On Fri, Sep 09, 2016 at 04:54:44PM +0300, Denis V. Lunev wrote:
> From: Konstantin Neumoin <kneumoin@xxxxxxxxxxxxx>
>
> At this moment oom notification in balloon does not work as expected.
> After virtballoon_oom_notify there is an infinitive loop:
> - virtballoon_oom_notify was called and balloon was deflated
> - balloon get notification that config was changed, compare target and
> actual and try to reach target again.
>
> This patch adds global variable fail_counter which indicates that oom has
> been happened. We check that fail_counter was changed between calls
> update_balloon_size_func. In this case we should not try to inflate balloon
> even if actual != target.
Doesn't look right to me. What if it triggered an hour ago?
We really need mm core to expose an oom_in_progress flag that we can test.
More implementation comments below.
>
> Signed-off-by: Konstantin Neumoin <kneumoin@xxxxxxxxxxxxx>
> Signed-off-by: Denis V. Lunev <den@xxxxxxxxxx>
> CC: Michael S. Tsirkin <mst@xxxxxxxxxx>
> ---
> drivers/virtio/virtio_balloon.c | 15 +++++++++++++++
> 1 file changed, 15 insertions(+)
>
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 4e7003d..253bf05 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -50,6 +50,8 @@ MODULE_PARM_DESC(oom_pages, "pages to free on OOM");
> static struct vfsmount *balloon_mnt;
> #endif
>
> +static unsigned long fail_count;
> +
> struct virtio_balloon {
> struct virtio_device *vdev;
> struct virtqueue *inflate_vq, *deflate_vq, *stats_vq;
> @@ -361,6 +363,8 @@ static int virtballoon_oom_notify(struct notifier_block *self,
> unsigned long *freed;
> unsigned num_freed_pages;
>
> + fail_count++;
> +
> vb = container_of(self, struct virtio_balloon, nb);
> if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
> return NOTIFY_OK;
OOM should not interfere with ballooning unless
VIRTIO_BALLOON_F_DEFLATE_ON_OOM has been negotiated.
> @@ -386,11 +390,22 @@ static void update_balloon_size_func(struct work_struct *work)
> {
> struct virtio_balloon *vb;
> s64 diff;
> + static unsigned long fc;
> +
> + if (fc == 0)
> + fc = fail_count;
Why?
>
> vb = container_of(work, struct virtio_balloon,
> update_balloon_size_work);
> diff = towards_target(vb);
>
> + if (fc != fail_count) {
> + fc = fail_count;
Unlikely to work correctly if there are multiple balloon devices.
> + /* Don't inflate balloon after oom notification */
> + if (diff > 0)
> + return;
> + }
> +
> if (diff > 0)
> diff -= fill_balloon(vb, diff);
> else if (diff < 0)
I'd rather make it per-device.
Absence of memory ordering primitives of any kind also
looks suspicious.
> --
> 2.7.4
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