include/linux/swap.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef _LINUX_SWAP_H
   3 #define _LINUX_SWAP_H
   4
   5 #include <linux/spinlock.h>
   6 #include <linux/linkage.h>
   7 #include <linux/mmzone.h>
   8 #include <linux/list.h>
   9 #include <linux/memcontrol.h>
  10 #include <linux/sched.h>
  11 #include <linux/node.h>
  12 #include <linux/fs.h>
  13 #include <linux/atomic.h>
  14 #include <linux/page-flags.h>
  15 #include <asm/page.h>
  16
  17 struct notifier_block;
  18
  19 struct bio;
  20
  21 #define SWAP_FLAG_PREFER        0x8000  /* set if swap priority specified */
  22 #define SWAP_FLAG_PRIO_MASK     0x7fff
  23 #define SWAP_FLAG_PRIO_SHIFT    0
  24 #define SWAP_FLAG_DISCARD       0x10000 /* enable discard for swap */
  25 #define SWAP_FLAG_DISCARD_ONCE  0x20000 /* discard swap area at swapon-time */
  26 #define SWAP_FLAG_DISCARD_PAGES 0x40000 /* discard page-clusters after use */
  27
  28 #define SWAP_FLAGS_VALID        (SWAP_FLAG_PRIO_MASK | SWAP_FLAG_PREFER | \
  29                                  SWAP_FLAG_DISCARD | SWAP_FLAG_DISCARD_ONCE | \
  30                                  SWAP_FLAG_DISCARD_PAGES)
  31 #define SWAP_BATCH 64
  32
  33 static inline int current_is_kswapd(void)
  34 {
  35         return current->flags & PF_KSWAPD;
  36 }
  37
  38 /*
  39  * MAX_SWAPFILES defines the maximum number of swaptypes: things which can
  40  * be swapped to.  The swap type and the offset into that swap type are
  41  * encoded into pte's and into pgoff_t's in the swapcache.  Using five bits
  42  * for the type means that the maximum number of swapcache pages is 27 bits
  43  * on 32-bit-pgoff_t architectures.  And that assumes that the architecture packs
  44  * the type/offset into the pte as 5/27 as well.
  45  */
  46 #define MAX_SWAPFILES_SHIFT     5
  47
  48 /*
  49  * Use some of the swap files numbers for other purposes. This
  50  * is a convenient way to hook into the VM to trigger special
  51  * actions on faults.
  52  */
  53
  54 /*
  55  * Unaddressable device memory support. See include/linux/hmm.h and
  56  * Documentation/vm/hmm.txt. Short description is we need struct pages for
  57  * device memory that is unaddressable (inaccessible) by CPU, so that we can
  58  * migrate part of a process memory to device memory.
  59  *
  60  * When a page is migrated from CPU to device, we set the CPU page table entry
  61  * to a special SWP_DEVICE_* entry.
  62  */
  63 #ifdef CONFIG_DEVICE_PRIVATE
  64 #define SWP_DEVICE_NUM 2
  65 #define SWP_DEVICE_WRITE (MAX_SWAPFILES+SWP_HWPOISON_NUM+SWP_MIGRATION_NUM)
  66 #define SWP_DEVICE_READ (MAX_SWAPFILES+SWP_HWPOISON_NUM+SWP_MIGRATION_NUM+1)
  67 #else
  68 #define SWP_DEVICE_NUM 0
  69 #endif
  70
  71 /*
  72  * NUMA node memory migration support
  73  */
  74 #ifdef CONFIG_MIGRATION
  75 #define SWP_MIGRATION_NUM 2
  76 #define SWP_MIGRATION_READ      (MAX_SWAPFILES + SWP_HWPOISON_NUM)
  77 #define SWP_MIGRATION_WRITE     (MAX_SWAPFILES + SWP_HWPOISON_NUM + 1)
  78 #else
  79 #define SWP_MIGRATION_NUM 0
  80 #endif
  81
  82 /*
  83  * Handling of hardware poisoned pages with memory corruption.
