linux-kernel - Re: [PATCH v2 06/14] init: fold build_all_zonelists() and page_alloc_init_cpuhp() to mm

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Message-ID: <f712fa24-91f7-38e7-fd6e-b33ab52ce88c@suse.cz>
Date:   Wed, 22 Mar 2023 17:10:10 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Mike Rapoport <rppt@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     David Hildenbrand <david@...hat.com>,
        Doug Berger <opendmb@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...nel.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH v2 06/14] init: fold build_all_zonelists() and
 page_alloc_init_cpuhp() to mm_init()

On 3/21/23 18:05, Mike Rapoport wrote:
> From: "Mike Rapoport (IBM)" <rppt@...nel.org>
> 
> Both build_all_zonelists() and page_alloc_init_cpuhp() must be called
> after SMP setup is complete but before the page allocator is set up.
> 
> Still, they both are a part of memory management initialization, so move
> them to mm_init().

Well, logic grouping is one thing, but not breaking a functional order is
more important. So this moves both calls to happen later than theyw ere. I
guess it could only matter for page_alloc_init_cpuhp() in case cpu hotplugs
would be processed in some of the calls we "skipped" over by moving this
later. And one of them is setup_arch()... so are we sure no arch does some
cpu hotplug for non-boot cpus there?

> Signed-off-by: Mike Rapoport (IBM) <rppt@...nel.org>
> Acked-by: David Hildenbrand <david@...hat.com>
> ---
>  init/main.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/init/main.c b/init/main.c
> index b2499bee7a3c..4423906177c1 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -833,6 +833,10 @@ static void __init report_meminit(void)
>   */
>  static void __init mm_init(void)
>  {
> +	/* Initializations relying on SMP setup */
> +	build_all_zonelists(NULL);
> +	page_alloc_init_cpuhp();
> +
>  	/*
>  	 * page_ext requires contiguous pages,
>  	 * bigger than MAX_ORDER unless SPARSEMEM.
> @@ -968,9 +972,6 @@ asmlinkage __visible void __init __no_sanitize_address start_kernel(void)
>  	smp_prepare_boot_cpu();	/* arch-specific boot-cpu hooks */
>  	boot_cpu_hotplug_init();
>  
> -	build_all_zonelists(NULL);
> -	page_alloc_init_cpuhp();
> -
>  	pr_notice("Kernel command line: %s\n", saved_command_line);
>  	/* parameters may set static keys */
>  	jump_label_init();