RE: [RFC PATCH v2 2/3] device-dax: use fallback nid when numa_node is invalid

[Justin He <Justin.He@arm.com>]

Hi David

> -----Original Message-----
> From: David Hildenbrand <david@redhat.com>
> Sent: Tuesday, July 7, 2020 7:34 PM
> To: Justin He <Justin.He@arm.com>; Catalin Marinas
> <Catalin.Marinas@arm.com>; Will Deacon <will@kernel.org>; Dan Williams
> <dan.j.williams@intel.com>; Vishal Verma <vishal.l.verma@intel.com>; Dave
> Jiang <dave.jiang@intel.com>
> Cc: Michal Hocko <mhocko@suse.com>; Andrew Morton <akpm@linux-
> foundation.org>; Mike Rapoport <rppt@linux.ibm.com>; Baoquan He
> <bhe@redhat.com>; Chuhong Yuan <hslester96@gmail.com>; linux-arm-
> kernel@lists.infradead.org; linux-kernel@vger.kernel.org; linux-
> mm@kvack.org; linux-nvdimm@lists.01.org; Kaly Xin <Kaly.Xin@arm.com>
> Subject: Re: [RFC PATCH v2 2/3] device-dax: use fallback nid when
> numa_node is invalid
> 
> On 07.07.20 07:59, Jia He wrote:
> > Previously, numa_off is set unconditionally at the end of
> dummy_numa_init(),
> > even with a fake numa node. Then ACPI detects node id as NUMA_NO_NODE(-1)
> in
> > acpi_map_pxm_to_node() because it regards numa_off as turning off the
> numa
> > node. Hence dev_dax->target_node is NUMA_NO_NODE on arm64 with fake numa.
> >
> > Without this patch, pmem can't be probed as a RAM device on arm64 if
> SRAT table
> > isn't present:
> > $ndctl create-namespace -fe namespace0.0 --mode=devdax --map=dev -s 1g -
> a 64K
> > kmem dax0.0: rejecting DAX region [mem 0x240400000-0x2bfffffff] with
> invalid node: -1
> > kmem: probe of dax0.0 failed with error -22
> >
> > This fixes it by using fallback memory_add_physaddr_to_nid() as nid.
> >
> > Suggested-by: David Hildenbrand <david@redhat.com>
> > Signed-off-by: Jia He <justin.he@arm.com>
> > ---
> > I noticed that on powerpc memory_add_physaddr_to_nid is not exported for
> module
> > driver. Set it to RFC due to this concern.
> >
> >  drivers/dax/kmem.c | 22 ++++++++++++++--------
> >  1 file changed, 14 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
> > index 275aa5f87399..68e693ca6d59 100644
> > --- a/drivers/dax/kmem.c
> > +++ b/drivers/dax/kmem.c
> > @@ -28,20 +28,22 @@ int dev_dax_kmem_probe(struct device *dev)
> >  	resource_size_t kmem_end;
> >  	struct resource *new_res;
> >  	const char *new_res_name;
> > -	int numa_node;
> > +	int numa_node, new_node;
> >  	int rc;
> >
> >  	/*
> >  	 * Ensure good NUMA information for the persistent memory.
> > -	 * Without this check, there is a risk that slow memory
> > -	 * could be mixed in a node with faster memory, causing
> > -	 * unavoidable performance issues.
> > +	 * Without this check, there is a risk but not fatal that slow
> > +	 * memory could be mixed in a node with faster memory, causing
> > +	 * unavoidable performance issues. Furthermore, fallback node
> > +	 * id can be used when numa_node is invalid.
> >  	 */
> >  	numa_node = dev_dax->target_node;
> >  	if (numa_node < 0) {
> > -		dev_warn(dev, "rejecting DAX region %pR with invalid
> node: %d\n",
> > -			 res, numa_node);
> > -		return -EINVAL;
> > +		new_node = memory_add_physaddr_to_nid(kmem_start);
> > +		dev_info(dev, "changing nid from %d to %d for DAX
> region %pR\n",
> > +			numa_node, new_node, res);
> > +		numa_node = new_node;
> 
> Now, the warning does not really make sense. We have NUMA_NO_NODE (< 0),
> that is not a change in the nid, but a selection of a nid. Printing
> NUMA_NO_NODE does not make too much sense. I suggest just getting rid of
> new_node and turning the dev_info() into something like
> 
> dev_info(dev, "using nid %d for DAX region with undefined nid %pR\n",
>          numa_node, res);
> 
Okay, I will update it as your sugguestion. Thanks

--
Cheers,
Justin (Jia He)


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