Re: [Qemu-devel] [PATCH V13 10/13] NUMA: add qmp command set-mem-policy to set memory policy for NUMA node

[Marcelo Tosatti <mtosatti@redhat.com>]

On Wed, Oct 02, 2013 at 11:13:29PM -0300, Marcelo Tosatti wrote:
> On Tue, Sep 17, 2013 at 11:16:22AM +0800, Wanlong Gao wrote:
> > This QMP command allows user set guest node's memory policy
> > through the QMP protocol. The qmp-shell command is like:
> >     set-mem-policy nodeid=0 policy=membind relative=true host-nodes=0-1
> > 
> > Reviewed-by: Luiz Capitulino <lcapitulino@redhat.com>
> > Signed-off-by: Wanlong Gao <gaowanlong@cn.fujitsu.com>
> 
> Wanlong Gao,
> 
> 1)
> 
> Exposing mbind via QMP/HMP on a live guest is interesting because,
> see mbind manpage: 
> 
> "By  default,  mbind() only has an effect for new allocations;
> if the pages inside the range have been already touched before
> setting the policy, then the policy has no effect.  This  default
> behavior  may  be  overridden  by  the  MPOL_MF_MOVE  and
> MPOL_MF_MOVE_ALL flags described below."
> 
> This means that executing set-mem-policy on a live guest is
> unpredictable: it depends on which pages have been faulted in already.
> 
> Should the command be restricted to offline guests?

In fact, unless there is a missing point, it should be removed: to solve
the device assignment case (memory pinning), mbind must be executed before
the memory regions are registered.

> 2)
> 
> Have you tested the patchset with hugetlbfs (-mem-path) backing ?
>