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Re: [Xen-devel] [PATCH] RFC: initial libxl support for xenpaging

On Fri, Feb 17, Ian Campbell wrote:

> On Thu, 2012-02-16 at 07:47 +0000, Olaf Hering wrote:
> > # HG changeset patch
> > # User Olaf Hering <olaf@xxxxxxxxx>
> > # Date 1329378376 -3600
> > # Node ID d368cf36d66c1e8df60bd0a4868c171b6a929edc
> > # Parent  bf0a7c205687857a8f8d3bd3841654ed61828193
> > RFC: initial libxl support for xenpaging
> > 
> > After the previous discussion about integration of xenpaging into xl/libxl 
> > it
> > was not clear to me wether my proposal as a whole or only parts of it were
> > rejected. So here is my current understanding of the comments I received.
> > 
> > Add initial support to libxl to start xenpaging for a HVM guest.
> > These are the considerations:
> > - a knob in domU.cfg is needed to start xenpaging
> > - xenpaging needs a target in KiB in "memory/target-tot_pages"
> >  -> the knob should be the target value in MiB: mem_target_paging=NUM
> >     if the value is 0, xenpaging is not started
> Wasn't the plan that the knob exported by xl should be a boolean and
> that libxl should have the full value in its API, or am I
> misremembering?

That was not clear to me, thats why I'm asking again.

> IOW at the libxl layer we have the full semantics available to callers
> but at the xl layer we only expose one "target memory" value to users
> which we expect the guest to use ballooning to reach but which we
> "enforce" with paging if they don't comply.

So if I understand that right there should be a new boolean, like

In the .cfg it can be either like this, which appears to mean the pager
is started but has no target (or target is N itself):


Or it could be like this (in which case the pager currently cant start
due to lack of PoD support):


In both cases "xl mem-set" will adjust both ballooning and paging values?
Should there be xl commands to adjust just ballooning and/or paging?

Regarding the tuning knobs, right now I can only think of the policy mru
size and the number of evicts before checking for new events.
So you propose to have something like "xl xenpaging domid knob value"?


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