  84  */
  85 #ifdef CONFIG_MEMORY_FAILURE
  86 #define SWP_HWPOISON_NUM 1
  87 #define SWP_HWPOISON            MAX_SWAPFILES
  88 #else
  89 #define SWP_HWPOISON_NUM 0
  90 #endif
  91
  92 #define MAX_SWAPFILES \
  93         ((1 << MAX_SWAPFILES_SHIFT) - SWP_DEVICE_NUM - \
  94         SWP_MIGRATION_NUM - SWP_HWPOISON_NUM)
  95
  96 /*
  97  * Magic header for a swap area. The first part of the union is
  98  * what the swap magic looks like for the old (limited to 128MB)
  99  * swap area format, the second part of the union adds - in the
 100  * old reserved area - some extra information. Note that the first
 101  * kilobyte is reserved for boot loader or disk label stuff...
 102  *
 103  * Having the magic at the end of the PAGE_SIZE makes detecting swap
 104  * areas somewhat tricky on machines that support multiple page sizes.
 105  * For 2.5 we'll probably want to move the magic to just beyond the
 106  * bootbits...
 107  */
 108 union swap_header {
 109         struct {
 110                 char reserved[PAGE_SIZE - 10];
 111                 char magic[10];                 /* SWAP-SPACE or SWAPSPACE2 */
 112         } magic;
 113         struct {
 114                 char            bootbits[1024]; /* Space for disklabel etc. */
 115                 __u32           version;
 116                 __u32           last_page;
 117                 __u32           nr_badpages;
 118                 unsigned char   sws_uuid[16];
 119                 unsigned char   sws_volume[16];
 120                 __u32           padding[117];
 121                 __u32           badpages[1];
 122         } info;
 123 };
 124
 125 /*
 126  * current->reclaim_state points to one of these when a task is running
 127  * memory reclaim
 128  */
 129 struct reclaim_state {
 130         unsigned long reclaimed_slab;
 131 };
 132
 133 #ifdef __KERNEL__
 134
 135 struct address_space;
 136 struct sysinfo;
 137 struct writeback_control;
 138 struct zone;
 139
 140 /*
 141  * A swap extent maps a range of a swapfile's PAGE_SIZE pages onto a range of
 142  * disk blocks.  A list of swap extents maps the entire swapfile.  (Where the
 143  * term `swapfile' refers to either a blockdevice or an IS_REG file.  Apart
 144  * from setup, they're handled identically.
 145  *
 146  * We always assume that blocks are of size PAGE_SIZE.
 147  */
 148 struct swap_extent {
 149         struct list_head list;
 150         pgoff_t start_page;
 151         pgoff_t nr_pages;
 152         sector_t start_block;
 153 };
 154
 155 /*
 156  * Max bad pages in the new format..
 157  */
 158 #define __swapoffset(x) ((unsigned long)&((union swap_header *)0)->x)
 159 #define MAX_SWAP_BADPAGES \
 160         ((__swapoffset(magic.magic) - __swapoffset(info.badpages)) / sizeof(int))
 161
 162 enum {
 163         SWP_USED        = (1 << 0),     /* is slot in swap_info[] used? */
 164         SWP_WRITEOK     = (1 << 1),     /* ok to write to this swap?    */
 165         SWP_DISCARDABLE = (1 << 2),     /* blkdev support discard */
 166         SWP_DISCARDING  = (1 << 3),     /* now discarding a free cluster */
 167         SWP_SOLIDSTATE  = (1 << 4),     /* blkdev seeks are cheap */
 168         SWP_CONTINUED   = (1 << 5),     /* swap_map has count continuation */
 169         SWP_BLKDEV      = (1 << 6),     /* its a block device */
 170         SWP_FILE        = (1 << 7),     /* set after swap_activate success */
 171         SWP_AREA_DISCARD = (1 << 8),    /* single-time swap area discards */
 172         SWP_PAGE_DISCARD = (1 << 9),    /* freed swap page-cluster discards */
 173         SWP_STABLE_WRITES = (1 << 10),  /* no overwrite PG_writeback pages */
 174                                         /* add others here before... */
 175         SWP_SCANNING    = (1 << 11),    /* refcount in scan_swap_map */
 176 };
 177
 178 #define SWAP_CLUSTER_MAX 32UL
 179 #define COMPACT_CLUSTER_MAX SWAP_CLUSTER_MAX
 180
 181 #define SWAP_MAP_MAX    0x3e    /* Max duplication count, in first swap_map */
 182 #define SWAP_MAP_BAD    0x3f    /* Note pageblock is bad, in first swap_map */
 183 #define SWAP_HAS_CACHE  0x40    /* Flag page is cached, in first swap_map */
 184 #define SWAP_CONT_MAX   0x7f    /* Max count, in each swap_map continuation */
 185 #define COUNT_CONTINUED 0x80    /* See swap_map continuation for full count */
 186 #define SWAP_MAP_SHMEM  0xbf    /* Owned by shmem/tmpfs, in first swap_map */
 187
 188 /*
 189  * We use this to track usage of a cluster. A cluster is a block of swap disk
 190  * space with SWAPFILE_CLUSTER pages long and naturally aligns in disk. All
 191  * free clusters are organized into a list. We fetch an entry from the list to
 192  * get a free cluster.
