linux-kernel - Re: [PATCH] drivers/arch_numa: remove rebudant setup_per_cpu

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Message-ID: <20210309140159.GA28395@willie-the-truck>
Date:   Tue, 9 Mar 2021 14:01:59 +0000
From:   Will Deacon <will@...nel.org>
To:     Pingfan Liu <kernelfans@...il.com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Atish Patra <atish.patra@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drivers/arch_numa: remove rebudant setup_per_cpu_areas()

[typo in subject "rebudant"]

On Tue, Mar 09, 2021 at 06:21:38PM +0800, Pingfan Liu wrote:
> There are two identical implementations of setup_per_cpu_areas() in
> mm/percpu.c and drivers/base/arch_numa.c.
> 
> Hence removing the one in arch_numa.c. And let arm64 drop
> HAVE_SETUP_PER_CPU_AREA.
> 
> Signed-off-by: Pingfan Liu <kernelfans@...il.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>
> Cc: Atish Patra <atish.patra@....com>
> Cc: linux-kernel@...r.kernel.org
> To: linux-arm-kernel@...ts.infradead.org
> ---
>  arch/arm64/Kconfig       |  4 ----
>  drivers/base/arch_numa.c | 22 ----------------------
>  2 files changed, 26 deletions(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 1f212b47a48a..d4bf8be0c3d5 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1022,10 +1022,6 @@ config USE_PERCPU_NUMA_NODE_ID
>  	def_bool y
>  	depends on NUMA
>  
> -config HAVE_SETUP_PER_CPU_AREA
> -	def_bool y
> -	depends on NUMA
> -
>  config NEED_PER_CPU_EMBED_FIRST_CHUNK
>  	def_bool y
>  	depends on NUMA
> diff --git a/drivers/base/arch_numa.c b/drivers/base/arch_numa.c
> index 4cc4e117727d..23e1e419a83d 100644
> --- a/drivers/base/arch_numa.c
> +++ b/drivers/base/arch_numa.c
> @@ -167,28 +167,6 @@ static void __init pcpu_fc_free(void *ptr, size_t size)
>  {
>  	memblock_free_early(__pa(ptr), size);
>  }
> -
> -void __init setup_per_cpu_areas(void)
> -{
> -	unsigned long delta;
> -	unsigned int cpu;
> -	int rc;
> -
> -	/*
> -	 * Always reserve area for module percpu variables.  That's
> -	 * what the legacy allocator did.
> -	 */
> -	rc = pcpu_embed_first_chunk(PERCPU_MODULE_RESERVE,
> -				    PERCPU_DYNAMIC_RESERVE, PAGE_SIZE,
> -				    pcpu_cpu_distance,
> -				    pcpu_fc_alloc, pcpu_fc_free);

This doesn't look identical to the version in mm/percpu.c -- that one passes
NULL instead of 'pcpu_cpu_distance' and tries to allocate the pcpu memory on
the relevant NUMA nodes. In fact, if you could remove this function, you
could probably remove the whole HAVE_SETUP_PER_CPU_AREA block here as the
other functions are just used as helpers. So I'm not sure this is valid.

Will