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 /*
  46  * Convert the arch-dependent pte representation of a swp_entry_t into an
  47  * arch-independent swp_entry_t.
  48  */
  49 static inline swp_entry_t pte_to_swp_entry(pte_t pte)
  50 {
  51         swp_entry_t arch_entry;
  52
  53         BUG_ON(pte_file(pte));
  54         arch_entry = __pte_to_swp_entry(pte);
  55         return swp_entry(__swp_type(arch_entry), __swp_offset(arch_entry));
  56 }
  57
  58 /*
  59  * Convert the arch-independent representation of a swp_entry_t into the
  60  * arch-dependent pte representation.
  61  */
  62 static inline pte_t swp_entry_to_pte(swp_entry_t entry)
  63 {
  64         swp_entry_t arch_entry;
  65
  66         arch_entry = __swp_entry(swp_type(entry), swp_offset(entry));
  67         BUG_ON(pte_file(__swp_entry_to_pte(arch_entry)));
  68         return __swp_entry_to_pte(arch_entry);
  69 }