Re: [PATCH v3 2/7] mm/page_owner: add MR_NEVER to enum migrate_reason and use it for last_migrate_reason

[Vlastimil Babka (SUSE)]

On 6/30/26 03:53, 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 by
> adding a proper MR_NEVER member to enum migrate_reason, defining a
> corresponding "never_migrated" string in the MIGRATE_REASON trace
> macro, and removing the local MIGRATE_REASON_NONE define.
> 
> No functional change.
> 
> Signed-off-by: Ye Liu <ye.liu@xxxxxxxxx>

Reviewed-by: Vlastimil Babka (SUSE) <vbabka@xxxxxxxxxx>

> ---
>  include/linux/migrate_mode.h   | 1 +
>  include/trace/events/migrate.h | 3 ++-
>  mm/page_owner.c                | 8 ++++----
>  3 files changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/migrate_mode.h b/include/linux/migrate_mode.h
> index 265c4328b36a..05102d4d2490 100644
> --- a/include/linux/migrate_mode.h
> +++ b/include/linux/migrate_mode.h
> @@ -25,6 +25,7 @@ enum migrate_reason {
>  	MR_LONGTERM_PIN,
>  	MR_DEMOTION,
>  	MR_DAMON,
> +	MR_NEVER,		/* page has never been migrated */
>  	MR_TYPES
>  };
>  
> diff --git a/include/trace/events/migrate.h b/include/trace/events/migrate.h
> index cd01dd7b3640..11bc0aa14c7e 100644
> --- a/include/trace/events/migrate.h
> +++ b/include/trace/events/migrate.h
> @@ -23,7 +23,8 @@
>  	EM( MR_CONTIG_RANGE,	"contig_range")			\
>  	EM( MR_LONGTERM_PIN,	"longterm_pin")			\
>  	EM( MR_DEMOTION,	"demotion")			\
> -	EMe(MR_DAMON,		"damon")
> +	EM( MR_DAMON,		"damon")			\
> +	EMe(MR_NEVER,		"never_migrated")
>  
>  /*
>   * First define the enums in the above macros to be exported to userspace
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index 342549891a8d..c2f43ab860eb 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -339,7 +339,7 @@ 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, MR_NEVER,
>  				   ts_nsec, current->pid, current->tgid,
>  				   current->comm);
>  	inc_stack_record_count(handle, gfp_mask, 1 << order);
> @@ -596,7 +596,7 @@ 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 != MR_NEVER) {
>  		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 +667,7 @@ 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 != MR_NEVER)
>  		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 +826,7 @@ 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,
> +						   MR_NEVER, local_clock(), current->pid,
>  						   current->tgid, current->comm);
>  			count++;
>  ext_put_continue: