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

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Date:   Tue, 19 Jun 2018 13:52:16 +0100
From:   Punit Agrawal <punit.agrawal@....com>
To:     Michal Hocko <mhocko@...nel.org>, Xie XiuQi <xiexiuqi@...wei.com>
Cc:     Hanjun Guo <guohanjun@...wei.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        <tnowicki@...iumnetworks.com>, <linux-pci@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Will Deacon <will.deacon@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        <linux-mm@...ck.org>, <wanghuiqiang@...wei.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        zhongjiang <zhongjiang@...wei.com>,
        linux-arm <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/2] arm64: avoid alloc memory on offline node

Michal Hocko <mhocko@...nel.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.

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);