include/linux/swap.h - kernel/msm-4.19 - Gitiles

 #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 dirty_balance_reserve;
 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_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_MEMCG
 extern int mem_cgroup_swappiness(struct mem_cgroup *mem);
 #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 void mem_cgroup_uncharge_swap(swp_entry_t entry);
 #else
 static inline void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
 {
 }
 static inline void mem_cgroup_uncharge_swap(swp_entry_t entry)
 {
 }
 #endif
 #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, int err);
 extern int __swap_writepage(struct page *page, struct writeback_control *wbc,
 	void (*end_write_func)(struct bio *, int));
 extern int swap_set_page_dirty(struct page *page);
 extern void end_swap_bio_read(struct bio *bio, int err);

 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 *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 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;

 #ifdef CONFIG_MEMCG
 extern void
 mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent, bool swapout);
 #else
 static inline void
 mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent, bool swapout)
 {
 }
 #endif

 #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;
 }

 #define reuse_swap_page(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;
 }

 static inline void
 mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent)
 {
 }

 #endif /* CONFIG_SWAP */
 #endif /* __KERNEL__*/
 #endif /* _LINUX_SWAP_H */
	#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 dirty_balance_reserve;
	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_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_MEMCG
	extern int mem_cgroup_swappiness(struct mem_cgroup *mem);
	#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 void mem_cgroup_uncharge_swap(swp_entry_t entry);
	#else
	static inline void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
	{
	}
	static inline void mem_cgroup_uncharge_swap(swp_entry_t entry)
	{
	}
	#endif
	#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, int err);
	extern int __swap_writepage(struct page page, struct writeback_control wbc,
	void (end_write_func)(struct bio , int));
	extern int swap_set_page_dirty(struct page *page);
	extern void end_swap_bio_read(struct bio *bio, int err);

	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 *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 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;

	#ifdef CONFIG_MEMCG
	extern void
	mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent, bool swapout);
	#else
	static inline void
	mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent, bool swapout)
	{
	}
	#endif

	#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;
	}

	#define reuse_swap_page(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;
	}

	static inline void
	mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent)
	{
	}

	#endif /* CONFIG_SWAP */
	#endif /* __KERNEL__*/
	#endif /* _LINUX_SWAP_H */