linux-kernel - Re: [PATCH v4 4/6] x86/mm: Introduce CONFIG_KEEP

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Date:   Thu, 13 Feb 2020 10:32:27 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     tglx@...utronix.de, mingo@...hat.com,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Michal Hocko <mhocko@...e.com>, vishal.l.verma@...el.com,
        hch@....de, linux-kernel@...r.kernel.org, linux-nvdimm@...ts.01.org
Subject: Re: [PATCH v4 4/6] x86/mm: Introduce CONFIG_KEEP_NUMA


* Dan Williams <dan.j.williams@...el.com> wrote:

> Currently x86 numa_meminfo is marked __initdata in the
> CONFIG_MEMORY_HOTPLUG=n case. In support of a new facility to allow
> drivers to map reserved memory to a 'target_node'
> (phys_to_target_node()), add support for removing the __initdata
> designation for those users. Both memory hotplug and
> phys_to_target_node() users select CONFIG_KEEP_NUMA to tell the arch to
> maintain its physical address to numa mapping infrastructure post init.
> 
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: <x86@...nel.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: David Hildenbrand <david@...hat.com>
> Cc: Michal Hocko <mhocko@...e.com>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> ---
>  arch/x86/mm/numa.c   |    6 +-----
>  include/linux/numa.h |    6 ++++++
>  mm/Kconfig           |    5 +++++
>  3 files changed, 12 insertions(+), 5 deletions(-)

The concept and the x86 portions look sane, just a few minor nits:

> 
> diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c
> index 99f7a68738f0..5289d9d6799a 100644
> --- a/arch/x86/mm/numa.c
> +++ b/arch/x86/mm/numa.c
> @@ -25,11 +25,7 @@ nodemask_t numa_nodes_parsed __initdata;
>  struct pglist_data *node_data[MAX_NUMNODES] __read_mostly;
>  EXPORT_SYMBOL(node_data);
>  
> -static struct numa_meminfo numa_meminfo
> -#ifndef CONFIG_MEMORY_HOTPLUG
> -__initdata
> -#endif
> -;
> +static struct numa_meminfo numa_meminfo __initdata_numa;
>  
>  static int numa_distance_cnt;
>  static u8 *numa_distance;
> diff --git a/include/linux/numa.h b/include/linux/numa.h
> index 20f4e44b186c..c005ed6b807b 100644
> --- a/include/linux/numa.h
> +++ b/include/linux/numa.h
> @@ -13,6 +13,12 @@
>  
>  #define	NUMA_NO_NODE	(-1)
>  
> +#ifdef CONFIG_KEEP_NUMA
> +#define __initdata_numa
> +#else
> +#define __initdata_numa __initdata
> +#endif
> +
>  #ifdef CONFIG_NUMA
>  int numa_map_to_online_node(int node);
>  #else
> diff --git a/mm/Kconfig b/mm/Kconfig
> index ab80933be65f..001f1185eadf 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -139,6 +139,10 @@ config HAVE_FAST_GUP
>  config ARCH_KEEP_MEMBLOCK
>  	bool
>  
> +# Keep arch numa mapping infrastructure post-init.

s/numa/NUMA

Please also capitalize consistently in the rest of the series.

> +config KEEP_NUMA
> +	bool


So most of our recent new NUMA options followed the naming pattern of:

  CONFIG_NUMA_*

Such as CONFIG_NUMA_BALANCING or CONFIG_NUMA_EMU.

So I'd suggesting naming it to CONFIG_NUMA_KEEP, or, a bit more 
descriptively, such as CONFIG_NUMA_KEEP_MAPPING or such?

'Keeping NUMA' is kind of lame - of course we keep NUMA. ;-)

Thanks,

	Ingo