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Date:   Mon, 7 Oct 2019 16:55:05 +0200
From:   Ingo Molnar <mingo@kernel.org>
To:     Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc:     linux-mm@kvack.org, linux-acpi@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        x86@kernel.org, Keith Busch <keith.busch@intel.com>,
        jglisse@redhat.com, "Rafael J . Wysocki" <rjw@rjwysocki.net>,
        linuxarm@huawei.com, Andrew Morton <akpm@linux-foundation.org>,
        Dan Williams <dan.j.williams@intel.com>
Subject: Re: [PATCH V5 3/4] x86: Support Generic Initiator only proximity
 domains
Message-ID: <20191007145505.GB88143@gmail.com>
References: <20191004114330.104746-1-Jonathan.Cameron@huawei.com>
 <20191004114330.104746-4-Jonathan.Cameron@huawei.com>
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* Jonathan Cameron <Jonathan.Cameron@huawei.com> wrote:

> Done in a somewhat different fashion to arm64.
> Here the infrastructure for memoryless domains was already
> in place.  That infrastruture applies just as well to
> domains that also don't have a CPU, hence it works for
> Generic Initiator Domains.
> 
> In common with memoryless domains we only register GI domains
> if the proximity node is not online. If a domain is already
> a memory containing domain, or a memoryless domain there is
> nothing to do just because it also contains a Generic Initiator.
> 
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> ---
>  arch/x86/include/asm/numa.h |  2 ++
>  arch/x86/kernel/setup.c     |  1 +
>  arch/x86/mm/numa.c          | 14 ++++++++++++++
>  3 files changed, 17 insertions(+)
> 
> diff --git a/arch/x86/include/asm/numa.h b/arch/x86/include/asm/numa.h
> index bbfde3d2662f..f631467272a3 100644
> --- a/arch/x86/include/asm/numa.h
> +++ b/arch/x86/include/asm/numa.h
> @@ -62,12 +62,14 @@ extern void numa_clear_node(int cpu);
>  extern void __init init_cpu_to_node(void);
>  extern void numa_add_cpu(int cpu);
>  extern void numa_remove_cpu(int cpu);
> +extern void init_gi_nodes(void);
>  #else	/* CONFIG_NUMA */
>  static inline void numa_set_node(int cpu, int node)	{ }
>  static inline void numa_clear_node(int cpu)		{ }
>  static inline void init_cpu_to_node(void)		{ }
>  static inline void numa_add_cpu(int cpu)		{ }
>  static inline void numa_remove_cpu(int cpu)		{ }
> +static inline void init_gi_nodes(void)			{ }
>  #endif	/* CONFIG_NUMA */
>  
>  #ifdef CONFIG_DEBUG_PER_CPU_MAPS
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index cfb533d42371..b6c977907ea5 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -1264,6 +1264,7 @@ void __init setup_arch(char **cmdline_p)
>  	prefill_possible_map();
>  
>  	init_cpu_to_node();
> +	init_gi_nodes();
>  
>  	io_apic_init_mappings();
>  
> diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c
> index 4123100e0eaf..50bf724a425e 100644
> --- a/arch/x86/mm/numa.c
> +++ b/arch/x86/mm/numa.c
> @@ -733,6 +733,20 @@ static void __init init_memory_less_node(int nid)
>  	 */
>  }
>  
> +/*
> + * Generic Initiator Nodes may have neither CPU nor Memory.
> + * At this stage if either of the others were present we would
> + * already be online.
> + */
> +void __init init_gi_nodes(void)
> +{
> +	int nid;
> +
> +	for_each_node_state(nid, N_GENERIC_INITIATOR)
> +		if (!node_online(nid))
> +			init_memory_less_node(nid);
> +}

Nit: missing curly braces.

How do these work in practice, will a system that only had nodes 0-1 
today grow a third node '2' that won't have any CPUs on memory on them?

Thanks,

	Ingo