Re: [PATCH v2 2/6] mm/page_owner: use MIGRATE_REASON_NONE instead of -1 for last_migrate_reason

[Zi Yan]

On Thu Jun 25, 2026 at 10:45 PM EDT, Ye Liu wrote:
> The last_migrate_reason field uses -1 as a sentinel value to mean "no
> migration has happened".  Replace the four bare -1 occurrences with a
> local MIGRATE_REASON_NONE define so the intent is explicit and the
> magic number is eliminated.
>
> No functional change.
>
> Signed-off-by: Ye Liu <ye.liu@xxxxxxxxx>
> ---
>  mm/page_owner.c | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index 342549891a8d..ebafa9d7ff07 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -21,6 +21,13 @@
>   */
>  #define PAGE_OWNER_STACK_DEPTH (16)
>  
> +/*
> + * Used to indicate that a page has never been migrated, as the valid
> + * migrate_reason values are non-negative enum members (MR_* in
> + * include/linux/migrate_mode.h).

Why not change last_migrate_reason to enum migrate_reason and functions
pass migrate reasons? MR_TYPES probably can be used to indicate no
migration has happened if we do not want to add MR_NO_MIGRATION.

folio_set_owner_migrate_reason(),
__folio_set_owner_migrate_reason(),
move_hugetlb_state(), and
__update_page_owner_handle() need to update their signatures for this.


> + */
> +#define MIGRATE_REASON_NONE (-1)
> +
>  struct page_owner {
>  	unsigned short order;
>  	short last_migrate_reason;
> @@ -339,7 +346,7 @@ noinline void __set_page_owner(struct page *page, unsigned short order,
>  	depot_stack_handle_t handle;
>  
>  	handle = save_stack(gfp_mask);
> -	__update_page_owner_handle(page, handle, order, gfp_mask, -1,
> +	__update_page_owner_handle(page, handle, order, gfp_mask, MIGRATE_REASON_NONE,
>  				   ts_nsec, current->pid, current->tgid,
>  				   current->comm);
>  	inc_stack_record_count(handle, gfp_mask, 1 << order);
> @@ -596,7 +603,7 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn,
>  	if (ret >= count)
>  		goto err;
>  
> -	if (page_owner->last_migrate_reason != -1) {
> +	if (page_owner->last_migrate_reason != MIGRATE_REASON_NONE) {
>  		ret += scnprintf(kbuf + ret, count - ret,
>  			"Page has been migrated, last migrate reason: %s\n",
>  			migrate_reason_names[page_owner->last_migrate_reason]);
> @@ -667,7 +674,7 @@ void __dump_page_owner(const struct page *page)
>  		stack_depot_print(handle);
>  	}
>  
> -	if (page_owner->last_migrate_reason != -1)
> +	if (page_owner->last_migrate_reason != MIGRATE_REASON_NONE)
>  		pr_alert("page has been migrated, last migrate reason: %s\n",
>  			migrate_reason_names[page_owner->last_migrate_reason]);
>  	page_ext_put(page_ext);
> @@ -826,7 +833,7 @@ static void init_pages_in_zone(struct zone *zone)
>  
>  			/* Found early allocated page */
>  			__update_page_owner_handle(page, early_handle, 0, 0,
> -						   -1, local_clock(), current->pid,
> +						   MIGRATE_REASON_NONE, local_clock(), current->pid,
>  						   current->tgid, current->comm);
>  			count++;
>  ext_put_continue:




-- 
Best Regards,
Yan, Zi