Re: [PATCH 12/12] swap: move swap_info_struct to mm/swap.h

["Darrick J. Wong" <djwong@kernel.org>]

On Tue, May 12, 2026 at 07:35:28AM +0200, Christoph Hellwig wrote:
> swap_info_struct is now internal to the MM subsystem, so remove it from
> the public header.
> 

Even more cleaning out of swap.h is nice, so
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  include/linux/swap.h | 98 +-------------------------------------------
>  mm/swap.h            | 92 +++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 94 insertions(+), 96 deletions(-)
> 
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 95237ee065c2..31eef9b74949 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -16,9 +16,9 @@
>  #include <uapi/linux/mempolicy.h>
>  #include <asm/page.h>
>  
> -struct notifier_block;
> -
>  struct bio;
> +struct notifier_block;
> +struct swap_info_struct;
>  
>  #define SWAP_FLAG_PREFER	0x8000	/* set if swap priority specified */
>  #define SWAP_FLAG_PRIO_MASK	0x7fff
> @@ -178,29 +178,6 @@ struct sysinfo;
>  struct writeback_control;
>  struct zone;
>  
> -/*
> - * Max bad pages in the new format..
> - */
> -#define MAX_SWAP_BADPAGES \
> -	((offsetof(union swap_header, magic.magic) - \
> -	  offsetof(union swap_header, info.badpages)) / sizeof(int))
> -
> -enum {
> -	SWP_USED	= (1 << 0),	/* is slot in swap_info[] used? */
> -	SWP_WRITEOK	= (1 << 1),	/* ok to write to this swap?	*/
> -	SWP_DISCARDABLE = (1 << 2),	/* blkdev support discard */
> -	SWP_DISCARDING	= (1 << 3),	/* now discarding a free cluster */
> -	SWP_SOLIDSTATE	= (1 << 4),	/* blkdev seeks are cheap */
> -	SWP_BLKDEV	= (1 << 6),	/* its a block device */
> -	SWP_ACTIVATED	= (1 << 7),	/* set after swap_activate success */
> -	SWP_FS_OPS	= (1 << 8),	/* swapfile operations go through fs */
> -	SWP_AREA_DISCARD = (1 << 9),	/* single-time swap area discards */
> -	SWP_PAGE_DISCARD = (1 << 10),	/* freed swap page-cluster discards */
> -	SWP_STABLE_WRITES = (1 << 11),	/* no overwrite PG_writeback pages */
> -	SWP_SYNCHRONOUS_IO = (1 << 12),	/* synchronous IO is efficient */
> -					/* add others here before... */
> -};
> -
>  #define SWAP_CLUSTER_MAX 32UL
>  #define SWAP_CLUSTER_MAX_SKIPPED (SWAP_CLUSTER_MAX << 10)
>  #define COMPACT_CLUSTER_MAX SWAP_CLUSTER_MAX
> @@ -219,56 +196,6 @@ enum {
>  #define SWAP_NR_ORDERS		1
>  #endif
>  
> -/*
> - * We keep using same cluster for rotational device so IO will be sequential.
> - * The purpose is to optimize SWAP throughput on these device.
> - */
> -struct swap_sequential_cluster {
> -	unsigned int next[SWAP_NR_ORDERS]; /* Likely next allocation offset */
> -};
> -
> -/*
> - * The in-memory structure used to track swap areas.
> - */
> -struct swap_info_struct {
> -	struct percpu_ref users;	/* indicate and keep swap device valid. */
> -	unsigned long	flags;		/* SWP_USED etc: see above */
> -	signed short	prio;		/* swap priority of this type */
> -	struct plist_node list;		/* entry in swap_active_head */
> -	signed char	type;		/* strange name for an index */
> -	unsigned int	max;		/* size of this swap device */
> -	unsigned long *zeromap;		/* kvmalloc'ed bitmap to track zero pages */
> -	struct swap_cluster_info *cluster_info; /* cluster info. Only for SSD */
> -	struct list_head free_clusters; /* free clusters list */
> -	struct list_head full_clusters; /* full clusters list */
> -	struct list_head nonfull_clusters[SWAP_NR_ORDERS];
> -					/* list of cluster that contains at least one free slot */
> -	struct list_head frag_clusters[SWAP_NR_ORDERS];
> -					/* list of cluster that are fragmented or contented */
> -	unsigned int pages;		/* total of usable pages of swap */
> -	atomic_long_t inuse_pages;	/* number of those currently in use */
> -	struct swap_sequential_cluster *global_cluster; /* Use one global cluster for rotating device */
> -	spinlock_t global_cluster_lock;	/* Serialize usage of global cluster */
> -	struct rb_root swap_extent_root;/* root of the swap extent rbtree */
> -	struct block_device *bdev;	/* swap device or bdev of swap file */
> -	struct file *swap_file;		/* seldom referenced */
> -	struct completion comp;		/* seldom referenced */
> -	spinlock_t lock;		/*
> -					 * protect map scan related fields like
> -					 * inuse_pages and all cluster lists.
