On Fri, May 09, 2014 at 02:54:15PM -0300, Eduardo Habkost wrote:
> On Fri, May 09, 2014 at 04:29:49PM +0800, Hu Tao wrote:
> > On Thu, May 08, 2014 at 04:51:56PM +0200, Paolo Bonzini wrote:
> > > Il 06/05/2014 11:27, Hu Tao ha scritto:
> > > > This series includes work on QOMifying the memory backends.
> > > > the idea is to delegate all properties of the memory backend to
> > > > a new QOM class hierarchy, in which the concrete classes
> > > > are hostmem-ram and hostmem-file. The backend is passed to the
> > > > machine via "-numa node,memdev=foo" where "foo" is the id of the
> > > > backend object.
> > >
> > > Hello,
> > >
> > > I noticed now that if you have the host-nodes property set Linux
> > > requires you to set a policy other than "default" too. If you don't,
> > > the mbind system call fails.
> > >
> > > What about squashing something like this?
> > >
> > > Paolo
> > >
> > > diff --git a/backends/hostmem.c b/backends/hostmem.c
> > > index d3f8476..a0a3111 100644
> > > --- a/backends/hostmem.c
> > > +++ b/backends/hostmem.c
> > > @@ -299,12 +299,23 @@ host_memory_backend_memory_init(UserCreatable *uc,
> > > Error **errp)
> > >
> > > #ifdef CONFIG_NUMA
> > > unsigned long maxnode = find_last_bit(backend->host_nodes,
> > > MAX_NODES);
> > > + unsigned policy = backend->policy;
> > > +
> > > + /* Linux does not accept MPOL_DEFAULT with nonzero bitmap, but
> > > + * "-object memory-ram,size=128M,hostnodes=0,policy=bind" is a
> > > + * bit of a mouthful. So if the host_nodes bitmap is nonzero,
> > > + * pick the BIND policy.
>
> Are we sure MPOL_BIND is a better default than MPOL_INTERLEAVE or
> MPOL_PREFERRED?
>
>
> > > + */
> > > + if (find_first_bit(backend->host_nodes, MAX_NODES) != MAX_NODES &&
> > > + policy == MPOL_DEFAULT) {
> > > + policy = MPOL_BIND;
> > > + }
> >
> > This only changes the policy applied to memory. But info memdev still
> > shows the policy as 'default'(the 'default' here is interpreted as
> > 'MPOL_DEFAULT', right?).
>
> That's what I would expect. With this, the user can't even check what is
> the actual result of the command-line they used.
>
> >
> > So this is related to how we deal with cases where 'policy' is not
> > specified in qemu:
> >
> > 1. if possible, the policy is set to MPOL_DEFAULT.
> > 2. if host-nodes is not zero, the policy is set to MPOL_BIND.(set
> > backend->policy too, other than just apply it)
>
> You mean, only if policy is omitted, right? host-nodes may be set if the
> user wants policy=preferred or policy=interleave, too.
Yes.
>
> >
> > Opinions?
>
> I find it confusing that an explicit policy=default option won't always
> mean MPOL_DEFAULT.
>
> So, what about:
>
> * If policy=default is set, it is always going to be MPOL_DEFAULT.
> * If policy=bind is set, it is always going to be MPOL_BIND.
> * if policy=preferred is set, it is always going to be MPOL_PREFERRED.
> * If policy is omitted, it will be be MPOL_DEFAULT is host-nodes is
> unset, and MPOL_BIND if host_nodes is set.
Agreed.
Regards,
Hu Tao
