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

[Olaf Hering <olaf@xxxxxxxxx>]

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
xenpaging=yes/no?

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):

memory=N
xenpaging=yes

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

memory=N
maxmem=N+X
xenpaging=yes


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"?

Olaf

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