linux-kernel - Re: [PATCH v2 2/2] mm/mm_init.c: remove reset_node_present

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Date:   Wed, 7 Jun 2023 12:33:34 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Haifeng Xu <haifeng.xu@...pee.com>
Cc:     david@...hat.com, rppt@...nel.org, osalvador@...e.de,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] mm/mm_init.c: remove reset_node_present_pages()

On Wed 07-06-23 02:50:56, Haifeng Xu wrote:
> reset_node_present_pages() only get called in hotadd_init_pgdat(), move
> the action that clear present pages to free_area_init_core_hotplug(), so
> the helper can be removed.

There is no explanation why moving the action is desirable and/or
needed. I do agree that removing this trivial helper which only has a
single caller. I guess the incentive is an overal simplification but
please spell that out.

> Signed-off-by: Haifeng Xu <haifeng.xu@...pee.com>
> Suggested-by: David Hildenbrand <david@...hat.com>

The patch itself makes sense
Acked-by: Michal Hocko <mhocko@...e.com>

> ---
> v2:
> - declare 'struct zone' within the for loop
> - fix comment layout
> ---
>  mm/memory_hotplug.c | 18 ------------------
>  mm/mm_init.c        | 15 +++++++++++++--
>  2 files changed, 13 insertions(+), 20 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 65e385f34679..ee1c0d9a4d5a 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1172,16 +1172,6 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
>  	return ret;
>  }
>  
> -static void reset_node_present_pages(pg_data_t *pgdat)
> -{
> -	struct zone *z;
> -
> -	for (z = pgdat->node_zones; z < pgdat->node_zones + MAX_NR_ZONES; z++)
> -		z->present_pages = 0;
> -
> -	pgdat->node_present_pages = 0;
> -}
> -
>  /* we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG */
>  static pg_data_t __ref *hotadd_init_pgdat(int nid)
>  {
> @@ -1204,14 +1194,6 @@ static pg_data_t __ref *hotadd_init_pgdat(int nid)
>  	 */
>  	build_all_zonelists(pgdat);
>  
> -	/*
> -	 * When memory is hot-added, all the memory is in offline state. So
> -	 * clear all zones' present_pages because they will be updated in
> -	 * online_pages() and offline_pages().
> -	 * TODO: should be in free_area_init_core_hotplug?
> -	 */
> -	reset_node_present_pages(pgdat);
> -
>  	return pgdat;
>  }
>  
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index 78e67041ae9f..a02ba9a79b3d 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -1507,6 +1507,8 @@ void __ref free_area_init_core_hotplug(struct pglist_data *pgdat)
>  	pgdat->kswapd_order = 0;
>  	pgdat->kswapd_highest_zoneidx = 0;
>  	pgdat->node_start_pfn = 0;
> +	pgdat->node_present_pages = 0;
> +
>  	for_each_online_cpu(cpu) {
>  		struct per_cpu_nodestat *p;
>  
> @@ -1514,8 +1516,17 @@ void __ref free_area_init_core_hotplug(struct pglist_data *pgdat)
>  		memset(p, 0, sizeof(*p));
>  	}
>  
> -	for (z = 0; z < MAX_NR_ZONES; z++)
> -		zone_init_internals(&pgdat->node_zones[z], z, nid, 0);
> +	/*
> +	 * When memory is hot-added, all the memory is in offline state. So
> +	 * clear all zones' present_pages and managed_pages because they will
> +	 * be updated in online_pages() and offline_pages().
> +	 */
> +	for (z = 0; z < MAX_NR_ZONES; z++) {
> +		struct zone *zone = pgdat->node_zones + z;
> +
> +		zone->present_pages = 0;
> +		zone_init_internals(zone, z, nid, 0);
> +	}
>  }
>  #endif
>  
> -- 
> 2.25.1

-- 
Michal Hocko
SUSE Labs