text: /* SPDX-License-Identifier: GPL-2.0 */
  #ifndef _LINUX_SWAP_H
  #define _LINUX_SWAP_H
  
  #include <linux/spinlock.h>
  #include <linux/linkage.h>
  #include <linux/mmzone.h>
  #include <linux/list.h>
  #include <linux/memcontrol.h>
  #include <linux/sched.h>
  #include <linux/node.h>
  #include <linux/fs.h>
  #include <linux/pagemap.h>
  #include <linux/atomic.h>
  #include <linux/page-flags.h>
  #include <uapi/linux/mempolicy.h>
  #include <asm/page.h>
  
  struct notifier_block;
  
  struct bio;
  
  struct pagevec;
  
  #define SWAP_FLAG_PREFER	0x8000	/* set if swap priority specified */
  #define SWAP_FLAG_PRIO_MASK	0x7fff
  #define SWAP_FLAG_PRIO_SHIFT	0
  #define SWAP_FLAG_DISCARD	0x10000 /* enable discard for swap */
  #define SWAP_FLAG_DISCARD_ONCE	0x20000 /* discard swap area at swapon-time */
  #define SWAP_FLAG_DISCARD_PAGES 0x40000 /* discard page-clusters after use */
  
  #define SWAP_FLAGS_VALID	(SWAP_FLAG_PRIO_MASK | SWAP_FLAG_PREFER | \
  				 SWAP_FLAG_DISCARD | SWAP_FLAG_DISCARD_ONCE | \
  				 SWAP_FLAG_DISCARD_PAGES)
  #define SWAP_BATCH 64
  
  static inline int current_is_kswapd(void)
  {
  	return current->flags & PF_KSWAPD;
  }
  
  /*
   * MAX_SWAPFILES defines the maximum number of swaptypes: things which can
   * be swapped to.  The swap type and the offset into that swap type are
   * encoded into pte's and into pgoff_t's in the swapcache.  Using five bits
   * for the type means that the maximum number of swapcache pages is 27 bits
   * on 32-bit-pgoff_t architectures.  And that assumes that the architecture packs
   * the type/offset into the pte as 5/27 as well.
   */
  #define MAX_SWAPFILES_SHIFT	5
  
  /*
   * Use some of the swap files numbers for other purposes. This
   * is a convenient way to hook into the VM to trigger special
   * actions on faults.
   */
  
  /*
   * Unaddressable device memory support. See include/linux/hmm.h and
   * Documentation/vm/hmm.rst. Short description is we need struct pages for
   * device memory that is unaddressable (inaccessible) by CPU, so that we can
   * migrate part of a process memory to device memory.
   *
   * When a page is migrated from CPU to device, we set the CPU page table entry
   * to a special SWP_DEVICE_{READ|WRITE} entry.
   *
   * When a page is mapped by the device for exclusive access we set the CPU page
   * table entries to special SWP_DEVICE_EXCLUSIVE_* entries.
   */
  #ifdef CONFIG_DEVICE_PRIVATE
  #define SWP_DEVICE_NUM 4
  #define SWP_DEVICE_WRITE (MAX_SWAPFILES+SWP_HWPOISON_NUM+SWP_MIGRATION_NUM)
  #define SWP_DEVICE_READ (MAX_SWAPFILES+SWP_HWPOISON_NUM+SWP_MIGRATION_NUM+1)
  #define SWP_DEVICE_EXCLUSIVE_WRITE (MAX_SWAPFILES+SWP_HWPOISON_NUM+SWP_MIGRATION_NUM+2)
  #define SWP_DEVICE_EXCLUSIVE_READ (MAX_SWAPFILES+SWP_HWPOISON_NUM+SWP_MIGRATION_NUM+3)
  #else
  #define SWP_DEVICE_NUM 0
  #endif
  
  /*
   * NUMA node memory migration support
   */
  #ifdef CONFIG_MIGRATION
  #define SWP_MIGRATION_NUM 2
  #define SWP_MIGRATION_READ	(MAX_SWAPFILES + SWP_HWPOISON_NUM)
  #define SWP_MIGRATION_WRITE	(MAX_SWAPFILES + SWP_HWPOISON_NUM + 1)
  #else
  #define SWP_MIGRATION_NUM 0
  #endif
  
