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 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?

2)

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