linux-kernel - Re: [PATCH 1/2] numa: Add simple generic NUMA emulation

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Date: Wed, 26 Jun 2024 09:39:10 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Tvrtko Ursulin <tursulin@...lia.com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kernel-dev@...lia.com,
	Maíra Canal <mcanal@...lia.com>,
	Tvrtko Ursulin <tvrtko.ursulin@...lia.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>
Subject: Re: [PATCH 1/2] numa: Add simple generic NUMA emulation

On Tue, Jun 25, 2024 at 01:58:02PM +0100, Tvrtko Ursulin wrote:
> From: Maíra Canal <mcanal@...lia.com>
> 
> Add some common code for splitting the memory into N emulated NUMA memory
> nodes.
> 
> Individual architecture can then enable selecting this option and use the
> existing numa=fake=<N> kernel argument to enable it.
> 
> Memory is always split into equally sized chunks.
> 
> Signed-off-by: Maíra Canal <mcanal@...lia.com>
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@...lia.com>
> Co-developed-by: Tvrtko Ursulin <tvrtko.ursulin@...lia.com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: “Rafael J. Wysocki" <rafael@...nel.org>
> ---
>  drivers/base/Kconfig          |  7 ++++
>  drivers/base/Makefile         |  1 +
>  drivers/base/arch_numa.c      |  6 ++++
>  drivers/base/numa_emulation.c | 67 +++++++++++++++++++++++++++++++++++
>  drivers/base/numa_emulation.h | 21 +++++++++++
>  5 files changed, 102 insertions(+)
>  create mode 100644 drivers/base/numa_emulation.c
>  create mode 100644 drivers/base/numa_emulation.h
> 
> diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
> index 2b8fd6bb7da0..1f60cd4dd057 100644
> --- a/drivers/base/Kconfig
> +++ b/drivers/base/Kconfig
> @@ -230,6 +230,13 @@ config GENERIC_ARCH_NUMA
>  	  Enable support for generic NUMA implementation. Currently, RISC-V
>  	  and ARM64 use it.
>  
> +config GENERIC_ARCH_NUMA_EMULATION
> +	bool
> +	depends on GENERIC_ARCH_NUMA
> +	help
> +	  Enable NUMA emulation. Note that NUMA emulation will only be used if
> +	  the machine has no NUMA node.
> +
>  config FW_DEVLINK_SYNC_STATE_TIMEOUT
>  	bool "sync_state() behavior defaults to timeout instead of strict"
>  	help
> diff --git a/drivers/base/Makefile b/drivers/base/Makefile
> index 3079bfe53d04..34fcf5bd7370 100644
> --- a/drivers/base/Makefile
> +++ b/drivers/base/Makefile
> @@ -25,6 +25,7 @@ obj-$(CONFIG_DEV_COREDUMP) += devcoredump.o
>  obj-$(CONFIG_GENERIC_MSI_IRQ) += platform-msi.o
>  obj-$(CONFIG_GENERIC_ARCH_TOPOLOGY) += arch_topology.o
>  obj-$(CONFIG_GENERIC_ARCH_NUMA) += arch_numa.o
> +obj-$(CONFIG_GENERIC_ARCH_NUMA_EMULATION) += numa_emulation.o
>  obj-$(CONFIG_ACPI) += physical_location.o
>  
>  obj-y			+= test/
> diff --git a/drivers/base/arch_numa.c b/drivers/base/arch_numa.c
> index 5b59d133b6af..6ad08f681b3c 100644
> --- a/drivers/base/arch_numa.c
> +++ b/drivers/base/arch_numa.c
> @@ -15,6 +15,8 @@
>  
>  #include <asm/sections.h>
>  
> +#include "numa_emulation.h"
> +
>  struct pglist_data *node_data[MAX_NUMNODES] __read_mostly;
>  EXPORT_SYMBOL(node_data);
>  nodemask_t numa_nodes_parsed __initdata;
> @@ -30,6 +32,8 @@ static __init int numa_parse_early_param(char *opt)
>  		return -EINVAL;
>  	if (str_has_prefix(opt, "off"))
>  		numa_off = true;
> +	if (str_has_prefix(opt, "fake="))
> +		return numa_emu_cmdline(opt + 5);

You did not document this at all :(