 193  *
 194  * The data field stores next cluster if the cluster is free or cluster usage
 195  * counter otherwise. The flags field determines if a cluster is free. This is
 196  * protected by swap_info_struct.lock.
 197  */
 198 struct swap_cluster_info {
 199         spinlock_t lock;        /*
 200                                  * Protect swap_cluster_info fields
 201                                  * and swap_info_struct->swap_map
 202                                  * elements correspond to the swap
 203                                  * cluster
 204                                  */
 205         unsigned int data:24;
 206         unsigned int flags:8;
 207 };
 208 #define CLUSTER_FLAG_FREE 1 /* This cluster is free */
 209 #define CLUSTER_FLAG_NEXT_NULL 2 /* This cluster has no next cluster */
 210 #define CLUSTER_FLAG_HUGE 4 /* This cluster is backing a transparent huge page */
 211
 212 /*
 213  * We assign a cluster to each CPU, so each CPU can allocate swap entry from
 214  * its own cluster and swapout sequentially. The purpose is to optimize swapout
 215  * throughput.
 216  */
 217 struct percpu_cluster {
 218         struct swap_cluster_info index; /* Current cluster index */
 219         unsigned int next; /* Likely next allocation offset */
 220 };
 221
 222 struct swap_cluster_list {
 223         struct swap_cluster_info head;
 224         struct swap_cluster_info tail;
 225 };
 226
 227 /*
 228  * The in-memory structure used to track swap areas.
 229  */
 230 struct swap_info_struct {
 231         unsigned long   flags;          /* SWP_USED etc: see above */
 232         signed short    prio;           /* swap priority of this type */
 233         struct plist_node list;         /* entry in swap_active_head */
 234         struct plist_node avail_lists[MAX_NUMNODES];/* entry in swap_avail_heads */
 235         signed char     type;           /* strange name for an index */
 236         unsigned int    max;            /* extent of the swap_map */
 237         unsigned char *swap_map;        /* vmalloc'ed array of usage counts */
 238         struct swap_cluster_info *cluster_info; /* cluster info. Only for SSD */
 239         struct swap_cluster_list free_clusters; /* free clusters list */
 240         unsigned int lowest_bit;        /* index of first free in swap_map */
 241         unsigned int highest_bit;       /* index of last free in swap_map */
 242         unsigned int pages;             /* total of usable pages of swap */
 243         unsigned int inuse_pages;       /* number of those currently in use */
 244         unsigned int cluster_next;      /* likely index for next allocation */
 245         unsigned int cluster_nr;        /* countdown to next cluster search */
 246         struct percpu_cluster __percpu *percpu_cluster; /* per cpu's swap location */
 247         struct swap_extent *curr_swap_extent;
 248         struct swap_extent first_swap_extent;
 249         struct block_device *bdev;      /* swap device or bdev of swap file */
 250         struct file *swap_file;         /* seldom referenced */
 251         unsigned int old_block_size;    /* seldom referenced */
 252 #ifdef CONFIG_FRONTSWAP
 253         unsigned long *frontswap_map;   /* frontswap in-use, one bit per page */
 254         atomic_t frontswap_pages;       /* frontswap pages in-use counter */
 255 #endif
 256         spinlock_t lock;                /*
 257                                          * protect map scan related fields like
 258                                          * swap_map, lowest_bit, highest_bit,
 259                                          * inuse_pages, cluster_next,
 260                                          * cluster_nr, lowest_alloc,
 261                                          * highest_alloc, free/discard cluster
 262                                          * list. other fields are only changed
 263                                          * at swapon/swapoff, so are protected
 264                                          * by swap_lock. changing flags need
 265                                          * hold this lock and swap_lock. If
 266                                          * both locks need hold, hold swap_lock
 267                                          * first.
