text: #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/atomic.h>
  #include <linux/page-flags.h>
  #include <asm/page.h>
  
  struct notifier_block;
  
  struct bio;
  
  #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)
  
  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.
   */
  
  /*
   * 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_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 list_head list;
  	pgoff_t start_page;
  	pgoff_t nr_pages;
  	sector_t start_block;
  };
  
  /*
   * Max bad pages in the new format..
   */
  #define __swapoffset(x) ((unsigned long)&((union swap_header *)0)->x)
  #define MAX_SWAP_BADPAGES \
  	((__swapoffset(magic.magic) - __swapoffset(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_FILE	= (1 << 7),	/* set after swap_activate success */
  	SWP_AREA_DISCARD = (1 << 8),	/* single-time swap area discards */
  	SWP_PAGE_DISCARD = (1 << 9),	/* freed swap page-cluster discards */
  					/* add others here before... */
  	SWP_SCANNING	= (1 << 10),	/* refcount in scan_swap_map */
  };
  
  #define SWAP_CLUSTER_MAX 32UL
  #define COMPACT_CLUSTER_MAX SWAP_CLUSTER_MAX
  
  /*
   * Ratio between zone->managed_pages and the "gap" that above the per-zone
   * "high_wmark". While balancing nodes, We allow kswapd to shrink zones that
   * do not meet the (high_wmark + gap) watermark, even which already met the
   * high_wmark, in order to provide better per-zone lru behavior. We are ok to
   * spend not more than 1% of the memory for this zone balancing "gap".
   */
  #define KSWAPD_ZONE_BALANCE_GAP_RATIO 100
  
  #define SWAP_MAP_MAX	0x3e	/* Max duplication count, in first swap_map */
  #define SWAP_MAP_BAD	0x3f	/* Note pageblock is bad, in first swap_map */
  #define SWAP_HAS_CACHE	0x40	/* Flag page is cached, in first swap_map */
  #define SWAP_CONT_MAX	0x7f	/* Max count, in each swap_map continuation */
  #define COUNT_CONTINUED	0x80	/* See swap_map continuation for full count */
  #define SWAP_MAP_SHMEM	0xbf	/* Owned by shmem/tmpfs, in first swap_map */
  
  /*
   * 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 {
  	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 */
  
  /*
   * 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 */
  };
  
  /*
   * The in-memory structure used to track swap areas.
   */
  struct swap_info_struct {
  	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 */
  	struct plist_node avail_list;	/* entry in swap_avail_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_info free_cluster_head; /* free cluster list head */
  	struct swap_cluster_info free_cluster_tail; /* free cluster list tail */
  	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 */
  	struct percpu_cluster __percpu *percpu_cluster; /* per cpu's swap location */
  	struct swap_extent *curr_swap_extent;
  	struct swap_extent first_swap_extent;
  	struct block_device *bdev;	/* swap device or bdev of swap file */
  	struct file *swap_file;		/* seldom referenced */
  	unsigned int old_block_size;	/* 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.
  					 */
  	struct work_struct discard_work; /* discard worker */
  	struct swap_cluster_info discard_cluster_head; /* list head of discard clusters */
  	struct swap_cluster_info discard_cluster_tail; /* list tail of discard clusters */
  };
  
  /* linux/mm/workingset.c */
  void *workingset_eviction(struct address_space *mapping, struct page *page);
  bool workingset_refault(void *shadow);
  void workingset_activation(struct page *page);
  extern struct list_lru workingset_shadow_nodes;
  
  static inline unsigned int workingset_node_pages(struct radix_tree_node *node)
  {
  	return node->count & RADIX_TREE_COUNT_MASK;
  }
  
  static inline void workingset_node_pages_inc(struct radix_tree_node *node)
  {
  	node->count++;
  }
  
  static inline void workingset_node_pages_dec(struct radix_tree_node *node)
  {
  	node->count--;
  }
  
  static inline unsigned int workingset_node_shadows(struct radix_tree_node *node)
  {
  	return node->count >> RADIX_TREE_COUNT_SHIFT;
  }
  
  static inline void workingset_node_shadows_inc(struct radix_tree_node *node)
  {
  	node->count += 1U << RADIX_TREE_COUNT_SHIFT;
  }
  
  static inline void workingset_node_shadows_dec(struct radix_tree_node *node)
  {
  	node->count -= 1U << RADIX_TREE_COUNT_SHIFT;
  }
  
  /* linux/mm/page_alloc.c */
  extern unsigned long totalram_pages;
  extern unsigned long totalreserve_pages;
  extern unsigned long nr_free_buffer_pages(void);
  extern unsigned long nr_free_pagecache_pages(void);
  
  /* Definition of global_page_state not available yet */
  #define nr_free_pages() global_page_state(NR_FREE_PAGES)
  
  
  /* linux/mm/swap.c */
  extern void lru_cache_add(struct page *);
  extern void lru_cache_add_anon(struct page *page);
  extern void lru_cache_add_file(struct page *page);
  extern void lru_add_page_tail(struct page *page, struct page *page_tail,
  			 struct lruvec *lruvec, struct list_head *head);
  extern void activate_page(struct page *);
  extern void mark_page_accessed(struct page *);
  extern void lru_add_drain(void);
  extern void lru_add_drain_cpu(int cpu);
  extern void lru_add_drain_all(void);
  extern void rotate_reclaimable_page(struct page *page);
  extern void deactivate_file_page(struct page *page);
  extern void deactivate_page(struct page *page);
  extern void swap_setup(void);
  
  extern void add_page_to_unevictable_list(struct page *page);
  
  extern void lru_cache_add_active_or_unevictable(struct page *page,
  						struct vm_area_struct *vma);
  