  /*
   * Handling of hardware poisoned pages with memory corruption.
   */
  #ifdef CONFIG_MEMORY_FAILURE
  #define SWP_HWPOISON_NUM 1
  #define SWP_HWPOISON		MAX_SWAPFILES
  #else
  #define SWP_HWPOISON_NUM 0
  #endif
  
  #define MAX_SWAPFILES \
  	((1 << MAX_SWAPFILES_SHIFT) - SWP_DEVICE_NUM - \
  	SWP_MIGRATION_NUM - SWP_HWPOISON_NUM)
  
  /*
   * Magic header for a swap area. The first part of the union is
   * what the swap magic looks like for the old (limited to 128MB)
   * swap area format, the second part of the union adds - in the
   * old reserved area - some extra information. Note that the first
   * kilobyte is reserved for boot loader or disk label stuff...
   *
   * Having the magic at the end of the PAGE_SIZE makes detecting swap
   * areas somewhat tricky on machines that support multiple page sizes.
   * For 2.5 we'll probably want to move the magic to just beyond the
   * bootbits...
   */
  union swap_header {
  	struct {
  		char reserved[PAGE_SIZE - 10];
  		char magic[10];			/* SWAP-SPACE or SWAPSPACE2 */
  	} magic;
  	struct {
  		char		bootbits[1024];	/* Space for disklabel etc. */
  		__u32		version;
  		__u32		last_page;
  		__u32		nr_badpages;
  		unsigned char	sws_uuid[16];
  		unsigned char	sws_volume[16];
  		__u32		padding[117];
  		__u32		badpages[1];
  	} info;
  };
  
  /*
   * current->reclaim_state points to one of these when a task is running
   * memory reclaim
   */
  struct reclaim_state {
  	unsigned long reclaimed_slab;
  };
  
  #ifdef __KERNEL__
  
  struct address_space;
  struct sysinfo;
  struct writeback_control;
  struct zone;
  
  /*
   * A swap extent maps a range of a swapfile's PAGE_SIZE pages onto a range of
   * disk blocks.  A list of swap extents maps the entire swapfile.  (Where the
   * term `swapfile' refers to either a blockdevice or an IS_REG file.  Apart
   * from setup, they're handled identically.
   *
   * We always assume that blocks are of size PAGE_SIZE.
   */
  struct swap_extent {
  	struct rb_node rb_node;
  	pgoff_t start_page;
  	pgoff_t nr_pages;
  	sector_t start_block;
  };
  
  /*
   * 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_CONTINUED	= (1 << 5),	/* swap_map has count continuation */
  	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... */
  	SWP_SCANNING	= (1 << 14),	/* refcount in scan_swap_map */
  };
  
  #define SWAP_CLUSTER_MAX 32UL
  #define COMPACT_CLUSTER_MAX SWAP_CLUSTER_MAX
  
  /* Bit flag in swap_map */
  #define SWAP_HAS_CACHE	0x40	/* Flag page is cached, in first swap_map */
  #define COUNT_CONTINUED	0x80	/* Flag swap_map continuation for full count */
  
  /* Special value in first swap_map */
  #define SWAP_MAP_MAX	0x3e	/* Max count */
  #define SWAP_MAP_BAD	0x3f	/* Note page is bad */
  #define SWAP_MAP_SHMEM	0xbf	/* Owned by shmem/tmpfs */
  
  /* Special value in each swap_map continuation */
  #define SWAP_CONT_MAX	0x7f	/* Max count */
  
