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 /* check whether a pte points to a swap entry */
  46 static inline int is_swap_pte(pte_t pte)
  47 {
  48         return !pte_none(pte) && !pte_present(pte) && !pte_file(pte);
  49 }
  50
  51 /*
  52  * Convert the arch-dependent pte representation of a swp_entry_t into an
  53  * arch-independent swp_entry_t.
  54  */
  55 static inline swp_entry_t pte_to_swp_entry(pte_t pte)
  56 {
  57         swp_entry_t arch_entry;
  58
  59         BUG_ON(pte_file(pte));
  60         arch_entry = __pte_to_swp_entry(pte);
  61         return swp_entry(__swp_type(arch_entry), __swp_offset(arch_entry));
  62 }
  63
  64 /*
  65  * Convert the arch-independent representation of a swp_entry_t into the
  66  * arch-dependent pte representation.
  67  */
  68 static inline pte_t swp_entry_to_pte(swp_entry_t entry)
  69 {
  70         swp_entry_t arch_entry;
  71
  72         arch_entry = __swp_entry(swp_type(entry), swp_offset(entry));
  73         BUG_ON(pte_file(__swp_entry_to_pte(arch_entry)));
  74         return __swp_entry_to_pte(arch_entry);
  75 }
  76
  77 #ifdef CONFIG_MIGRATION
  78 static inline swp_entry_t make_migration_entry(struct page *page, int write)
  79 {
  80         BUG_ON(!PageLocked(page));
  81         return swp_entry(write ? SWP_MIGRATION_WRITE : SWP_MIGRATION_READ,
  82                         page_to_pfn(page));
  83 }
  84
  85 static inline int is_migration_entry(swp_entry_t entry)
  86 {
  87         return unlikely(swp_type(entry) == SWP_MIGRATION_READ ||
  88                         swp_type(entry) == SWP_MIGRATION_WRITE);
  89 }
  90
  91 static inline int is_write_migration_entry(swp_entry_t entry)
  92 {
  93         return unlikely(swp_type(entry) == SWP_MIGRATION_WRITE);
  94 }
  95
  96 static inline struct page *migration_entry_to_page(swp_entry_t entry)
  97 {
  98         struct page *p = pfn_to_page(swp_offset(entry));
  99         /*
 100          * Any use of migration entries may only occur while the
 101          * corresponding page is locked
 102          */
 103         BUG_ON(!PageLocked(p));
 104         return p;
 105 }
 106
 107 static inline void make_migration_entry_read(swp_entry_t *entry)
 108 {
 109         *entry = swp_entry(SWP_MIGRATION_READ, swp_offset(*entry));
 110 }
 111
 112 extern void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
 113                                         unsigned long address);
 114 #else
 115
 116 #define make_migration_entry(page, write) swp_entry(0, 0)
 117 static inline int is_migration_entry(swp_entry_t swp)
 118 {
 119         return 0;
 120 }
 121 #define migration_entry_to_page(swp) NULL
 122 static inline void make_migration_entry_read(swp_entry_t *entryp) { }
 123 static inline void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
 124                                          unsigned long address) { }
 125 static inline int is_write_migration_entry(swp_entry_t entry)
 126 {
 127         return 0;
 128 }
 129
 130 #endif
 131