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Date:   Wed, 22 Mar 2023 22:26:09 +0200
From:   Mike Rapoport <rppt@kernel.org>
To:     Vlastimil Babka <vbabka@suse.cz>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        David Hildenbrand <david@redhat.com>,
        Doug Berger <opendmb@gmail.com>,
        Matthew Wilcox <willy@infradead.org>,
        Mel Gorman <mgorman@suse.de>, Michal Hocko <mhocko@kernel.org>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCH v2 06/14] init: fold build_all_zonelists() and
 page_alloc_init_cpuhp() to mm_init()
Message-ID: <ZBtkYQyxulcNV8gG@kernel.org>
References: <20230321170513.2401534-1-rppt@kernel.org>
 <20230321170513.2401534-7-rppt@kernel.org>
 <f712fa24-91f7-38e7-fd6e-b33ab52ce88c@suse.cz>
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On Wed, Mar 22, 2023 at 05:10:10PM +0100, Vlastimil Babka wrote:
> On 3/21/23 18:05, Mike Rapoport wrote:
> > From: "Mike Rapoport (IBM)" <rppt@kernel.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?

mm_init() happens after the point build_all_zonelists() and
page_alloc_init_cpuhp() were originally, so they are essentially moved
later in the init sequence and in either case called after setup_arch().

We skip the code below and it does not do neither cpu hotplug nor
non-memblock allocations.

	jump_label_init();
	parse_early_param();
	after_dashes = parse_args("Booting kernel",
				  static_command_line, __start___param,
				  __stop___param - __start___param,
				  -1, -1, NULL, &unknown_bootoption);
	print_unknown_bootoptions();
	if (!IS_ERR_OR_NULL(after_dashes))
		parse_args("Setting init args", after_dashes, NULL, 0, -1, -1,
			   NULL, set_init_arg);
	if (extra_init_args)
		parse_args("Setting extra init args", extra_init_args,
			   NULL, 0, -1, -1, NULL, set_init_arg);

	/* Architectural and non-timekeeping rng init, before allocator init */
	random_init_early(command_line);

	/*
	 * These use large bootmem allocations and must precede
	 * kmem_cache_init()
	 */
	setup_log_buf(0);
	vfs_caches_init_early();
	sort_main_extable();
	trap_init();

 
> > Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org>
> > Acked-by: David Hildenbrand <david@redhat.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();
> 

-- 
Sincerely yours,
Mike.