 268                                          */
 269         spinlock_t cont_lock;           /*
 270                                          * protect swap count continuation page
 271                                          * list.
 272                                          */
 273         struct work_struct discard_work; /* discard worker */
 274         struct swap_cluster_list discard_clusters; /* discard clusters list */
 275 };
 276
 277 #ifdef CONFIG_64BIT
 278 #define SWAP_RA_ORDER_CEILING   5
 279 #else
 280 /* Avoid stack overflow, because we need to save part of page table */
 281 #define SWAP_RA_ORDER_CEILING   3
 282 #define SWAP_RA_PTE_CACHE_SIZE  (1 << SWAP_RA_ORDER_CEILING)
 283 #endif
 284
 285 struct vma_swap_readahead {
 286         unsigned short win;
 287         unsigned short offset;
 288         unsigned short nr_pte;
 289 #ifdef CONFIG_64BIT
 290         pte_t *ptes;
 291 #else
 292         pte_t ptes[SWAP_RA_PTE_CACHE_SIZE];
 293 #endif
 294 };
 295
 296 /* linux/mm/workingset.c */
 297 void *workingset_eviction(struct address_space *mapping, struct page *page);
 298 bool workingset_refault(void *shadow);
 299 void workingset_activation(struct page *page);
 300 void workingset_update_node(struct radix_tree_node *node, void *private);
 301
 302 /* linux/mm/page_alloc.c */
 303 extern unsigned long totalram_pages;
 304 extern unsigned long totalreserve_pages;
 305 extern unsigned long nr_free_buffer_pages(void);
 306 extern unsigned long nr_free_pagecache_pages(void);
 307
 308 /* Definition of global_zone_page_state not available yet */
 309 #define nr_free_pages() global_zone_page_state(NR_FREE_PAGES)
 310
 311
 312 /* linux/mm/swap.c */
 313 extern void lru_cache_add(struct page *);
 314 extern void lru_cache_add_anon(struct page *page);
 315 extern void lru_cache_add_file(struct page *page);
 316 extern void lru_add_page_tail(struct page *page, struct page *page_tail,
 317                          struct lruvec *lruvec, struct list_head *head);
 318 extern void activate_page(struct page *);
 319 extern void mark_page_accessed(struct page *);
 320 extern void lru_add_drain(void);
 321 extern void lru_add_drain_cpu(int cpu);
 322 extern void lru_add_drain_all(void);
 323 extern void lru_add_drain_all_cpuslocked(void);
 324 extern void rotate_reclaimable_page(struct page *page);
 325 extern void deactivate_file_page(struct page *page);
 326 extern void mark_page_lazyfree(struct page *page);
 327 extern void swap_setup(void);
 328
 329 extern void add_page_to_unevictable_list(struct page *page);
 330
 331 extern void lru_cache_add_active_or_unevictable(struct page *page,
 332                                                 struct vm_area_struct *vma);
 333
 334 /* linux/mm/vmscan.c */
 335 extern unsigned long zone_reclaimable_pages(struct zone *zone);
 336 extern unsigned long pgdat_reclaimable_pages(struct pglist_data *pgdat);
 337 extern unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
 338                                         gfp_t gfp_mask, nodemask_t *mask);
 339 extern int __isolate_lru_page(struct page *page, isolate_mode_t mode);
 340 extern unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
 341                                                   unsigned long nr_pages,
 342                                                   gfp_t gfp_mask,
 343                                                   bool may_swap);
 344 extern unsigned long mem_cgroup_shrink_node(struct mem_cgroup *mem,
 345                                                 gfp_t gfp_mask, bool noswap,
 346                                                 pg_data_t *pgdat,
 347                                                 unsigned long *nr_scanned);
 348 extern unsigned long shrink_all_memory(unsigned long nr_pages);
 349 extern int vm_swappiness;
