Re: [PATCH v2] hostmem: Honor multiple preferred nodes if possible

[David Hildenbrand]

On 19.12.22 10:57, Michal Prívozník wrote:
> On 12/19/22 10:55, David Hildenbrand wrote:
> > On 16.12.22 14:47, Michal Prívozník wrote:
> > > On 12/16/22 14:41, David Hildenbrand wrote:
> > > > On 15.12.22 10:55, Michal Privoznik wrote:
> > > > > If a memory-backend is configured with mode
> > > > > HOST_MEM_POLICY_PREFERRED then
> > > > > host_memory_backend_memory_complete() calls mbind() as:
> > > > >
> > > > >      mbind(..., MPOL_PREFERRED, nodemask, ...);
> > > > >
> > > > > Here, 'nodemask' is a bitmap of host NUMA nodes and corresponds
> > > > > to the .host-nodes attribute. Therefore, there can be multiple
> > > > > nodes specified. However, the documentation to MPOL_PREFERRED
> > > > > says:
> > > > >
> > > > >      MPOL_PREFERRED
> > > > >        This mode sets the preferred node for allocation. ...
> > > > >        If nodemask specifies more than one node ID, the first node
> > > > >        in the mask will be selected as the preferred node.
> > > > >
> > > > > Therefore, only the first node is honored and the rest is
> > > > > silently ignored. Well, with recent changes to the kernel and
> > > > > numactl we can do better.
> > > > >
> > > > > The Linux kernel added in v5.15 via commit cfcaa66f8032
> > > > > ("mm/hugetlb: add support for mempolicy MPOL_PREFERRED_MANY")
> > > > > support for MPOL_PREFERRED_MANY, which accepts multiple preferred
> > > > > NUMA nodes instead.
> > > > >
> > > > > Then, numa_has_preferred_many() API was introduced to numactl
> > > > > (v2.0.15~26) allowing applications to query kernel support.
> > > > >
> > > > > Wiring this all together, we can pass MPOL_PREFERRED_MANY to the
> > > > > mbind() call instead and stop ignoring multiple nodes, silently.
> > > > >
> > > > > Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
> > > > > ---
> > > >
> > > > [...]
> > > >
> > > > > +#ifdef HAVE_NUMA_SET_PREFERRED_MANY
> >
> > That should be HAVE_NUMA_HAS_PREFERRED_MANY, right?
>
> Oops, yes. Do you want me to send v3?

I'll fixup. I just queued the fixed-up patch to

https://github.com/davidhildenbrand/qemu.git mem-next

Please double-check. Thanks!

--
Thanks,

David / dhildenb