linux-kernel - Re: [PATCH v1] virtio_pmem: populate numa information

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Date:   Fri, 21 Oct 2022 10:08:31 -0700
From:   Michael Sammler <sammler@...gle.com>
To:     Pankaj Gupta <pankaj.gupta.linux@...il.com>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        nvdimm@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] virtio_pmem: populate numa information

Hi Pankaj,
Thank you for looking at the patch.

>
> > Compute the numa information for a virtio_pmem device from the memory
> > range of the device. Previously, the target_node was always 0 since
> > the ndr_desc.target_node field was never explicitly set. The code for
> > computing the numa node is taken from cxl_pmem_region_probe in
> > drivers/cxl/pmem.c.
> >
> > Signed-off-by: Michael Sammler <sammler@...gle.com>
> > ---
> >  drivers/nvdimm/virtio_pmem.c | 11 +++++++++--
> >  1 file changed, 9 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/nvdimm/virtio_pmem.c b/drivers/nvdimm/virtio_pmem.c
> > index 20da455d2ef6..a92eb172f0e7 100644
> > --- a/drivers/nvdimm/virtio_pmem.c
> > +++ b/drivers/nvdimm/virtio_pmem.c
> > @@ -32,7 +32,6 @@ static int init_vq(struct virtio_pmem *vpmem)
> >  static int virtio_pmem_probe(struct virtio_device *vdev)
> >  {
> >         struct nd_region_desc ndr_desc = {};
> > -       int nid = dev_to_node(&vdev->dev);
> >         struct nd_region *nd_region;
> >         struct virtio_pmem *vpmem;
> >         struct resource res;
> > @@ -79,7 +78,15 @@ static int virtio_pmem_probe(struct virtio_device *vdev)
> >         dev_set_drvdata(&vdev->dev, vpmem->nvdimm_bus);
> >
> >         ndr_desc.res = &res;
> > -       ndr_desc.numa_node = nid;
> > +
> > +       ndr_desc.numa_node = memory_add_physaddr_to_nid(res.start);
> > +       ndr_desc.target_node = phys_to_target_node(res.start);
> > +       if (ndr_desc.target_node == NUMA_NO_NODE) {
> > +               ndr_desc.target_node = ndr_desc.numa_node;
> > +               dev_dbg(&vdev->dev, "changing target node from %d to %d",
> > +                       NUMA_NO_NODE, ndr_desc.target_node);
> > +       }
>
> As this memory later gets hotplugged using "devm_memremap_pages". I don't
> see if 'target_node' is used for fsdax case?
>
> It seems to me "target_node" is used mainly for volatile range above
> persistent memory ( e.g kmem driver?).
>
I am not sure if 'target_node' is used in the fsdax case, but it is
indeed used by the devdax/kmem driver when hotplugging the memory (see
'dev_dax_kmem_probe' and '__dax_pmem_probe').

Best,
Michael
> Thanks,
> Pankaj
>
> > +
> >         ndr_desc.flush = async_pmem_flush;
> >         ndr_desc.provider_data = vdev;
> >         set_bit(ND_REGION_PAGEMAP, &ndr_desc.flags);
> > --