  /*
   * We use this to track usage of a cluster. A cluster is a block of swap disk
   * space with SWAPFILE_CLUSTER pages long and naturally aligns in disk. All
   * free clusters are organized into a list. We fetch an entry from the list to
   * get a free cluster.
   *
   * The data field stores next cluster if the cluster is free or cluster usage
   * counter otherwise. The flags field determines if a cluster is free. This is
   * protected by swap_info_struct.lock.
   */
  struct swap_cluster_info {
  	spinlock_t lock;	/*
  				 * Protect swap_cluster_info fields
  				 * and swap_info_struct->swap_map
  				 * elements correspond to the swap
  				 * cluster
  				 */
  	unsigned int data:24;
  	unsigned int flags:8;
  };
  #define CLUSTER_FLAG_FREE 1 /* This cluster is free */
  #define CLUSTER_FLAG_NEXT_NULL 2 /* This cluster has no next cluster */
  #define CLUSTER_FLAG_HUGE 4 /* This cluster is backing a transparent huge page */
  
  /*
   * We assign a cluster to each CPU, so each CPU can allocate swap entry from
   * its own cluster and swapout sequentially. The purpose is to optimize swapout
   * throughput.
   */
  struct percpu_cluster {
  	struct swap_cluster_info index; /* Current cluster index */
  	unsigned int next; /* Likely next allocation offset */
  };
  
  struct swap_cluster_list {
  	struct swap_cluster_info head;
  	struct swap_cluster_info tail;
  };
  
  /*
   * 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;		/* extent of the swap_map */
  	unsigned char *swap_map;	/* vmalloc'ed array of usage counts */
  	struct swap_cluster_info *cluster_info; /* cluster info. Only for SSD */
  	struct swap_cluster_list free_clusters; /* free clusters list */
  	unsigned int lowest_bit;	/* index of first free in swap_map */
  	unsigned int highest_bit;	/* index of last free in swap_map */
  	unsigned int pages;		/* total of usable pages of swap */
  	unsigned int inuse_pages;	/* number of those currently in use */
  	unsigned int cluster_next;	/* likely index for next allocation */
  	unsigned int cluster_nr;	/* countdown to next cluster search */
  	unsigned int __percpu *cluster_next_cpu; /*percpu index for next allocation */
  	struct percpu_cluster __percpu *percpu_cluster; /* per cpu's swap location */
  	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 */
  	unsigned int old_block_size;	/* seldom referenced */
  	struct completion comp;		/* seldom referenced */
  #ifdef CONFIG_FRONTSWAP
  	unsigned long *frontswap_map;	/* frontswap in-use, one bit per page */
  	atomic_t frontswap_pages;	/* frontswap pages in-use counter */
  #endif
  	spinlock_t lock;		/*
  					 * protect map scan related fields like
  					 * swap_map, lowest_bit, highest_bit,
  					 * inuse_pages, cluster_next,
  					 * cluster_nr, lowest_alloc,
  					 * highest_alloc, free/discard cluster
  					 * list. 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.
  					 */
  	spinlock_t cont_lock;		/*
  					 * protect swap count continuation page
  					 * list.
  					 */
  	struct work_struct discard_work; /* discard worker */
  	struct swap_cluster_list discard_clusters; /* discard clusters list */
  	struct plist_node avail_lists[]; /*
  					   * entries in swap_avail_heads, one
  					   * entry per node.
  					   * Must be last as the number of the
  					   * array is nr_node_ids, which is not
  					   * a fixed value so have to allocate
  					   * dynamically.
  					   * And it has to be an array so that
  					   * plist_for_each_* can work.
  					   */
  };
  
  #ifdef CONFIG_64BIT
  #define SWAP_RA_ORDER_CEILING	5
  #else
  /* Avoid stack overflow, because we need to save part of page table */
  #define SWAP_RA_ORDER_CEILING	3
  #define SWAP_RA_PTE_CACHE_SIZE	(1 << SWAP_RA_ORDER_CEILING)
  #endif
  
  struct vma_swap_readahead {
  	unsigned short win;
  	unsigned short offset;
  	unsigned short nr_pte;
  #ifdef CONFIG_64BIT
  	pte_t *ptes;
  #else
  	pte_t ptes[SWAP_RA_PTE_CACHE_SIZE];
  #endif
  };
  
  static inline swp_entry_t folio_swap_entry(struct folio *folio)
  {
  	swp_entry_t entry = { .val = page_private(&folio->page) };
  	return entry;
  }
  
