include/asm-generic/getorder.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef __ASM_GENERIC_GETORDER_H
   3 #define __ASM_GENERIC_GETORDER_H
   4
   5 #ifndef __ASSEMBLY__
   6
   7 #include <linux/compiler.h>
   8 #include <linux/log2.h>
   9
  10 /*
  11  * Runtime evaluation of get_order()
  12  */
  13 static inline __attribute_const__
  14 int __get_order(unsigned long size)
  15 {
  16         int order;
  17
  18         size--;
  19         size >>= PAGE_SHIFT;
  20 #if BITS_PER_LONG == 32
  21         order = fls(size);
  22 #else
  23         order = fls64(size);
  24 #endif
  25         return order;
  26 }
  27
  28 /**
  29  * get_order - Determine the allocation order of a memory size
  30  * @size: The size for which to get the order
  31  *
  32  * Determine the allocation order of a particular sized block of memory.  This
  33  * is on a logarithmic scale, where:
  34  *
  35  *      0 -> 2^0 * PAGE_SIZE and below
  36  *      1 -> 2^1 * PAGE_SIZE to 2^0 * PAGE_SIZE + 1
  37  *      2 -> 2^2 * PAGE_SIZE to 2^1 * PAGE_SIZE + 1
  38  *      3 -> 2^3 * PAGE_SIZE to 2^2 * PAGE_SIZE + 1
  39  *      4 -> 2^4 * PAGE_SIZE to 2^3 * PAGE_SIZE + 1
  40  *      ...
  41  *
  42  * The order returned is used to find the smallest allocation granule required
  43  * to hold an object of the specified size.
  44  *
  45  * The result is undefined if the size is 0.
  46  *
  47  * This function may be used to initialise variables with compile time
  48  * evaluations of constants.
  49  */
  50 #define get_order(n)                                            \
  51 (                                                               \
  52         __builtin_constant_p(n) ? (                             \
  53                 ((n) == 0UL) ? BITS_PER_LONG - PAGE_SHIFT :     \
  54                 (((n) < (1UL << PAGE_SHIFT)) ? 0 :              \
  55                  ilog2((n) - 1) - PAGE_SHIFT + 1)               \
  56         ) :                                                     \
  57         __get_order(n)                                          \
  58 )
  59
  60 #endif  /* __ASSEMBLY__ */
  61
  62 #endif  /* __ASM_GENERIC_GETORDER_H */