> -					 * Other fields are only changed
> -					 * at swapon/swapoff, so are protected
> -					 * by swap_lock. changing flags need
> -					 * hold this lock and swap_lock. If
> -					 * both locks need hold, hold swap_lock
> -					 * first.
> -					 */
> -	struct work_struct discard_work; /* discard worker */
> -	struct work_struct reclaim_work; /* reclaim worker */
> -	struct list_head discard_clusters; /* discard clusters list */
> -	struct plist_node avail_list;   /* entry in swap_avail_head */
> -};
> -
>  static inline swp_entry_t page_swap_entry(struct page *page)
>  {
>  	struct folio *folio = page_folio(page);
> @@ -423,10 +350,7 @@ int find_first_swap(dev_t *device);
>  extern unsigned int count_swap_pages(int, int);
>  extern sector_t swapdev_block(int, pgoff_t);
>  extern int __swap_count(swp_entry_t entry);
> -extern bool swap_entry_swapped(struct swap_info_struct *si, swp_entry_t entry);
>  extern int swp_swapcount(swp_entry_t entry);
> -struct backing_dev_info;
> -extern struct swap_info_struct *get_swap_device(swp_entry_t entry);
>  sector_t swap_folio_sector(struct folio *folio);
>  
>  /*
> @@ -452,20 +376,7 @@ bool folio_free_swap(struct folio *folio);
>  swp_entry_t swap_alloc_hibernation_slot(int type);
>  void swap_free_hibernation_slot(swp_entry_t entry);
>  
> -static inline void put_swap_device(struct swap_info_struct *si)
> -{
> -	percpu_ref_put(&si->users);
> -}
> -
>  #else /* CONFIG_SWAP */
> -static inline struct swap_info_struct *get_swap_device(swp_entry_t entry)
> -{
> -	return NULL;
> -}
> -
> -static inline void put_swap_device(struct swap_info_struct *si)
> -{
> -}
>  
>  #define get_nr_swap_pages()			0L
>  #define total_swap_pages			0L
> @@ -497,11 +408,6 @@ static inline int __swap_count(swp_entry_t entry)
>  	return 0;
>  }
>  
> -static inline bool swap_entry_swapped(struct swap_info_struct *si, swp_entry_t entry)
> -{
> -	return false;
> -}
> -
>  static inline int swp_swapcount(swp_entry_t entry)
>  {
>  	return 0;
> diff --git a/mm/swap.h b/mm/swap.h
> index a77016f2423b..70974495bf15 100644
> --- a/mm/swap.h
> +++ b/mm/swap.h
> @@ -8,6 +8,79 @@ struct swap_iocb;
>  
>  extern int page_cluster;
>  
> +/*
> + * We keep using same cluster for rotational device so IO will be sequential.
> + * The purpose is to optimize SWAP throughput on these device.
> + */
> +struct swap_sequential_cluster {
> +	unsigned int next[SWAP_NR_ORDERS]; /* Likely next allocation offset */
> +};
> +
> +/*
> + * The in-memory structure used to track swap areas.
