Re: [PATCH 1/2] arm64: avoid alloc memory on offline node

[Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>]

On Tue, Jun 19, 2018 at 01:52:16PM +0100, Punit Agrawal wrote:
> Michal Hocko <mhocko@kernel.org> writes:
> 
> > On Tue 19-06-18 20:03:07, Xie XiuQi wrote:
> > [...]
> >> I tested on a arm board with 128 cores 4 numa nodes, but I set CONFIG_NR_CPUS=72.
> >> Then node 3 is not be created, because node 3 has no memory, and no cpu.
> >> But some pci device may related to node 3, which be set in ACPI table.
> >
> > Could you double check that zonelists for node 3 are generated
> > correctly?
> 
> The cpus in node 3 aren't onlined and there's no memory attached - I
> suspect that no zonelists are built for this node.
> 
> We skip creating a node, if the number of SRAT entries parsed exceeds
> NR_CPUS[0]. This in turn prevents onlining the numa node and so no
> zonelists will be created for it.
> 
> I think the problem will go away if the cpus are restricted via the
> kernel command line by setting nr_cpus.
> 
> Xie, can you try the below patch on top of the one enabling memoryless
> nodes? I'm not sure this is the right solution but at least it'll
> confirm the problem.

This issue looks familiar (or at least related):

git log d3bd058826aa

The reason why the NR_CPUS guard is there is to avoid overflowing
the early_node_cpu_hwid array. IA64 does something different in
that respect compared to x86, we have to have a look into this.

Regardless, AFAICS the proximity domains to nodes mappings should not
depend on CONFIG_NR_CPUS, it seems that there is something wrong in that
in ARM64 ACPI SRAT parsing.

Lorenzo

> 
> Thanks,
> Punit
> 
> [0] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/kernel/acpi_numa.c?h=v4.18-rc1#n73
> 
> -- >8 --
> diff --git a/arch/arm64/kernel/acpi_numa.c b/arch/arm64/kernel/acpi_numa.c
> index d190a7b231bf..fea0f7164f1a 100644
> --- a/arch/arm64/kernel/acpi_numa.c
> +++ b/arch/arm64/kernel/acpi_numa.c
> @@ -70,11 +70,9 @@ void __init acpi_numa_gicc_affinity_init(struct acpi_srat_gicc_affinity *pa)
>         if (!(pa->flags & ACPI_SRAT_GICC_ENABLED))
>                 return;
> 
> -   if (cpus_in_srat >= NR_CPUS) {
> + if (cpus_in_srat >= NR_CPUS)
>                 pr_warn_once("SRAT: cpu_to_node_map[%d] is too small, may not be able to use all cpus\n",
>                              NR_CPUS);
> -           return;
> -   }
> 
>         pxm = pa->proximity_domain;
>         node = acpi_map_pxm_to_node(pxm);