -30,6 +30,7 @@
> /* The feature bitmap for virtio balloon */
> #define VIRTIO_BALLOON_F_MUST_TELL_HOST 0 /* Tell before reclaiming pages */
> #define VIRTIO_BALLOON_F_STATS_VQ 1 /* Memory stats virtqueue */
> +#define VIRTIO_BALLOON_F_DEFLATE_ON_OOM 2 /* Deflate balloon on OOM */
>
> /* Size of a PFN in the balloon interface. */
> #define VIRTIO_BALLOON_PFN_SHIFT 12
> @@ -67,6 +68,7 @@ typedef struct VirtIOBalloon {
> QEMUTimer *stats_timer;
> int64_t stats_last_update;
> int64_t stats_poll_interval;
> + bool deflate_on_oom;
> } VirtIOBalloon;
>
> #endif
You don't need an extra bool, and open-coding.
Do it same as we do for other features please,
set bit in feature mask directly.
> diff --git a/qemu-options.hx b/qemu-options.hx
> index da9851d..14ede0b 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -324,7 +324,8 @@ ETEXI
> DEF("balloon", HAS_ARG, QEMU_OPTION_balloon,
> "-balloon none disable balloon device\n"
> "-balloon virtio[,addr=str]\n"
> - " enable virtio balloon device (default)\n",
> QEMU_ARCH_ALL)
> + " enable virtio balloon device (default)\n"
> + " [,deflate-on-oom=on|off]\n", QEMU_ARCH_ALL)
> STEXI
> @item -balloon none
> @findex -balloon
> @@ -332,6 +333,9 @@ Disable balloon device.
> @item -balloon virtio[,addr=@var{addr}]
> Enable virtio balloon device (default), optionally with PCI address
> @var{addr}.
> +@item -balloon virtio[,deflate-on-oom=@var{deflate-on-oom}]
> +@var{deflate-on-oom} is "on" or "off" and enables whether to let Guest OS
> +to deflate virtio balloon on OOM. Default is off.
> ETEXI
>
> DEF("device", HAS_ARG, QEMU_OPTION_device,
Please don't add stuff to legacy -balloon.
New -device is enough, you don't need to touch qemu-options.hx
for it.
> --
> 1.9.1
