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Message-ID: <7d3725ec-1586-e697-1602-713bfd38daf9@suse.cz>
Date:   Thu, 23 Mar 2023 08:09:01 +0100
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Subject: Re: [PATCH v2 06/14] init: fold build_all_zonelists() and
 page_alloc_init_cpuhp() to mm_init()
To:     Mike Rapoport <rppt@kernel.org>
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
References: <20230321170513.2401534-1-rppt@kernel.org>
 <20230321170513.2401534-7-rppt@kernel.org>
 <f712fa24-91f7-38e7-fd6e-b33ab52ce88c@suse.cz> <ZBtkYQyxulcNV8gG@kernel.org>
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From:   Vlastimil Babka <vbabka@suse.cz>
In-Reply-To: <ZBtkYQyxulcNV8gG@kernel.org>
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On 3/22/23 21:26, Mike Rapoport wrote:
> 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().

Right, I looked at a wrong place in start_kernel() for the original location
of the calls, sorry for the noise.

> 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();
> 

Yeah, that looks safe.

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

Reviewed-by: Vlastimil Babka <vbabka@suse.cz>