include/linux/swapops.h

   1 /*
   2  * swapcache pages are stored in the swapper_space radix tree.  We want to
   3  * get good packing density in that tree, so the index should be dense in
   4  * the low-order bits.
   5  *
   6  * We arrange the `type' and `offset' fields so that `type' is at the five
   7  * high-order bits of the swp_entry_t and `offset' is right-aligned in the
   8  * remaining bits.
   9  *
  10  * swp_entry_t's are *never* stored anywhere in their arch-dependent format.
  11  */
  12 #define SWP_TYPE_SHIFT(e)       (sizeof(e.val) * 8 - MAX_SWAPFILES_SHIFT)
  13 #define SWP_OFFSET_MASK(e)      ((1UL << SWP_TYPE_SHIFT(e)) - 1)
  14
  15 /*
  16  * Store a type+offset into a swp_entry_t in an arch-independent format
  17  */
  18 static inline swp_entry_t swp_entry(unsigned long type, pgoff_t offset)
  19 {
  20         swp_entry_t ret;
  21
  22         ret.val = (type << SWP_TYPE_SHIFT(ret)) |
  23                         (offset & SWP_OFFSET_MASK(ret));
  24         return ret;
  25 }
  26
  27 /*
  28  * Extract the `type' field from a swp_entry_t.  The swp_entry_t is in
  29  * arch-independent format
  30  */
  31 static inline unsigned swp_type(swp_entry_t entry)
  32 {
  33         return (entry.val >> SWP_TYPE_SHIFT(entry));
  34 }
  35
  36 /*
  37  * Extract the `offset' field from a swp_entry_t.  The swp_entry_t is in
  38  * arch-independent format
  39  */
  40 static inline pgoff_t swp_offset(swp_entry_t entry)
  41 {
  42         return entry.val & SWP_OFFSET_MASK(entry);
  43 }
  44
  45 #ifdef CONFIG_MMU
  46 /* check whether a pte points to a swap entry */
  47 static inline int is_swap_pte(pte_t pte)
  48 {
  49         return !pte_none(pte) && !pte_present(pte) && !pte_file(pte);
  50 }
  51 #endif
  52
  53 /*
  54  * Convert the arch-dependent pte representation of a swp_entry_t into an
  55  * arch-independent swp_entry_t.
  56  */
  57 static inline swp_entry_t pte_to_swp_entry(pte_t pte)
  58 {
  59         swp_entry_t arch_entry;
  60
  61         BUG_ON(pte_file(pte));
  62         arch_entry = __pte_to_swp_entry(pte);
  63         return swp_entry(__swp_type(arch_entry), __swp_offset(arch_entry));
  64 }
  65
  66 /*
  67  * Convert the arch-independent representation of a swp_entry_t into the
  68  * arch-dependent pte representation.
  69  */
  70 static inline pte_t swp_entry_to_pte(swp_entry_t entry)
  71 {
  72         swp_entry_t arch_entry;
  73
  74         arch_entry = __swp_entry(swp_type(entry), swp_offset(entry));
  75         BUG_ON(pte_file(__swp_entry_to_pte(arch_entry)));
  76         return __swp_entry_to_pte(arch_entry);
  77 }
  78
  79 #ifdef CONFIG_MIGRATION
  80 static inline swp_entry_t make_migration_entry(struct page *page, int write)
  81 {
  82         BUG_ON(!PageLocked(page));
  83         return swp_entry(write ? SWP_MIGRATION_WRITE : SWP_MIGRATION_READ,
  84                         page_to_pfn(page));
  85 }
  86
  87 static inline int is_migration_entry(swp_entry_t entry)
  88 {
  89         return unlikely(swp_type(entry) == SWP_MIGRATION_READ ||
  90                         swp_type(entry) == SWP_MIGRATION_WRITE);
  91 }
  92
  93 static inline int is_write_migration_entry(swp_entry_t entry)
  94 {
  95         return unlikely(swp_type(entry) == SWP_MIGRATION_WRITE);
  96 }
  97
  98 static inline struct page *migration_entry_to_page(swp_entry_t entry)
  99 {
 100         struct page *p = pfn_to_page(swp_offset(entry));
 101         /*
 102          * Any use of migration entries may only occur while the
 103          * corresponding page is locked
 104          */
 105         BUG_ON(!PageLocked(p));
 106         return p;
 107 }
 108
 109 static inline void make_migration_entry_read(swp_entry_t *entry)
 110 {
 111         *entry = swp_entry(SWP_MIGRATION_READ, swp_offset(*entry));
 112 }
 113
 114 extern void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
 115                                         unsigned long address);
 116 #else
 117
 118 #define make_migration_entry(page, write) swp_entry(0, 0)
 119 static inline int is_migration_entry(swp_entry_t swp)
 120 {
 121         return 0;
 122 }
 123 #define migration_entry_to_page(swp) NULL
 124 static inline void make_migration_entry_read(swp_entry_t *entryp) { }
 125 static inline void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
 126                                          unsigned long address) { }
 127 static inline int is_write_migration_entry(swp_entry_t entry)
 128 {
 129         return 0;
 130 }
 131
 132 #endif
 133