linux-kernel - Re: [PATCH v1 0/2] support NUMA emulation for genertic arch

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Date: Wed, 21 Feb 2024 16:51:57 +0100
From: Pierre Gondois <pierre.gondois@....com>
To: Mike Rapoport <rppt@...nel.org>,
 Rongwei Wang <rongwei.wang@...ux.alibaba.com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, akpm@...ux-foundation.org, gregkh@...uxfoundation.org,
 rafael@...nel.org, mingo@...hat.com, dave.hansen@...ux.intel.com,
 luto@...nel.org, teng.ma@...ux.alibaba.com
Subject: Re: [PATCH v1 0/2] support NUMA emulation for genertic arch



On 2/21/24 07:12, Mike Rapoport wrote:
> On Tue, Feb 20, 2024 at 07:36:00PM +0800, Rongwei Wang wrote:
>> A brief introduction
>> ====================
>>
>> The NUMA emulation can fake more node base on a single
>> node system, e.g.
> 
> ...
>   
>> Lastly, it seems not a good choice to realize x86 and other genertic
>> archs separately. But it can indeed avoid some architecture related
>> APIs adjustments and alleviate future maintenance.
> 
> Why is it a good choice? Copying 1k lines from x86 to a new place and
> having to maintain two copies does not sound like a good choice to me.

I agree it would be better to avoid duplication and extract the common
code from the original x86 implementation. The RFC seemed to go more
in this direction.
Also NITs:
- genertic -> generic
- there is a 'ifdef CONFIG_X86' in drivers/base/numa_emulation.c,
   but the file should not be used by x86 as the arch doesn't set
   CONFIG_GENERIC_ARCH_NUMA

Regards,
Pierre

> 
>> The previous RFC link see [1].
>>
>> Any advice are welcome, Thanks!
>>
>> Change log
>> ==========
>>
>> RFC v1 -> v1
>> * add new CONFIG_NUMA_FAKE for genertic archs.
>> * keep x86 implementation, realize numa emulation in driver/base/ for
>>    genertic arch, e.g, arm64.
>>
>> [1] RFC v1: https://patchwork.kernel.org/project/linux-arm-kernel/cover/20231012024842.99703-1-rongwei.wang@linux.alibaba.com/
>>
>> Rongwei Wang (2):
>>    arch_numa: remove __init for early_cpu_to_node
>>    numa: introduce numa emulation for genertic arch
>>
>>   drivers/base/Kconfig          |   9 +
>>   drivers/base/Makefile         |   1 +
>>   drivers/base/arch_numa.c      |  32 +-
>>   drivers/base/numa_emulation.c | 909 ++++++++++++++++++++++++++++++++++
>>   drivers/base/numa_emulation.h |  41 ++
>>   include/asm-generic/numa.h    |   2 +-
>>   6 files changed, 992 insertions(+), 2 deletions(-)
>>   create mode 100644 drivers/base/numa_emulation.c
>>   create mode 100644 drivers/base/numa_emulation.h
>>
>> -- 
>> 2.32.0.3.gf3a3e56d6
>>
>>
>