Re: pkgsrc: patch-ba

[Christoph Egger <Christoph_Egger%gmx.de@localhost>]

On Thursday 29 November 2007 14:08:20 Manuel Bouyer wrote:
> On Thu, Nov 29, 2007 at 01:48:56PM +0100, Christoph Egger wrote:
> > On Wednesday 28 November 2007 15:58:10 Manuel Bouyer wrote:
> > > Hi,
> > >
> > > On Wed, Nov 28, 2007 at 02:49:17PM +0100, Christoph Egger wrote:
> > > > Hi Manuel!
> > > >
> > > > I just noticed your xenkernel3 package update:
> > > >
> > > > RCS file: /cvsroot/pkgsrc/sysutils/xenkernel3/patches/patch-ba,v
> > > > Working file: patch-ba
> > > > head: 1.2
> > > > branch:
> > > > locks: strict
> > > > access list:
> > > > symbolic names:
> > > >         pkgsrc-2007Q3: 1.1.0.2
> > > >         pkgsrc-2007Q3-base: 1.1
> > > > keyword substitution: kv
> > > > total revisions: 2;     selected revisions: 2
> > > > description:
> > > > ----------------------------
> > > > revision 1.2
> > > > date: 2007/11/26 19:35:25;  author: bouyer;  state: Exp;  lines: +12
> > > > -3 Properly initialize physaddr_bitsize for native 64bit dom0. Makes
> > > > NetBSD/xenamd64 boot on systems with more than 4Gb RAM.
> > > > Bump pkgrevision.
> > > >
> > > >
> > > > Looking at the diff, you unconditionally initialize
> > > > d->arch.physaddr_bitsize. Are you sure this is correct for 32bit /
> > > > 32bit pae Dom0 ?
> > > >
> > > > Further, for 64bit xen-kernels this is already initialized some lines
> > > > further below and overrides your hardcoded value. So I don't
> > > > understand in which way your patch fixes the boot problem with more
> > > > than 4GB RAM.
> > > >
> > > > Can you explain this, please?
> >
> > Thank you for the explanation.
> >
> > > I tracked down my problem with more than 4GB RAM to
> > > d->arch.physaddr_bitsize being 0 in domain_clamp_alloc_bitsize(). This
> > > cause all attemps to XENMEM_increase_reservation with bits > 0 to fail
> >
> > More precisely, __alloc_domheap_pages() returns NULL. This impacts
> > Xen heap allocation in general and on featurewise this impacts ballooning
> > and NUMA support in Xen.
> >
> > It makes no difference if the Linux Dom0 has 1GB or 7GB.
> > I don't understand how this can show no effect on Linux Dom0.
>
> I don't know how linux deals with devices that can't acces memory above
> 4GB. This is where NetBSD failed, when allocating DMA-safe memory.

I got an explanation from XenSource:

-----------------------------------------------------
Yes, that's pretty broken. It works for Linux because Linux allocates its
lowmem I/o pages (e.g., swiotlb) using the XENMEM_exchange command, and that
allocates the new memory anonymously in the first instance. This defeats the
bitsize clamp check (which is okay just now because our truncation of the
phsyical memory map to 166GB is sufficient to ensure that compat domUs can
address all memory).
-----------------------------------------------------

There are actually people having machines with 192GB RAM and reported a bug in 
Xen that physical memory is truncated to 166GB.

I would like to have an Opteron-Cluster to reproduce this problem ;-)

> > > So, if I got it right, my patch should cause physaddr_bitsize to be 64
> > > by default, and set to some other value later if needed; and if "not
> > > needed" 64 is the right value. If the hypervisor is not 64bits,
> > > physaddr_bitsize isn't used at all anyway.
> >
> > That's right.
> > I submitted the patch.
>
> Thanks !

You're welcome.