linux-kernel - Re: [RFC Patch V1 29/30] mm, x86: Enable memoryless node support to better support CPU/memory hotplug

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Date:	Thu, 24 Jul 2014 16:26:05 -0700
From:	Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>
To:	Jiang Liu <jiang.liu@...ux.intel.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	David Rientjes <rientjes@...gle.com>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	Toshi Kani <toshi.kani@...com>,
	Igor Mammedov <imammedo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Tang Chen <tangchen@...fujitsu.com>,
	Zhang Yanfei <zhangyanfei@...fujitsu.com>,
	Lans Zhang <jia.zhang@...driver.com>,
	Tony Luck <tony.luck@...el.com>, linux-mm@...ck.org,
	linux-hotplug@...r.kernel.org, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...nel.org>, linux-pm@...r.kernel.org
Subject: Re: [RFC Patch V1 29/30] mm, x86: Enable memoryless node support to
 better support CPU/memory hotplug

On 11.07.2014 [15:37:46 +0800], Jiang Liu wrote:
> With current implementation, all CPUs within a NUMA node will be
> assocaited with another NUMA node if the node has no memory installed.

<snip>

> ---
>  arch/x86/Kconfig            |    3 +++
>  arch/x86/kernel/acpi/boot.c |    5 ++++-
>  arch/x86/kernel/smpboot.c   |    2 ++
>  arch/x86/mm/numa.c          |   42 +++++++++++++++++++++++++++++++++++-------
>  4 files changed, 44 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index a8f749ef0fdc..f35b25b88625 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1887,6 +1887,9 @@ config USE_PERCPU_NUMA_NODE_ID
>  	def_bool y
>  	depends on NUMA
> 
> +config HAVE_MEMORYLESS_NODES
> +	def_bool NUMA
> +
>  config ARCH_ENABLE_SPLIT_PMD_PTLOCK
>  	def_bool y
>  	depends on X86_64 || X86_PAE
> diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
> index 86281ffb96d6..3b5641703a49 100644
> --- a/arch/x86/kernel/acpi/boot.c
> +++ b/arch/x86/kernel/acpi/boot.c
> @@ -612,6 +612,8 @@ static void acpi_map_cpu2node(acpi_handle handle, int cpu, int physid)
>  	if (nid != -1) {
>  		set_apicid_to_node(physid, nid);
>  		numa_set_node(cpu, nid);
> +		if (node_online(nid))
> +			set_cpu_numa_mem(cpu, local_memory_node(nid));

How common is it for this method to be called for a CPU on an offline
node? Aren't you fixing this in the next patch (so maybe the order
should be changed?)?

>  	}
>  #endif
>  }
> @@ -644,9 +646,10 @@ int acpi_unmap_lsapic(int cpu)
>  {
>  #ifdef CONFIG_ACPI_NUMA
>  	set_apicid_to_node(per_cpu(x86_cpu_to_apicid, cpu), NUMA_NO_NODE);
> +	set_cpu_numa_mem(cpu, NUMA_NO_NODE);
>  #endif
> 
> -	per_cpu(x86_cpu_to_apicid, cpu) = -1;
> +	per_cpu(x86_cpu_to_apicid, cpu) = BAD_APICID;

I think this is an unrelated change?

>  	set_cpu_present(cpu, false);
>  	num_processors--;
> 
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index 5492798930ef..4a5437989ffe 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -162,6 +162,8 @@ static void smp_callin(void)
>  		      __func__, cpuid);
>  	}
> 
> +	set_numa_mem(local_memory_node(cpu_to_node(cpuid)));
> +

Note that you might hit the same issue I reported on powerpc, if
smp_callin() is part of smp_init(). The waitqueue initialization code
depends on cpu_to_node() [and eventually cpu_to_mem()] to be initialized
quite early.

Thanks,
Nish

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