RE: [PATCH 1/3] arm64/numa: set numa_off to false when numa node is fake

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

Hi David, thanks for the comments. See my answer please:

> -----Original Message-----
> From: David Hildenbrand <david@redhat.com>
> Sent: Monday, July 6, 2020 4:03 PM
> To: Justin He <Justin.He@arm.com>; Catalin Marinas
> <Catalin.Marinas@arm.com>; Will Deacon <will@kernel.org>
> Cc: 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; Kaly Xin <Kaly.Xin@arm.com>
> Subject: Re: [PATCH 1/3] arm64/numa: set numa_off to false when numa node
> is fake
> 
> On 06.07.20 03:19, Jia He wrote:
> > Previously, numa_off is set to true unconditionally in dummy_numa_init(),
> > even if there is a fake numa node.
> >
> > But acpi will translate node id to NUMA_NO_NODE(-1) in
> acpi_map_pxm_to_node()
> > because it regards numa_off as turning off the numa node.
> >
> > 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 setting numa_off to false.
> >
> > Signed-off-by: Jia He <justin.he@arm.com>
> > ---
> >  arch/arm64/mm/numa.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/mm/numa.c b/arch/arm64/mm/numa.c
> > index aafcee3e3f7e..7689986020d9 100644
> > --- a/arch/arm64/mm/numa.c
> > +++ b/arch/arm64/mm/numa.c
> > @@ -440,7 +440,8 @@ static int __init dummy_numa_init(void)
> >  		return ret;
> >  	}
> >
> > -	numa_off = true;
> > +	/* force numa_off to be false since we have a fake numa node here
> */
> > +	numa_off = false;
> >  	return 0;
> >  }
> >
> >
> 
> What would happen if we use something like this in drivers/dax/kmem.c
> instead:
> 
> numa_node = dev_dax->target_node;
> if (numa_node == NUMA_NO_NODE)
> 	numa_node = memory_add_physaddr_to_nid(kmem_start);
> 
> and eventually dropping the pr_warn in
> arm64/memory_add_physaddr_to_nid() ? Would that work?

Yes, it works. I sent a similar patch [1] before. But seems pmem
maintainer didn't satisfy it. Do you think memory_add_physaddr_to_nid()
is better than numa_mem_id()? 

[1] https://lkml.org/lkml/2019/8/16/367

--
Cheers,
Justin (Jia He)