include/linux/swap.h

/* 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>

#define SWAP_FLAG_PREFER	0x8000	/* set if swap priority specified */
#define SWAP_FLAG_PRIO_MASK	0x7fff
#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.
 */

/*
 * PTE markers are used to persist information onto PTEs that otherwise
 * should be a none pte.  As its name "PTE" hints, it should only be
 * applied to the leaves of pgtables.
 */
#define SWP_PTE_MARKER_NUM 1
#define SWP_PTE_MARKER     (MAX_SWAPFILES + SWP_HWPOISON_NUM + \
			    SWP_MIGRATION_NUM + SWP_DEVICE_NUM)

/*
 * Unaddressable device memory support. See include/linux/hmm.h and
 * Documentation/mm/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 a special SWP_DEVICE_EXCLUSIVE entry.
 */
#ifdef CONFIG_DEVICE_PRIVATE
#define SWP_DEVICE_NUM 3
#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 (MAX_SWAPFILES+SWP_HWPOISON_NUM+SWP_MIGRATION_NUM+2)
#else
#define SWP_DEVICE_NUM 0
#endif

/*
 * Page migration support.
 *
 * SWP_MIGRATION_READ_EXCLUSIVE is only applicable to anonymous pages and
 * indicates that the referenced (part of) an anonymous page is exclusive to
 * a single process. For SWP_MIGRATION_WRITE, that information is implicit:
 * (part of) an anonymous page that are mapped writable are exclusive to a
 * single process.
 */
#ifdef CONFIG_MIGRATION
#define SWP_MIGRATION_NUM 3
#define SWP_MIGRATION_READ (MAX_SWAPFILES + SWP_HWPOISON_NUM)
#define SWP_MIGRATION_READ_EXCLUSIVE (MAX_SWAPFILES + SWP_HWPOISON_NUM + 1)
#define SWP_MIGRATION_WRITE (MAX_SWAPFILES + SWP_HWPOISON_NUM + 2)
#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 - \
	SWP_PTE_MARKER_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 {
	/* pages reclaimed outside of LRU-based reclaim */
	unsigned long reclaimed;
#ifdef CONFIG_LRU_GEN
	/* per-thread mm walk data */
	struct lru_gen_mm_walk *mm_walk;
#endif
};

/*
 * mm_account_reclaimed_pages(): account reclaimed pages outside of LRU-based
 * reclaim
 * @pages: number of pages reclaimed
 *
 * If the current process is undergoing a reclaim operation, increment the
 * number of reclaimed pages by @pages.
 */
static inline void mm_account_reclaimed_pages(unsigned long pages)
{
	if (current->reclaim_state)
		current->reclaim_state->reclaimed += pages;
}

#ifdef __KERNEL__

struct address_space;
struct sysinfo;
struct zone;

/*
 * A swap extent maps a range of a swapfile's PAGE_SIZE pages onto a range of
 * disk blocks.  A rbtree 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_BLKDEV	= (1 << 6),	/* its a block device */
	SWP_ACTIVATED	= (1 << 7),	/* set after swap_activate success */
	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 */
	SWP_HIBERNATION = (1 << 13),	/* pinned for hibernation */
					/* 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

/*
 * The first page in the swap file is the swap header, which is always marked
 * bad to prevent it from being allocated as an entry. This also prevents the
 * cluster to which it belongs being marked free. Therefore 0 is safe to use as
 * a sentinel to indicate an entry is not valid.
 */
#define SWAP_ENTRY_INVALID	0

#ifdef CONFIG_THP_SWAP
#define SWAP_NR_ORDERS		(PMD_ORDER + 1)
#else
#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 */
	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 */
	const struct swap_ops *ops;
};

static inline swp_entry_t page_swap_entry(struct page *page)
{
	struct folio *folio = page_folio(page);
	swp_entry_t entry = folio->swap;

	entry.val += folio_page_idx(folio, page);
	return entry;
}

/* linux/mm/page_alloc.c */
extern unsigned long totalreserve_pages;

/* Definition of global_zone_page_state not available yet */
#define nr_free_pages() global_zone_page_state(NR_FREE_PAGES)

/* linux/mm/folio.c */
void folio_add_lru(struct folio *folio);
void folio_mark_accessed(struct folio *folio);
void lru_add_drain_all(void);

enum lru_cache_drained {
	LRU_CACHE_NOT_DRAINED,
	LRU_CACHE_DRAINED,
	LRU_CACHE_DRAINED_ALL,
};
void lru_cache_drain_for_folio(const struct folio *folio,
		unsigned int extra_refs, enum lru_cache_drained *drained);

/* linux/mm/folio-compat.c */
void mark_page_accessed(struct page *page);

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);
}

void lru_cache_disable(void);

extern unsigned long shrink_all_memory(unsigned long nr_pages);
long remove_mapping(struct address_space *mapping, struct folio *folio);

#if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
extern int reclaim_register_node(struct node *node);
extern void reclaim_unregister_node(struct node *node);

#else

static inline int reclaim_register_node(struct node *node)
{
	return 0;
}

static inline void reclaim_unregister_node(struct node *node)
{
}
#endif /* CONFIG_SYSFS && CONFIG_NUMA */

void check_move_unevictable_folios(struct folio_batch *fbatch);

extern void __meminit kswapd_run(int nid);
extern void __meminit kswapd_stop(int nid);

