linux-kernel - Re: [PATCH v2] mm/mm_init: use node's number of cpus in deferred_page_init_max

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Date: Thu, 23 May 2024 17:59:57 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Eric Chanudet <echanude@...hat.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>,
	Andy Lutomirski <luto@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Baoquan He <bhe@...hat.com>, Michael Ellerman <mpe@...erman.id.au>,
	Nick Piggin <npiggin@...il.com>, x86@...nel.org,
	linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2] mm/mm_init: use node's number of cpus in
 deferred_page_init_max_threads

On Wed, May 22, 2024 at 04:38:01PM -0400, Eric Chanudet wrote:
> x86_64 is already using the node's cpu as maximum threads. Make that the
> default for all archs setting DEFERRED_STRUCT_PAGE_INIT.
> 
> This returns to the behavior prior making the function arch-specific
> with commit ecd096506922 ("mm: make deferred init's max threads
> arch-specific").
> 
> Signed-off-by: Eric Chanudet <echanude@...hat.com>
> 
> ---
> Setting DEFERRED_STRUCT_PAGE_INIT and testing on a few arm64 platforms
> shows faster deferred_init_memmap completions:
> 
> |         | x13s        | SA8775p-ride | Ampere R137-P31 | Ampere HR330 |
> |         | Metal, 32GB | VM, 36GB     | VM, 58GB        | Metal, 128GB |
> |         | 8cpus       | 8cpus        | 8cpus           | 32cpus       |
> |---------|-------------|--------------|-----------------|--------------|
> | threads |  ms     (%) | ms       (%) |  ms         (%) |  ms      (%) |
> |---------|-------------|--------------|-----------------|--------------|
> | 1       | 108    (0%) | 72      (0%) | 224        (0%) | 324     (0%) |
> | cpus    |  24  (-77%) | 36    (-50%) |  40      (-82%) |  56   (-82%) |
> 
> - v1: https://lore.kernel.org/linux-arm-kernel/20240520231555.395979-5-echanude@redhat.com
> - Changes since v1:
>  - Make the generic function return the number of cpus of the node as
>    max threads limit instead overriding it for arm64.
> - Drop Baoquan He's R-b on v1 since the logic changed.
> - Add CCs according to patch changes (ppc and s390 set
>   DEFERRED_STRUCT_PAGE_INIT by default).
> 
>  arch/x86/mm/init_64.c | 12 ------------
>  mm/mm_init.c          |  2 +-
>  2 files changed, 1 insertion(+), 13 deletions(-)
> 
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index 7e177856ee4f..adec42928ec1 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -1354,18 +1354,6 @@ void __init mem_init(void)
>  	preallocate_vmalloc_pages();
>  }
>  
> -#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
> -int __init deferred_page_init_max_threads(const struct cpumask *node_cpumask)
> -{
> -	/*
> -	 * More CPUs always led to greater speedups on tested systems, up to
> -	 * all the nodes' CPUs.  Use all since the system is otherwise idle
> -	 * now.
> -	 */
> -	return max_t(int, cpumask_weight(node_cpumask), 1);
> -}
> -#endif
> -
>  int kernel_set_to_readonly;
>  
>  void mark_rodata_ro(void)
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index f72b852bd5b8..e0023aa68555 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -2126,7 +2126,7 @@ deferred_init_memmap_chunk(unsigned long start_pfn, unsigned long end_pfn,
>  __weak int __init

If s390 folks confirm there's no regression for them I think we can make
this static.

>  deferred_page_init_max_threads(const struct cpumask *node_cpumask)
>  {
> -	return 1;
> +	return max_t(int, cpumask_weight(node_cpumask), 1);
>  }
>  
>  /* Initialise remaining memory on a node */
> -- 
> 2.44.0
> 

-- 
Sincerely yours,
Mike.