Re: Users of ballooning, please come forth!

[Rusty Russell <rusty@rustcorp.com.au>]

Adam Litke <alitke@redhat.com> writes:
> On 20/02/14 14:53 +1030, Rusty Russell wrote:
>>I think we're headed to the same destination here; the variant which I
>>came up with (and suggested to Daniel and Luiz, CC'd) is similar: the
>>guest self-balloons, giving up pages when it can, but the host sets a
>>ceiling.
>>
>>This way, if the host really needs to set a limit, it can: a disobedient
>>guest will start paging.  But generally, a guest should use its
>>judgement to balloon its own pages as it can (below the ceiling).
>
> It sounds similar but it sounds like you are suggesting one limit
> value and I am suggesting two.  Your ceiling value sounds like a soft
> limit on total guest memory (aka minimum balloon size).  This is the
> more important limit of the two I have suggested.  Do you think it's
> also worthwhile to have a maximum balloon size (floor value) to keep
> the allowable balloon size between two points?

It's a little simpler to have a ceiling only.

And if everyone (guests and host) are feeling like they have plenty of
memory, it's probably best sitting in the host.

1) It can quickly go to a guest if necessary.
2) The host could coalesce/shuffle memory.
3) The host could turn off RAM to save power.

Cheers,
Rusty.