#ifdef CONFIG_SWAP
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 *);

static inline unsigned long total_swapcache_pages(void)
{
	return global_node_page_state(NR_SWAPCACHE);
}

void free_swap_cache(struct folio *folio);
void free_folio_and_swap_cache(struct folio *folio);
void free_pages_and_swap_cache(struct encoded_page **, int);
/* linux/mm/swapfile.c */
extern atomic_long_t nr_swap_pages;
extern long total_swap_pages;
extern atomic_t nr_rotate_swap;

/* 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 int pin_hibernation_swap_type(dev_t device, sector_t offset);
extern void unpin_hibernation_swap_type(int type);
extern int find_hibernation_swap_type(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 __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);
extern struct swap_info_struct *get_swap_device(swp_entry_t entry);
sector_t swap_folio_sector(struct folio *folio);

/*
 * If there is an existing swap slot reference (swap entry) and the caller
 * guarantees that there is no race modification of it (e.g., PTL
 * protecting the swap entry in page table; shmem's cmpxchg protects t
 * he swap entry in shmem mapping), these two helpers below can be used
 * to put/dup the entries directly.
 *
 * All entries must be allocated by folio_alloc_swap(). And they must have
 * a swap count > 1. See comments of folio_*_swap helpers for more info.
 */
int swap_dup_entry_direct(swp_entry_t entry);
void swap_put_entries_direct(swp_entry_t entry, int nr);

/*
 * folio_free_swap tries to free the swap entries pinned by a swap cache
 * folio, it has to be here to be called by other components.
 */
bool folio_free_swap(struct folio *folio);

/* Allocate / free (hibernation) exclusive entries */
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
#define total_swapcache_pages()			0UL
#define vm_swap_full()				0

#define si_swapinfo(val) \
	do { (val)->freeswap = (val)->totalswap = 0; } while (0)
#define free_folio_and_swap_cache(folio) \
	folio_put(folio)
#define free_pages_and_swap_cache(pages, nr) \
	release_pages((pages), (nr));

static inline void free_swap_cache(struct folio *folio)
{
}

static inline int swap_dup_entry_direct(swp_entry_t ent)
{
	return 0;
}

static inline void swap_put_entries_direct(swp_entry_t ent, int nr)
{
}

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;
}

static inline bool folio_free_swap(struct folio *folio)
{
	return false;
}

static inline int add_swap_extent(struct swap_info_struct *sis,
				  unsigned long start_page,
				  unsigned long nr_pages, sector_t start_block)
{
	return -EINVAL;
}
#endif /* CONFIG_SWAP */
#ifdef CONFIG_MEMCG
void lru_reparent_memcg(struct mem_cgroup *memcg, struct mem_cgroup *parent, int nid);
#endif

#if defined(CONFIG_SWAP) && defined(CONFIG_MEMCG) && defined(CONFIG_BLK_CGROUP)
void __folio_throttle_swaprate(struct folio *folio, gfp_t gfp);
static inline void folio_throttle_swaprate(struct folio *folio, gfp_t gfp)
{
	if (mem_cgroup_disabled())
		return;
	__folio_throttle_swaprate(folio, gfp);
}
#else
static inline void folio_throttle_swaprate(struct folio *folio, gfp_t gfp)
{
}
#endif

#if defined(CONFIG_MEMCG) && defined(CONFIG_SWAP)
int __mem_cgroup_try_charge_swap(struct folio *folio);
static inline int mem_cgroup_try_charge_swap(struct folio *folio)
{
	if (mem_cgroup_disabled())
		return 0;
	return __mem_cgroup_try_charge_swap(folio);
}

extern void __mem_cgroup_uncharge_swap(unsigned short id, unsigned int nr_pages);
static inline void mem_cgroup_uncharge_swap(unsigned short id, unsigned int nr_pages)
{
	if (mem_cgroup_disabled())
		return;
	__mem_cgroup_uncharge_swap(id, nr_pages);
}

extern long mem_cgroup_get_nr_swap_pages(struct mem_cgroup *memcg);
extern bool mem_cgroup_swap_full(struct folio *folio);
#else
static inline int mem_cgroup_try_charge_swap(struct folio *folio)
{
	return 0;
}

static inline void mem_cgroup_uncharge_swap(unsigned short id,
					    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 folio *folio)
{
	return vm_swap_full();
}
#endif

/* for_each_managed_zone_pgdat - helper macro to iterate over all managed zones in a pgdat up to
 * and including the specified highidx
 * @zone: The current zone in the iterator
 * @pgdat: The pgdat which node_zones are being iterated
 * @idx: The index variable
 * @highidx: The index of the highest zone to return
 *
 * This macro iterates through all managed zones up to and including the specified highidx.
 * The zone iterator enters an invalid state after macro call and must be reinitialized
 * before it can be used again.
 */
#define for_each_managed_zone_pgdat(zone, pgdat, idx, highidx)	\
	for ((idx) = 0, (zone) = (pgdat)->node_zones;		\
	    (idx) <= (highidx);					\
	    (idx)++, (zone)++)					\
		if (!managed_zone(zone))			\
			continue;				\
		else

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