Re: [PATCH] libxl: remove LIBXL_MAXMEM_CONSTANT

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

On Thu, 2015-02-26 at 12:19 +0000, Stefano Stabellini wrote:
> On Wed, 25 Feb 2015, Don Slutz wrote:
> > On 02/25/15 10:07, Stefano Stabellini wrote:
> > > LIBXL_MAXMEM_CONSTANT is used to increase the maxmem setting for a
> > > domain by a constant amount. As it is not clear the reason why we should
> > > be doing this, remove the constant.
> > > 
> > > Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> > > CC: mlatimer@suse.com
> > > CC: ian.campbell@citrix.com
> > > ---
> > 
> > I think that some sort of link to commit 901230f in QEMU:
> > 
> > ----
> > commit 901230fd8ce053cc21312a2eca2f3ba9f1d103f2
> > Author: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> > Date:   Wed Dec 3 08:15:19 2014 -0500
> > 
> >     xen-hvm: increase maxmem before calling xc_domain_populate_physmap
> > 
> >     Increase maxmem before calling xc_domain_populate_physmap_exact to
> >     avoid the risk of running out of guest memory. This way we can also
> >     avoid complex memory calculations in libxl at domain construction
> >     time.
> > 
> >     This patch fixes an abort() when assigning more than 4 NICs to a VM.
> > 
> >     upstream-commit-id: c1d322e6048796296555dd36fdd102d7fa2f50bf
> > 
> >     Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> >     Signed-off-by: Don Slutz <dslutz@verizon.com>
> > ----
> > 
> > Because after this patch and without a "correct" QEMU, the number of
> > e1000 NICs a guest can use is less then 4.
> 
> That is true, in fact is not even a single emulated NIC in my tests.
> I can either ask for a backport of
> c1d322e6048796296555dd36fdd102d7fa2f50bf "xen-hvm: increase maxmem
> before calling xc_domain_populate_physmap" to all QEMU stable branches,

It can't hurt to ask, I think?

> or we just have to keep this around for now and maybe just add a comment
> on why it is needed.

(assuming they say no to the backports)

Could we at least make it x86/HVM specific?

Ian.