Re: [PATCH RFC 11/29] mm/migrate: move movable_ops page handling out of move_to_new_folio()

[David Hildenbrand <david@redhat.com>]

On 18.06.25 19:39, David Hildenbrand wrote:
> Let's move that handling directly into migrate_folio_move(), so we can
> simplify move_to_new_folio(). While at it, fixup the documentation a
> bit.
> 
> Note that unmap_and_move_huge_page() does not care, because it only
> deals with actual folios. (we only support migration of
> individual movable_ops pages)
> 
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>   mm/migrate.c | 61 ++++++++++++++++++++++++----------------------------
>   1 file changed, 28 insertions(+), 33 deletions(-)
> 
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 456e41dad83a2..db807f9bbf975 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1024,11 +1024,12 @@ static int fallback_migrate_folio(struct address_space *mapping,
>   }
>   
>   /*
> - * Move a page to a newly allocated page
> - * The page is locked and all ptes have been successfully removed.
> + * Move a src folio to a newly allocated dst folio.
>    *
> - * The new page will have replaced the old page if this function
> - * is successful.
> + * The src and dst folios are locked and the src folios was unmapped from
> + * the page tables.
> + *
> + * On success, the src folio was replaced by the dst folio.
>    *
>    * Return value:
>    *   < 0 - error code
> @@ -1037,34 +1038,30 @@ static int fallback_migrate_folio(struct address_space *mapping,
>   static int move_to_new_folio(struct folio *dst, struct folio *src,
>   				enum migrate_mode mode)
>   {
> +	struct address_space *mapping = folio_mapping(src);
>   	int rc = -EAGAIN;
> -	bool is_lru = !__folio_test_movable(src);
>   
>   	VM_BUG_ON_FOLIO(!folio_test_locked(src), src);
>   	VM_BUG_ON_FOLIO(!folio_test_locked(dst), dst);
>   
> -	if (likely(is_lru)) {
> -		struct address_space *mapping = folio_mapping(src);
> -
> -		if (!mapping)
> -			rc = migrate_folio(mapping, dst, src, mode);
> -		else if (mapping_inaccessible(mapping))
> -			rc = -EOPNOTSUPP;
> -		else if (mapping->a_ops->migrate_folio)
> -			/*
> -			 * Most folios have a mapping and most filesystems
> -			 * provide a migrate_folio callback. Anonymous folios
> -			 * are part of swap space which also has its own
> -			 * migrate_folio callback. This is the most common path
> -			 * for page migration.
> -			 */
> -			rc = mapping->a_ops->migrate_folio(mapping, dst, src,
> -								mode);
> -		else
> -			rc = fallback_migrate_folio(mapping, dst, src, mode);
> +	if (!mapping)
> +		rc = migrate_folio(mapping, dst, src, mode);
> +	else if (mapping_inaccessible(mapping))
> +		rc = -EOPNOTSUPP;
> +	else if (mapping->a_ops->migrate_folio)
> +		/*
> +		 * Most folios have a mapping and most filesystems
> +		 * provide a migrate_folio callback. Anonymous folios
> +		 * are part of swap space which also has its own
> +		 * migrate_folio callback. This is the most common path
> +		 * for page migration.
> +		 */
> +		rc = mapping->a_ops->migrate_folio(mapping, dst, src,
> +							mode);
> +	else
> +		rc = fallback_migrate_folio(mapping, dst, src, mode);
>   
> -		if (rc != MIGRATEPAGE_SUCCESS)
> -			goto out;
> +	if (rc == MIGRATEPAGE_SUCCESS) {
>   		/*
>   		 * For pagecache folios, src->mapping must be cleared before src
>   		 * is freed. Anonymous folios must stay anonymous until freed.
> @@ -1074,10 +1071,7 @@ static int move_to_new_folio(struct folio *dst, struct folio *src,
>   
>   		if (likely(!folio_is_zone_device(dst)))
>   			flush_dcache_folio(dst);
> -	} else {
> -		rc = migrate_movable_ops_page(&dst->page, &src->page, mode);
>   	}
> -out:
>   	return rc;
>   }
>   
> @@ -1328,20 +1322,21 @@ static int migrate_folio_move(free_folio_t put_new_folio, unsigned long private,
>   	int rc;
>   	int old_page_state = 0;
>   	struct anon_vma *anon_vma = NULL;
> -	bool is_lru = !__folio_test_movable(src);
>   	struct list_head *prev;
>   
>   	__migrate_folio_extract(dst, &old_page_state, &anon_vma);
>   	prev = dst->lru.prev;
>   	list_del(&dst->lru);
>   
> +	if (unlikely(__folio_test_movable(src))) {
> +		rc = migrate_movable_ops_page(&dst->page, &src->page, mode);
> +		goto out_unlock_both;
> +	}
> +


I suspect this was the issue I was chasing:

diff --git a/mm/migrate.c b/mm/migrate.c
index 9dd327a63abc5..22c115710d0e2 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1330,6 +1330,8 @@ static int migrate_folio_move(free_folio_t put_new_folio, unsigned long private,
  
         if (unlikely(__folio_test_movable(src))) {
                 rc = migrate_movable_ops_page(&dst->page, &src->page, mode);
+               if (rc)
+                       goto out;
                 goto out_unlock_both;
         }
  

Testing ...

-- 
Cheers,

David / dhildenb