 350 extern int remove_mapping(struct address_space *mapping, struct page *page);
 351 extern unsigned long vm_total_pages;
 352
 353 #ifdef CONFIG_NUMA
 354 extern int node_reclaim_mode;
 355 extern int sysctl_min_unmapped_ratio;
 356 extern int sysctl_min_slab_ratio;
 357 extern int node_reclaim(struct pglist_data *, gfp_t, unsigned int);
 358 #else
 359 #define node_reclaim_mode 0
 360 static inline int node_reclaim(struct pglist_data *pgdat, gfp_t mask,
 361                                 unsigned int order)
 362 {
 363         return 0;
 364 }
 365 #endif
 366
 367 extern int page_evictable(struct page *page);
 368 extern void check_move_unevictable_pages(struct page **, int nr_pages);
 369
 370 extern int kswapd_run(int nid);
 371 extern void kswapd_stop(int nid);
 372
 373 #ifdef CONFIG_SWAP
 374
 375 #include <linux/blk_types.h> /* for bio_end_io_t */
 376
 377 /* linux/mm/page_io.c */
 378 extern int swap_readpage(struct page *page, bool do_poll);
 379 extern int swap_writepage(struct page *page, struct writeback_control *wbc);
 380 extern void end_swap_bio_write(struct bio *bio);
 381 extern int __swap_writepage(struct page *page, struct writeback_control *wbc,
 382         bio_end_io_t end_write_func);
 383 extern int swap_set_page_dirty(struct page *page);
 384
 385 int add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
 386                 unsigned long nr_pages, sector_t start_block);
 387 int generic_swapfile_activate(struct swap_info_struct *, struct file *,
 388                 sector_t *);
 389
 390 /* linux/mm/swap_state.c */
 391 /* One swap address space for each 64M swap space */
 392 #define SWAP_ADDRESS_SPACE_SHIFT        14
 393 #define SWAP_ADDRESS_SPACE_PAGES        (1 << SWAP_ADDRESS_SPACE_SHIFT)
 394 extern struct address_space *swapper_spaces[];
 395 extern bool swap_vma_readahead;
 396 #define swap_address_space(entry)                           \
 397         (&swapper_spaces[swp_type(entry)][swp_offset(entry) \
 398                 >> SWAP_ADDRESS_SPACE_SHIFT])
 399 extern unsigned long total_swapcache_pages(void);
 400 extern void show_swap_cache_info(void);
 401 extern int add_to_swap(struct page *page);
 402 extern int add_to_swap_cache(struct page *, swp_entry_t, gfp_t);
 403 extern int __add_to_swap_cache(struct page *page, swp_entry_t entry);
 404 extern void __delete_from_swap_cache(struct page *);
 405 extern void delete_from_swap_cache(struct page *);
 406 extern void free_page_and_swap_cache(struct page *);
 407 extern void free_pages_and_swap_cache(struct page **, int);
 408 extern struct page *lookup_swap_cache(swp_entry_t entry,
 409                                       struct vm_area_struct *vma,
 410                                       unsigned long addr);
 411 extern struct page *read_swap_cache_async(swp_entry_t, gfp_t,
 412                         struct vm_area_struct *vma, unsigned long addr,
 413                         bool do_poll);
 414 extern struct page *__read_swap_cache_async(swp_entry_t, gfp_t,
 415                         struct vm_area_struct *vma, unsigned long addr,
 416                         bool *new_page_allocated);
 417 extern struct page *swapin_readahead(swp_entry_t, gfp_t,
 418                         struct vm_area_struct *vma, unsigned long addr);
 419
 420 extern struct page *swap_readahead_detect(struct vm_fault *vmf,
 421                                           struct vma_swap_readahead *swap_ra);
 422 extern struct page *do_swap_page_readahead(swp_entry_t fentry, gfp_t gfp_mask,
 423                                            struct vm_fault *vmf,
 424                                            struct vma_swap_readahead *swap_ra);
 425
 426 /* linux/mm/swapfile.c */
 427 extern atomic_long_t nr_swap_pages;
 428 extern long total_swap_pages;
 429 extern atomic_t nr_rotate_swap;
