Re: [PATCH] Revert "xen-hvm: increase maxmem before calling xc_domain_populate_physmap"

[Ian Campbell <ian.campbell@citrix.com>]

On Tue, 2015-06-16 at 16:51 +0100, Stefano Stabellini wrote:
> > I think reverting this change in QEMU and relevant changes in libxl
> > would be the most viable solution to solve this for this release.
> 
> Reverting this patch doesn't really solve the problem: instead of
> breaking on migration when the VM has more than 3 emulated NICs, the VM
> simply refuses to start in that case. I guess it can be considered a
> small improvement but certainly not a fix.
> 
> Given that the migration issue only happens in an "unusual corner case",
> are we really in a hurry to revert this commit and go back to the
> failure to start, even before we actually figure out what the proper fix
> is?

I don't care about migration (particularly). I care about the brokeness
in libxl which has been introduced while trying to cope with this QEMU
change.

We should revert now so that we can revert those libxl changes too and
get ourselves to a known state which doesn't have races in the memory
setting code.

It will also be much easier to move forward from a state where QEMU is
not messing with the memory limit for a domain in an uncoordinated way
and only libxl is doing so. Every QEMU release which we delay this
revert will just make it harder to find a path safe forward towards
whatever design we finally settle on.

Ian.