  /* linux/mm/vmscan.c */
  extern unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
  					gfp_t gfp_mask, nodemask_t *mask);
  extern int __isolate_lru_page(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_zone(struct mem_cgroup *mem,
  						gfp_t gfp_mask, bool noswap,
  						struct zone *zone,
  						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 vm_total_pages;
  
  #ifdef CONFIG_NUMA
  extern int zone_reclaim_mode;
  extern int sysctl_min_unmapped_ratio;
  extern int sysctl_min_slab_ratio;
  extern int zone_reclaim(struct zone *, gfp_t, unsigned int);
  #else
  #define zone_reclaim_mode 0
  static inline int zone_reclaim(struct zone *z, gfp_t mask, unsigned int order)
  {
  	return 0;
  }
  #endif
  
  extern int page_evictable(struct page *page);
  extern void check_move_unevictable_pages(struct page **, int nr_pages);
  
  extern int kswapd_run(int nid);
  extern void kswapd_stop(int nid);
  
  #ifdef CONFIG_SWAP
  /* linux/mm/page_io.c */
  extern int swap_readpage(struct page *);
  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 */
  extern struct address_space swapper_spaces[];
  #define swap_address_space(entry) (&swapper_spaces[swp_type(entry)])
  extern unsigned long total_swapcache_pages(void);
  extern void show_swap_cache_info(void);
  extern int add_to_swap(struct page *, struct list_head *list);
  extern int add_to_swap_cache(struct page *, swp_entry_t, gfp_t);
  extern int __add_to_swap_cache(struct page *page, swp_entry_t entry);
  extern void __delete_from_swap_cache(struct page *);
  extern void delete_from_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);
  extern struct page *read_swap_cache_async(swp_entry_t, gfp_t,
  			struct vm_area_struct *vma, unsigned long addr);
  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 *swapin_readahead(swp_entry_t, gfp_t,
  			struct vm_area_struct *vma, unsigned long addr);
  
  /* linux/mm/swapfile.c */
  extern atomic_long_t nr_swap_pages;
  extern long total_swap_pages;
  
  /* 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(void);
  extern swp_entry_t get_swap_page_of_type(int);
  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(swp_entry_t);
  extern int free_swap_and_cache(swp_entry_t);
  extern int swap_type_of(dev_t, sector_t, struct block_device **);
  extern unsigned int count_swap_pages(int, int);
  extern sector_t map_swap_page(struct page *, struct block_device **);
  extern sector_t swapdev_block(int, pgoff_t);
  extern int page_swapcount(struct page *);
  extern int swp_swapcount(swp_entry_t entry);
  extern struct swap_info_struct *page_swap_info(struct page *);
  extern int reuse_swap_page(struct page *);
  extern int try_to_free_swap(struct page *);
  struct backing_dev_info;
  
  #else /* CONFIG_SWAP */
  
  #define swap_address_space(entry)		(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 page_cache_release and release_pages undeclared... */
  #define free_page_and_swap_cache(page) \
  	page_cache_release(page)
  #define free_pages_and_swap_cache(pages, nr) \
  	release_pages((pages), (nr), false);
  
  static inline void show_swap_cache_info(void)
  {
  }
  
  #define free_swap_and_cache(swp)	is_migration_entry(swp)
  #define swapcache_prepare(swp)		is_migration_entry(swp)
  
  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 swapcache_free(swp_entry_t swp)
  {
  }
  
  static inline struct page *swapin_readahead(swp_entry_t swp, gfp_t gfp_mask,
  			struct vm_area_struct *vma, unsigned long addr)
  {
  	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)
  {
  	return NULL;
  }
  
  static inline int add_to_swap(struct page *page, struct list_head *list)
  {
  	return 0;
  }
  
  static inline int add_to_swap_cache(struct page *page, swp_entry_t entry,
  							gfp_t gfp_mask)
  {
  	return -1;
  }
  
  static inline void __delete_from_swap_cache(struct page *page)
  {
  }
  
  static inline void delete_from_swap_cache(struct page *page)
  {
  }
  
  static inline int page_swapcount(struct page *page)
  {
  	return 0;
  }
  
  static inline int swp_swapcount(swp_entry_t entry)
  {
  	return 0;
  }
  
  #define reuse_swap_page(page) \
  	(!PageTransCompound(page) && page_mapcount(page) == 1)
  
  static inline int try_to_free_swap(struct page *page)
  {
  	return 0;
  }
  
  static inline swp_entry_t get_swap_page(void)
  {
  	swp_entry_t entry;
  	entry.val = 0;
  	return entry;
  }
  
  #endif /* CONFIG_SWAP */
  
  #ifdef CONFIG_MEMCG
  static inline int mem_cgroup_swappiness(struct mem_cgroup *memcg)
  {
  	/* root ? */
  	if (mem_cgroup_disabled() || !memcg->css.parent)
  		return vm_swappiness;
  
  	return memcg->swappiness;
  }
  
  #else
  static inline int mem_cgroup_swappiness(struct mem_cgroup *mem)
  {
  	return vm_swappiness;
  }
  #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);
  extern void mem_cgroup_uncharge_swap(swp_entry_t entry);
  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)
  {
  }
  
  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 */
  