Re: [PATCH v1 6/6] virtio-balloon: Add support for aerating memory via hinting

Michael S. Tsirkin
2019-07-18T20:28:15Z

On Thu, Jul 18, 2019 at 12:03:23PM -0400, Nitesh Narayan Lal wrote:
> >>>> For example we allocate pages until shrinker kicks in.
> >>>> Fair enough but in fact many it would be better to
> >>>> do the reverse: trigger shrinker and then send as many
> >>>> free pages as we can to host.
> >>> I'm not sure I understand this last part.
> >> Oh basically what I am saying is this: one of the reasons to use page
> >> hinting is when host is short on memory. In that case, why don't we use
> >> shrinker to ask kernel drivers to free up memory? Any memory freed could
> >> then be reported to host.
> > Didn't the balloon driver already have a feature like that where it
> > could start shrinking memory if the host was under memory pressure?
> If you are referring to auto-ballooning (I don't think it is merged). It
> has its own set of disadvantages such as it could easily lead to OOM,
> memory corruption and so on.

Right. So what I am saying is: we could have a flag that triggers a
shrinker once before sending memory hints.
Worth considering.

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MST