  /* linux/mm/workingset.c */
  void workingset_age_nonresident(struct lruvec *lruvec, unsigned long nr_pages);
  void *workingset_eviction(struct page *page, struct mem_cgroup *target_memcg);
  void workingset_refault(struct folio *folio, void *shadow);
  void workingset_activation(struct folio *folio);
  
  /* Only track the nodes of mappings with shadow entries */
  void workingset_update_node(struct xa_node *node);
  #define mapping_set_update(xas, mapping) do {				\
  	if (!dax_mapping(mapping) && !shmem_mapping(mapping))		\
  		xas_set_update(xas, workingset_update_node);		\
  } while (0)
  
  /* linux/mm/page_alloc.c */
  extern unsigned long totalreserve_pages;
  extern unsigned long nr_free_buffer_pages(void);
  
  /* Definition of global_zone_page_state not available yet */
  #define nr_free_pages() global_zone_page_state(NR_FREE_PAGES)
  
  
  /* linux/mm/swap.c */
  extern void lru_note_cost(struct lruvec *lruvec, bool file,
  			  unsigned int nr_pages);
  extern void lru_note_cost_folio(struct folio *);
  extern void folio_add_lru(struct folio *);
  extern void lru_cache_add(struct page *);
  void mark_page_accessed(struct page *);
  void folio_mark_accessed(struct folio *);
  
  extern atomic_t lru_disable_count;
  
  static inline bool lru_cache_disabled(void)
  {
  	return atomic_read(&lru_disable_count);
  }
  
  static inline void lru_cache_enable(void)
  {
  	atomic_dec(&lru_disable_count);
  }
  
  extern void lru_cache_disable(void);
  extern void lru_add_drain(void);
  extern void lru_add_drain_cpu(int cpu);
  extern void lru_add_drain_cpu_zone(struct zone *zone);
  extern void lru_add_drain_all(void);
  extern void deactivate_file_page(struct page *page);
  extern void deactivate_page(struct page *page);
  extern void mark_page_lazyfree(struct page *page);
  extern void swap_setup(void);
  
  extern void lru_cache_add_inactive_or_unevictable(struct page *page,
  						struct vm_area_struct *vma);
  
  /* linux/mm/vmscan.c */
  extern unsigned long zone_reclaimable_pages(struct zone *zone);
  extern unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
  					gfp_t gfp_mask, nodemask_t *mask);
  extern bool __isolate_lru_page_prepare(struct page *page, isolate_mode_t mode);
  extern unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
  						  unsigned long nr_pages,
  						  gfp_t gfp_mask,
  						  bool may_swap);
  extern unsigned long mem_cgroup_shrink_node(struct mem_cgroup *mem,
  						gfp_t gfp_mask, bool noswap,
  						pg_data_t *pgdat,
  						unsigned long *nr_scanned);
  extern unsigned long shrink_all_memory(unsigned long nr_pages);
  extern int vm_swappiness;
  extern int remove_mapping(struct address_space *mapping, struct page *page);
  
  extern unsigned long reclaim_pages(struct list_head *page_list);
  #ifdef CONFIG_NUMA
  extern int node_reclaim_mode;
  extern int sysctl_min_unmapped_ratio;
  extern int sysctl_min_slab_ratio;
  #else
  #define node_reclaim_mode 0
  #endif
  
  static inline bool node_reclaim_enabled(void)
  {
  	/* Is any node_reclaim_mode bit set? */
  	return node_reclaim_mode & (RECLAIM_ZONE|RECLAIM_WRITE|RECLAIM_UNMAP);
  }
  
  extern void check_move_unevictable_pages(struct pagevec *pvec);
  
  extern void kswapd_run(int nid);
  extern void kswapd_stop(int nid);
  