 430 extern bool has_usable_swap(void);
 431
 432 static inline bool swap_use_vma_readahead(void)
 433 {
 434         return READ_ONCE(swap_vma_readahead) && !atomic_read(&nr_rotate_swap);
 435 }
 436
 437 /* Swap 50% full? Release swapcache more aggressively.. */
 438 static inline bool vm_swap_full(void)
 439 {
 440         return atomic_long_read(&nr_swap_pages) * 2 < total_swap_pages;
 441 }
 442
 443 static inline long get_nr_swap_pages(void)
 444 {
 445         return atomic_long_read(&nr_swap_pages);
 446 }
 447
 448 extern void si_swapinfo(struct sysinfo *);
 449 extern swp_entry_t get_swap_page(struct page *page);
 450 extern void put_swap_page(struct page *page, swp_entry_t entry);
 451 extern swp_entry_t get_swap_page_of_type(int);
 452 extern int get_swap_pages(int n, bool cluster, swp_entry_t swp_entries[]);
 453 extern int add_swap_count_continuation(swp_entry_t, gfp_t);
 454 extern void swap_shmem_alloc(swp_entry_t);
 455 extern int swap_duplicate(swp_entry_t);
 456 extern int swapcache_prepare(swp_entry_t);
 457 extern void swap_free(swp_entry_t);
 458 extern void swapcache_free_entries(swp_entry_t *entries, int n);
 459 extern int free_swap_and_cache(swp_entry_t);
 460 extern int swap_type_of(dev_t, sector_t, struct block_device **);
 461 extern unsigned int count_swap_pages(int, int);
 462 extern sector_t map_swap_page(struct page *, struct block_device **);
 463 extern sector_t swapdev_block(int, pgoff_t);
 464 extern int page_swapcount(struct page *);
 465 extern int __swp_swapcount(swp_entry_t entry);
 466 extern int swp_swapcount(swp_entry_t entry);
 467 extern struct swap_info_struct *page_swap_info(struct page *);
 468 extern bool reuse_swap_page(struct page *, int *);
 469 extern int try_to_free_swap(struct page *);
 470 struct backing_dev_info;
 471 extern int init_swap_address_space(unsigned int type, unsigned long nr_pages);
 472 extern void exit_swap_address_space(unsigned int type);
 473
 474 #else /* CONFIG_SWAP */
 475
 476 #define swap_address_space(entry)               (NULL)
 477 #define get_nr_swap_pages()                     0L
 478 #define total_swap_pages                        0L
 479 #define total_swapcache_pages()                 0UL
 480 #define vm_swap_full()                          0
 481
 482 #define si_swapinfo(val) \
 483         do { (val)->freeswap = (val)->totalswap = 0; } while (0)
 484 /* only sparc can not include linux/pagemap.h in this file
 485  * so leave put_page and release_pages undeclared... */
 486 #define free_page_and_swap_cache(page) \
 487         put_page(page)
 488 #define free_pages_and_swap_cache(pages, nr) \
 489         release_pages((pages), (nr), false);
 490
 491 static inline void show_swap_cache_info(void)
 492 {
 493 }
 494
 495 #define free_swap_and_cache(e) ({(is_migration_entry(e) || is_device_private_entry(e));})
 496 #define swapcache_prepare(e) ({(is_migration_entry(e) || is_device_private_entry(e));})
 497
 498 static inline int add_swap_count_continuation(swp_entry_t swp, gfp_t gfp_mask)
 499 {
 500         return 0;
 501 }
 502
 503 static inline void swap_shmem_alloc(swp_entry_t swp)
 504 {
 505 }
 506
 507 static inline int swap_duplicate(swp_entry_t swp)
 508 {
 509         return 0;
 510 }
 511
 512 static inline void swap_free(swp_entry_t swp)
 513 {
 514 }
 515
 516 static inline void put_swap_page(struct page *page, swp_entry_t swp)
 517 {
 518 }
 519
 520 static inline struct page *swapin_readahead(swp_entry_t swp, gfp_t gfp_mask,
 521                         struct vm_area_struct *vma, unsigned long addr)
 522 {
 523         return NULL;
 524 }
 525
 526 static inline bool swap_use_vma_readahead(void)
 527 {
 528         return false;
 529 }
 530
 531 static inline struct page *swap_readahead_detect(
 532         struct vm_fault *vmf, struct vma_swap_readahead *swap_ra)
 533 {
