Re: [PATCH v2 08/22] mm: introduce for_each_free_list()

["Vlastimil Babka (SUSE)" <vbabka@kernel.org>]

On 3/20/26 19:23, Brendan Jackman wrote:
> Later patches will rearrange the free areas, but there are a couple of
> places that iterate over them with the assumption that they have the
> current structure.
> 
> It seems ideally, code outside of mm should not be directly aware of
> struct free_area in the first place, but that awareness seems relatively
> harmless so just make the minimal change.

I think we should lift the code from kernel/power/snapshot.c to under mm/
eventually, ISTR discussing it somewhere recently. But doesn't have to be in
this series.

> Now instead of letting users manually iterate over the free lists, just
> provide a macro to do that. Then adopt that macro in a couple of places.
> 
> Signed-off-by: Brendan Jackman <jackmanb@google.com>

Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>

> ---
>  include/linux/mmzone.h  |  7 +++++--
>  kernel/power/snapshot.c |  8 ++++----
>  mm/mm_init.c            | 11 +++++++----
>  3 files changed, 16 insertions(+), 10 deletions(-)
> 
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 7bd0134c241ce..c49e3cdf4f6bb 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -177,9 +177,12 @@ static inline bool migratetype_is_mergeable(int mt)
>  	return mt < MIGRATE_PCPTYPES;
>  }
>  
> -#define for_each_migratetype_order(order, type) \
> +#define for_each_free_list(list, zone, order) \
>  	for (order = 0; order < NR_PAGE_ORDERS; order++) \
> -		for (type = 0; type < MIGRATE_TYPES; type++)
> +		for (unsigned int type = 0; \
> +		     list = &zone->free_area[order].free_list[type], \
> +		     type < MIGRATE_TYPES; \
> +		     type++) \
>  
>  extern int page_group_by_mobility_disabled;
>  
> diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
> index 7dcccf378cc2f..abd33ca13eec4 100644
> --- a/kernel/power/snapshot.c
> +++ b/kernel/power/snapshot.c
> @@ -1245,8 +1245,9 @@ unsigned int snapshot_additional_pages(struct zone *zone)
>  static void mark_free_pages(struct zone *zone)
>  {
>  	unsigned long pfn, max_zone_pfn, page_count = WD_PAGE_COUNT;
> +	struct list_head *free_list;
>  	unsigned long flags;
> -	unsigned int order, t;
> +	unsigned int order;
>  	struct page *page;
>  
>  	if (zone_is_empty(zone))
> @@ -1270,9 +1271,8 @@ static void mark_free_pages(struct zone *zone)
>  			swsusp_unset_page_free(page);
>  	}
>  
> -	for_each_migratetype_order(order, t) {
> -		list_for_each_entry(page,
> -				&zone->free_area[order].free_list[t], buddy_list) {
> +	for_each_free_list(free_list, zone, order) {
> +		list_for_each_entry(page, free_list, buddy_list) {
>  			unsigned long i;
>  
>  			pfn = page_to_pfn(page);
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index 969048f9b320c..f6f9455bc42b6 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -1445,11 +1445,14 @@ static void __meminit zone_init_internals(struct zone *zone, enum zone_type idx,
>  
>  static void __meminit zone_init_free_lists(struct zone *zone)
>  {
> -	unsigned int order, t;
> -	for_each_migratetype_order(order, t) {
> -		INIT_LIST_HEAD(&zone->free_area[order].free_list[t]);
> +	struct list_head *list;
> +	unsigned int order;
> +
> +	for_each_free_list(list, zone, order)
> +		INIT_LIST_HEAD(list);
> +
> +	for (order = 0; order < NR_PAGE_ORDERS; order++)
>  		zone->free_area[order].nr_free = 0;
> -	}
>  
>  #ifdef CONFIG_UNACCEPTED_MEMORY
>  	INIT_LIST_HEAD(&zone->unaccepted_pages);
>