Re: [Xen-devel] "xm mem-max" problem on PAE xenlinux

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 12 Nov 2005, at 03:01, Nakajima, Jun wrote:

> > > > > kernel BUG at arch/xen/i386/mm/hypervisor.c:381 (xen_create_con
> > > > > tiguous_region)!'
> > > > This may possibly be fixed by changeset 7771 (in staging tree) Patch
> > > > attached.
> > > Actually this causes a hang like:
> > I'd be pretty surprised if that patch caused the hang as it's a pretty
> > clear cut bug fix.
> > Are you sure?
> Okay, I just remember this nasty issue with menuconfig. If you make SMP
> dom0, and go back to UP using memuconfig, the config file gets broken
> (CONFIG_APIC stuff). The UP dom0 does not boot anymore.
>
> Sorry, it worked fine.
I'm surprised as the original bug you reported was actually a misuse of 
'xm mem-max' (which almost certainly should not be exported to users in 
its raw form).
You set the Xen memory limit for that domain to less than its current 
allocation. Then, next time it tried to alloc a pgd, it tried to 
exchange the underlying mfn for one below 4GB. Xen took the old mfn 
away from the domain, but then failed the reallocation because the 
domain already had too much memory!
'xm mem-set' is all that should be exported to users, and the hard 
limit should be under the control of xend.
 -- Keir


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