Re: [Xen-devel] RE: tmem - really default to on?

[Tim Deegan <Tim.Deegan@xxxxxxxxxx>]

At 13:31 +0000 on 09 Feb (1265722267), Keir Fraser wrote:
> On 09/02/2010 13:00, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:
> 
> >> I think the correct approach to all of this is to move system-wide to
> >> allocating memory in 2MB contiguous aligned chunks.  There's no sense in
> >> doing guest allocations any finer-grained than that and there are
> >> noticeable performance wins from all the superpage support that's gone
> >> in recently.  Then little things like needing 16k contiguous areas just
> >> go away.
> > 
> > I have to admit that I can't see how this would work with ballooning,
> > or (if the balloon driver was adjusted to deal with this) with
> > fragmentation inside Dom0 (or any other guest that memory is
> > intended to be removed from). Nor am I sure tmem could be
> > changed to deal with 2Mb chunks instead of 4k ones.
> 
> Balloon driver is the obvious fly in the ointment that I can see, too.

Good point.  That's going to be a problem for HVM ballooning, especially
on EPT/NPT where having superpage allocations makes a big difference.

In the meantime we can fix the shadow code.  Unfortunately I won't be
able to look at it immediately but maybe Christian has a patch.

Tim.

-- 
Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, XenServer Engineering
Citrix Systems UK Ltd.  (Company #02937203, SL9 0BG)

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