RE: [Xen-devel] Re: Xenheap disappearance: (was: xen_phys_start for32b)

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

 -----Original Message-----
> From: Jan Beulich [mailto:jbeulich@xxxxxxxxxx]
> Sent: Friday, January 16, 2009 1:12 AM
> >>> Keir Fraser <keir.fraser@xxxxxxxxxxxxx> 15.01.09 19:51 >>>
> >I think the patch you attached will work just fine for you 
> for now. If your
> >stuff goes in before getting rid of xenheap restrictions on 
> x86/64, then I
> >would take this patch at that time. But I think that's 
> unlikely. Well, I
> >hope it is, unless I stall on my xenheap patch again. :-)
> 
> I'd hope that too, because the patch as is must not go in, as 
> it would break
> other assumptions afaics: At present, the tools balloon out 
> of Dom0 exactly
> the amount needed for creating pv domains (I think there's 
> some slack for
> hvm ones), so the fact that the domain heap now serves 
> xmalloc requires
> that there always be some extra space available in Xen (also to serve
> dynamic allocations). Additionally I think the minimum even a 
> temporary
> patch like this should do is fall back to allocating from the 
> Xen heap when
> the domain heap is unable the supply the requested amount.

Jan --

I'm not sure what you are getting at.  Are you saying that
creating a domain takes (big)MB from domheap, then later
(little)KB from xenheap, and if we combine domheap and xenheap,
the tools might launch a domain when available memory is
greater than (big)MB but smaller than (big)MB+(small)KB,
and that will result in the tools thinking the domain
can launch but it won't?  I suppose that's possible,
but exceedingly unlikely.  And I think Keir's plan will
have the same problem.  Sounds like a tools bug, not a
reason to avoid modernizing Xen memory management.

Dan

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