Re: [PATCH 2/7] mm/migrate: use migrate_info field instead of private

[Huang, Ying]

Shivank Garg <shivankg@xxxxxxx> writes:

> Add an unsigned long migrate_info member to the struct folio union and
> use it to store migration state (anon_vma pointer and FOLIO_WAS_*
> flags) instead of using folio->private.
>
> No functional change.
>
> Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
> Signed-off-by: Shivank Garg <shivankg@xxxxxxx>
> ---
>  include/linux/mm_types.h |  1 +
>  mm/migrate.c             | 14 +++++++-------
>  2 files changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index a308e2c23b82..f52818dcf4d2 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -426,6 +426,7 @@ struct folio {
>  			union {
>  				void *private;
>  				swp_entry_t swap;
> +				unsigned long migrate_info;
>  			};
>  			atomic_t _mapcount;
>  			atomic_t _refcount;
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 0c6a0ab6ecce..03c2a6f7e5e4 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1130,7 +1130,7 @@ static int move_to_new_folio(struct folio *dst, struct folio *src,
>  }
>  
>  /*
> - * To record some information during migration, we use unused private
> + * To record some information during migration, we use the migrate_info
>   * field of struct folio of the newly allocated destination folio.
>   * This is safe because nobody is using it except us.
>   */
> @@ -1143,17 +1143,17 @@ enum {
>  static void __migrate_folio_record(struct folio *dst,
>  		int old_folio_state, struct anon_vma *anon_vma)
>  {
> -	dst->private = (void *)anon_vma + old_folio_state;
> +	dst->migrate_info = (unsigned long)anon_vma | old_folio_state;
>  }
>  
>  static void __migrate_folio_extract(struct folio *dst,
>  		int *old_folio_state, struct anon_vma **anon_vmap)
>  {
> -	unsigned long private = (unsigned long)dst->private;
> +	unsigned long info = dst->migrate_info;
>  
> -	*anon_vmap = (struct anon_vma *)(private & ~FOLIO_OLD_STATES);
> -	*old_folio_state = private & FOLIO_OLD_STATES;
> -	dst->private = NULL;
> +	*anon_vmap = (struct anon_vma *)(info & ~FOLIO_OLD_STATES);
> +	*old_folio_state = info & FOLIO_OLD_STATES;
> +	dst->migrate_info = 0;
>  }
>  
>  /* Restore the source folio to the original state upon failure */
> @@ -1217,7 +1217,7 @@ static int migrate_folio_unmap(new_folio_t get_new_folio,
>  		return -ENOMEM;
>  	*dstp = dst;
>  
> -	dst->private = NULL;
> +	dst->migrate_info = 0;
>  
>  	if (!folio_trylock(src)) {
>  		if (mode == MIGRATE_ASYNC)

LGTM!  Feel free to add my

Reviewed-by: Huang Ying <ying.huang@xxxxxxxxxxxxxxxxx>

in the future versions.

---
Best Regards,
Huang, Ying