  #ifdef CONFIG_SWAP
  
  #include <linux/blk_types.h> /* for bio_end_io_t */
  
  /* linux/mm/page_io.c */
  extern int swap_readpage(struct page *page, bool do_poll);
  extern int swap_writepage(struct page *page, struct writeback_control *wbc);
  extern void end_swap_bio_write(struct bio *bio);
  extern int __swap_writepage(struct page *page, struct writeback_control *wbc,
  	bio_end_io_t end_write_func);
  extern int swap_set_page_dirty(struct page *page);
  
  int add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
  		unsigned long nr_pages, sector_t start_block);
  int generic_swapfile_activate(struct swap_info_struct *, struct file *,
  		sector_t *);
  
  /* linux/mm/swap_state.c */
  /* One swap address space for each 64M swap space */
  #define SWAP_ADDRESS_SPACE_SHIFT	14
  #define SWAP_ADDRESS_SPACE_PAGES	(1 << SWAP_ADDRESS_SPACE_SHIFT)
  extern struct address_space *swapper_spaces[];
  #define swap_address_space(entry)			    \
  	(&swapper_spaces[swp_type(entry)][swp_offset(entry) \
  		>> SWAP_ADDRESS_SPACE_SHIFT])
  static inline unsigned long total_swapcache_pages(void)
  {
  	return global_node_page_state(NR_SWAPCACHE);
  }
  
  extern void show_swap_cache_info(void);
  extern int add_to_swap(struct page *page);
  extern void *get_shadow_from_swap_cache(swp_entry_t entry);
  extern int add_to_swap_cache(struct page *page, swp_entry_t entry,
  			gfp_t gfp, void **shadowp);
  extern void __delete_from_swap_cache(struct page *page,
  			swp_entry_t entry, void *shadow);
  extern void delete_from_swap_cache(struct page *);
  extern void clear_shadow_from_swap_cache(int type, unsigned long begin,
  				unsigned long end);
  extern void free_swap_cache(struct page *);
  extern void free_page_and_swap_cache(struct page *);
  extern void free_pages_and_swap_cache(struct page **, int);
  extern struct page *lookup_swap_cache(swp_entry_t entry,
  				      struct vm_area_struct *vma,
  				      unsigned long addr);
  struct page *find_get_incore_page(struct address_space *mapping, pgoff_t index);
  extern struct page *read_swap_cache_async(swp_entry_t, gfp_t,
  			struct vm_area_struct *vma, unsigned long addr,
  			bool do_poll);
  extern struct page *__read_swap_cache_async(swp_entry_t, gfp_t,
  			struct vm_area_struct *vma, unsigned long addr,
  			bool *new_page_allocated);
  extern struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t flag,
  				struct vm_fault *vmf);
  extern struct page *swapin_readahead(swp_entry_t entry, gfp_t flag,
  				struct vm_fault *vmf);
  
  /* linux/mm/swapfile.c */
  extern atomic_long_t nr_swap_pages;
  extern long total_swap_pages;
  extern atomic_t nr_rotate_swap;
  extern bool has_usable_swap(void);
  
  /* Swap 50% full? Release swapcache more aggressively.. */
  static inline bool vm_swap_full(void)
  {
  	return atomic_long_read(&nr_swap_pages) * 2 < total_swap_pages;
  }
  
  static inline long get_nr_swap_pages(void)
  {
  	return atomic_long_read(&nr_swap_pages);
  }
  
