include/asm-generic/getorder.h

   1 #ifndef __ASM_GENERIC_GETORDER_H
   2 #define __ASM_GENERIC_GETORDER_H
   3
   4 #ifndef __ASSEMBLY__
   5
   6 #include <linux/compiler.h>
   7 #include <linux/log2.h>
   8
   9 /*
  10  * Runtime evaluation of get_order()
  11  */
  12 static inline __attribute_const__
  13 int __get_order(unsigned long size)
  14 {
  15         int order;
  16
  17         size--;
  18         size >>= PAGE_SHIFT;
  19 #if BITS_PER_LONG == 32
  20         order = fls(size);
  21 #else
  22         order = fls64(size);
  23 #endif
  24         return order;
  25 }
  26
  27 /**
  28  * get_order - Determine the allocation order of a memory size
  29  * @size: The size for which to get the order
  30  *
  31  * Determine the allocation order of a particular sized block of memory.  This
  32  * is on a logarithmic scale, where:
  33  *
  34  *      0 -> 2^0 * PAGE_SIZE and below
  35  *      1 -> 2^1 * PAGE_SIZE to 2^0 * PAGE_SIZE + 1
  36  *      2 -> 2^2 * PAGE_SIZE to 2^1 * PAGE_SIZE + 1
  37  *      3 -> 2^3 * PAGE_SIZE to 2^2 * PAGE_SIZE + 1
  38  *      4 -> 2^4 * PAGE_SIZE to 2^3 * PAGE_SIZE + 1
  39  *      ...
  40  *
  41  * The order returned is used to find the smallest allocation granule required
  42  * to hold an object of the specified size.
  43  *
  44  * The result is undefined if the size is 0.
  45  *
  46  * This function may be used to initialise variables with compile time
  47  * evaluations of constants.
  48  */
  49 #define get_order(n)                                            \
  50 (                                                               \
  51         __builtin_constant_p(n) ? (                             \
  52                 ((n) == 0UL) ? BITS_PER_LONG - PAGE_SHIFT :     \
  53                 (((n) < (1UL << PAGE_SHIFT)) ? 0 :              \
  54                  ilog2((n) - 1) - PAGE_SHIFT + 1)               \
  55         ) :                                                     \
  56         __get_order(n)                                          \
  57 )
  58
  59 #endif  /* __ASSEMBLY__ */
  60
  61 #endif  /* __ASM_GENERIC_GETORDER_H */