> + */
> +struct swap_info_struct {
> +	struct percpu_ref users;	/* indicate and keep swap device valid. */
> +	unsigned long	flags;		/* SWP_USED etc: see above */
> +	signed short	prio;		/* swap priority of this type */
> +	struct plist_node list;		/* entry in swap_active_head */
> +	signed char	type;		/* strange name for an index */
> +	unsigned int	max;		/* size of this swap device */
> +	unsigned long *zeromap;		/* kvmalloc'ed bitmap to track zero pages */
> +	struct swap_cluster_info *cluster_info; /* cluster info. Only for SSD */
> +	struct list_head free_clusters; /* free clusters list */
> +	struct list_head full_clusters; /* full clusters list */
> +	struct list_head nonfull_clusters[SWAP_NR_ORDERS];
> +					/* list of cluster that contains at least one free slot */
> +	struct list_head frag_clusters[SWAP_NR_ORDERS];
> +					/* list of cluster that are fragmented or contented */
> +	unsigned int pages;		/* total of usable pages of swap */
> +	atomic_long_t inuse_pages;	/* number of those currently in use */
> +	struct swap_sequential_cluster *global_cluster; /* Use one global cluster for rotating device */
> +	spinlock_t global_cluster_lock;	/* Serialize usage of global cluster */
> +	struct rb_root swap_extent_root;/* root of the swap extent rbtree */
> +	struct block_device *bdev;	/* swap device or bdev of swap file */
> +	struct file *swap_file;		/* seldom referenced */
> +	struct completion comp;		/* seldom referenced */
> +	spinlock_t lock;		/*
> +					 * protect map scan related fields like
> +					 * inuse_pages and all cluster lists.
> +					 * Other fields are only changed
> +					 * at swapon/swapoff, so are protected
> +					 * by swap_lock. changing flags need
> +					 * hold this lock and swap_lock. If
> +					 * both locks need hold, hold swap_lock
> +					 * first.
> +					 */
> +	struct work_struct discard_work; /* discard worker */
> +	struct work_struct reclaim_work; /* reclaim worker */
> +	struct list_head discard_clusters; /* discard clusters list */
> +	struct plist_node avail_list;   /* entry in swap_avail_head */
> +};
> +
> +/*
> + * Max bad pages in the new format..
> + */
> +#define MAX_SWAP_BADPAGES \
> +	((offsetof(union swap_header, magic.magic) - \
> +	  offsetof(union swap_header, info.badpages)) / sizeof(int))
> +
> +enum {
> +	SWP_USED	= (1 << 0),	/* is slot in swap_info[] used? */
> +	SWP_WRITEOK	= (1 << 1),	/* ok to write to this swap?	*/
> +	SWP_DISCARDABLE = (1 << 2),	/* blkdev support discard */
> +	SWP_DISCARDING	= (1 << 3),	/* now discarding a free cluster */
> +	SWP_SOLIDSTATE	= (1 << 4),	/* blkdev seeks are cheap */
> +	SWP_BLKDEV	= (1 << 6),	/* its a block device */
> +	SWP_ACTIVATED	= (1 << 7),	/* set after swap_activate success */
> +	SWP_FS_OPS	= (1 << 8),	/* swapfile operations go through fs */
> +	SWP_AREA_DISCARD = (1 << 9),	/* single-time swap area discards */
> +	SWP_PAGE_DISCARD = (1 << 10),	/* freed swap page-cluster discards */
> +	SWP_STABLE_WRITES = (1 << 11),	/* no overwrite PG_writeback pages */
> +	SWP_SYNCHRONOUS_IO = (1 << 12),	/* synchronous IO is efficient */
> +					/* add others here before... */
> +};
> +
>  #ifdef CONFIG_THP_SWAP
>  #define SWAPFILE_CLUSTER	HPAGE_PMD_NR
>  #define swap_entry_order(order)	(order)
> @@ -352,6 +425,13 @@ static inline int non_swapcache_batch(swp_entry_t entry, int max_nr)
>  	return i;
>  }
>  
> +bool swap_entry_swapped(struct swap_info_struct *si, swp_entry_t entry);
> +struct swap_info_struct *get_swap_device(swp_entry_t entry);
> +static inline void put_swap_device(struct swap_info_struct *si)
> +{
> +	percpu_ref_put(&si->users);
> +}
> +
>  #else /* CONFIG_SWAP */
>  struct swap_iocb;
>  static inline struct swap_cluster_info *swap_cluster_lock(
> @@ -498,5 +578,17 @@ static inline int non_swapcache_batch(swp_entry_t entry, int max_nr)
>  {
>  	return 0;
>  }
> +static inline bool swap_entry_swapped(struct swap_info_struct *si,
> +		swp_entry_t entry)
> +{
> +	return false;
> +}
> +static inline struct swap_info_struct *get_swap_device(swp_entry_t entry)
> +{
> +	return NULL;
> +}
> +static inline void put_swap_device(struct swap_info_struct *si)
> +{
> +}
>  #endif /* CONFIG_SWAP */
>  #endif /* _MM_SWAP_H */
> -- 
> 2.53.0
> 
>