  extern void si_swapinfo(struct sysinfo *);
  extern swp_entry_t get_swap_page(struct page *page);
  extern void put_swap_page(struct page *page, swp_entry_t entry);
  extern swp_entry_t get_swap_page_of_type(int);
  extern int get_swap_pages(int n, swp_entry_t swp_entries[], int entry_size);
  extern int add_swap_count_continuation(swp_entry_t, gfp_t);
  extern void swap_shmem_alloc(swp_entry_t);
  extern int swap_duplicate(swp_entry_t);
  extern int swapcache_prepare(swp_entry_t);
  extern void swap_free(swp_entry_t);
  extern void swapcache_free_entries(swp_entry_t *entries, int n);
  extern int free_swap_and_cache(swp_entry_t);
  int swap_type_of(dev_t device, sector_t offset);
  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 page_swapcount(struct page *);
  extern int __swap_count(swp_entry_t entry);
  extern int __swp_swapcount(swp_entry_t entry);
  extern int swp_swapcount(swp_entry_t entry);
  extern struct swap_info_struct *page_swap_info(struct page *);
  extern struct swap_info_struct *swp_swap_info(swp_entry_t entry);
  extern bool reuse_swap_page(struct page *, int *);
  extern int try_to_free_swap(struct page *);
  struct backing_dev_info;
  extern int init_swap_address_space(unsigned int type, unsigned long nr_pages);
  extern void exit_swap_address_space(unsigned int type);
  extern struct swap_info_struct *get_swap_device(swp_entry_t entry);
  sector_t swap_page_sector(struct page *page);
  
  static inline void put_swap_device(struct swap_info_struct *si)
  {
  	percpu_ref_put(&si->users);
  }
  
  #else /* CONFIG_SWAP */
  
  static inline int swap_readpage(struct page *page, bool do_poll)
  {
  	return 0;
  }
  
  static inline struct swap_info_struct *swp_swap_info(swp_entry_t entry)
  {
  	return NULL;
  }
  
  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)
  {
  }
  
  static inline struct address_space *swap_address_space(swp_entry_t entry)
  {
  	return NULL;
  }
  
  #define get_nr_swap_pages()			0L
  #define total_swap_pages			0L
  #define total_swapcache_pages()			0UL
  #define vm_swap_full()				0
  
  #define si_swapinfo(val) \
  	do { (val)->freeswap = (val)->totalswap = 0; } while (0)
  /* only sparc can not include linux/pagemap.h in this file
   * so leave put_page and release_pages undeclared... */
  #define free_page_and_swap_cache(page) \
  	put_page(page)
  #define free_pages_and_swap_cache(pages, nr) \
  	release_pages((pages), (nr));
  
  static inline void free_swap_cache(struct page *page)
  {
  }
  
  static inline void show_swap_cache_info(void)
  {
  }
  
  /* used to sanity check ptes in zap_pte_range when CONFIG_SWAP=0 */
  #define free_swap_and_cache(e) is_pfn_swap_entry(e)
  
  static inline int add_swap_count_continuation(swp_entry_t swp, gfp_t gfp_mask)
  {
  	return 0;
  }
  
  static inline void swap_shmem_alloc(swp_entry_t swp)
  {
  }
  
  static inline int swap_duplicate(swp_entry_t swp)
  {
  	return 0;
  }
  
  static inline void swap_free(swp_entry_t swp)
  {
  }
  
  static inline void put_swap_page(struct page *page, swp_entry_t swp)
  {
  }
  
  static inline struct page *swap_cluster_readahead(swp_entry_t entry,
  				gfp_t gfp_mask, struct vm_fault *vmf)
  {
  	return NULL;
  }
  
  static inline struct page *swapin_readahead(swp_entry_t swp, gfp_t gfp_mask,
  			struct vm_fault *vmf)
  {
  	return NULL;
  }
  
  static inline int swap_writepage(struct page *p, struct writeback_control *wbc)
  {
  	return 0;
  }
  
  static inline struct page *lookup_swap_cache(swp_entry_t swp,
  					     struct vm_area_struct *vma,
  					     unsigned long addr)
  {
  	return NULL;
  }
  
  static inline
  struct page *find_get_incore_page(struct address_space *mapping, pgoff_t index)
  {
  	return find_get_page(mapping, index);
  }
  
  static inline int add_to_swap(struct page *page)
  {
  	return 0;
  }
  
  static inline void *get_shadow_from_swap_cache(swp_entry_t entry)
  {
  	return NULL;
  }
  
  static inline int add_to_swap_cache(struct page *page, swp_entry_t entry,
  					gfp_t gfp_mask, void **shadowp)
  {
  	return -1;
  }
  
  static inline void __delete_from_swap_cache(struct page *page,
  					swp_entry_t entry, void *shadow)
  {
  }
  
