Re: [PATCH v1 0/3] Virtio-balloon Improvement

[Michael S. Tsirkin]

On Fri, Oct 20, 2017 at 07:54:23PM +0800, Wei Wang wrote:
> This patch series intends to summarize the recent contributions made by
> Michael S. Tsirkin, Tetsuo Handa, Michal Hocko etc. via reporting and
> discussing the related deadlock issues on the mailinglist. Please check
> each patch for details.
> 
> >From a high-level point of view, this patch series achieves:
> 1) eliminate the deadlock issue fundamentally caused by the inability
> to run leak_balloon and fill_balloon concurrently;

We need to think about this carefully. Is it an issue that
leak can now bypass fill? It seems that we can now
try to leak a page before fill was seen by host,
but I did not look into it deeply.

I really like my patch for this better at least for
current kernel. I agree we need to work more on 2+3.

> 2) enable OOM to release more than 256 inflated pages; and

Does just this help enough? How about my patch + 2?
Tetsuo, what do you think?

> 3) stop inflating when the guest is under severe memory pressure
> (i.e. OOM).

But when do we finally inflate?  Question is how does host know it needs
to resend an interrupt, and when should it do it?


> Here is an example of the benefit brought by this patch series:
> The guest sets virtio_balloon.oom_pages=100000. When the host requests
> to inflate 7.9G of an 8G idle guest, the guest can still run normally
> since OOM can guarantee at least 100000 pages (400MB) for the guest.
> Without the above patches, the guest will kill all the killable
> processes and fall into kernel panic finally.
> 
> Wei Wang (3):
>   virtio-balloon: replace the coarse-grained balloon_lock
>   virtio-balloon: deflate up to oom_pages on OOM
>   virtio-balloon: stop inflating when OOM occurs
> 
>  drivers/virtio/virtio_balloon.c | 149 ++++++++++++++++++++++++----------------
>  1 file changed, 91 insertions(+), 58 deletions(-)
> 
> -- 
> 2.7.4