 534         return NULL;
 535 }
 536
 537 static inline struct page *do_swap_page_readahead(
 538         swp_entry_t fentry, gfp_t gfp_mask,
 539         struct vm_fault *vmf, struct vma_swap_readahead *swap_ra)
 540 {
 541         return NULL;
 542 }
 543
 544 static inline int swap_writepage(struct page *p, struct writeback_control *wbc)
 545 {
 546         return 0;
 547 }
 548
 549 static inline struct page *lookup_swap_cache(swp_entry_t swp,
 550                                              struct vm_area_struct *vma,
 551                                              unsigned long addr)
 552 {
 553         return NULL;
 554 }
 555
 556 static inline int add_to_swap(struct page *page)
 557 {
 558         return 0;
 559 }
 560
 561 static inline int add_to_swap_cache(struct page *page, swp_entry_t entry,
 562                                                         gfp_t gfp_mask)
 563 {
 564         return -1;
 565 }
 566
 567 static inline void __delete_from_swap_cache(struct page *page)
 568 {
 569 }
 570
 571 static inline void delete_from_swap_cache(struct page *page)
 572 {
 573 }
 574
 575 static inline int page_swapcount(struct page *page)
 576 {
 577         return 0;
 578 }
 579
 580 static inline int __swp_swapcount(swp_entry_t entry)
 581 {
 582         return 0;
 583 }
 584
 585 static inline int swp_swapcount(swp_entry_t entry)
 586 {
 587         return 0;
 588 }
 589
 590 #define reuse_swap_page(page, total_map_swapcount) \
 591         (page_trans_huge_mapcount(page, total_map_swapcount) == 1)
 592
 593 static inline int try_to_free_swap(struct page *page)
 594 {
 595         return 0;
 596 }
 597
 598 static inline swp_entry_t get_swap_page(struct page *page)
 599 {
 600         swp_entry_t entry;
 601         entry.val = 0;
 602         return entry;
 603 }
 604
 605 #endif /* CONFIG_SWAP */
 606
 607 #ifdef CONFIG_THP_SWAP
 608 extern int split_swap_cluster(swp_entry_t entry);
 609 #else
 610 static inline int split_swap_cluster(swp_entry_t entry)
 611 {
 612         return 0;
 613 }
 614 #endif
 615
 616 #ifdef CONFIG_MEMCG
 617 static inline int mem_cgroup_swappiness(struct mem_cgroup *memcg)
 618 {
 619         /* Cgroup2 doesn't have per-cgroup swappiness */
 620         if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
 621                 return vm_swappiness;
 622
 623         /* root ? */
 624         if (mem_cgroup_disabled() || !memcg->css.parent)
 625                 return vm_swappiness;
 626
 627         return memcg->swappiness;
 628 }
 629
 630 #else
 631 static inline int mem_cgroup_swappiness(struct mem_cgroup *mem)
 632 {
 633         return vm_swappiness;
 634 }
 635 #endif
 636
 637 #ifdef CONFIG_MEMCG_SWAP
 638 extern void mem_cgroup_swapout(struct page *page, swp_entry_t entry);
 639 extern int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry);
 640 extern void mem_cgroup_uncharge_swap(swp_entry_t entry, unsigned int nr_pages);
 641 extern long mem_cgroup_get_nr_swap_pages(struct mem_cgroup *memcg);
 642 extern bool mem_cgroup_swap_full(struct page *page);
 643 #else
 644 static inline void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
 645 {
 646 }
 647
 648 static inline int mem_cgroup_try_charge_swap(struct page *page,
 649                                              swp_entry_t entry)
 650 {
 651         return 0;
 652 }
 653
 654 static inline void mem_cgroup_uncharge_swap(swp_entry_t entry,
 655                                             unsigned int nr_pages)
 656 {
 657 }
 658
 659 static inline long mem_cgroup_get_nr_swap_pages(struct mem_cgroup *memcg)
 660 {
 661         return get_nr_swap_pages();
 662 }
 663
 664 static inline bool mem_cgroup_swap_full(struct page *page)
 665 {
 666         return vm_swap_full();
 667 }
 668 #endif
 669
 670 #endif /* __KERNEL__*/
 671 #endif /* _LINUX_SWAP_H */