  static inline void delete_from_swap_cache(struct page *page)
  {
  }
  
  static inline void clear_shadow_from_swap_cache(int type, unsigned long begin,
  				unsigned long end)
  {
  }
  
  static inline int page_swapcount(struct page *page)
  {
  	return 0;
  }
  
  static inline int __swap_count(swp_entry_t entry)
  {
  	return 0;
  }
  
  static inline int __swp_swapcount(swp_entry_t entry)
  {
  	return 0;
  }
  
  static inline int swp_swapcount(swp_entry_t entry)
  {
  	return 0;
  }
  
  #define reuse_swap_page(page, total_map_swapcount) \
  	(page_trans_huge_mapcount(page, total_map_swapcount) == 1)
  
  static inline int try_to_free_swap(struct page *page)
  {
  	return 0;
  }
  
  static inline swp_entry_t get_swap_page(struct page *page)
  {
  	swp_entry_t entry;
  	entry.val = 0;
  	return entry;
  }
  
  #endif /* CONFIG_SWAP */
  
  #ifdef CONFIG_THP_SWAP
  extern int split_swap_cluster(swp_entry_t entry);
  #else
  static inline int split_swap_cluster(swp_entry_t entry)
  {
  	return 0;
  }
  #endif
  
  #ifdef CONFIG_MEMCG
  static inline int mem_cgroup_swappiness(struct mem_cgroup *memcg)
  {
  	/* Cgroup2 doesn't have per-cgroup swappiness */
  	if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
  		return vm_swappiness;
  
  	/* root ? */
  	if (mem_cgroup_disabled() || mem_cgroup_is_root(memcg))
  		return vm_swappiness;
  
  	return memcg->swappiness;
  }
  #else
  static inline int mem_cgroup_swappiness(struct mem_cgroup *mem)
  {
  	return vm_swappiness;
  }
  #endif
  
  #if defined(CONFIG_SWAP) && defined(CONFIG_MEMCG) && defined(CONFIG_BLK_CGROUP)
  extern void __cgroup_throttle_swaprate(struct page *page, gfp_t gfp_mask);
  static inline  void cgroup_throttle_swaprate(struct page *page, gfp_t gfp_mask)
  {
  	if (mem_cgroup_disabled())
  		return;
  	__cgroup_throttle_swaprate(page, gfp_mask);
  }
  #else
  static inline void cgroup_throttle_swaprate(struct page *page, gfp_t gfp_mask)
  {
  }
  #endif
  
  #ifdef CONFIG_MEMCG_SWAP
  extern void mem_cgroup_swapout(struct page *page, swp_entry_t entry);
  extern int __mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry);
  static inline int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry)
  {
  	if (mem_cgroup_disabled())
  		return 0;
  	return __mem_cgroup_try_charge_swap(page, entry);
  }
  
  extern void __mem_cgroup_uncharge_swap(swp_entry_t entry, unsigned int nr_pages);
  static inline void mem_cgroup_uncharge_swap(swp_entry_t entry, unsigned int nr_pages)
  {
  	if (mem_cgroup_disabled())
  		return;
  	__mem_cgroup_uncharge_swap(entry, nr_pages);
  }
  
  extern long mem_cgroup_get_nr_swap_pages(struct mem_cgroup *memcg);
  extern bool mem_cgroup_swap_full(struct page *page);
  #else
  static inline void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
  {
  }
  
  static inline int mem_cgroup_try_charge_swap(struct page *page,
  					     swp_entry_t entry)
  {
  	return 0;
  }
  
  static inline void mem_cgroup_uncharge_swap(swp_entry_t entry,
  					    unsigned int nr_pages)
  {
  }
  
  static inline long mem_cgroup_get_nr_swap_pages(struct mem_cgroup *memcg)
  {
  	return get_nr_swap_pages();
  }
  
  static inline bool mem_cgroup_swap_full(struct page *page)
  {
  	return vm_swap_full();
  }
  #endif
  
  #endif /* __KERNEL__*/
  #endif /* _LINUX_SWAP_H */
  